V) Oxide Cluster Complex

Communication pubs.acs.org/IC

Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Reductive Formation of a Vanadium(IV/V) Oxide Cluster Complex [V8O19(4,4′‑tBubpy)3] Having a C3‑Symmetric Propeller-Shaped Nonionic V8O19 Core Yuta Inoue,† Shintaro Kodama,*,†,‡ Nobuto Taya,† Hirohiko Sato,§ Katsuyoshi Oh-ishi,† and Youichi Ishii*,† †

Department of Applied Chemistry, Faculty of Science and Engineering, and §Department of Physics, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan S Supporting Information *

rare example of interconversion among nonionic vanadium(V) oxide clusters with different nuclearities. In the present study, we envisioned that the core conversion reaction of nonionic vanadium(V) oxide clusters involving reduction of the VV atom would open a route to unprecedented clusters not available by the redox-neutral assembly of nonionic oxidovanadium(V) species. After examination of reducing agents for the conversion of V8, we finally found that the reaction of V8 with triphenylphosphine (PPh3) under N2 affords a C3symmetric propeller-shaped vanadium(IV/V) oxide cluster complex, [V8O19(4,4′-tBubpy)3] (V8′), whereas similar reactions with ROH (R = Me, Et) resulted in the formation of tetranuclear alkoxido(oxido)vanadium(IV/V) complexes, [V4O6(OR)6(4,4′-tBubpy)2] (V4′). When a toluene solution of V8 and PPh3 was heated at reflux for 5 min and then cooled to room temperature under N2, darkblue crystals were deposited upon standing overnight.6 Singlecrystal X-ray structure analysis has revealed that the product is a novel mixed-valent octavanadium oxide cluster V8′ (18% isolated yield) with crystallographic C3 symmetry, where the C3 axis passes through the two atoms V1 and V4 (Figure 1). The V8O19N6 core in V8′ may be viewed as a combination of two types of C3-symmetric propeller-shaped cluster units, the V4O13 and V4O12N6 cores, linked to each other by sharing bridging O atoms (Figure 2). In the V4O13 part, which is

ABSTRACT: A novel C3-symmetric propeller-shaped vanadium(IV/V) oxide cluster complex, [V8O19(4,4′-tBubpy)3] (V8′), has been synthesized from the reaction of the windmill-shaped vanadium(V) oxide cluster complex [V8O20(4,4′-tBubpy)4] (V8) with PPh3 under N2, whereas refluxing V8 in methanol or ethanol under N2 provides tetranuclear oxido(alkoxido)vanadium(IV/V) complexes [V4O6(OR)6(4,4′-tBubpy)2] [R = Me (V4′-Me) and Et (V4′-Et)]. The mixed-valent vanadium(IV/V) clusters V8′ and V4′ are converted back to V8 under O2. Interconversions of V4′ and the oxido(alkoxido)vanadium(V) complexes [V4O8(OMe)4(4,4′-tBubpy)2] (V4) and [V7O17(OEt)(4,4′-tBubpy)3] (V7-Et) are also presented.

P

olyoxovanadates (POVs), anionic vanadium oxide clusters, have played a significant role in a wide range of application areas such as catalysts, medicine, and electronic and magnetic materials.1 Nonionic vanadium oxide clusters have recently attracted increasing attention not only as models for the catalytic active sites of vanadium oxides in a gas-phase study2 but also as useful precursors for both cationic vanadium oxide clusters and POVs.3 However, nonionic vanadium oxide clusters are still much less common than POVs, and therefore their detailed properties and application have largely been unexplored. Nonionic vanadium oxide clusters are typically isolated as organic-ligand-functionalized POVs,1b,3,4 and their syntheses have often been achieved by the assembly of monomeric oxidovanadium species, whereas synthetic methods utilizing a preformed cluster have been quite limited probably because of the low solubility of nonionic clusters in both water and organic solvents. Recently, we reported the synthesis and interconversion of a series of nonionic vanadium(V) oxide clusters functionalized with 4,4′-di-tert-butyl-2,2′-bipyridine (4,4′-tBubpy): the windmill-shaped5 octanuclear cluster [V8O20(4,4′-tBubpy)4] (V8), the tetranuclear methoxido cluster [V4O8(OMe)4(4,4′-tBubpy)2] (V4), and the heptanuclear alkoxido clusters [V7O17(OR)(4,4′-tBubpy)3] (V7; R = Et, MeOC2H4).4d,e It is noteworthy not only that the structures of the cluster cores in V8 and V7 are unprecedented but also that V8, V4, and V7 can be interconverted by changing the solvent systems under air, which provides a very © XXXX American Chemical Society

