Synthesis and Structures of [LCu(I)(SSiiPr3)] (L = triphos, carbene

Aug 31, 2016 - Synopsis. The mononuclear Cu(I) complexes [LCuI(SSiiPr3)] (L = triphos or IMes) have been prepared by ligand displacement from [LCuICl]...
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Synthesis and Structures of [LCu(I)(SSiiPr3)] (L = triphos, carbene) and Related Compounds Skylar J. Ferrara, Bo Wang, Elaine Haas, Karry Wright LeBlanc, Joel T. Mague, and James P. Donahue* Department of Chemistry, Tulane University, 6400 Freret Street, New Orleans, Louisiana 70118-5698, United States S Supporting Information *

ABSTRACT: The mononuclear Cu(I) complexes [LCuI(SSiiPr3)] (L = 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos), 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes)) have been prepared by ligand displacement from [LCuICl] with iPr3SiS−. Both compounds are colorless, diamagnetic species and have been characterized structurally by X-ray crystallography. The compounds [(IMes)Cu(η1κS-SC(O)CH3)] and [(triphos)Cu(η1κS-SC(S)OCH3)] have been prepared in the context of synthesis aimed at [LCu(η1κSSCOS)] and [LCu(η1κS-SCS2)] complexes, which are intended as synthons toward an analogue of the Mo(μ-OSCO)Cu intermediate proposed as occurring in the catalytic cycle of carbon monoxide dehydrogenase (CODH).

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INTRODUCTION The carbon monoxide dehydrogenase (CODH) metalloenzymes elicit attention both because of their unusual active site compositions and because of the fundamental importance of the reaction that they mediate, the interconversion of CO and CO2 according to CO + H2O ↔ CO2 + 2H+ + 2e−. The CODH enzymes are composed of two distinct and unrelated groups, one being the Ni−Fe−S CODHs that occur in anaerobic bacteria and additionally operate in conjunction with acetyl CoA synthase.1,2 A more recently identified type of CODH, found in aerobic, soil-dwelling bacteria, features an unusual heterodimetallic Mo−Cu composition at the catalytic site (Figure 1) and an unsupported

sulfide ion, and a hydroxide ligand at molybdenum (Scheme 1, complex c). Scheme 1. Proposed Catalytic Cycle for CO Oxidation by O. carboxidovorans CO Dehydrogenase

The structural features and putative reactivity cycle for the MoCu CODH present a considerable challenge for the synthesis of a small molecule analogue of this active site that might yield further insights into the enzyme’s structure and/or mechanistic workings. Young and co-workers reported in 2006 the coupling of separate MoVOS and CuI fragments to afford a heterodimetallic compound that incorporates the linear Mo−S−Cu connectivity at the active site core (Figure 2a).4 It remains the only such model compound with fidelity to this core composition of the enzyme, and it is additionally notable in displaying a distinctive quartet resonance in the EPR for the unpaired electron at MoV coupling to a single 63,65Cu ion. The research groups of Tatsumi6 and Holm7 have separately

Figure 1. Oxidized catalytic site of carbon monoxide dehydrogenase from Oligotropha carboxidovorans.

sulfide bridge between metal ions with a two-coordinate environment at copper in the enzyme’s oxidized resting state.3 On the basis of crystallographic data obtained from a t BuNC inhibited form of this enzyme, it has been proposed that a thiocarbonate intermediate precedes the elimination of CO2 and is formed from the CO substrate, the bridging © XXXX American Chemical Society

Received: December 3, 2015

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DOI: 10.1021/acs.inorgchem.5b02811 Inorg. Chem. XXXX, XXX, XXX−XXX

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that this molecule type is a masked form of copper sulfide that, under the appropriate conditions, might be amenable to in situ desilylation and subsequent fusion with a mononuclear molybdenum fragment. The proposed thiocarbonate intermediate for CODH has been calculated by independent research groups8,9 to be a stable species, so much so that its viability as a pathway in the catalytic cycle is uncertain. The stability calculated for this possible monothiocarbonate intermediate makes any Mo(μ-E,OCE) Cu compound (E = O or S) a worthwhile target for synthesis, inasmuch as an assessment of its thermal stability would offer a useful experimental check on this computational work. Toward this end, we have considered monothiocarbonate, dithiocarbonate, xanthate, and related complexes of Cu(I) with sulfur donor ligands and join a description of a few of these complexes to the set of iPr3SiS− compounds.

