Magnetostructural Properties of Some Doubly-Bridged Phenoxido Copper(II) Complexes

Abstract

Three new tripod tetradentate phenolate-amines (H₂L¹, H₂L⁴ and H₂L⁹), together with seven more already related published ligands, were synthesized, and characterized. With these ligands, two new dinuclear doubly-bridged-phenoxido copper(II) complexes (3, 4), and six more complexes (1, 2, 5–8), a new trinuclear complex (9) with an alternative doubly-bridged-phenoxido and –methoxido, as well as the 1D polymer (10) were synthesized, and their molecular structures were characterized by spectroscopic methods and X-ray single crystal crystallography. The Cu(II) centers in these complexes exhibit distorted square-pyramidal arrangement in 1–4, mixed square pyramidal and square planar in 5, 6, and 9, and distorted octahedral (5+1) arrangements in 7 and 8. The temperature dependence magnetic susceptibility study over the temperature range 2–300 K revealed moderate–relatively strong antiferromagnetic coupling (AF) (|J| = 289–145 cm⁻¹) in complexes 1–6, weak-moderate AF (|J| = 59 cm⁻¹) in the trinuclear complex 9, but weak AF interactions (|J| = 3.6 & 4.6 cm⁻¹) were obtained in 7 and 8. No correlation was found between the exchange coupling J and the geometrical structural parameters of the four-membered Cu₂O₂ rings.

1. Introduction

Dinuclear copper(II) complexes in which the Cu(II) ions are bridged by a phenolate oxygen atoms (L-O) and an exogenous bridging atom X with the coordination core Cu(µ-L-O)(µ-X) Cu (X = L-O, OH⁻, OR⁻, O²⁻, OAc⁻, N₃⁻and Cl⁻) have been reported for a number of ligands with different skeletons frames [1,2,3,4,5,6,7,8,9,10,11,12]. Some of these complexes have served as cooperative model systems to mimic the active sites in metalloproteins, such as hemocyanin [12,13,14,15,16], metalloenzymes, such as tyrosinase [16,17,18], galactose oxidase (GOase) [19,20,21,22,23,24], superoxide dismutase (SOD) [25,26,27], and as artificial nucleases for promoting the cleavage of DNA [5,6,28,29] as well as anticancer agents [30,31].

The dinuclear copper(II) compounds constructed from the cores Cu(µ-L-O)(µ-X)Cu and Cu(µ-L-O)₂Cu are stable and the two metal ions are located in close proximity, which lead to strong implications regarding their reactivity and magnetic properties due to the interactions between the two paramagnetic Cu(II) centers [32,33]. Different strategies have been employed in the design of this class of compounds. The first approach was achieved though the interaction Cu(II) salts with tridentate ligand-based phenolates in their skeletons [34,35,36,37,38,39,40,41], and the second approach was via the design of bicompartmental phenolates bearing two pendent arms of N-donor groups [1,2,3,4,5,6,42,43]. A third approach was also used through the design of tripodal pyridyl tetradentate ligands containing one or two phenolate arms [12,14,15,20,29,44,45,46,47,48,49,50,51].

The structures and magnetic properties of singly-bridged Cu(µ-L-O)Cu and doubly-bridged phenolate Cu(µ-L-O)₂Cu compounds were the subject of numerous investigations [1,2,3,4,31,33,34,41,42,44] as well as theoretical studies [31,33,41,51,52,53,54]. The energy gap 2J arising from the spin singlet-triplet (S-T) state interactions between the two local Cu(II) doublets were evaluated. Many structural parameters were reported to affect the magnitude of the magnetic interactions in the four membered ring, Cu₂O₂ [41,54]. These include the Cu···Cu bond distance and the bridged Cu−O−Cu bond angle [41,54], the geometrical distortion, the dihedral angle between the two copper planes as well as the electronegativity in the bridging phenolate [53]. The presence of electron-withdrawing groups leads to substantial reduction in the antiferromagnetic exchange [53]. The steric effect incorporated into ligand skeleton, which may distort the copper coordination geometry, cannot be ruled out either. The non-covalent bonding interactions (H-bonding, π···π, stacking interactions, and van der Waals’ force) have also been reported to affect the molecular magnetism in these systems [54,55,56,57,58,59,60,61,62]. In general, strong super exchange antiferromagnetic coupling (AF) was observed in the bridged phenolate compounds [25,26,27,33,41,43,51,52,53,54] but, in a few cases very weak ferromagnetic properties (F) were found [4,22,25,54].

Herein, we describe a general effective procedure for the design of novel series of tripodal phenolate compounds containing pyridyl or aliphatic amine arms with N₃O and N₂O₂ chromophores, where the donor O atoms are provided by one or two phenolate groups (Scheme 1) and their corresponding doubly-bridged phenoxido-Cu(II) complexes. The magnetic properties of the complexes were investigated at variable temperatures and the evaluated exchange coupling constants, J, are discussed in relation to their molecular structures.

2. Results and Discussion

2.1. Synthesis of the Ligands and Complexes

The new tetradentate tripodal-phenolate amines (H₂L¹, H₂L⁴ and H₂L⁹) used in this work, together with related ligands (Scheme 1), were synthesized by a standard general procedure. In a typical experiment, a methanolic mixture containing 2,4-disubstituted phenol and the corresponding amine (2:1), as well as two molar amounts of an aqueous 37% HCHO and triethylamine (Et₃N) are used, whereas in the case of 2-methoxy-phenols and pyridyl derivatives (HL⁷ and HL⁸ ligands, Scheme 1), equimolar ratios were employed for all reagents. Refluxing the solutions for 3 to 4 days, followed by evaporation of the solution resulted in the formation of the solid products in reasonable yields, but about 30% were observed in the bromo-phenolate H₂L³. We should mention that too much evaporation of the resulting solutions may lead to the formation of an oily product and/or a semi-solid, which is hard to recrystallize and leads to impure products. The pure desired products were obtained upon recrystallization from ethyl acetate and activated charcoal (see Experimental section). The synthesis and characterization of H₂L², H₂L³, H₂L⁵, H₂L⁶, HL⁷, HL⁸, and H₂L¹⁰ were recently reported by our group [30].

The doubly-bridged phenoxido Cu(II) complexes 1–6, 9, and the polymeric 1D 10 were obtatined by the reaction of a methanolic solution of Cu(NO₃)₂·3H₂O with the corresponding tripodal-phenolate amine ligand and Et₃N in the stochiometric 1:1:2 molar ratio. In the cationic complexes 7 and 8, copper(II) perchlorate was used with the bipyridyl-phenolates HL⁷ and HL⁸, and Et₃N (1:1:1), respectively. These reactions afforded the desired complexes in moderate to good yields (55–90%). An illustration for the synthesis of the doubly-bridged phenoxido moieties in the complexes derived from N,N-dialkylethylenediamines is shown in Scheme 2. Interestingly, although all double bridged phenoxido compounds display green or olive-green color, brownish-green and purple colored complexes were obtained in case of the trimeric complex 9 and the 1D-polymeric 10. Single crystals suitable for X-ray structural determination were obtained either from dilute methanolic solution and/or recrystallization from CH₃CN or acetone. The complexes are slightly soluble in MeOH, but are more soluble in less polar solvents, such as CH₃CN and DMSO. The isolated compounds were characterized by elemental microanalyses, spectroscopic techniques, and conductivity measurements as well as by single X-ray crystallography for the copper complexes.

