Photoluminescent Layered Crystal Consisting of Anderson-Type Polyoxometalate and Surfactant toward a Potential Inorganic–Organic Hybrid Laser

Abstract

The hybridization of inorganic and organic components is a promising strategy to build functional materials. Among several functions, luminescence is an important function which should be considered for practical usage. Inorganic–organic hybrid luminescent materials have been investigated as phosphors, sensors, and lasers. Organic luminescent centers such as dye molecules have often been hybridized with inorganic matrices. Polyoxometalate anions (POMs) are effective inorganic luminescent centers due to their luminescent properties and structural designability. However, most luminescent POM components are limited to lanthanide-based POMs. In this report, a photoluminescent inorganic–organic hybrid crystal based on a non-lanthanide POM was successfully synthesized as a single crystal. Anderson-type hexamolybdochromate ([CrMo₆O₁₈(OH)₆]³⁻, CrMo₆) anion exhibiting emission derived from Cr³⁺ was utilized with n-dodecylammonium ([C₁₂H₂₅NH₃]⁺, C₁₂NH₃) surfactant cation to obtain a photoluminescent hybrid crystal. The grown single crystal of C₁₂NH₃-CrMo₆ comprised a distinct layered structure consisting of inorganic CrMo₆ layers and interdigitated C₁₂NH₃ layers. In the CrMo₆ layers, the CrMo₆ anions were associated with water molecules by hydrogen bonding to form a densely packed two-dimensional network. Steady-state and time-resolved photoluminescence spectroscopy revealed that the C₁₂NH₃-CrMo₆ hybrid crystal exhibited characteristic emission from the CrMo₆ anion. Preliminary lasing properties were also observed for C₁₂NH₃-CrMo₆, which shows the possibility of using the C₁₂NH₃-CrMo₆ hybrid crystal as an inorganic–organic hybrid laser.

1. Introduction

Synthetic methodology is crucial for the construction of functional compounds and/or materials. The hybridization of inorganic and organic components is a promising strategy to build functional materials [1,2,3]. Unprecedented functions can emerge from the combination of inorganic and organic components. Inorganic motifs can contribute to thermal stability and elemental variation, whereas organic motifs enable flexible molecular design. The synergy of inorganic and organic characteristics has been realized in conductive [4], adsorbent [5], and magnetic materials [6].

Luminescence is another important function which should be considered for several reasons. Inorganic–organic hybrid materials have been investigated as phosphors, sensors, and lasers [7,8,9,10]. Organic luminophores or dyes are often utilized in inorganic matrices [11]. Several inorganic–organic hybrids contain inorganic luminescent centers such as lanthanides, which behave as distinct luminescent centers exhibiting sharp spectra due to the transitions of inner-shell 4f electrons [12,13,14,15].

Polyoxometalate molecular clusters (POMs) are also effective inorganic luminescent centers due to their luminescent properties and structural designability [16,17,18]. Lanthanide-containing POMs [19,20,21] are typically employed, and several luminescent inorganic–organic hybrids have been reported [22,23]. Anderson-type POMs [24,25,26] are another class of luminescent POMs. Hexamolybdochromate [CrMo₆O₁₈(OH)₆]³⁻ (CrMo₆, Figure 1a) anion comprises Cr³⁺ surrounded by six oxygen atoms exhibiting red emission similar to ruby lasers [27,28,29,30,31]. In addition, Anderson-type POMs possess planar molecular shapes leading to layered structures [32,33,34,35]. Layered packing of luminescent species gives rise to anisotropic emission, which is beneficial for lasing properties. However, Anderson-type POMs have rarely been employed as luminescent centers in inorganic–organic hybrid materials [30,31,35].

In this report, we constructed an inorganic–organic hybrid with a luminescent Anderson-type CrMo₆ anion and surfactant cation. The use of n-dodecylammonium ([C₁₂H₂₅NH₃]⁺, C₁₂NH₃, Figure 1b) derived from aliphatic primary amines enabled the crystallization of the CrMo₆-surfactant hybrid as single crystals. The C₁₂NH₃-CrMo₆ hybrid crystal possessed a distinct layered structure due to the planar CrMo₆ anion and the structure-directing C₁₂NH₃ surfactant. The emission properties, including the preliminary lasing behavior, were investigated.

