Hexameric Silver(I) Pyrazolate: Synthesis, Structure, and Isomerization

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Hexameric Silver(I) Pyrazolate: Synthesis, Structure, and Isomerization Xing-Pu Lv, Dong-Hui Wei, and Guang Yang* College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, China

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S Supporting Information *

ABSTRACT: The first binary hexameric silver(I) pyrazolate (Ag6pz6) has been prepared, and X-ray analysis demonstrated that it takes a rare figure-eight shape (pz− = deprotonated tertbutyl 3,5-diphenyl-1H-pyrazole-4-carboxylate). The hexamer can be easily converted to its tetrameric isomer (Ag4pz4) by recrystallization from ether. On the basis of the 1H NMR and mass spectrometry measurements, it is conjectured that the hexamer, after dissolving in CHCl3, quickly achieves equilibrium with Ag4pz4 and Ag3pz3, with the equilibrium lying far to the side of smaller rings.

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INTRODUCTION

although only the tetranuclear species can be isolated as crystals from solution.12 The substituents on the pyrazolyl ring have proven to exert an influence on the geometry and/or electronic properties of metal pyrazolates.6d,13,14 As a part of our ongoing project in the coordination chemistry of pyrazole, tert-butyl 3,5-diphenyl-1Hpyrazole-4-carboxylate (abbreviated as pzH, Scheme 1)15 has

It has long been known that binary monovalent coinage metal pyrazolates exhibit structural isomerism with nuclearity of 3, 4, 6, or infinity for the generic formula of MInpzn, where M = Cu, Ag, Au, pz− = pyrazolate, and n = 3, 4, 6, ∞.1−4 While the triangular isomer MI3pz3 has so far been the most often encountered,5 the saddlelike MI4pz46 and the infinite chain (MIpz)∞7 are relatively less common. The hexameric isomer is still rare; as a matter of fact, there is only one example hitherto known, namely, AuI6(Ph2pz)6 (Ph2pz− = 3,5-diphenylpyrazolate), whose synthesis and structure were reported by Raptis et al. in 1987.8 X-ray analysis demonstrated that this hexamer has an uncommon shape of “figure-eight”. Since then, no other similar hexameric pyrazolate has appeared in the literature, although a few other types of “figure-eight” compounds are known.9 The solution chemistry of metal pyrazolates might be more complicated than one thought of based on solid-state structures, and in several cases, conversions between different structural isomers have been observed. As early as 1993, Bonati and co-workers noted that the different oligomers of (AuIpz)n (n = 3, 4) may simultaneously be present in solution, based on NMR and mass spectrometry (MS) measurements (pz− = 3,5di-tert-butylpyrazolate or 3,4-dimethyl-5-ethylpyrazolate).10 We later isolated the crystals of tetranuclear gold(I) 3,5-di-tertbutylpyrazolate from a CH2Cl2 solution and determined its structure using X-ray diffraction.6d Stavropoulos’ group once reported that recrystallization of a triangular copper(I) pyrazolate [Cu3(py)(2-(3-pz),6-Mepy)3] from toluene led to the formation of a tetrameric species (py = pyridine).11 Using diffusion ordered spectroscopy (DOSY) and variable-temperature 1H NMR spectroscopy, Meyer’s group has shown that the copper(I) complexes with 3,5-bifunctionalized pyrazoles exist in solution as a mixture of tetrameric and trimeric species, © 2017 American Chemical Society

Scheme 1. Structure of the Ligand pzH

been used as a ligand for two reasons: (1) the carboxylic acid ester group is strongly electron-withdrawing,16 which may increase the π acidity of the trimeric M3pz3 if desired; (2) the tert-butyl group may render the metal pyrazolates better solubility in organic solvents, thus facilitating crystal growth and the study of solution behaviors. In this paper, we report the synthesis, crystal structures of the hexameric Ag6pz6 and tetrameric Ag4pz4, and structural conversion between the isomers of Agnpzn, where n may be 3, 4, or 6.