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Figure 2. Analogues of the MoCu CODH active site: (a) a Mo−S−Cu compound with tris(pyrazolyl)borate supporting ligand reported by Young;5 (b, c) M(μ-S)2Cu compounds reported by Tatsumi (M = Mo)6 and Holm (M = W).7

EXPERIMENTAL SECTION

Published procedures were employed in the syntheses of [(IMes)CuCl]10 (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), [(triphos)CuCl]11 (triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane), and [(triphos)Cu(NCMe)][PF6].12 Solvents either were dried with a system of drying columns from the Glass Contour Company (CH2Cl2, Et2O, THF) or freshly distilled according to standard procedures13 (MeOH, CH3CN). Other reagents were used as received from commercial sources. All 1H, 13C, and 31P NMR spectra were recorded at 25 °C with a Varian Unity Inova spectrometer operating at 400, 100.5, and 168.1 MHz for these respective nuclei; peak positions are reported relative to the solvent signal (1H and 13C) or to an external 85% phosphoric acid sample (31P). The 29Si NMR spectrum was obtained with a Bruker Avance 300 spectrometer and referenced internally to added Me4Si. Elemental analyses were performed by Midwest Microlab, LLC of Indianapolis, IN. Descriptions of the instrumentation and procedures employed in X-ray diffraction data collection and processing, and for the structure solutions and refinements, are deferred to Supporting Information, as are figures showing complete atom labeling for all compounds (Figures S1−S4). Unit cell data and refinement statistics for all structures reported are presented in Table 1, while selected interatomic distances and angles are collected in Table 2.

reported the synthesis of M−(μ-S)2−Cu compounds (M = Mo or W) that incorporate thiolate ligation at copper and a dithiolene-type ligand at Mo or W but which have two, rather than one, bridging chalcogenide ligands between metal ions (Figure 2b,c, respectively). Motivated by the importance of CODH in the context of activation of important small molecules, we have been considering synthetic approaches to Mo−Cu heterodimetallic complexes with a single chalcogenide bridging ligand between metal ions and, preferably, a two-coordinate geometry at copper. Two plausible strategies can be envisioned, which we refer to as “silane-mediated coupling” and as “cupration of molybdenum sulfide complexes.” The former of these reaction types was applied by Holm, while the latter was applied by Young and co-workers. In this report, we describe the synthesis and properties of mononuclear Cu(I) complexes with the i Pr3SiS− ligand, which are potential synthons toward sulfidebridged Mo−Cu CODH analogues. The motivating rationale is

Table 1. Crystal and Refinement Data for Compounds Characterized by X-ray Crystallography formula fw cryst syst space group color, habit a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 T, K Z μ, mm−1 R1,a wR2b R1,a wR2b Flack param GooFc

1

2

3

4

C57H68CuP3SSi 969.71 monoclinic P21/n colorless block 14.5029(10) 16.1500(11) 22.0822(15) 90 93.455(1) 90 5162.7(6) 150 4 0.616 0.0321, 0.0870 0.0391, 0.0923

C43H42CuOP3S2 795.33 monoclinic P21 colorless tablet 9.9391(13) 17.044(2) 12.5225(16) 90 111.329(2) 90 1976.1(4) 150 2 0.812 0.0514, 0.0950 0.0674, 0.1054 0.023(8) 1.046

C30H45CuN2SSi 557.37 monoclinic P21/c colorless block 19.4065(18) 10.8938(10) 15.2754(14) 90 104.834(1) 90 3121.7(5) 150 4 0.824 0.0314, 0.0823 0.0372, 0.0884

C23H27CuN2OS 443.06 orthorhombic P212121 colorless block 8.8709(7) 13.4554(10) 19.1905(15) 90 90 90 2290.6(3) 150 4 1.059 0.0340, 0.0858 0.0388, 0.0894 0.403(15) 1.053