2. Results

2.1. Synthesis of C₁₂NH₃-CrMo₆ Hybrid Crystal

The C₁₂NH₃-CrMo₆ hybrid crystal was obtained by an ion exchange reaction between the sodium salt of CrMo₆ (Na₃[CrMo₆O₁₈(OH)₆]·8H₂O, Na-CrMo₆) and C₁₂NH₃ cations. The single crystals of C₁₂NH₃-CrMo₆ were successfully grown from the synthetic filtrate after the removal of a precipitate of the C₁₂NH₃-CrMo₆ hybrid crystal. The IR spectra (Figure 2) exhibited characteristic peaks of CrMo₆ (400–1100 cm⁻¹), which were assigned as terminal Mo–O_t bonds (950–890 cm⁻¹) and bridging Mo–O–Mo bonds (700–400 cm⁻¹) [36,37,38]. Characteristic peaks of C₁₂NH₃ were observed in the range of 2800–3000 cm⁻¹, 2920 cm⁻¹ for ν_as(−CH₂−), and 2850 cm⁻¹ for ν_s(−CH₂−), respectively. The almost identical IR spectra of the precipitate (Figure 2b) and single crystal (Figure 2c) indicated that the precipitate and single crystal of the C₁₂NH₃-CrMo₆ hybrid were the same in terms of their molecular structures.

The precipitate and single crystal of the C₁₂NH₃-CrMo₆ hybrid crystal exhibited slightly different XRD patterns (Figure 3a,b). Both XRD patterns showed strong peaks assignable to 001 and 002 reflections in the lower 2-theta range featuring layered materials. Estimated interlayer spacing was 24.5 Å for the C₁₂NH₃-CrMo₆ precipitate and 26.6 Å for the C₁₂NH₃-CrMo₆ single crystal, respectively. The XRD pattern of the C₁₂NH₃-CrMo₆ single crystal was similar to that calculated from the single-crystal X-ray analysis data (Figure 3c). Subtle differences in the peak intensity and position of the patterns may be due to the difference in the measurement temperature (powder: room temperature, single crystal: 103 K), and to the preferred orientation derived from the predominant layered structure of C₁₂NH₃-CrMo₆.

2.2. Crystal Structure of C₁₂NH₃-CrMo₆ Hybrid Crystal

The presence and molecular structure of the CrMo₆ anion were revealed via X-ray structural analysis (Table 1, Figure 4). The asymmetric unit consisted of two half-anions of CrMo₆ and three C₁₂NH₃ cations including water of crystallization (Figure 4a). This indicates that one CrMo₆ anion (3− charge) was connected with the three C₁₂NH₃ cations due to charge compensation, which was verified by CHN elemental analysis. Four water molecules (O25, O26, O27, and O28) were assigned unambiguously. Some terminal atoms (C11 and C12) in the C₁₂NH₃ dodecyl chain were disordered, and a small electron density (2.62 eÅ⁻³) remained ca. 2.8 Å away from C12A in the main part of the disordered atoms (Supplementary Material, Figure S1). We assigned this small electron density to a disordered water molecule (O29B) in the minor disordered part together with C11B and C12B, which was refined to have a site occupancy of 0.32. Therefore, the C₁₂NH₃-CrMo₆ single crystal contained 4.32 water molecules per CrMo₆ anion, leading to the chemical formula of [C₁₂H₂₅NH₃]₃[CrMo₆O₁₈(OH)₆]·4.32H₂O. The six H atoms in the hydroxo group of CrMo₆ were identified using the X-ray diffraction analysis and bond valence sum (BVS) calculations [39]. The BVS values of the protonated O atoms (O8, O11, O12, O16, O23, and O24) in CrMo₆ were in the range of 1.19–1.28, whereas those for other O atoms were in the range of 1.65–1.86.

The crystal of C₁₂NH₃-CrMo₆ was composed of alternating CrMo₆ inorganic monolayers and C₁₂NH₃ organic bilayers parallel to the ab plane (Figure 4b), as typically observed for surfactant-POM hybrid single crystals [40]. The layered periodicity was 26.7 Å, which was consistent with the powder XRD pattern (Figure 3b). The aliphatic chains of C₁₂NH₃ were interdigitated in a straight line. Some solvent water molecules (O27, O28, and O29B) were located at the interface between the CrMo₆ and C₁₂NH₃ layers (Figure 4b). On the other hand, two water molecules (O25 and O26) were located inside the inorganic CrMo₆ monolayer. These CrMo₆ anions and water molecules were densely packed to form a two-dimensional network via short contacts, including O–H⋯O hydrogen bonding (Figure 4c) [41]. The O⋯O distance ranged from 2.71 to 3.00 Å (mean value: 2.80 Å). The hydrophilic heads of C₁₂NH₃ did not penetrate the densely packed CrMo₆-H₂O monolayers, but were located at the dip between the CrMo₆ anions [42] by forming N–H⋯O hydrogen bonds with distances of 2.71–2.84 Å (mean value: 2.78 Å) [41].