Figure 1. Ball-and-stick representations of V8′: (a) top view; (b) side view of the partial structure of V8′. Color code: green, V; red, O; blue, N; gray, C. H atoms are omitted for clarity. Received: March 15, 2018

A

DOI: 10.1021/acs.inorgchem.8b00651 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

Figure 2. Crystal structure of V8′ with numbered atoms. Ellipsoids are shown at the 50% probability level. H and C atoms are omitted for clarity. Symmetry operators: (i) −Y + 1, X − Y, Z; (ii) −X + Y + 1, − X + 1, Z. Selected interatomic distances (Å) and angles (deg): V1−O1 1.603(4), V1−O5 1.761(3), V2−O2 1.595(3), V2−O4ii 1.881(3), V2− O6 2.347(3), V2−O7i 1.809(3), V2−N1 2.142(4), V2−N2 2.128(3), V3−O3 1.608(4), V3−O4 1.747(3), V3−O5 1.829(3), V3−O6 1.743(2), V4−O6 2.051(3), V4−O7 1.844(4), V2···V4 3.0771(10); V1−O5−V3 128.42(14), V2i−O4−V3 127.51(15), V3−O6−V4 120.18(16), V2−O6−V3 145.49(19), V2−O6−V4 88.53(9), V2ii− O7−V4 114.75(14).

Figure 3. χMT versus T plots for V8′·0.42C7H8.

On the other hand, upon further lowering of the temperature, χMT begins to increase sharply, reaches a maximum (1.16 emu mol−1 K) at 45 K, and then decreases to 0.98 emu mol−1 K at 5 K. This behavior is probably due to a ferromagnetic interaction between the two VIV ions through the oxo bridge, and the decrease of χMT below 45 K may be attributed to thermal depopulation of the excited substates. From these results, we assume that magnetic phase transition occurs at ca. 150 K.12 We further investigated the conversion of V8 using alcohols as reducing agents. When V8 was dissolved in MeOH and heated at reflux under N2, the reaction mixture turned to a green suspension, from which a dark-green powder was obtained (56% isolated yield). An X-ray diffraction study of crystals grown from a crude MeOH solution revealed that the product is not the octanuclear vanadium(IV/V) oxide cluster complex V8′ but the tetranuclear alkoxido(oxido) vanadium(IV/V) complex [V4O6(OMe)6(4,4′-tBubpy)2] (V4′-Me) formed via splitting of the core of V8 and partial reduction of the VV atoms. Similarly, the reaction of V8 with EtOH under N2 afforded the analogous complex [V4O6(OEt)6(4,4′-tBubpy)2] (V4′-Et) (for crystal structures, see Figures S2 and S3). 1 3 , 1 4 Although [V4O6(OEt)6(phen)2] (phen = 1,10-phenanthroline), which is structurally related to V4′, has already been reported by Kitagawa et al., its synthesis is based on formal oxidative conversion of the vanadium(III) complex [VCl3(thf)3], and the details of this reaction have not been clarified.15 SQUID measurements of V4′-Me and V4′-Et have been performed at 5−300 K. The χMT versus T plots are represented in Figure S7. The χMT value of V4′-Et at 300 K is 0.75 emu mol−1 K, which is consistent with the expected spin-only value of 0.75 emu mol−1 K for two VIV ions (S = 1/2 spins) with g = 2.0. Upon cooling, the χMT value decreases to reach ca. zero at 5 K. These results suggest the existence of an antiferromagnetic interaction between the two VIV ions around the center of the cluster through the methoxido bridge. Furthermore, the present data were fitted using the Bleaney−Bowers equation for an S = 1/2 isolated dimer (eq 1).16