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RESULTS AND DISCUSSION Synthesis and Characterization. Colorless needles (sometimes pale-yellow blocks) can be obtained by the solvothermal reaction of AgNO3 and an equivalent amount of pzH in methanol at 100 °C for 3 days. Elemental analysis indicated that the molar ratio of M/L is 1:1 for the two forms Received: July 9, 2017 Published: September 5, 2017 11310

DOI: 10.1021/acs.inorgchem.7b01717 Inorg. Chem. 2017, 56, 11310−11316

Article

Inorganic Chemistry

On the other hand, the needle polymorph crystallizes in the monoclinic space group C2/c and its asymmetric unit contains one and a half molecules of Ag6pz6, the latter of which is related to its remaining half via a 2-fold axis passing through the midpoint of the central Ag···Ag contact (Figures S8 and S9).

of crystals. Subsequent X-ray analysis verified that these two kinds of crystals consist of hexmeric Ag6pz6 molecules; however, they have different space groups; therefore, both are the polymorphs of Ag6pz6. The synthesis was also conducted at ambient conditions: mixing of equivalent amounts of AgNO3, pzH, and Et3N in methanol afforded a white powder, which was demonstrated to be the same as the needlelike Ag6pz6, based on powder X-ray diffraction (PXRD) measurements (Figure S1). This observation implies that the solvothermal condition is not a prerequisite to producing the hexamer. Interestingly, recrystallization of the powdery sample of Ag6pz6 from ether gave rise to colorless squares, which were determined to be the tetrameric Ag4pz4 by single-crystal X-ray diffraction and a comparison of the PXRD patterns (Figure S2). It thus represents a rare example of conversion triggered by recrystallization between different isomers of coinage metal pyrazolates; we are aware of another example, as mentioned in the Introduction: transforming a trimeric copper(I) pyrazolate to a tetrameric species through recrystallization.11 The preparation of Ag6pz6 and Ag4pz4 is summarized in Scheme 2. Scheme 2. Synthesis of Ag6pz6 and Ag4pz4

The IR spectra of Ag6pz6 and Ag4pz4 display characteristic absorption bands for carboxylate groups: the strong peaks at 1705 and 1129 cm−1 for Ag6pz6 and 1699 and 1135 cm−1 for Ag4pz4 can be assigned to the stretching vibration of CO and the asymmetric vibration of C−O−C, respectively (Figure S3). Thermogravimetry (TG) measurements indicated that Ag6pz6 (needle polymorph) and Ag4pz4 started to lose weight at 242.6 or 233.2 °C, respectively. However, the differential scanning calorimetry curve of Ag6pz6 shows that it also experienced a small endothermic process at 236.4 °C before weight loss. From the onset points of weight loss to 600 °C, both complexes underwent first a small endothermic event (at 252.9 °C for Ag6pz6 and 244.8 °C for Ag4pz4) and then a huge exothermic event (at 496.6 °C for Ag6pz6 and 492.1 °C for Ag4pz4), accompanying a successive severe weight loss, indicative of the decomposition of the complexes. The final residue accounts for 27.75% or 26.36% of the total mass for Ag6pz6 or Ag4pz4, respectively, which might be Ag2O, based on the calculated residual weight percentage (27.18% for both complexes; Figures S4 and S5). A preliminary screening of the photoluminescence properties of Ag4pz4 and Ag6pz6 was performed. At room temperature, neither complex emitted under UV irradiation. However, at 83 K, they exhibited luminescence with maxima at 451 and 452 nm when excited at 285 and 274 nm, respectively (Figure S6). Their almost identical luminescent spectra suggest that the emissions observed are mainly ligand-centered for Ag6pz6 and Ag4pz4.17 Description of the Crystal Structures. As we mentioned before, Ag6pz6 displays polymorphism. The block polymorph of Ag6pz6 crystallizes in the monoclinic space group P21/n, the asymmetric unit consists of one Ag6pz6 molecule (Figure S7).

Figure 1. Molecular structure of Ag6pz6 (as in the block polymorph). (a) Top view of Ag6pz6. H atoms have been omitted for clarity. (b) Skeleton of (Ag−N−N)6, showing the shortest Ag···Ag contact as the dashed red line. Selected distances (Å): Ag1···Ag2 3.4050(1), Ag1··· Ag5 3.8537(2), Ag1···Ag6 3.6659(2), Ag2···Ag3 3.3502(3), Ag2···Ag4 4.1533(2), Ag2···Ag5 3.2052(3), Ag2···Ag6 4.1435(2), Ag3···Ag4 3.7435(2), Ag3···Ag5 4.2093(2), Ag4···Ag5 3.3915(2), Ag5···Ag6 3.3338(2). Selected angles (deg): N2−Ag1−N1 173.66(8), N3− Ag2−N3 174.77(8), N3−Ag3−N4 176.44(9), N6−Ag4−N7 174.51(8), N9−Ag5−N8 169.79(8), N11−Ag6−N10 174.93(8).