2.3. Photoluminescent Properties of C₁₂NH₃-CrMo₆ Hybrid Crystal

As mentioned above, the CrMo₆ anion exhibits a distinct red emission due to the presence of Cr³⁺ like ruby lasers [27,28,29,30,31]. The photoluminescent properties of C₁₂NH₃-CrMo₆ were evaluated using steady-state and time-resolved spectroscopy. The diffuse reflectance spectra (Figure 5a) of both C₁₂NH₃-CrMo₆ and Na-CrMo₆ (starting material) showed broad peaks around 390 and 540 nm, corresponding to the transitions of the d³ electron in Cr³⁺ from the ⁴A₂ ground state to the ⁴T₁ and ⁴T₂ excited states, respectively [27]. These electron transitions were also observed in the excitation spectra of C₁₂NH₃-CrMo₆ and Na-CrMo₆, as shown in Figure 5b. Characteristic emission derived from Cr³⁺ was observed around 680–710 nm (Figure 5b), which was investigated in detail using time-resolved spectroscopy.

Figure 6a shows the emission spectra of C₁₂NH₃-CrMo₆ and Na-CrMo₆ obtained using a single pulse excitation. Emission peaks at around 682, 688, 701, and 707 nm were derived from the ²T₁ → ⁴A₂ transition known as “R-lines” [27,28,29,30,31]. The peaks at around 730 nm were assigned to the ²E → ⁴A₂ transition. The spectral shapes of C₁₂NH₃-CrMo₆ were almost identical to those of Na-CrMo₆ irrespective of the measurement temperatures. On the other hand, the emission intensity of C₁₂NH₃-CrMo₆ was lower than that of Na-CrMo₆ (Figure 6a), and the emission of C₁₂NH₃-CrMo₆ decayed faster than that of Na-CrMo₆ at each temperature (Figure 6b). The estimated emission lifetimes were 26 μs (15 K) and 11 μs (300 K) for C₁₂NH₃-CrMo₆ and 55 μs (15 K) and 24 μs (300 K) for Na-CrMo₆.

The title compound C₁₂NH₃-CrMo₆ had a distinct layered structure together with characteristic emission as described above, which is associated with the plausible emergence of lasing properties. To evaluate the possibility of inorganic–organic hybrid laser materials, the emission intensity of C₁₂NH₃-CrMo₆ was explored by changing the excitation laser power. Figure 7 shows the emission intensity-excitation laser power dependency at 15 and 300 K. The emission intensity increased linearly with an increase in the excitation laser power above the threshold value, which indicates the emergence of preliminary lasing properties [43,44,45,46]. The threshold values were 22.4 mJ cm⁻² for 15 K and 26.7 mJ cm⁻² for 300 K, respectively.

3. Discussion

We first synthesized a photoluminescent polyoxometalate-surfactant hybrid crystal by using an Anderson-type CrMo₆ anion and C₁₂NH₃ surfactant cation. Using primary alkylammonium cations seems essentially effective for the crystallization of the CrMo₆ anion with surfactant cations. The powder XRD patterns of the C₁₂NH₃-CrMo₆ hybrid crystal (Figure 3) suggest that the precipitates and single crystals of the C₁₂NH₃-CrMo₆ hybrid crystal had slightly different phases in their interlayer periodicities. The interlayer spacing was 24.5 Å for the precipitate and 26.6 Å for the single crystal. The precipitate and single crystal possessed distinct layered structures, both of which are believed to be essentially similar, except for the interlayer distances. The difference is derived from the desorption of water molecules (O27, O28, and O29B highlighted in Figure 4b) from the crystalline lattice, shrinking the layered distance to 24.5 Å of the precipitate from 26.6 Å of the single crystal.