composed of four VO4 tetrahedra, the bond distances around the V centers are in agreement with those in vanadium oxide clusters having VO4 subunits.4d,7 Likewise, in the V4O12N6 part composed of one VO6 and three VO4N2 octahedra, the V Oterminal (1.60 Å) distance as well as the V−Obridging distances cis (1.81−2.05 Å) or trans (2.35 Å) to a terminal oxido ligand fall in the range of literature values for these bonds.4c−e Although oxidovanadium structures similar to the V4O13 moiety in V8′ have been found in some heteronuclear oxide cluster complexes,7 the present C3-symmetric propeller-shaped nonionic V8O19 core is unprecedented. In addition, intermolecular π−π interactions are present between 4,4′-tBubpy ligands (see Figure S4), which resulted in the formation of a threedimensional honeycomb structure having channels (ca. 6 Å in diameter) parallel to the c axis (Figure S5).8 Bond-valence-sum (BVS) calculations (Table S5) suggest that the tetrahedrally coordinated V atoms, V1 and V3, are in an oxidation state of 5+, whereas the oxidation state of the octahedrally coordinated V4 atom is 4+. For the three V2 atoms (V2, V2i, and V2ii) that are related by the crystallographic 3-fold axis, BVS calculations suggest that they are in a mixed-valence state (one VIV and two VV atoms).9 We next examined the magnetic properties of V8′.10,11 Unfortunately, crystals of V8′·3C7H8 lose toluene molecules upon drying under reduced pressure to give a sample with the empirical formula V8′·0.42C7H8, and therefore the magnetic susceptibility of the V8′·0.42C7H8 sample was measured in the temperature range of 5−300 K by a superconducting quantum interference device (SQUID; Figure 3). At room temperature (300 K), the value of χMT is 1.04 emu mol−1 K, which is larger than the expected spin-only value of 0.75 emu mol−1 K for the two uncoupled VIV ions (S = 1/2 spins) with g = 2.0. This observation is probably due to the existence of dominant ferromagnetic interactions between the VIV centers, contributions from a not fully quenched orbital momentum, and/or the presence of temperature-independent paramagnetism. Upon lowering of the temperature, χMT continuously decreases to reach a minimum (0.83 emu mol−1 K) at 145 K, which is considered to be due to the single-ion effect of the V4 atom.

χM =

2Ng 2μB 2 ⎡ ⎤−1 1 ⎢⎣1 + exp( −2J /kBT )⎥⎦ 3kBT 3

(1)

−1

The best-fit parameters are J = −37.1 cm and g = 2.09, and the fitting curve is represented in Figure S7b. The value of J = −37.1 cm−1 confirms an antiferromagnetic interaction in V4′-Et and falls within the range of values reported for binuclear oxidovanadium(IV) complexes having a [V(O)(μ-O)]2 unit related to the partial structure of V4′ (Figures S2 and S3).17,18 It is interesting to note that reductive conversions of other vanadium(V) oxide cluster complexes, B

DOI: 10.1021/acs.inorgchem.8b00651 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry Scheme 1. Interconversion of Nonionic Vanadium Oxide Clusters Involving Redox Reactions

*E-mail: [email protected].

[V 4 O 8 (OMe) 4 (4,4′- t Bubpy) 2 ] (V 4 ) and [V 7 O 17 (OEt)(4,4′-tBubpy)3] (V7-Et),4d,e also proceeded in ROH (R = Me for V4 and Et for V7-Et) to form V4′-Me and V4′-Et, respectively. In addition, when the mixed-valent vanadium(IV/V) oxide clusters V8′ and V4′ were dissolved in a CHCl3−CH2Cl2 mixed solvent, followed by the addition of Et2O under O2, the vanadium(V) cluster V8 regenerated, whereas in MeOH and EtOH under O2, V4′-Me and V4′-Et were oxidatively converted to the oxido(alkoxido)vanadium(V) clusters V4 and V7-Et, respectively (for details, see the Supporting Information).19 To the best of our knowledge, the present results provide a very rare example of an interconversion network between nonionic vanadium oxide clusters involving redox reactions between VV and VIV atoms (Scheme 1). Further studies concerning reductive conversions of nonionic vanadium(V) oxide clusters using other reducing agents are in progress.

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ORCID

Shintaro Kodama: 0000-0003-4190-9539 Youichi Ishii: 0000-0002-1914-7147 Present Address ‡

S. K.: Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531, Japan. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge Prof. Tamejiro Hiyama at Chuo University for providing a single-crystal X-ray diffractometer.