As shown in Figures 1 and S9 and S10 and Table 1, the structures of the Ag6pz6 molecules are almost identical from different sources (e.g., in different polymorphs or in the same crystals but crystallographically independent): All of them exhibit the shape of a two-blade propeller of D2 symmetry. Looking down the paper, the 18-membered twisted ring −(Ag−N−N)6 looks like a figure-eight (Figure 1b). While the Ag−N bond lengths of the hexamer are quite normal, compared with those of reported trimers,5c,18 some of the intramolecular Ag···Ag distances in Ag6pz6 are much longer than those in trimers, and the N−Ag−N bond angles deviate significantly from the ideal 180° for linear two-coordination. The distances between a pair of the central Ag atoms are 3.2052(3) Å (Ag2···Ag5) for the block polymorph and 3.2708(3) Å (Ag6···Ag7) and 3.1995(3) Å (Ag3···Ag3A) for the needle polymorph, which are the shortest Ag···Ag contacts 11311

DOI: 10.1021/acs.inorgchem.7b01717 Inorg. Chem. 2017, 56, 11310−11316

Article

Inorganic Chemistry Table 1. Comparison of the Structural Parameters of Ag6pz6, Ag4pz4, and Ag3pz3 Ag6pz6 block Ag−N (Å) av. Ag−N (Å)

2.061−2.119 2.0901

shortest Ag−Ag (Å)

3.2052

N−Ag−N (deg)

169.79−176.44

Ag6pz6 needle a

2.0573−2.0987, 2.0718−2.0970 2.0788 2.0846 3.2708 3.1995 172.15−177.00, 173.99−176.74

Ag4pz4 b

Ag3pz3c

2.063−2.087 2.0755

2.000−2.007 2.004

3.5278

3.3420

178.40−179.65

175.34−179.48

a

Data for the whole hexameric molecule in the asymmetric unit of the needle polymorph of Ag6pz6. bData for the half hexameric molecule in the asymmetric unit of the needle polymorph of Ag6pz6. cData obtained by theoretical calculation.

within the hexamers, implying that the argentophilic attraction here may play an important role in stabilization of the structure.19 Extensive intra- or intermolecular π interactions including π−π stacking and C−H π interactions are observed in all of the complexes, which might provide additional stabilization energy for the formation of compounds20,21 (Figures S11−S17). Figure 2 shows a common structural feature for Ag6pz6 molecules, a triple-decker motif formed by two phenyl rings and one pyrazolyl ring via π−π stacking.

Figure 3. Ball-and-stick diagram of Ag4pz4. H atoms have been omitted for clarity. Selected distances (Å): Ag−N 2.065−2.087(3), Ag1···Ag2 3.5278(3), Ag2···Ag3 3.6354(4), Ag3···Ag4 3.5870(3), Ag1···Ag4 3.7676(4), Ag1···Ag3 5.1667(4), Ag2···Ag4 5.0989(4). Selected angles (deg): N1−Ag1−N8 179.7(1), N2−Ag2−N3 178.4(1), N4−Ag3−N5 179.3(1), N6−Ag4−N7 179.1(1). Figure 2. Triple-decker structural motif as in the block polymorph of Ag6pz6.

groups from two adjacent Ag4pz4 molecules; C(tBu)H···pz and C(Ph)H···Ph interactions may cooperatively contribute to such an arrangement (Figures 4 and S21). Table 1 also lists the geometric parameters of the hypothetical Ag3pz3 molecule. The presence of the trimer was supported by the MS measurements (as discussed in the following part); however, our attempt has so far been

It is worth noting that this Ag6pz6 hexamer strikingly resembles Au6(Ph2pz)6, the latter of which was reported by Raptis et al. in 1987.8 Close inspection reveals that the central Au···Au distance is 3.495(1) Å in Au6(Ph2pz)6, indicative of aurophilicity.22 However, unlike Ag6pz6 reported here, the shortest Au···Au is not the one between a pair of central Au atoms but one of those bridged by one pyrazolate [3.085(2) Å]. This observation implies that the central Ag···Ag contact may be more important than that of Au···Au in stabilization of the corresponding silver(I) or gold(I) hexamers. Ag4pz4 crystallizes in the monoclinic space group P21/c, and the asymmetric unit consists of one Ag4pz4 molecule (Figure S18). The Ag4pz4 molecule adopts a saddlelike shape: the four Ag atoms form an approximate Ag4 square, with the bridging pyrazolato ligands being placed alternatively above and below the Ag4 plane (Figure 3). This arrangement is common for M4pz4-type and some related complexes.6c,b,23 The shortest Ag···Ag contact in Ag4pz4 is the one bridged by one pyrazolate [3.5278(3) Å], much longer than that in Ag6pz6. Extensive intra- and intermolecular π interactions are present in the crystal structure of Ag4pz4; Figures S19−S22 show some crucial patterns highlighting the π interactions. It is interesting to find that two clefts of Ag4pz4 have been filled by two tert-butyl