Single-crystal X-ray diffraction analysis confirmed a distinct layered structure consisting of the CrMo₆ inorganic layers and C₁₂NH₃ organic layers. Notably, the CrMo₆ anions formed a two-dimensional infinite layer with the water molecules through O–H⋯O hydrogen bonding in the CrMo₆ inorganic layers. The hydrophilic heads of the C₁₂NH₃ surfactant did not penetrate the inorganic CrMo₆-H₂O monolayers as observed in another POM crystal hybridized with C₁₂NH₃ [42]. This implies that a densely packed POM inorganic layer is easily formed by using a primary alkylammonium cation with a smaller hydrophobic head [40].

The photoluminescent properties of C₁₂NH₃-CrMo₆ were investigated by steady-state and time-resolved spectroscopy, revealing the characteristic ruby-like emission derived from Cr³⁺ in the CrMo₆ anion. As shown in Figure 6a, the emission spectra of C₁₂NH₃-CrMo₆ were almost identical in shape to those of Na-CrMo₆ irrespective of the measurement temperature. This suggests that the crystal fields of Cr³⁺ in C₁₂NH₃-CrMo₆ and Na-CrMo₆ were similar due to the structural rigidity of the CrMo₆ anion. The spectral shape of the C₁₂NH₃-CrMo₆ emission was similar to that of previous compounds containing the CrMo₆ anion [29,30,31]. On the other hand, the emission lifetimes of C₁₂NH₃-CrMo₆ (26 μs at 15 K and 11 μs at 300 K) were shorter than those (55 μs at 15 K and 24 μs at 300 K) of Na-CrMo₆ and another inorganic–organic hybrid consisting of CrMo₆ anions (240 μs) [30]. These results indicate that the emission efficiency of the CrMo₆ anion depends on the countercation and that the C₁₂NH₃ cation reduces the emission efficiency. In C₁₂NH₃-CrMo₆, nonradiative deactivation of the excitation energy (O → Mo ligand-to-metal charge transfer) occurs more easily than in Na-CrMo₆ through the vibration states of the high-frequency C–H oscillators in C₁₂NH₃ [35].

The distinct layered structure of the C₁₂NH₃-CrMo₆ hybrid crystal is beneficial for the emergence of lasing properties. Preliminary lasing behavior was observed by changing the excitation laser power, exhibiting the lasing threshold values of 22.4 mJ cm⁻² at 15 K and 26.7 mJ cm⁻² at 300 K, respectively (Figure 7). These threshold values were much larger than those of recent organic lasers (order of μJ cm⁻²) [44,45,46], indicating a lower lasing efficiency in C₁₂NH₃-CrMo₆, probably due to the use of randomly oriented crystalline powder [47]. In the future, the fabrication of large single crystals [48,49] in higher yields or the construction of microcavity structures [47] will be a promising strategy to improve the lasing emission efficiency. The thermal gravimetric (TG) profiles (Figure S2) suggest that the hybrid crystal of C₁₂NH₃-CrMo₆ started to decompose from ca. 423 K (150 °C) due to the removal of the C₁₂NH₃ cation. A temperature of 423 K (150 °C) may be rather low for the removal of the C₁₂NH₃ cation, and the details of this phenomenon are still unclear. Our previous results showed that three hybrid crystals consisting of decavanadate anions and double-headed primary ammonium cation started to decompose from ca. 473 K (200 °C) [50]. In these cases, the organic ammonium cation was divalent and more strongly associated with the polyoxometalate anion than the monovalent C₁₂NH₃ cation. Therefore, we speculate that the C₁₂NH₃-CrMo₆ hybrid crystal could start to decompose due to the removal of the C₁₂NH₃ cation at ca. 423 K (150 °C). The thermal stability of the C₁₂NH₃-CrMo₆ hybrid crystal may be improved by blending C₁₂NH₃-CrMo₆ with other polymers or glassy matrices to dilute the C₁₂NH₃-CrMo₆ component. Although a more sophisticated fabrication process should be applied to improve the lasing efficiency, the C₁₂NH₃-CrMo₆ hybrid crystal has shown potential as another category of inorganic–organic hybrid laser materials.