2.2. Characterization of the Ligands

Some very general features exist in the IR spectra of the tetradentate tripodal phenolate amine ligands, such as a very weak broad band or a shoulder over the frequency region 3140–3230 cm⁻¹, which was attributed to the stretching vibration, ν(O-H) of the phenolic groups, in addition to a series of weak to very weak bands observed over the range 2700–3050 cm⁻¹ due to ν(C-H) stretching of the aliphatic and aromatic groups. The moderate intense band detected around the 1590–1600 cm⁻¹ region is assigned to ν(C=N), whereas the moderate to strong series of bands shown in 1200–1590 cm⁻¹ are most likely attributed to ν(C=C, C-O). The ESI-MS of the ligands in MeOH, showed the 100% m/z base peak that corresponds to the protonation of parent ligand (H₂Lⁿ + H]⁺ (n =2–5, 9, 10). The ¹H NMR (d₆-DMSO) spectra displayed peak positions at 7.1–6.8 (protons-ph); 5.0–4.9 (phenolate-protons), 3.8–3.7 (CH₂-py); 3.5–3.3 (CH₂-ph); 2.5–2.1 ppm (CH₃-ph). The pyridyl protons reveal their signals at δ = 8.7–7.1 in compounds H₂L¹, HL⁴ and HL⁸. The hydroxyl phenolate protons were clearly observed in H₂L¹ and H₂L⁵ compounds but was not seen in most compounds, most likely due to their low solubility in DMSO.

2.3. Characterization of the Complexes

The IR spectra of the complexes under investigation were almost similar to the spectral pattern observed in their parent ligands, except for the disappearance of the broad band or shoulder in the region 3140–3230 cm⁻¹ of the ν(O-H) of the phenolic groups upon its deprotonation and/or coordination to the Cu²⁺ ion. The two cationic perchlorate complexes 7 and 8 displayed a very strong band at 1079 and 1076 cm⁻¹, respectively, due to ν_as(O-Cl) of the perchlorate counter ions. The O-H stretching frequency, ν(O-H), for the water of crystallization in 5 and 6 and were shown as a broad band over the 3320–3400 cm⁻¹ region. The ESI-MS (CH₃CN) of the cationic pyridyl complexes 7 and 8 revealed the monomeric species with m/z = [Cu(L^7,8)]⁺ (100%), where the base peak (100%) of the remaining complexes was consistent with the release of the parent protonated ligands with m/z = [H₂L^2−6,9,10 + H]⁺.

The UV-vis spectra of the complexes under investigation, measured in DMSO and/or CH₃CN at room temperature, displayed a single broad/shoulder band in the 610–750 nm region and a strong absorption band over wavelength region 410–500 nm. The latter intense band can be assigned to the bridged phenoxido charge transfer transition (L-O → Cu^II LMCT) [12,20,63,64], whereas the former low intense broad band is attributed to d-d transition in five-coordinate Cu(II) complexes, which was occasionally accompanied with a weaker intense broad band around 850–890 nm. The d-d transition feature in solution is consistent with a distorted square pyramidal geometry (SP) around the central Cu(II) ion [32,48,49]. Thus, the distorted SP geometrical assignments observed in DMSO, CH₃CN, or acetone solution, were retained in the solid state (see X-ray section). The solution spectra of the complexes in these media did not show any appreciable change over the one-week period, reflecting their high stability.

The position of λ_max in the 610–750 nm region can be used as a criterion for the ligand field strength of the tripodal phenolate ligands; λ_max decreases in the order: 9 (λ_max = 748 nm) > 2 (λ_max = 733 nm) > 5 (λ_max = 708 nm) > 10 (λ_max = 687 nm) > 6 (λ_max = 655 nm) > 4 ≈ 8 (λ_max = 630 nm) > 7 (λ_max = 625 nm) > 1 (λ_max = 620 nm). This means that the ligand field strength is decreasing in the reverse order and the strongest fields are for phenolate compounds containing pyridyl arms. However, we should mention that broadening and close location of this band in some complexes did not permit precise prediction of their actual ligand field strength, but results are consistent with previous results [65,66]. In general, ligand field strengths decrease with increasing chelate ring size, the presence of electronegative chlorine or bromine atoms in the phenolate groups, and/or steric effect on the coordinated N-aliphatic amine arms, which tends to reduce the electron density on the coordinated centers and hence its ligand field [65,66].

The non-electronic nature of all complexes, with the exception of 7 and 8, was supported by measuring the molar conductivities, Λ_M in CH₃CN or DMSO, whenever the solubility permits. The measured Λ_M values were ≤ 5 Ω⁻¹·cm²·mol⁻¹, which were fully consistent with their non-ionic properties as predicted by their molecular formulas. The measured Λ_M values (DMSO) of the perchlorate complexes 7 and 8 were within the range of 280 ± 2 Ω⁻¹·cm²·mol⁻¹. These values are in full agreement with the 1:2 electrolytic behavior of the doubly-bridged phenoxido compounds ([Cu₂(µ₂-L^7,8)₂](ClO₄)₂ (7, 8) [30,67].

2.4. Description of the Structures of Complexes

The crystal structure of title compounds 3 and 4 consist of neutral dinuclear [Cu₂(L³)₂] and [Cu₂(L⁴)₂] units, respectively; the latter co-crystallizes with an acetone solvent molecule per dinuclear unit (Figure 1,b). In both structures, the phenolate oxygen atoms O2 and O4 of two tripod ligand L³ or L⁴ anions are bridging the two copper metal centers to form four-membered Cu₂O₂ rings [Cu-O from 1.9465(16) to 2.0349(16) Å, Cu1 Cu2 = 3.047(2) (3) and 2.9949(4) Å (4); Cu1-O-Cu2 from 97.17(7) to 100.4(4)°, O-Cu-O from 74.8(4) to 75.78(7)°] (Table 1). Each Cu1 center is penta-coordinated with further three terminal sites occupied by the amine N1 and N2 atoms as well as the phenolate O1 atom. Each Cu2 center is also penta-coordinated with amine N3, N4, and phenolate O3 atoms. While the CuN₂O₃ chromophore of Cu1 may be described as less distorted square pyramid (SP) with a τ₅ -value of 0.06; the CuN₂O₃ chromophore of Cu2 is strongly distorted SP with τ₅ -value of 0.21 (3) and 0.45 (4) (τ = 0 for ideal SP) and τ₅ = 1 for ideal trigonal bipyramid (TBP)) [68]. Their apical positions are occupied by N2 and N4 atoms [Cu-N(apical) from 2.180(10) to 2.449(2) Å]. The Cu-N1/N3(basal) bonds vary from 2.0627(19) to 2.160(10) Å, and the Cu-O1/O3(basal) bonds from 1.8783(17) to 1.905(8) Å. The trans-basal bond angles vary from 138.62(7) to 165.55(7)°.