Figure 4. Clefts of Ag4pz4 are filled by tert-butyl groups from adjacent Ag4pz4 molecules, C(tBu)-H···pz interaction may contribute to such an arrangement. 11312

DOI: 10.1021/acs.inorgchem.7b01717 Inorg. Chem. 2017, 56, 11310−11316

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Inorganic Chemistry

therefore, we infer that smaller isomers may prevail over the larger ones at room temperature and a decrease in the temperature would favor the hexameric isomer. As shown in Figure 6, the signal of the tert-butyl group is a singlet (1.19

unsuccessful in isolating it as crystals from the solution. Therefore, a theoretical calculation has been carried out on this veiled species. As we can see in Figure S23, the Ag−N bonds in Ag3pz3 do not differ significantly from those in other oligomers; thus, the energies of different oligomers may be determined, to a considerable extent, by the intramolecular argentophilic contacts and π interactions. Furthermore, weak intermolecular interactions may have an additional influence on which species can crystallize from the solution. Solution Behavior. The 1H NMR spectra of the hexamer and tetramer are almost identical in CDCl3, which remained so even recorded directly after dissolving the samples of Ag6pz6 and Ag4pz4 (Figure S24). This observation suggests that Ag6pz6 and Ag4pz4 quickly reached an identical equilibrium pattern, respectively, after dissolution in CDCl3 at room temperature. The 13C NMR spectra of both are also very alike (Figure S25). Because only one set of signals was observed in the NMR spectra, it is inferred that either there is only one major species present in the solution or two or more species exist simultaneously at a fast dynamic equilibrium. MS measurements were therefore conducted to evaluate or identify the most possible isomer in solution. As shown in Figure 5, it is not surprising to find that both isomers gave rise

Figure 6. Variable-temperature 1H NMR spectra of Ag6pz6 in CDCl3.

ppm) in CDCl3 at 298 K. When the temperature was lowered to 273 K, two peaks appeared at 1.20 and 0.95 ppm with an intensity ratio of ca. 1:2, which is consistent with the pattern expected for a hexamer with a figure-eight shape and therefore tentatively assigned to the hexameric isomer. At even lower temperature, the peak at 1.17 ppm, corresponding to the tertbutyl group, further split into two unequal peaks; a new weak peak appeared at 1.27 ppm. These two peaks may be caused by the tert-butyl groups of Ag4pz4 and Ag3pz3, the exchange between which became slower with the lowering of the temperature. From the above discussion, it is inferred that several structural isomers of Agnpzn, including the elusive Ag3pz3, may coexist at fast equilibrium in solution, with the tetramer and/or trimer dominating over the hexamer.

Figure 5. MALDI-TOF MS spectra of Ag6pz6 (A) and Ag4pz4 (B).

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to almost identical MS spectra in CHCl3. The most abundant peak at 962.5 is assigned to [Ag3pz2]+, which is probably generated from the Ag3pz3 trimer (Figure S26). The major peaks at m/z 1730.3, 1388.4, and 1304.4 are assigned as [Ag4pz4] + Na+, [Ag4pz3]+, and [Ag4pz2pz′]+, respectively, by considering their isotopic distribution patterns (pz′ = 3,5diphenylpyrazole-4-carboxylic acid, possibly formed through ditert-butylation of the original pyrazole; Figures S27−S29). It is thus concluded that the major species are Ag3pz3 and Ag4pz4 after dissolving both isomers in CHCl3. Interestingly, several weak peaks at higher m/z can also be clearly spotted; one of them at m/z 2241.8 has been thought to be the ion peak caused by [Ag6pz5]+, implying the existence of the hexameric species in solution, although as a minor component (Figure S30). To further investigate the equilibrium between several possible oligomers of Agnpzn in solution, a variable-temperature 1 H NMR test was carried out. It is assumed that the enthalpy change would be negligible for conversion between a pair of oligomers in solution because the Ag−N bond energies for different oligomers should be close, and the metallophilic contacts and π weak interactions contribute less to ΔH. It is thus expected that the entropy contribution would dominate;