4. Materials and Methods

4.1. Materials

Chemical reagents including n-dodecylammonium chloride (C₁₂NH₃-Cl) were obtained from commercial sources (FUJIFILM Wako Pure Chemical Corporation, Osaka, Japan, and Tokyo Chemical Industry Co., Ltd. (TCI), Tokyo, Japan) and used without further purification. The sodium salt of CrMo₆ (Na₃[CrMo₆O₁₈(OH)₆]·8H₂O, Na-CrMo₆) was prepared according to the literature [26,27]: Na₂MoO₄·2H₂O (36.3 g, 150 mmol) was dissolved in 75 mL of H₂O, and the solution pH was adjusted to 4.4 with HNO₃. An aqueous solution (10 mL) containing 10 g of Cr(NO₃)₃·9H₂O (25.0 mmol) was added to a pH-adjusted solution, and the solution was sequentially heated at 353 K for 1 h. The resultant supernatant was obtained by filtration and kept at room temperature for a week to isolate pink-purple block crystals of Na-CrMo₆ (7.0 g, yield: 23% based on Mo).

4.2. Synthesis of C₁₂NH₃-CrMo₆ Hybrid Crystal

An ethanol solution (30 mL) of C₁₂NH₃-Cl (0.11 g, 0.50 mmol) was added to an aqueous solution (30 mL) of Na-CrMo₆ (0.34 g, 0.28 mmol) with heating at 333 or 343 K, and stirred for 5 min. The resultant suspension was filtrated and dried in the air to obtain a pale pink precipitate of C₁₂NH₃-CrMo₆ (0.21–0.25 g, yield 45–54%). Single crystals of C₁₂NH₃-CrMo₆ were grown from the synthetic filtrate kept at 315 or 323 K (0.01 g, yield ca. 2%). Some water molecules were removed from the crystal lattice in an ambient atmosphere. Anal. Calcd for C₃₆H₉₄N₃CrMo₆O₂₄: C, 26.81; H, 5.87; N, 2.61%. Found: C, 26.85; H, 5.75; N, 2.69%. IR (KBr disk): 956 (m), 917 (s), 888 (s), 806 (w), 693 (m), 646 (s), 570 (w), 551 (w), 518 (w), and 416 (w) cm⁻¹.

4.3. Measurements

Infrared (IR) spectra were measured using an FT/IR-4200ST spectrometer (Jasco Corporation, Tokyo, Japan, KBr pellet method). Powder X-ray diffraction (XRD) patterns were recorded using a MiniFlex300 diffractometer (Rigaku Corporation, Tokyo, Japan, Cu Kα radiation, λ = 1.54056 Å) under an ambient atmosphere. CHN (carbon, hydrogen, and nitrogen) elemental analyses were performed using a 2400II elemental analyzer (PerkinElmer, Inc., Waltham, MA, USA). Thermal gravimetric (TG) analyses were carried out on a TG/DTA-6200 (Seiko Instruments, Chiba, Japan) at a heating rate of 10 °C min⁻¹ in a nitrogen atmosphere.

Steady-state diffuse reflectance, excitation, and emission spectra were recorded at 300 K using an FP-6500 fluorescence spectrometer (Jasco Corporation, Tokyo, Japan) equipped with an Xe lamp. Time-resolved emission spectra were obtained at 15 and 300 K with an Ultra CFR 400 YAG:Nd³⁺ laser (Big Sky Laser Technologies, Inc., Bozeman, MT, USA, 266 nm fourth harmonics, pulse duration 10 ns with a repetition rate of 10 Hz) as an excitation source. A Spectra Pro 2300i (Princeton Instruments, Inc., Trenton, NJ, USA) was utilized as a spectrometer, and a PI-Max with an intensified CCD camera (Princeton Instruments, Inc., Trenton, NJ, USA) was used as a detector. Pelletized samples of the C₁₂NH₃-CrMo₆ precipitate were used for the aforementioned photoluminescence measurements.

4.4. X-ray Crystallography

Single crystal X-ray diffraction was measured with an XtaLAB PRO P200 diffractometer (Rigaku Corporation, Tokyo, Japan) using graphite monochromated Mo Kα radiation (λ = 0.71073 Å). The acquisition and processing of diffraction images including absorption correction were performed using CrysAlisPro (Version 1.171.39.46) [51]. Crystal structures were solved using SHELXT (Version 2018/2) [52] and refined by the full-matrix least-squares using SHELXL (Version 2018/3) [53]. The diffraction data recorded at the 2D beamline of the Pohang Accelerator Laboratory (PAL) confirmed the same crystal structure. CCDC 2312544.