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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.8b00651. Listings of experimental details of the synthetic procedures, tabulated X-ray crystallographic data, selected interatomic distances and angles, BVS calculations, χMT versus T data, TG−DTA data, and additional references (PDF) Accession Codes

CCDC 1828015−1828017 and 1828019 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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REFERENCES

(1) (a) Monakhov, K. Y.; Bensch, W.; Kögerler, P. SemimetalFunctionalised Polyoxovanadates. Chem. Soc. Rev. 2015, 44, 8443− 8483. (b) Gao, Y.; Chi, Y.; Hu, C. Organic-Functionalized, Substituted Polyoxovanadium and Vanadoniobates: Synthesis, Structure and Application. Polyhedron 2014, 83, 242−258. (c) Hayashi, Y. Hetero and Lacunary Polyoxovanadate Chemistry: Synthesis, Reactivity and Structural Aspects. Coord. Chem. Rev. 2011, 255, 2270−2280. (d) Mizuno, N.; Kamata, K. Catalytic Oxidation of Hydrocarbons with Hydrogen Peroxide by Vanadium-Based Polyoxometalates. Coord. Chem. Rev. 2011, 255, 2358−2370. (2) (a) Dietl, N.; Schlangen, M.; Schwarz, H. Thermal HydrogenAtom Transfer from Methane: The Role of Radicals and Spin States in Oxo-Cluster Chemistry. Angew. Chem., Int. Ed. 2012, 51, 5544−5555. (b) Dong, F.; Heinbuch, S.; Xie, Y.; Rocca, J. J.; Bernstein, E. R.; Wang, Z.-C.; Deng, K.; He, S.-G. Experimental and Theoretical Study of the Reactions between Neutral Vanadium Oxide Clusters and Ethane, Ethylene, and Acetylene. J. Am. Chem. Soc. 2008, 130, 1932−1943. (3) Spandl, J.; Daniel, C.; Brüdgam, I.; Hartl, H. Synthesis and Structural Characterization of Redox-Active Dodecamethoxoheptaoxohexavanadium Clusters. Angew. Chem., Int. Ed. 2003, 42, 1163−1166. (4) For selected recent papers concerning nonionic vanadium oxide cluster complexes, see: (a) Tang, J.; Yao, P.-F.; Xu, X.-L.; Li, H.-Y.; Huang, F.-P.; Nie, Q.-Q.; Luo, M.-Y.; Yu, Q.; Bian, H.-D. Asymmetric Catalytic Sulfoxidation by a Novel VIV8 Cluster Catalyst in the Presence

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. C

DOI: 10.1021/acs.inorgchem.8b00651 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