CONCLUSION In summary, the hexameric Ag6pz6 has been successfully prepared and structurally characterized. As far as we know, it is the first silver(I) pyrazolato hexamer, and this work also represents the reappearance of this structural motif 30 years after the report of a gold pyrazolato hexamer in 1987.8 In the solid state, Ag6pz6 adopts a rare figure-eight shape, which is stabilized by Ag−N bonds, Ag···Ag contacts, and π interactions. In a CHCl3 solution, the hexamer may quickly reach equilibrium with Ag4pz4 and Ag3pz3, with the balance heavily lying to the side of smaller rings. It is conjectured that the hexamer may be present as a minor composition in some coinage metal pyrazolato systems. Because the hexameric M6pz6 is a true isomer of the so-called “dimer of trimer” (M3pz3)2,24 the assignment of the latter should be cautious based on consideration of the molecular weights. Although much effort has been devoted to understanding the mechanism of isomerization among different oligomers of Agnpzn, details about the conversion are still unclear in this work, and the role of the substituents and control of the nuclearity of metal pyrazolates remains an open issue for further investigation. 11313

DOI: 10.1021/acs.inorgchem.7b01717 Inorg. Chem. 2017, 56, 11310−11316

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Inorganic Chemistry Table 2. Crystallographic Data

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formula mol wt cryst syst space group a [Å] b [Å] c [Å] β [deg] V [Å3] Z T [K] ρcalcd [mg m−3] μ [mm−1] reflns collected unique reflns final R indices [I > 2σ(I)]

Ag6pz6 block

Ag6pz6 needle

Ag4pz4

C120H114Ag6N12O12 2563.45 monoclinic P21/n 18.3496(11) 19.7639(12) 33.2795(18) 97.879(2) 11955.2(12) 4 298(2) 1.424 1.025 200382 27279 (Rint = 0.0494) R1 = 0.0514, wR2 = 0.1357

C180H171Ag9N18O18 3845.18 monoclinic C2/c 62.391(3) 29.9037(15) 18.5831(9) 102.294(2) 33876(3) 8 298(2) 1.508 1.085 190392 39146 (Rint = 0.1092) R1 = 0.0630, wR2 = 0.1099

C80H76Ag4N8O8 1705.02 monoclinic P21/c 16.2697(6) 22.4467(9) 22.7434(8) 109.7940(10) 7815.2(5) 4 298(2) 1.449 1.043 164133 17959 (Rint = 0.0704) R1 = 0.0366, wR2 = 0.0715

in the LUMO of Ag3pz3, indicative of π-acidic character at the center of the Ag3 plane.13,14 Synthesis of Ag6pz6. Method A. AgNO3 (0.0017 g, 0.01 mmol) and pzH (0.0032 g, 0.01 mmol) were mixed in a 25 mL Teflon-lined autoclave. The mixture was sealed and heated at 100 °C for 3 days and then cooled to room temperature at a rate of 10 °C h−1. The needle crystals (sometimes pale-yellow blocks) were obtained after several days. Yield: 15.4 mg, 0.006 mmol, 60%. Method B. To a clear methanol solution (4 mL) of AgNO3 (0.0034 g, 0.02 mmol) and pzH (0.0064 g, 0.02 mmol) was added an equivalent amount of Et3N. The resulting solution was stirred for 0.5 h. The supernatant was removed, and the residue was washed twice with methanol. A white solid was obtained by filtration. Yield: 24.6 mg, 0.0096 mmol, 80%. 1H NMR (400 MHz, CDCl3): δ 1.19 (s, 9H), 7.17−7.41 (m, 10H). 13C NMR (101 MHz, CDCl3): δ 156.41 (s), 133.03 (s), 128.59 (d, J = 14.8 Hz), 128.08 (s), 110.26 (s), 80.02 (s), 27.79 (s). Anal. Calcd for C180H171Ag9N18O18: C, 56.22; H, 4.48; N, 6.56. Found: C, 56.65; H, 4.42; N, 6.87. FTIR (KBr pellets, cm−1): νmax 3446 (br), 3063 (vw), 2976 (w), 2929 (w), 1705 (s), 1519 (w), 1478 (m), 1458 (m), 1412 (w), 1391 (w), 1366 (w), 1313 (w), 1129 (s), 1073 (w), 1034 (w), 1008 (w), 915 (w), 843 (w), 763 (m), 698 (m). Synthesis of Ag4pz4. Recrystallization of the white powdery sample of Ag6pz6 (0.01 mmol, 0.0256 g) from ether afforded the colorless squares of Ag4pz4, together with some uncharacterized microcrystals. Yield: 7.0 mg, 0.004 mmol, 40%. 1H NMR (400 MHz, CDCl3): δ 1.19 (s, 9H), 7.22−7.40 (m, 10H). 13C NMR (101 MHz, CDCl3): δ 156.24 (s), 133.02 (s), 128.61 (d, J = 16.1 Hz), 128.08 (s), 110.26 (s), 80.05 (s), 27.79 (s). Anal. Calcd for C82H80Ag4N8O8: C, 56.22; H, 4.48; N, 6.55. Found: C, 57.27; H, 4.22; N, 6.08. FTIR (KBr pellets, cm−1): νmax 3454 (br), 3069 (vw), 2975 (w), 2927 (w), 2840 (vw), 1699 (vs), 1519 (w), 1493 (m), 1478 (m), 1458 (w), 1412 (w), 1391 (w), 1366 (w), 1314 (w), 1250 (w), 1135 (s), 1036 (w), 1008 (m), 911 (w), 844 (m), 798 (w), 762 (m), 697 (m).