The non-planar Cu₂O₂ four-membered rings have hinge distortion expressed by their Cu-O-Cu-O dihedral angles of 24.3° and 26.9° for 3 and 4, respectively. The phenoxido groups deviate from phenyl out-of-plane angles (τ) of 10.5 and 12.2° in 3, and of 3.2 and 12.8° in 4, and phenyl ring torsion angles Cu-O-C-C of 50.9 and 71.0° in 3 and 52.5 and 67.5° in 4.

The crystal structure of 9 features trinuclear complex units (Figure 1c) and partially disordered MeOH solvent molecules. The phenolato O2 and O5 atoms of two tripod ligand L⁹ anions and O3 and O4 of two MeO⁻ anions are bridging the central Cu2 center with the two external Cu1 and Cu3 centers to form two four-membered Cu₂O₂ rings [Cu-O from 1.920(2) to 2.000(2) Å, Cu1···Cu2 = 2.9652(5), Cu2···Cu3 = 2.9418(5) Å; Cu1···Cu2···Cu3 = 154.63(2)°; Cu-O-Cu from 96.48(9) to 100.19(9)°, O-Cu-O from 75.43(8) to 77.91(8)°] (Table 1). The four oxygen atoms around Cu2 center form a tetragonally distorted square planar CuO₄ geometry with a τ₄-value of 0.17 (τ₄ = 0 for ideal square planar (SQP) and τ₄ = 1 for ideal tetrahedral, (T_d) geometry) [9]. Coordination number 5 around the Cu1 and Cu3 center is completed by two N and one O donor atoms of two tripod L⁹ anions. Their CuN₂O₃ chromophores form SP geometry with τ₅(Cu1) of 0.01 and τ₅(Cu3) of 0.23. Their apical positions are occupied by N2 and N4 atoms [Cu1-N2 = 2.351(2), Cu3-N4 = 2.324(2) Å]. The Cu-N1/N3(basal) bonds are 2.054(2) and 2.066(2) Å, and the Cu-O1/O3(basal) bonds are 1.929(2) and 1.944(2) Å. The trans-basal bond angles vary from 153.32(9) to 167.39(9)°. The non-planar Cu₂O₂ four-membered rings have hinge distortion expressed by their Cu-O-Cu-O dihedral angles of 22.9° and 23.5°. The phenoxido groups deviate from phenyl out-of-plane angles, τ of 8.2 and 20.0°, and phenyl ring torsion angles Cu-O-C-C of 44.2 and 41.9°. The trinuclear subunit may formally be created by the insertion of a “Cu(MeO)₂” moiety in the center of a bis(phenolato)-bridged Cu₂O₂ four-membered ring of a dinuclear compound (e.g., of 3).

Perspective views of the dinuclear complexes 1, 2, 5–8 containing the Cu₂O₂ bis(phenolato)-bridged subunits, as well as a section of the polymeric chain of 10, are presented in Figure 2. The crystal structures have been reported previously, along with their anticancer properties [30].

2.5. Magnetic Properties

According to the crystal structures, the complexes under investigations can be divided into six groups as follows:

Group 1: Centrosymmetric di-µ-phenoxido-bridged dinuclear complexes with a distorted square-pyramidal geometries (1 and 2). Complex [Cu₂(L¹)₂] (1) shows a distorted square-pyramidal arrangement (SP) (τ₅ = 0.23) around each copper(II) center with an axial Cu-N distance of 2.310(3) Å, Cu···Cu distance and Cu-O-Cu angle are 3.0915(7) Å and 103.44(9)°, respectively [30]. Thus, Complex 1 is expected to exhibit antiferromagnetic interaction (AF) between the two S = ½ spins through the two phenoxido bridges. Temperature dependence of magnetic susceptibilities, measured under an external magnetic field of 0.5 T, ranging from 2 K to 300 K are represented in Figure 3 in the form of χ_M and µ_M vs T plots, where χ_M is the magnetic susceptibility per Cu₂ unit, µ_M is the magnetic moment per Cu₂ unit, and T is the absolute temperature. The magnetic moment of 1.30 BM at 300 K is considerably lower than the spin-only value (2.45 BM) for two non-interacting copper(II) S = ½ ions. The magnetic moment exhibits a continuous decrease with lowering the temperature over the range 2–300 K and reaches 0.28 BM at 2 K. This magnetic behavior reveals significant AF interaction between the copper(II) ions. The magnetic data were analyzed by the Bleaney–Bowers equation based on the Heisenberg model:

χ_M = (1 − p)(2Ng²µ_B²/kT)[3 + exp(−2J/kT)]⁻¹ + pNg²µ_B²/2kT + 2Nα(1)

where g is the g value, J is the exchange coupling constant between the two copper(II) ions, p is the fraction of mononuclear copper(II) impurity, and Nα is the temperature-independent paramagnetism for each copper(II) ion [8]. The best-fitting parameters (g = 2.1 (fixed), 2J = −578 cm⁻¹, p = 0.016, and Nα = 60 × 10⁻⁶ cm³ mol⁻¹ (fixed)) are in complete support for strong AF interaction.

The crystal structure of [Cu₂(L²)₂] (2) also shows the same crystallographic similarity as 1 (τ = 0.24) [68] around each copper(II) center with the axial Cu-N distance of 2.3580(17) Å. The Cu···Cu distance and Cu-O-Cu angle are 3.0064(5) Å and 99.12(6)°, respectively. The µ_M of 2 is 1.62 BM per dinuclear unit at 300 K, which is also considerably lower than the spin-only value and decreases with lowering of the temperature and reaching to 0.12 BM at 2 K. The best-fitting parameters (g = 2.10, 2J = −403 cm⁻¹, p = 0.0007, and Nα = 60 × 10⁻⁶ cm³ mol⁻¹) disclose the expected strong AF interaction. The absolute 2J value is smaller than that of 1, but it reflects the strong AF interaction in 1 compared 2 and is in harmony with the associated wider Cu-O-Cu angle observed in 1.

Group 2: Pseudo-symmetric di-µ-phenoxido-bridged dinuclear complexes with distorted SP geometries (3 and 4). The crystal structure of [Cu₂(L³)₂] (3) showed that the complex exhibits distorted SP arrangements (τ = 0.06 and 0.37) around two copper(II) centers with axial Cu-N distances of 2.180(10) and 2.235(10) Å. The Cu···Cu distance is 3.047(2) Å and Cu-O-Cu angles are 98.8(4) and 100.4(4)°. Complex 3 crystallizes in non-centrosymmetric with different distortion around each copper(II) center. The magnetic properties of 3 is illustrated in Figure 4. The magnetic moment of 2.07 BM at 300 K is a little higher than those of 1 and 2, and it exhibits a gradual decrease with lowering the temperature, reaching 0.20 BM at 2 K. The magnetic data were analyzed by Equation (1), and the obtained best-fitting parameters (g = 2.14(1), 2J = −291 cm⁻¹, p = 0.009, and Nα = 60 × 10⁻⁶ cm³ mol⁻¹ (fixed)) demonstrates the AF interaction between the two copper(II) centers. The absolute 2J value of 3 is smaller than those of 1 and 2, but with a weaker interaction. This may be attributed to the different distortion between the two copper(II) coordination environments, which causes poor overlap between the two magnetic orbitals compared to 1 and 2.