calculation suggested that V2 is a VV atom, but the oxidation states of V3 and V4 could not be determined unambiguously from this structure (mixed-valence state or disordered VIV/VV) because there can be crystallographic disorder between the V3 and V4 parts (Table S5). (10) For recent papers concerning the magnetochemistry of mixedvalent vanadium(IV/V) oxide clusters with ferro- and antiferromagnetic exchange interactions, see: (a) Linnenberg, O.; Kozlowski, P.; Besson, C.; van Leusen, J.; Englert, U.; Monakhov, K. Y. A V16-type Polyoxovanadate Structure with Intricate Electronic Distribution: Insights from Magnetochemistry. Cryst. Growth Des. 2017, 17, 2342− 2350. (b) Kozłowski, P.; Notario-Estévez, A.; de Graaf, C.; López, X.; Monakhov, K. Y. Reconciling the Valence State with Magnetism in Mixed-Valent Polyoxometalates: the Case of a {VO2F2@V22O54} Cluster. Phys. Chem. Chem. Phys. 2017, 19, 29767−29771. (11) We are grateful to one of the reviewers for insightful comments and suggestions to improve the discussion of the magnetic data. (12) There was no significant increase of the χMT values in the case of V8′·1.28C8H10 (Figure S8). We must await further studies to clarify the reason for the difference in the magnetic behavior between V8′· 0.42C7H8 and V8′·1.28C8H10. A bending at ca. 50 K might be due to a structural phase transition. (13) The oxidation states of the inner (V1) and outer (V2) V atoms in V4′ were confirmed to be 4+ and 5+, respectively, by BVS calculations (Figures S2 and S3 and Table S5). (14) We examined the detection of acetaldehyde in the reductive conversion of V8 using EtOH. In a pressure-resistant NMR tube, a CDCl3 solution of V8 (5.6 μmol) and EtOH (115 μmol) was heated at 80 °C for 48 h under N2, and the resulting mixture was analyzed by 1H NMR spectroscopy. As a result, the signals assignable to acetaldehyde were observed at δ 9.78 (q, J = 2.7 Hz, 1H) and 2.19 (d, J = 2.5 Hz, 3H), and its amount was determined to be 3.7 μmol using the internal standard (1,3,5-trimethoxybenzene). In addition, no formation of acetic acid was observed in this reaction. Although we must await further investigation to clarify the stoichiometry of this reaction, we assume that a 2 molar amount of EtOH is oxidized to acetaldehyde by a 1 molar amount of V8 to afford a 2 molar amount of V4′-Et. (15) Kumagai, H.; Endo, M.; Kawata, S.; Kitagawa, S. A Mixed-Valence Tetranuclear Vanadium(IV,V) Complex, [V 4 O 4 (μ-OEt) 2 (μO)2(OEt)4(phen)2]. Acta Crystallogr. 1996, C52, 1943−1945. (16) Bleaney, B.; Bowers, K. D. Anomalous Paramagnetism of Copper Acetate. Proc. R. Soc. London, Ser. A 1952, 214, 451−465. (17) (a) del Río, D.; Galindo, A.; Vicente, R.; Mealli, C.; Ienco, A.; Masi, D. Synthesis, Molecular Structure and Properties of OxoVanadium(IV) Complexes Containing the Oxydiacetate Ligand. Dalton Trans. 2003, 1813−1820. (b) Ceccato, A. S.; Neves, A.; de Brito, M. A.; Drechsel, S. M.; Mangrich, A. S.; Werner, R.; Haase, W.; Bortoluzzi, A. J. Magneto-Structural Correlation for Binuclear Octahedral Vanadium(IV)−Oxo Complexes. Synthesis, Structure and Magnetic Properties of a VIVO2+ Complex with a New Ligand Derived from Glycine. J. Chem. Soc., Dalton Trans. 2000, 1573−1577. (18) In the case of χMT versus T plots for V4′-Me (Figure S7a), a bending appears at ca. 110 K, which might result from a structural phase transition. The preliminary best-fit parameters were determined to be J = − 36.7 cm−1 and g = 2.09. (19) Unfortunately, the redox reactions of V8 seem to be too slow to use this compound for the catalytic air oxidation of alcohols. In addition, we measured the cyclic voltammetry (CV) of V8′·0.42C7H8 in CH2Cl2 (supporting electrolyte: Bu4NPF6) at a scan rate of 0.1 V s−1. As a result, the CV showed an irreversible oxidation wave at 0.63 V (vs Ag/Ag+) with a shoulder at 0.55 V (vs Ag/Ag+), and no significant reduction wave was observed. These results indicate that the degradation of V8′· 0.42C7H8 occurred under oxidative conditions.