1.010

1.048

R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = − w = 1/[σ + (aP) + bP], where P = [2Fc2 + Max(Fo2,0)]/3. cGooF = 2 2 2 1/2 {∑[w(Fo − Fc ) /(n − p)} , where n = number of reflections, p = total number of parameters refined. a

b

{[∑w(Fo2

Fc2)/∑w(Fo2)2]}1/2;

2

B

(Fo2)

2

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filtration. Yield: 0.278 g, 47%. 1H NMR (δ, ppm in C6D6): 7.62 (broad m, 12H), 7.01−6.75 (m, 18H), 2.24 (s, 6H), 1.56 (broad d, 18H), 1.20 (s, 3H), 0.87 (septet, 3H). 31P (δ, ppm in C6D6): −32.3. This compound was further identified by an X-ray crystal structure. [(triphos)Cu(η1κS-SC(S)OCH3)], 2. In a 25 mL Schlenk flask, Et4N+OH− in MeOH (1.5 M, 0.30 mL, 0.45 mmol) was diluted with 5 mL of dry MeOH. To this solution, CS2 (0.014 mL, 0.018 g, 0.23 mmol) was added via gastight syringe, and vigorous stirring was maintained for 20 min. A solution of [(triphos)Cu(NCMe)][PF6] (0.200 g) in 5 mL of dry MeOH was then transferred via cannula to the Et4N+OH−/CS2 mixture. A color change from deep yellow to tan was observed, along with some lightly colored precipitate. Stirring was continued overnight at room temperature. After ∼12 h, the reaction mixture was filtered, and the solvent was removed from the filtrate under reduced pressure. The beige residual solid was crystallized under N2 as white block crystals by the diffusion of pentane vapor into a CH2Cl2 solution. Yield (before crystallization): 0.180 g, 99%. 1H NMR (δ, ppm in CDCl3): 7.46 (broad singlet, arene CH), 7.06 (m, arene CH), 3.99 (singlet, −OCH3), 2.39 (singlet, (Ph2PCH2)3CCH3)), 1.34 (singlet, (Ph2PCH2)3CCH3)). 13C NMR (δ, ppm in CDCl3): 7.85, 28.27, 52.75 (−OCH3), 128.54−129.38 (aromatic), 132.21 (C S). This compound was further identified by an X-ray crystal structure. [(IMes)Cu(SSiiPr3)], 3. A solution of iPr3SiSH (0.29 mL, 1.35 mmol) in 10 mL of dry THF was treated with nBuLi (0.54 mL, 2.5 M in hexanes, 1.35 mmol) at 0 °C. Stirring was continued for 45 min at 0 °C, and the mixture was then allowed to warm to room temperature with stirring for an additional hour. This colorless solution was then slowly transferred via cannula into a solution of [(IMes)CuCl] (0.544 g, 1.35 mmol) in 20 mL of dry THF at 0 °C. The reaction mixture was warmed to ambient temperature, and stirring was maintained for an additional 16 h. Removal of the solvent under reduced pressure afforded a pale yellow residue to which 40 mL of dry Et2O was added with stirring. The mixture was filtered and the filtrate concentrated to a volume of ∼20 mL. Colorless plate crystals formed upon cooling to −20 °C for 24 h. Yield: 0.458 g, 61%. This compound is thermally sensitive and is best stored under an inert atmosphere at −20 °C. 1 H NMR (δ, ppm in C6D6): 6.68 (s, 4H, arene CH), 5.92 (s, 2H, −NCHCHN−), 2.08 (s, 6H, mesityl p-CH3), 1.94 (s, 12H, mesityl o-CH3), 1.23 (d, 18H, (CH3)2CH−, J = 7.30 Hz), 0.99 (septet, 3H, (CH3)2CH−, J = 7.40 Hz). 13C NMR (δ, ppm in C6D6: 180.7, 139.3, 135.7, 134.8, 129.6, 121.5, 21.1, 19.8, 17.8, 16.0. 29Si NMR (δ, ppm in C6D6): 25.71. Anal. Calcd for C30H45CuN2SSi: C, 64.64; H, 8.14; N, 5.03. Found: C, 64.40; H, 8.08; N, 5.08. This compound was further identified by an X-ray crystal structure. [(IMes)Cu(η1κS-SC(O)CH3)], 4. A 100 mL Schlenk flask was charged with [(IMes)CuCl] (0.100 g, 0.25 mmol) in 20 mL of dry MeCN. A solution of potassium thioacetate (0.0297 g, 0.26 mmol, a 5% molar excess) in dry MeCN was then added to the [(IMes)CuCl] solution