The complex [Cu₂(µ₂-L²)₂] (4) exhibits crystallographic similarities comparable to 3. The molecule is a non-centrosymmetric di-µ-phenoxido-bridged complex with distorted SP arrangements (τ₅ = 0.07 and 0.45) around the central copper(II) centers with the axial Cu-N distances of 2.449(2) and 2.3532(19) Å. The Cu···Cu distance and Cu-O-Cu angles are 2.9949(4) Å and 97.17(7) and 97.78(7)°, respectively. The magnetic moment µ_M (1.98 BM at 300 K) shows a gradual decrease with lowering the temperature, reaching 0.20 BM at 2 K. The magnetic data were analyzed by Equation (1) and the obtained best-fitting parameters (g = 2.10 (fixed), 2J = −293 cm⁻¹, p = 0.008, and Nα = 60 × 10⁻⁶ cm³ mol⁻¹ (fixed)) showed a comparable AF interaction to that observed in 3. This is in accordance with the relationship between the 2J and Cu-O-Cu values.

Group 3: Unsymmetric di-µ-phenoxido-bridged dinuclear complexes with distorted square-pyramidal (SP) and square-planar (SQP) geometries (5 and 6). The crystal structure of complex [Cu₂(L⁵)₂(H₂O)]·2H₂O (5) showed that the molecule exhibits a distorted SP copper(II) (τ₅ = 0.011) with an axial Cu-O bond of 2.538(3) Å, and a distorted SQP copper(II) with the τ₄ value of 0.17. Thus, if we consider the long axial distance of 2.538(3) Å, then both of the magnetic orbitals of the two copper(II) centers are expected to exist within the basal NO₃ and NO₃ square plane, favoring a strong magnetic interaction. The Cu···Cu distance and Cu-O-Cu angles are 2.9331 Å, and 96.70(9) and 97.58(9)°, respectively. The magnetic moment, µ_M (1.82 BM at 300 K), is lower than the spin-only value (2.45 BM) for two non-interacting copper(II) S = ½ ions. The magnetic moment revealed a gradual decrease with lowering the temperature and reaches 0.31 BM at 2 K (Figure 5). The best-fitting parameters to Equation (1) (g = 2.1 (fixed), 2J = −352 cm⁻¹, p = 0.036, and Nα = 60 × 10⁻⁶ cm³ mol⁻¹ (fixed)) are consistent with considerable AF interaction between the two copper(II) ions. The absolute 2J value is comparable to those obtained in 3 and 4.

The crystal structure of [Cu₂(L⁶)₂(H₂O)]·2H₂O (6) shows crystallographic parameters similar to 5, having a distorted SP copper(II) (τ₅ = 0.013) with the axial Cu-O bond of 2.512(2) Å and a distorted SP copper(II) with τ₄ value of 0.17. The Cu···Cu distance and Cu-O-Cu angles are 2.9410(4) Å and 97.56(7) and 96.93(7)°, respectively. The magnitude of the magnetic moment of 6 is 1.68 BM at 300 K. This value is lower than the spin-only value for copper(II), S = ½ ion, and the magnetic moment exhibits a continuous decrease with lowering temperature and reaches 0.11 BM at 2 K. The best-fitting parameters to Equation (1) (g = 2.10 (fixed), 2J = −500 cm⁻¹, p = 0.0009, and Na = 170 × 10⁻⁶ cm³ mol⁻¹) showed a significant AF interaction between the two copper(II) ions. The magnetic behavior of 6 should be considered as similar to that of 5, irrespective of the relatively large –J value of 5, taking into consideration the similarity of the Cu-O-Cu angle, Cu-O-Cu-O dihedral angle, phenyl ring torsion angle (Cu-O-C-C angle), and phenyl out-of-plane shift angle t (Table 2), then one should expect strong AF interaction between the copper(II) centers in the two compounds 5 and 6.

Group 4: Centrosymmetric di(phenoxido)-bridged dinuclear complexes with a distorted (5 + 1) octahedral geometries (7 and 8). The crystal structural analysis of [Cu₂(L⁷)₂](ClO₄)₂ (7) shows a distorted octahedral (5 + 1) geometry with a semi-coordination Cu-OMe of 2.785(4) Å around each copper(II) center. If this semi-coordination is neglected as a substantial bond because of its long distance, then the coordination geometry can be regarded as a distorted square-pyramidal geometry with the τ₅ value of 0.41. Therefore, taking into consideration the long distance of the axial Cu-O(phenoxido) bond of 2.213(3) Å, as a result the magnetic orbital of each copper(II) ion may exist around the basal N₃O plane mainly and not in the direction of the axial phenoxido-bridging bond, which leads to a poor magnetic interaction. The Cu···Cu distance and Cu-O-Cu angle are 3.130 Å and 97.72 (14)°, respectively. The magnetic data of 7 are illustrated in Figure 6. The µ_B (2.65 BM at 300 K) is higher than the spin-only value (2.45 BM) for two non-interacting copper(II), S = ½ ions. The magnetic moment exhibits a continuous decrease with lowering temperature and reaches 0.51 BM at 2 K, suggesting an AF interaction. The best-fitting parameters (g = 2.14, 2J = −7.2 cm⁻¹, and Nα = 60 × 10⁻⁶ cm³ mol⁻¹ (fixed)) are consistent with a weak AF interaction between the two copper(II) ions.

Complex [Cu₂(L⁸)₂](ClO₄)₂ (8) exhibits very close crystallographic parameters like 7; distorted octahedral (5 + 1) arrangement with a semi-coordination of Cu-OMe of 2.791(3) Å around each copper(II) ion. The coordination geometry of this complex is similar to 7 and can be regarded as indicated above as a distorted SP geometry (τ₅ value of 0.40) with a relatively long axial phenoxido-bridging of Cu-O distance of 2.215(2) Å. The Cu···Cu distance and the Cu-O-Cu angle are 3.098(2) Å and 96.63(10)°, respectively. The similarity was also extended to the magnetic properties of 7. The best-fitting parameters (g = 2.1 (fixed), 2J = −9.2 cm⁻¹, and Nα = 60 × 10⁻⁶ cm³ mol⁻¹ (fixed)) shows a weak AF interaction between the two copper(II) ions.

In 7 and 8, the Cu₂O₂ bridging ring with the axial phenoxido-bridges is planar, as can be seen from the Cu-O-Cu-O dihedral angle of 0° (Table 2), and thus the magnetic orbitals of each copper(II) ion should be parallel to each other. This suggests that the phenoxido oxygens are rather axially located relative to the basal dx²-y² orbital plane. Such axial bridging oxygens cannot effectively participate in mediating the magnetic interaction through the phenoxido-bridges.