of Serum Albumin: A Simple and Green Oxidation System. RSC Adv. 2016, 6, 44154−44162. (b) Chen, B.; Huang, X.; Wang, B.; Lin, Z.; Hu, J.; Chi, Y.; Hu, C. Three New Imidazole-Functionalized Hexanuclear Oxidovanadium Clusters with Exceptional Catalytic Oxidation Properties for Alcohols. Chem. - Eur. J. 2013, 19, 4408−4413. (c) Marino, N.; Lloret, F.; Julve, M.; Doyle, R. P. Synthetically Persistent, Self Assembled [VIV2VV4] Polyoxovanadates: Facile Synthesis, Structure and Magnetic Analysis. Dalton Trans. 2011, 40, 12248−12256. (d) Kodama, S.; Taya, N.; Inoue, Y.; Ishii, Y. Synthesis and Interconversion of V4, V7, and V8 Oxide Clusters: Unexpected Formation of Neutral Heptanuclear Oxido(alkoxido)vanadium(V) Clusters [V7O17(OR)(4,4’-tBubpy)3] (R = Et, MeOC2H4). Inorg. Chem. 2016, 55, 6712−6718. (e) Kodama, S.; Taya, N.; Ishii, Y. A Novel Octanuclear Vanadium(V) Oxide Cluster Complex Having an Unprecedented Neutral V8O20 Core Functionalized with 4,4’-Di-tert-butyl-2,2’-bipyridine. Inorg. Chem. 2014, 53, 2754−2756. (f) Kastner, K.; Puscher, B.; Streb, C. Self-Assembly of a Tetrahedral 58-Nuclear Barium Vanadium Oxide Cluster. Chem. Commun. 2013, 49, 140−142. (g) Tucher, J.; Nye, L. C.; IvanovicBurmazovic, I.; Notarnicola, A.; Streb, C. Chemical and Photochemical Functionality of the First Molecular Bismuth Vanadium Oxide. Chem. Eur. J. 2012, 18, 10949−10953. (5) Transition-metal oxide cluster complexes having a windmill-shaped structure similar to that of V8 have been reported. See: (a) Laurencin, D.; Garcia Fidalgo, E.; Villanneau, R.; Villain, F.; Herson, P.; Pacifico, J.; Stoeckli-Evans, H.; Bénard, M.; Rohmer, M.-M.; Süss-Fink, G.; Proust, A. Framework Fluxionality of Organometallic Oxides: Synthesis, Crystal Structure, EXAFS, and DFT Studies on [{Ru(η6-arene)}4Mo4O16] Complexes. Chem. - Eur. J. 2004, 10, 208−217. (b) Nishikawa, K.; Kido, K.; Yoshida, J.; Nishioka, T.; Kinoshita, I.; Breedlove, B. K.; Hayashi, Y.; Uehara, A.; Isobe, K. Synthesis and Behavior in Solution of the Triple Cubane- and Windmill-Type Framework Isomers of an Organorhodium Tungsten Oxide Cluster [(Cp*Rh)4W4O16]. Appl. Organomet. Chem. 2003, 17, 446−448. (c) Artero, V.; Proust, A.; Herson, P.; Gouzerh, P. Interplay of Cubic Building Blocks in (η6-arene)Ruthenium-Containing Tungsten and Molybdenum Oxides. Chem. - Eur. J. 2001, 7, 3901−3910. (d) Süss-Fink, G.; Plasseraud, L.; Ferrand, V.; Stoeckli-Evans, H. [(pPriC6H4Me)4Ru4Mo4O16)]: An Amphiphilic Organoruthenium Oxomolybdenum Cluster Presenting a Unique Framework Geometry. Chem. Commun. 1997, 1657−1658. (6) To gain insight into the present reduction reaction, organic products were analyzed by means of 1 H NMR to detect triphenylphosphine oxide (O = PPh3). When a toluene solution of V8 (0.051 mmol) and PPh3 (0.20 mmol) was refluxed for 30 min under N2, a dark-blue suspension was formed. The resulting suspension was filtered, and the dark-purple filtrate was evaporated in vacuo. The residue was suspended with Et2O and then filtered, and the ether solution was evaporated to yield a white solid. The 1H and 31P{1H} NMR analyses of the solid in CDCl3 using 1,3,5-trimethoxybenzene as an internal standard suggested that OPPh3 (0.089 mmol) was formed along with free 4,4′-tBubpy (0.083 mmol). We consider that V8 oxidizes an equimolar amount of PPh3 to afford V8′ with the generation of O PPh3 and free 4,4′-tBubpy, although more than the expected amount of OPPh3 was observed. The formation of excess OPPh3 and 4,4′-tBubpy is probably due to the oxidation of PPh3 with unidentified vanadium(V) species generated in situ via splitting of the core of V8. (7) (a) Huang, Y.; Zhang, J.; Ge, J.; Sui, C.; Hao, J.; Wei, Y. [V4Mo3O14(NAr)3(μ2-NAr)3]2−: The First Polyarylimido-Stabilized Molybdovanadate Cluster. Chem. Commun. 2017, 53, 2551−2554. (b) Liu, C.-M.; Gao, S.; Hu, H.-M.; Wang, Z.-M. A Novel Bimetallic Cage Complex Constructed from Six V4Co Pentatomic Rings: Hydrothermal Synthesis and Crystal Structure of [(2,2’Py2NH)2Co]3V8O23. Chem. Commun. 2001, 1636−1637. (8) When V8′ was synthesized from the reaction of V8 and PPh3 in pxylene (C8H10), crystals of V8′·3C8H10 were obtained, and with this material, no honeycomb structure was observed in the crystal packing (Figure S6). (9) No crystallographic symmetry element is present in V8′·3C8H10, and therefore the three V atoms (V2, V3, and V4) coordinated by 4,4′-tBubpy are inequivalent (Figure S1 and Tables S1 and S2). The BVS D

DOI: 10.1021/acs.inorgchem.8b00651 Inorg. Chem. XXXX, XXX, XXX−XXX