Table 2. Selected Interatomic Distances and Angles for Structurally Characterized Compounds [(triphos)Cu(SSiiPr3)], 1 Cu(1)−P(1) Cu(1)−P(2) Cu(1)−P(3) Cu(1)−S(1) S(1)−Si(1)

2.3029(4) S(1)−Cu(1)−P(1) 2.3124(4) S(1)−Cu(1)−P(2) 2.2921(4) S(1)−Cu(1)−P(3) 2.2670(4) Si(1)−S(1)−Cu(1) 2.1019(5) [(triphos)Cu(SC(S)OCH3)], 2

Cu(1)−P(1) Cu(1)−P(2) Cu(1)−P(3) Cu(1)−S(1) S(1)−C(42) S(2)−C(42) O(1)−C(42) O(1)−C(43)

2.2805(15) S(1)−Cu(1)−P(1) 2.2719(16) S(1)−Cu(1)−P(2) 2.2504(15) S(1)−Cu(1)−P(3) 2.2425(16) Cu(1)−S(1)−C(42) 1.691(7) S(1)−C(42)−S(2) 1.658(7) O(1)−C(42)−S(1) 1.358(8) O(1)−C(42)−S(2) 1.423(8) C(42)−O(1)−C(43) [(IMes)Cu(SSiiPr3)], 3

118.050(16) 117.236(16) 132.490(14) 118.93(2)

108.82(6) 121.10(6) 133.85(6) 112.2(2) 124.8(4) 112.7(5) 122.5(5) 118.8(6)

Cu(1)−C(1) 1.8830(13) Cu(1)−S(1) 2.1336(4) S(1)−Si(1) 2.1207(5) S(1)−Cu(1)−C(1) 174.77(4) Si(1)−S(1)−Cu(1) 102.556(17) [(IMes)Cu(SC(O)CH3)], 4 Cu(1)−C(1) Cu(1)−S(1) S(1)−C(22) S(1)−Cu(1)−C(1) C(22)−S(1)−Cu(1)

1.885(3) 2.1483(9) 1.773(4) 177.40(10) 106.84(12)

The numbering system by which all compounds are identified is defined pictorially in Scheme 2. Syntheses. [(triphos)Cu(SSiiPr3)], 1. A solution of iPr3SiSH (0.14 mL, 0.65 mmol) in 10 mL of dry THF was treated with n BuLi (0.28 mL, 2.5 M in hexanes, 0.70 mmol) at 0 °C, stirred for 45 min at 0 °C, and then allowed to warm to room temperature with stirring for an additional 1 h. This colorless solution was then slowly transferred via cannula to a suspension of [(triphos)CuCl] (0.486 g, 0.672 mmol) in dry THF (20 mL) at 0 °C, which brought all components into solution. The reaction mixture was slowly warmed to room temperature with stirring for an additional 16 h. This off-white solution was filtered through Celite and concentrated to a volume of ∼10 mL under reduced pressure. Compound 2 was precipitated as a white solid by the addition of hexanes (30 mL) and was isolated by

Scheme 2. Synthesis of Monocopper Compounds with Varying Sulfur Ligands

C

DOI: 10.1021/acs.inorgchem.5b02811 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry via cannula, which immediately induced the formation of a fine white precipitate. The mixture was stirred vigorously overnight at room temperature, affording additional white precipitate. The reaction mixture was filtered through a 1 in. Celite pad, and the solvent was removed from the filtrate under reduced pressure. The white residue was extracted with dry THF, and the solvent was removed. Colorless crystals of diffraction quality were grown from THF/tBuOMe. Yield: 0.018 g, 16%. IR (KBr, cm−1): 1636 (s, CO). 1H NMR (δ, ppm in CDCl3): 7.08 (singlet, 2H, −NCHCHN−), 7.01 (s, 4H, arene CH), 2.34 (s, 6H, mesityl p-CH3), 2.13 (s, 12H, mesityl o-CH3), 2.06 (singlet, 3H, −C(O)CH3). 13C NMR (δ, ppm in CDCl3): 139.56, 135.16, 134.76, 134.42, 129.46, 129.28, 122.16, 38.69, 20.98, 17.66, 16.91. Anal. Calcd for C23H27CuN2OS: C, 62.35; H, 6.14; N, 6.32. Found: C, 62.08; H, 6.01; N, 6.66. This compound was further identified by an X-ray crystal structure.