Group 5: linear trinuclear complex 9. The crystal structure of [Cu₃(L⁹)₂(µ-OCH₃)₂]·CH₃COCH₃ (9) shows that the molecule has a µ-phenoxido-µ-methoxido-bridged trinuclear copper(II) complex with a linear arrangement of the three copper(II) ions. The magnetic data (Figure 7) revealed a magnetic moment of 2.50 BM at 300 K, which is lower than the spin-only value (3.00 BM) for three non-interacting copper(II), S = ½ ions. The magnetic moment exhibits a gradual decrease with lowering temperature and reaches 1.46 BM at 2 K. This behavior suggests a remarkable AF interaction between the copper(II) ions. The magnetic analysis was carried out with the susceptibility equation for the linear trinuclear copper(II) ions based on $\mathcal{H}$ = −2J_Cu3(S₁·S₂ + S₂·S₃). However, the fitting was not good, and rather better fitting was obtained when the magnetic data were analyzed by the dinuclear model using Equation (1). The results indicated that the magnetic data of 9 contain some impurities arising from the presence of dinuclear copper(II) species. Therefore, the magnetic data were analyzed with the aid of Equation (2) of linear trinuclear and dinuclear copper(II) model.

χ_M = (1 − p_Cu2)(Ng²µ_B²/4kT)[1 + exp(−2J_Cu3/kT) + 10exp(J_Cu3/kT)]/[1 + exp(−2J_Cu3/kT) + 2exp(J_Cu3/kT)] + p_Cu2(2Ng²µ_B²/kT)[3 + exp(−2J/kT)]⁻¹ + (3−p_Cu2)Nα(2)

where p_Cu2 is the fraction of dinuclear copper(II) impurity. The best-fitting parameters (g = 2.1 (fixed), J_Cu3 = −59 cm⁻¹, p_Cu2 = 0.315, 2J = −592 cm⁻¹, and Nα = 60 × 10⁻⁶ cm³ mol⁻¹ (fixed)) revealed the existence of a considerable amount of dinuclear copper(II) species in the sample.

Group 6: polynuclear chain complex 10. The X-ray structure analysis revealed that catena-[Cu(µ-L¹⁰)] (10) is a polynuclear chain molecule constructed of tetrahedrally distorted square-planar [Cu(L¹⁰)] units (τ₄ = 0.23) [9] with Cu···Cu distance of 7.269 Å. The temperature dependence of magnetic susceptibilities χ_A and magnetic moments µ_A are represented in Figure 8, where χ_A and µ_A are per Cu unit. The µ_A value of 1.83 BM at 300 K is a little bit higher than the spin-only value (1.73 BM) for copper(II), S = ½ ion. The µ_A vs. T plot shows a slight gradual increase with a lowering of the temperature over the range 50–300 K and a gradual decrease on lowering the temperature from 50 to 2 K, reaching, 1.70 BM at 2 K. While the increase of the µ_A value suggests F interaction between two adjacent Cu(II) centers via the L¹⁰ anion ligand, the corresponding decrease in µ_A values indicates an AF intermolecular interaction. The magnetic data were analyzed by the molecular field approximation (Equation (3) [8]), where for this series Equation (4) for the Heisenberg model for ferromagnetically coupled S = ½ ions (derived by Baker et al. [10]), considering the magnetic interaction between the neighboring chain molecules as zJ’ (z = number of interacting neighbors), was used:

χ_A’ = χ_A/{1−(2zJ’/Ng²µ_B²)χ_A}(3)

χ_A = (Ng²µ_B²/4kT)[(1.0 + 5.7979916x + 16.902653x² + 29.376885x³ + 29.832959x⁴ + 14.036918x⁵)/(1.0 + 2.7979916x + 7.0086780x² + 8.6538644x³ + 4.5743114x⁴)]^2/3 + Nα(4)

where x = J/2kT. The solid line in Figure 8 shows the calculated curve with best-fitting parameters of g = 2.1 (fixed), J = 3.5 cm⁻¹, Nα = 60 × 10⁻⁶ cm³ mol⁻¹ (fixed), and zJ’ = −2.9 cm⁻¹.

3. Conclusions

In this work eight dinuclear doubly-bridged-phenoxido copper(II) complexes revealed antiferromagnetic coupling (AF) varied from strong AF interaction (−J = 289–145 cm⁻¹) for complexes 1–6 to very weak AF interaction (−J = 3.6 & 4.6 cm⁻¹) in 7 and 8. The geometry around the central Cu(II) centers exhibits distorted square-pyramidal arrangement in the first four complexes, mixed square pyramidal and distorted square planar in 5 and 6, and distorted pseudo octahedral (5 + 1) arrangements in 7 and 8. Attempts were made to correlate the exchange coupling (J) to the structural parameters of the non-planar Cu₂O₂ four-membered rings. These parameters include the Cu···Cu distances (2.941–3.130 Å), Cu-O-Cu bond angles (96.93–103.44°) [69,70], Cu-O-Cu-O dihedral angles (0–29.8°), and the deviation angles of the phenoxido groups from the phenyl out-of-plane angles (11.3–71.0°) as well as the phenyl ring torsion angles Cu-O-C-C (2.7–31.3). Unfortunately, no satisfied correlations were observed between J and the mentioned geometrical parameters [69,70]. This is most likely due to the influence of the steric environment incorporated by the substituents into phenolate groups, and the terminal coordinated dialkylamine, and hence the geometrical arrangement around the central Cu(II) ions as well as the coplanarity of the phenolate groups with the bridging Cu₂O₂ moiety [53,70,71]. These factors may play a key role in reducing the efficient overlap between the 3d Cu²⁺ and 2p O-phenoxido magnetic orbitals bearing the unpaired electrons. In general and focusing the discussion only on Cu(II) complexes containing mono- and doubly-bridged phenoxido compounds with no other bridging ligands, our results agree with the magnetic properties determined in many phenoxido-bridged copper complexes, where relatively strong AF couplings were reported [1,54,69,70,72], regardless of the fact that some of these compounds were ferromagnetically coupled [1,54,72,73].

In contrast and unlike the bridged bis(phenoxido) dinuclear copper(II) complexes, where no correlation was observed between J and Cu–O–Cu bond angle, linear relationships were obtained in the corresponding bis(hydroxido) [74] and bis(alkoxido) [75] bridged copper(II) complexes. In addition, a similar linear correlation was reported in bis(phenoxido) macrocyclic complexes in which the unique conjugated π-electron inherited into the macrocycle skeleton constrained the ligand to adopt a planar configuration [71]. On the other hand, a relatively moderate AF coupling (-J = 59 cm⁻¹) was evaluated in the trinuclear 9, where alternative bridged phenoxido and methoxido groups were determined. However, in the 1D polymer 10, a weak ferromagnetic interaction (J = + 3.5 cm⁻¹) was obtained. Interestingly, in the latter complex, the Cu(II) centers were linked via the N,N-dimethylpropyl arms with long Cu···Cu distance (7.269 Å) and a tetrahedral distorted square planar four-coordinate geometry around each Cu(II) center [30].