EXPERIMENTAL SECTION

Materials and Methods. The CHN microanalyses were carried out with a Vario EL elemental analyzer. Powder X-ray diffraction (PXRD) patterns were recorded on a PANalytical X’Pert PRO diffractometer. Room-temperature 1H and 13C NMR spectra were recorded on a Bruker DPX-400 spectrometer. Variable-temperature 1 H NMR spectra were recorded on a Bruker Avance III-500 spectrometer. Chemical shifts were reported in ppm using tetramethylsilane as the internal standard. Fluorescence spectra were recorded on a Horiba Scientific Fluorolog-3 spectrofluorometer. TG measurements were performed by heating the sample from 20 to 800 °C at a rate of 10 °C min−1 in air on a Netzsch STA 409PC differential thermal analyzer. MS spectra were measured with a Bruker Autoflex speed matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer (matrix, 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB); ionic agent, sodium trifluoroacetate; solvent, CHCl3). The Fourier transform infrared (FTIR) spectra were obtained in the range 400−4000 cm−1 as KBr pellets on a Nicolet Impact 470 FTIR spectrometer. All reagents were obtained commercially and used without further purification. X-ray Crystallography. Single-crystal X-ray diffraction data were collected on a Bruker AXS GmbH diffractometer with graphitemonochromated Mo Kα radiation (λ = 0.7107 Å) at 298 K. Absorption corrections were applied using the multiscan program. All of the structures were solved by direct methods and refined by full matrix least squares based on F2 using the SHELXTL program package.25 All non-H atoms were refined with anisotropic displacement parameters. H atoms were generated geometrically. The SQUEEZE routine in PLATON was used in the refinements of Ag6pz6 and Ag4pz4 to cope with the unidentifiable solvent molecules.26 Crystallographic data are listed in Table 2. CCDC 1537233− 1537235 contain the supplementary crystallographic data for this paper. Computational Details. All of the theoretical calculations were carried out in the Gaussian 09 suite of programs.27 The structures of all of the compounds were optimized by the ωB97X method28 in a chloroform solvent using the integral equation formalism polarizable continuum model.29 The basis set 6-31G(d,p) was employed for the H, C, N, and O atoms, while LANL2DZ was used for the Ag atom. The molecular structure, highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) of the hypothetical Ag3pz3 are shown in Figure S23. The calculated total energies are −3537.23373061 and −4716.32008767 au for Ag3pz3 and Ag4pz4, respectively, which correspond to an energy difference of 5.55 kJ mol−1 between the trimer and tetramer based on an Agpz unit in CHCl3. There is a delocalized empty orbital covering three Ag atoms

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01717. Additional Figures S1−S30, which include PXRD, IR, TG, luminescence spectra, ORTEP plots of the asymmetric units, ball-and-stick diagrams of the Ag6pz6 molecules from the needle polymorph, and 1H and 13C NMR and MS spectra (PDF) 11314

DOI: 10.1021/acs.inorgchem.7b01717 Inorg. Chem. 2017, 56, 11310−11316

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Inorganic Chemistry Accession Codes

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CCDC 1537233−1537235 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Dong-Hui Wei: 0000-0003-2820-282X Guang Yang: 0000-0002-1379-0684 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work has been supported by the National Natural Science Foundation of China (Grant 21471132). REFERENCES

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DOI: 10.1021/acs.inorgchem.7b01717 Inorg. Chem. 2017, 56, 11310−11316

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