provide tractable materials that could be handled in small amounts with control over the reaction stoichiometry. Thermal ellipsoid plots for 1 and 3 are presented in Figure 3. Compound 3 shows a linear, two-coordinate geometry at CuI, a feature supported by the steric shielding offered by the IMes ligand. A related compound, [(IPr)Cu(SSiMe3)], has been very recently reported in separate work by Corrigan18 and Hillhouse.19 Two-coordinate copper(I) silylthiolate complexes are rather rare, with the only other examples being [(Ph3SiS)Cu(PtBu3)],20 [(TripS)Cu(SSiPh3)]1− (Trip = triptycyl),21 and homoleptic [(Ph3SiS)2Cu]1−.7 The 2.1336(4) Å Cu−S bond length in 3 (Table 2) is indistinguishable from the corresponding value in [(IPr)Cu(SSiMe3)] (2.133(1) Å) but modestly shorter than the Cu−S bond distance in [(Ph3SiS)Cu(PtBu3)], 2.1578(11) Å, which may be attributed to a smaller trans influence for IMes as compared to the highly basic PtBu3 ligand. The Si(1)−S(1)−Cu(1) angle of 102.56(2)° for 3 is slightly greater than the analogous angle in [(Ph3SiS)Cu(PtBu3)], 97.63(5)°. Despite the substantially greater steric profile of i Pr3Si compared to that of Me3Si, the Cu−S bond length in 1 is notably shorter, at 2.2670(4) Å, than the corresponding bond lengths in the related compounds of Corrigan: 2.371(1), 2.3970(10), and 2.4022(5) Å for [(Me3SiS)Cu(PPh2Et)3], [(Me3SiS)Cu(PnPr3)3], and [(Me3SiS)Cu(PEt3)3], respectively. This difference is likely correlated with the larger S−Cu−P angles in 1 (∼123°) compared to the compounds of Corrigan where the monodentate nature of the phosphine ligands allows for S−Cu−P angles much closer to the ideal tetrahedral value of 104.5°. The possible involvement of a thiocarbonate bridge between molybdenum and copper in the mechanistic cycle of CODH engenders interest in copper thiocarbonate complexes, and related species, for their potential usefulness in the synthesis of heterodimetal Mo−Cu complexes that feature such bridging ligands. In this connection, thioacetate complex [(IMes)Cu(η1κS-SC(O)CH3)] was prepared by displacement of Cl− from

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RESULTS AND DISCUSSION Although experimentally assessed bond strengths of the type are scant, the Si−S bond has a comparatively weak character that draws attention to compounds of the type [LCu(SSiR3)] (L = charge neutral donor ligand) as potentially useful synthons for the preparation of heterodimetallic compounds featuring unsupported Mo−S−Cu linkages. Toward such an end, [(IMes)Cu(SSiiPr3)] and [(triphos)Cu(SSiiPr3)] were obtained by substitution of Cl− in the corresponding [(IMes)CuCl] and [(triphos)CuCl] compounds (Scheme 2). Both are white crystalline compounds that are readily solubilized and thermally stable at ambient temperature under N2. The room temperature NMR spectra (1H, 13C, 31P) for 1 reveal broadened signals, which we attribute to fluxional binding/dissociation of the triphos arms. This dynamic behavior by the triphos ligand and even complete ligand dissociation have been noted by others.12,14 Related [(PR2R′ 1) 3Cu(SSiMe3)] compounds (R = Et, R′ = Ph; R = Ph, R′ = Et; R = R′ = Et or nPr) reported by Corrigan and co-workers15−17 require preparation and handling at rather low temperatures and are useful for the synthesis of metal chalcogenide clusters owing to their inherent reactivity. The iPr3Si group in 1 and 3 was selected so as to