4. Experimental

4.1. Materials and Physical Measurements

N,N-Dimethyl-, N,N-diethyl-, N,N-isopropyl-ethylenediamine, 3-dimethylamino-propylamine, 2,4-dimethylphenol, 4-chloro-2-methylphenol, 2-bromo-4-methylphenol, 2-methoxy-4-methylphenol, 4-chloro-2-methoxyphenol and 2-tert-butyl-4-methylphenol, picolylamine as well as dipicolylamine were purchased from TCI-America. All other chemicals were commercially available and used without further purification.

Electronic spectra were recorded using an Agilent 8453 HP diode array UV-Vis spectrophotometer. Infrared spectra were recorded on a Cary 630 (ATR-IR) spectrometer. ¹H spectra were obtained at room temperature on a Varian 400 NMR spectrometer operating at 400 MHz (¹H). ¹H NMR chemical shifts (δ) are reported in ppm and were referenced internally to residual solvent resonances (d₆-DMSO: δ_H = 2.49) or TMS. ESI-MS of organic compounds and their Cu(II) were measured in MeOH and CH₃CN, respectively, on a LC-MS Varian Saturn 2200 Spectrometer. Conductivity measurements were performed using a Mettler Toledo Seven Easy conductivity meter and calibrated by 1413 μS/cm conductivity standard. The molar conductivity of the complexes was determined from Λ_M = (1.0 × 10³ κ)/[Cu(II)], where κ = specific conductance and [Cu^II] is the molar concentration of the complex. Elemental microanalyses were carried out by Atlantic Microlaboratory, Norcross, Georgia U.S.A.

The temperature dependent magnetic susceptibilities were measured over 2–300 K at the constant field of 0.5 T with a Quantum Design MPMS 3 (installed at Shimane University) for 1–3, 4, 6–10, and with a Quantum Design MPMS-7 (installed at Institute for Molecular Science (IMS)) for 5. The measured data were corrected for diamagnetic contributions [76].

4.2. Synthesis of the Organic Ligands

The new ligands H₂L³, H₂L⁴ and H₂L⁹ illustrated in Scheme 1, and their characterization are given below, whereas the rest of the ligands shown in this scheme (H₂L¹, H₂L², H₂L⁵, H₂L⁶, and H₂L¹⁰ as well as HL⁷ and H₂L⁸) were recently reported [30].

4.2.1. 6,6′-(((2-(Dimethylamino)ethyl)azanediyl)bis(methylene))bis(2-bromo-4-methylphenol) (H₂L³)

To a mixture containing 2-bromo-4-methylphenol (3.740 g, 20 mmol), Et₃N (2.04 g, 20 mmol) and aqueous 37% HCHO (1.63 g, 20 mmol) dissolved in methanol (50 mL), N,N-dimethylethylenediamine (0.882 g, 10 mmol). The mixture was stirred and refluxed gently for 3 days. Evaporating the resulting solution under reduced pressure resulted in the formation of white crystalline compound, which was then filtered, washed with Et₂O, and air dried (yield: 4.35 g, 89.5%). Characterization: calcd for C₂₀H₂₆Br₂N₂O₂ (MM = 486.241 g/mol): C, 49.40; H, 5.39; N, 5.76%. Found: C, 49.44; H, 5.51; N, 5.78% m.p. 189° C. IR bands (ATR, cm⁻¹): 2972 (w), 2950 (vw), 2820 (w), ν(C-H); 1480 (s), 1458 (vs), 1446 (s), 1374 (s), 1291 (s), 1231 (s), 1204 (s) ν(C=C, C-N, C-O); 1165 (s), 1122 (s), 1047 (m), 924 (s), 902 (s), 809 (vs). ESI-MS: m/z = 487.042, calcd [H₂L⁶ + H]⁺ = 487.042.

4.2.2. 6,6′-(((2-(Diethylamino)ethyl)azanediyl)bis(methylene))bis(2,4-dimethylphenol) (H₂L⁴)

This compound was synthesized using a similar procedure and the same molar ratios as that described above for H₂L³, except 2,4-dimethylphenol (2.44 g, 20 mmol) and N,N-dimethylethylenediamine (1.162 g, 10 mmol) were used instead of 2-bromo-4-methylphenol and N,N-dimethylethylenediamine, respectively (yield: 2.57 g, 66.8%). Characterization: m.p. 137–140° C. Anal. calcd for C₂₄H₃₆N₂O₂ (MM = 384.555 g/mol): C, 74.96; H, 9.44; N, 7.28%. Found: C, 74.81; H, 9.56; N, 7.28%. IR bands (ATR, cm⁻¹): 2978 (vw), 2937 (vw), 2913 (vw), 2904 (m), 2802 (w) ν(C-H); 1484 (vs), 1376 (m), 1224 (vs) ν(C=C, C-O); 1152 (s), 1129 (m), 1096 (m), 1024 (m), 922 (m), 864 (s), 805 (m), 743 (vs). ESI-MS: m/z = 585.286 (100%), calcd [H₂L² + H]⁺ = 585.285. ¹H NMR (d₆-DMSO, 400 MHz, δ in ppm): 6.84, 6.66 (2H, 2s, 1:1, ph); 3.55 (2H, s, CH₂-ph); 2.59 (2H, m, N-CH₂-CH₃); 2.40 (4H, m, N-CH₂-CH₂-N); 2.14, 2.07 (3H, 2s, 1:1, 2xCH₃-ph); 0.96 (3H, t, CH₃-CH₂). ¹³C NMR: 152 (HO-Cph); 131.0, 128.2, 127,3, 125.39, 121.44 C-ph); 55.8 (N-CH₂ph); 49.8, 48.7 (N-CH₂-CH₂-N); 45.7 (CH₂CH₃); 20.4 (H₃C4ph); 16.1 (H₃C2ph); 9.9 (CH₂CH₃).

4.2.3. 6,6′-(((2-(Diethylamino)ethyl)azanediyl)bis(methylene))bis(4-chloro-2-methylphenol) (H₂L⁹)

A mixture of 4-chloro-2-methylphenol (2.825 g, 20 mmol), Et₃N (2.022 g, 20 mmol), aqueous 37% HCHO (1.627 g, 20 mmol) and N,N-diethylethylenediamine (1.162 g, 10 mmol) was dissolved in methanol (60 mL). The mixture was stirred and refluxed gently for 3 days. Evaporating this solution under reduced pressure resulted in the formation of white precipitate, which was then collected by filtration, washed with Et₂O, and air dried (yield: 2.35 g, 55.3%). Characterization: m.p. 137–141 °C. Cacd for C₂₂H₃₀Cl₂N₂O₂ (MM = 424.168 g/mol): C, 62.12; H, 7.11; N, 6.59%. Found: C, 62.29; H, 7.21; N, 6.53%. IR bands (ATR, cm⁻¹): 2981 (w), 2915 (vw), 2814 (w) ν(C-H); 1583 (w), 1467 (vs), 1378 (m), 1324 (m), 1273 (s), 1226 (vs) ν(C=C, C-O); 1126 (m), 1093 (s), 1063 (m), 1023 (m), 976 (m), 929 (m), 864 (vs), 804 (m) 739 (vs), 669 (m). ESI-MS: m/z = 425.175 (100%), calcd [H₂L⁴ + H]⁺ = 425.176. ¹H NMR (d₆-DMSO, 400 MHz, δ in ppm): 7.05, 7.00 (2H, 2s, 1:1, 2xHph); 3.58 (2H, s, CH₂-ph); 3.37 (2H, m, N-CH₂-CH₃); 2.44 (3H, t, N-CH₂-CH₂-N); 2.11 (3H, s, CH₃-ph); 0.97 (3H, t, CH₃-CH₂−).