Author Contributions

Conceptualization, T.I; methodology, A.M., K.M. and T.S.; validation, T.K., Y.S. and T.I.; formal analysis, T.I., T.K., Y.S., H.I., Y.O. (Yoshiki Oda) and Y.O. (Yosuke Okamura); investigation, A.M., T.K., Y.S., K.M., T.S., N.M. and A.W.; resources, Y.S., Y.O. (Yoshiki Oda) and Y.O. (Yosuke Okamura); writing—original draft preparation, T.I.; writing—review and editing, T.I. and Y.S.; visualization, T.I., Y.S. and A.M.; funding acquisition, T.I. 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

Further details of the crystal structure investigation (CCDC 2312544) can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif (accessed on 7 December 2023), or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: [phone].

Acknowledgments

X-ray diffraction measurements with synchrotron radiation were performed at the Pohang Accelerator Laboratory (Beamline 2D, proposal No. 2019-3rd-2D-M003), a synchrotron radiation facility in Pohang, Republic of Korea, supported by Pohang University of Science and Technology (POSTECH).

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Footnotes

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Figures and Table

Figure 1. (a) Molecular structure of hexamolybdochromate (CrMo6) anion. Mo: teal, Cr: light green, O: red, H: white in ball-and-stick representation, Mo: pink, and Cr: light blue in polyhedral representation; (b) molecular structure of n-dodecylammonium (C12NH3) cation.

Figure 2. IR spectra of C12NH3-CrMo6 hybrid crystal: (a) starting material of Na-CrMo6; (b) precipitate of C12NH3-CrMo6; (c) single crystal of C12NH3-CrMo6.

Figure 3. Powder X-ray diffraction patterns of C12NH3-CrMo6 hybrid crystal: (a) precipitate of C12NH3-CrMo6; (b) single crystal of C12NH3-CrMo6; (c) calculated pattern of C12NH3-CrMo6 from the structure revealed by single-crystal X-ray diffraction.

Figure 4. Crystal structure of C12NH3-CrMo6 (Mo: teal, Cr: light green, C: gray, N: blue, O: red, and H: white). H atoms of C12NH3 cations and solvents were omitted for clarity: (a) asymmetric unit. Disordered atoms (C11B, C12B, and O29B) in the minor part are indicated in transparent color; (b) packing diagram along a-axis. CrMo6 anions are depicted in a polyhedral model (Mo: pink; Cr: light blue). Some solvents (O27, O28, and O29B) are highlighted by green circles; (c) molecular arrangement of the inorganic monolayer (ab plane) in ball-and-stick (left) and polyhedral (right) representations. Broken lines represent short contacts including O–H···O hydrogen bonding between the CrMo6 anions and solvents.

Figure 5. Steady-state spectra of C12NH3-CrMo6 and Na-CrMo6 (starting material). The measurement temperature was 300 K: (a) diffuse reflectance spectra; (b) excitation and emission spectra. Excitation spectra were monitored for the emission at 705 nm. Emission spectra were measured with an excitation wavelength of 300 nm.

Figure 6. Photoluminescence properties of C12NH3-CrMo6 and Na-CrMo6 (starting material) investigated using time-resolved spectroscopy. Each spectrum or decay profile was obtained using a single-pulse excitation with a wavelength of 266 nm: (a) emission spectra measured at 15 K (left) and 300 K (right) with an acquisition time of 0–50 μs; (b) emission decay profiles measured at 15 K (left) and 300 K (right) on the emission at 688 nm.

Figure 7. Emission intensity-excitation laser power dependency of C12NH3-CrMo6 at 15 and 300 K. Each data point was obtained using a single-pulse excitation with a wavelength of 266 nm on the emission at 688 nm. Data acquisition time: 0–50 μs.

Table 1

Crystallographic data.

Compound	C12NH3-CrMo6
Chemical formula	C36H98.63N3CrMo6O28.32
Formula weight	1654.50
Crystal system	triclinic
Space group	P$\overline{1}$ (No. 2)
a (Å)	7.8562(4)
b (Å)	15.0256(6)
c (Å)	26.7754(13)
α (°)	94.034(4)
β (°)	91.871(4)
γ (°)	90.861(4)
V (Å3)	3150.7(3)
Z	2
ρcalcd (g cm−3)	1.744
T (K)	103(2)
Wavelength (Å)	0.71073
μ (mm−1)	1.399
No. of reflections measured	53,171
No. of independent reflections	16,383
R int	0.1024
No. of parameters	724
R1 (I > 2σ(I))	0.0535
wR2 (all data)	0.1041

Supplementary Materials

The supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/ijms25010345/s1.

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