Figure 3. Thermal ellipsoid plots at the 50% probability level for 1−4. H atoms are omitted for clarity. D

DOI: 10.1021/acs.inorgchem.5b02811 Inorg. Chem. XXXX, XXX, XXX−XXX

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[(IMes)CuCl] and crystallized (4 in Figure 3). The η1-binding mode for thiocarboxylate has been observed in one previous instance for two-coordinate Cu(I), namely, in [Cu(η1κSSC(O)CH3)2]1−,22 where a Cu−S bond length (2.151(3) Å) similar to that in [(IMes)Cu(η1κS-SC(O)CH3)] is found. Thermal decomposition of [Cu(η1κS-SC(O)CH3)2]1− to form copper sulfide by a programmed thermal gravimetric analysis is analogous to thermal elimination of CO2 from [Mo(OSCO)Cu] by CODH to afford [Mo−S−Cu]. With monothiocarbonate and dithiocarbonate salts being known for their thermal sensitivity,23 presumably a susceptibility to CO2/COS elimination, our initial foray toward simple coordination complexes began with an effort to generate [OCS2]2− in situ and coordinate it to copper without first isolating it. Thus, CS2 was treated with 2 equiv of OH−/MeOH and shortly thereafter was introduced to [(triphos)Cu(MeCN)]+. Although the targeted copper complex was [(triphos)Cu(η1κSS2CO)]1−, the conditions employed favor formation of xanthate over dithiocarbonate, indicating a need for a strict aqueous medium if the desired [(triphos)Cu(η1κS-S2CO)]1−, which is better suited for the further synthesis of heterodimetallic species, is to be formed. While numerous Cu(I) xanthate complexes have been reported,24−26 generally from isolated xanthate ligands, previous examples reveal the xanthate ligand in a chelating or bridging mode and not in the monodentate η1κS mode. The provision of only one coordination site at copper by the tridentate triphos is undoubtedly necessary to ensure this monodentate binding mode.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The Louisiana Board of Regents is thanked for enhancement Grant LEQSF-(2002-03)-ENH-TR-67 with which Tulane’s X-ray diffractometer was purchased, and Tulane University is acknowledged for its ongoing support with operational costs for the diffraction facility. Support from the National Science Foundation (Grant CHE-0845829 to J.P.D.) is gratefully acknowledged.

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REFERENCES

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SUMMARY AND CONCLUDING REMARKS The synthesis and physical characterization of the new compounds [LCuI(SSiiPr3)] (L = triphos, IMes) are reported here for their possible application as masked forms of [LCuIS−], an anion envisioned as useful for the preparation of dimetallic sulfidebridged species. The feasibility of this objective is validated by the recently described syntheses of [(IPr)Cu(μ2-S)]2Hg by Corrigan18 and [{(IPr)Cu}3(μ3-S)][BF4] and [{(IPr*)Cu}2(μ2-S)] (IPr* = 1,3-bis(2,6-(diphenylmethyl)-4-methylphenyl)imidazole-2-ylidene) by Hillhouse,19,27 the preparations of which hinged upon unmasking of sulfide ligand from its SiMe3 protecting group by use of a suitable source of anion (AcO−, F−). Similarly, we anticipate that a soluble source of F− or Cl− will provide a decisive driving force for liberating [LCuIS]− by forming iPrSiX (X = F, Cl). As possible synthons toward the Mo(OSCO)Cu intermediate that has been proposed to occur during CO oxidation by CODH, [(IMes)CuI(η1κS-SC(O)CH3)] and [(triphos)CuI(η1κS-SC(S)OCH3)] have been prepared and characterized. The foregoing new Cu(I) complexes have been characterized structurally by X-ray diffraction, and representative elemental analyses confirm bulk purity. In continuing work, we endeavor to couple separate copper and molybdenum fragments to produce species with the Mo−S−Cu core composition that is pertinent to CODH.

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02811. Thermal ellipsoid plots with complete atom labeling; 1 H, 13C, and 31P NMR spectra; IR spectrum of 4 (PDF) Complete crystal data for 1−4 (CIF) E

DOI: 10.1021/acs.inorgchem.5b02811 Inorg. Chem. XXXX, XXX, XXX−XXX