4.3. Synthesis of Copper(II) Complexes

A general method was used to synthesize the copper(II) complexes 3, 4, and 9: to a mixture containing the appropriate tripod phenolate-amine ligand (0.5 mmol) and Et₃N (0.102 g, 1.00 mmol) dissolved in MeOH (20–30 mL), Cu(NO₃)₂·3H₂O (0.122 g, 0.5 mmol) was added, and the resulting solution was heated for 5–10 min, filtered while hot through celite and allowed to crystallize at room temperature. The precipitate, which was collected by filtration, was washed with Et₂O and dried in air. Crystals suitable for X-ray analysis were obtained from dilute methanolic solutions or by recrystallization from CH₃CN, but acetone was used in complex 4.

4.3.1. [Cu₂(µ₂-L³)₂] (3)

The reaction of Cu(NO₃)₂·3H₂O with H₂L³ and Et₃N (1:1:2) in MeOH, as indicated above, resulted in the formation a crude product, which upon recrystallization from CH₃CN, afforded large dark green crystalline compound (yield: 81.6%). Anal: calcd for C₄₀H₄₈Br₄Cu₂N₄O₄ (MM = 1089.90 g/mol): C, 43.85; H, 4.42; N, 5.11%. Found: C, 44.03; H, 4.47; N, 5.42%. IR bands (ATR, cm⁻¹): 2969 (vw), 2860 (vw), 2831 (vw), 2784 (vw) ν(C-H); 1603 (w), 1464 (vs), 1378 (w), 1278 (m), 1238 (s) ν(C=C, C-O, C-N); 1125 (m), 839 (s), 795 (s), 768 (s), 594 (m), 569 (m), 493 (m), 467 (m), 411 (s). ESI-MS (CH₃CN): m/z = 487.042. (100%), calcd [H₂L³ + H]⁺ = 487.042. UV-VIS: λ_max in nm (ε_max, M⁻¹cm⁻¹): in DMSO: 452 (2330), 763 (216, b). Λ_M (DMSO) = 3.0 Ω⁻¹·cm²·mol⁻¹.

4.3.2. [Cu₂(µ₂-L⁴)₂]·CH₃COCH₃ (4)

This complex was isolated as big chunks of light olive-green solid (yield: 98 mg, 82.9%.). Recrystallization from acetone afforded X-ray quality crystals. Anal: calcd for C₅₁H₇₄Cu₂N₄O₅ (MM = 948.425 g/mol): C, 64.46; H, 7.85; N, 5.90%. Found: C, 64.62; H, 7.88; N, 6.03%. IR bands (ATR, cm⁻¹): 2966 (w), 2903 (w), 2840 (w) ν(C-H); 1609 (w) ν(C=N); 1479 (s), 1377 (m), 1319 (s), 1243 (s) ν(C=C, C-O); 1158 (m), 1091 (m), 1017 (m), 972 (m), 855 (vs), 794 (s), 751 (s), 729 (m). ESI-MS (CH₃CN): 385.285 (100%), calcd [H₂L⁴ + H]⁺ = 385.286. UV-VIS in acetone: λ_max in nm (saturated solution): 409, 630 (b).

4.3.3. [Cu₃(µ₂-L⁹)₂(µ-OCH₃)₂]·CH₃OH (9)

The complex was isolated as shiny brownish-green crystalline compound atter recrystallization from acetone (yield: 69.3%). Anal: calcd for C₄₇H₆₆Cl₄Cu₃N₄O₆ (MM = 1131.500 g/mol): C, 49.89; H, 4.88; N, 4.95%. Found: C, 50.44; H, 5.16; N, 5.37%. IR bands (ATR, cm⁻¹): 2976 (w), 2922 (vw), 2845 (w) ν(C-H); 1585 (w) ν(C=N); 1462 (vs), 1285 (s), 1243 (vs) ν(C=C, C-O, C-N); 1010 (m), 935 (w), 864 (s), 766 (vs), 747 (s), 661 (m), 449 (s). ESI-MS: m/z = 425.176 (100%), calcd [H₂L⁹ + H]⁺ = 425.176. UV-VIS: λ_max in nm (ε_max, M⁻¹cm⁻¹): in DMSO: 447 (2650), 748 (251, b). Λ_M (DMSO) = 3.5 Ω⁻¹·cm²·mol⁻¹.

4.4. X-ray Crystal Structure Analysis

The X-ray single-crystal data of the title compounds 3, 4, and 9 were collected on a Bruker-AXS APEX II CCD diffractometer at 100 (2) K. The crystallographic data, conditions retained for the intensity data collection and some features of the structure refinements are listed in Table 3. Data collections were performed with Mo-Kα radiation (λ= 0.71073 Å); data processing, Lorentz-polarization, and absorption corrections were performed using APEX and the SADABS computer programs [77,78,79]. The structures were solved by direct methods and refined by full-matrix least-squares methods on F², using the SHELX [80,81,82] program library. Additional programs used: Mercury and PLATON [83]. Packing plots are given in the Supplementary Materials (Figures S1–S3).

Author Contributions

Conceptualization, Methodology, Validation, Investigation, Resources, Data curation, Writing—original draft, Writing—review & editing, Visualization, Supervision, Project administration, Funding acquisition: S.S.M., F.A.M., M.M. and M.H.; Methodology, Validation, Formal analysis, Investigation. Writing—review & editing: F.R.L. and N.N.M.H.S.; Methodology, Software, Validation, Formal analysis, Investigation, Data curation: R.C.F. and A.T.; Methodology, Formal analysis, Investigation, Data curation, Investigation, Resources, Data curation: M.T.D. and K.N. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the available article and Supplementary Materials.

Acknowledgments

This research was financially supported by the Department of Chemistry—University of Louisiana at Lafayette. Our thanks also to the reviewers for their constructive comments and suggestions.

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Samples of the compounds 1–10 are not available.

Footnotes

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Figures, Schemes and Tables

Scheme 1. Phenolate ligands used in this study and their abbreviations.

Scheme 2. Synthesis of the tripodal phenolate amine ligands and the doubly-bridged phenoxido-Cu(II) coordination core of complexes derived from N,N-dialkylethylenediamine backbone.

Figure 1. Perspective views of (a) 3, (b) 4, and (c) trinuclear subunit of 9.

Figure 2. Perspective views of 1, 2, 5–8, and 10 represented as (a–g), respectively.

Figure 3. Temperature dependence of magnetic susceptibility χM (Δ) and magnetic moment µeff (◦) of [Cu2(L1)2] (1).

Figure 4. Temperature dependence of magnetic susceptibility χM (Δ) and magnetic moment µeff (◦) of [Cu2(L3)2] (3).

Figure 5. Temperature dependence of magnetic susceptibility χM (◦) and magnetic moment µeff (◦) of [Cu2(L5)2(H2O)]·2H2O (5).

Figure 6. Temperature dependence of magnetic susceptibility χM (Δ) and magnetic moment µeff (◦) of [Cu2(L7)2](ClO4)2 (7).

Figure 7. Temperature dependence of magnetic susceptibility χM (Δ) and magnetic moment µeff (◦) of [Cu3(L9)2(µ-OCH3)2] (9).

Figure 8. Temperature dependence of magnetic susceptibility χM (Δ) and magnetic moment µeff (◦) of [Cu(L10)] (10).

Table 1

Selected bond distances (Å) and angles (°) of 3, 4, and 9.

3
Cu1-N1	2.089(10)	Cu2-N3	2.160(10)
Cu1-N2	2.325(10)	Cu2-N4	2.180(10)
Cu1-O1	1.892(8)	Cu2-O3	1.905(8)
Cu1-O2	1.963(9)	Cu2-O2	2.002(8)
Cu1-O4	2.013(8)	Cu2-O4	1.999(8)
Cu1-O2-Cu2	100.4(4)	O2-Cu1-O4	75.4(3)
Cu1-O4-Cu2	98.8(4)	O2-Cu2-O4	74.8(4)
O1-Cu1-O2	157.0(4)	O3-Cu2-O4	164.3(4)
O4-Cu1-N1	160.4(4)	O2-Cu2-N4	142.0(4)
4
Cu1-N1	2.0627(19)	Cu2-N3	2.090(2)
Cu1-N2	2.449(2)	Cu2-N4	2.3532(19)
Cu1-O1	1.8783(17)	Cu2-O3	1.8805(17)
Cu1-O2	1.9580(17)	Cu2-O2	2.0349(16)
Cu1-O4	2.0218(16)	Cu2-O4	1.9465(16)
Cu1-O2-Cu2	97.17(7)	O2-Cu1-O4	75.78(7)
Cu1-O4-Cu2	97.98(7)	O2-Cu2-O4	75.73(7)
O1-Cu1-O2	160.59(7)	O3-Cu2-O4	165.55(7)
O4-Cu1-N1	156.88(7)	O2-Cu2-N4	138.62(7)
9
Cu1-N1	2.054(2)	Cu3-N3	2.066(2)
Cu1-N2	2.351(2)	Cu3-N4	2.324(2)
Cu1-O1	1.929(2)	Cu3-O4	1.941(2)
Cu1-O2	2.000(2)	Cu3-O5	1.985(2)
Cu1-O3	1.957(2)	Cu3-O6	1.944(2)
Cu2-O2	1.9488(19)	Cu2-O3	1.999(2)
Cu2-O4	1.920(2)	Cu2-O5	1.959(2)
Cu1-O2-Cu2	97.33(9)	O2-Cu1-O3	75.43(8)
Cu1-O3-Cu2	100.19(9)	O2-Cu2-O3	77.73(8)
Cu2-O4-Cu3	99.27(9)	O4-Cu2-O5	77.91(8)
Cu2-O5-Cu3	96.48(9)	O4-Cu3-O5	76.79(8)
O2-Cu2-O4	102.80(8)	O3-Cu2-O5	103.85(9)
O1-Cu1-O2	161.11(8)	O5-Cu3-O6	153.32(9)
O3-Cu1-N1	161.70(8)	O4-Cu3-N3	167.39(9)

Table 2

Magnetostructural correlation of Cu₂O₂-phenoxido complexes.

Complex	J (cm−1)	C.N. (Geom., τ5 or τ4)	Cu…Cu(Å)	Cu-O-Cu’ (°)	Cu-O-Cu-O (°)	Cu-O-C-C(°)	τ (°)
1	−289	5 (SP, 0.23)	3.092	103.44	15.9	52.1	7.8
2	−202	5 (SP, 0.24)	3.006	99.12	24.9	57.3	3.6
3	−145	5 (SP, 0.06/0.37)	3.047	98.8, 100.4	24.8	50.9, 71.0	10.5, 12.2
4	−146	5(SP, 0.07/0.45)	2.995	97.17, 97.78	26.9	52.5, 67.5	3.2, 12.8
5	−176	4(SQP, 0.17)5(SP, 0.011)	2.9331	96.70, 97.58	29.4	50.5, 49.9	2.7, 5.5
6	−250	4(SQP, 0.17)5(SP, 0.013)	2.941	97.56, 96.93	29.8	49.9, 51.7	6.5, 4.6
7	−3.6	5(SP, 0.41) + 1	3.130	97.72	0	11.3	31.3
8	−4.6	5(SP, 0.40) + 1	3.098	96.63	0	11.3	30.9
9	−59	4(SQP, 0.17)5(SP: 0.01, 0.23)	2.9652 2.9418	96.48, 97.33, 99.27, 100.19	22.9, 23.5	44.2, 41.9	8.2, 20.0
10	+3.5	4(SQP, 0.23)	7.269

Table 3

Crystallographic data and processing parameters of 3, 4, and 9.

Compound	3	4	9
Empirical formula	C40H48Br4Cu2N4O4	C51H74Cu2N4O5	C47H62Cl4Cu3N4O7
Formula mass	1095.53	950.22	1131.45
System	Monoclinic	Triclinic	Monoclinic
Space group	P21/c	P-1	P21/n
a (Å)	15.433(3)	12.6538(12)	10.7647(5)
b (Å)	14.198(3)	13.0192(12)	29.4374(14)
c (Å)	20.973(4)	15.4646(15)	16.5922(8)
α (°)	90	95.347(5)	90
β (°)	100.460(7)	101.633(5)	90.673(2)
γ (°)	90	103.880(4)	90
V (Å3)	4519.2(16)	2395.5(4)	5275.5(4)
Z	4	2	4
θ max (°)	26.000	30.558	24.999
Data collected	82442	133738	159804
Unique refl.	8840	14144	9251
Parameters	495	573	600
Goodness-of-fit on F2	1.069	1.057	1.109
R1/wR2 (all data)	0.1102/0.2845	0.0528/0.1336	0.0357/0.0923

Supplementary Materials

The following are available online at www.mdpi.com/xxx/s1.CCDC 2241168-2241170 contains the supplementary crystallographic data for 3, 4, and 9, respectively. These data can be obtained free of charge via http//www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: [phone]; or e-mail: deposit@ccdc cam.ac.uk. Further supplementary data for Packing plots (Figures S1–S3) and Figure S4 for temperature dependence of magnetic susceptibility and magnetic moment µ_eff of 2. Table S1: Crystallographic data and processing parameters of 3, 4 and 9.

References

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