Extended Mo₃^IV-Polyoxometalates: 1D-[Mo₆^IVMo₄^VIGe₂ZnO₃₁py₉ (H₂O)]^4– and 2D-[Mo₃^IVMo₉^VIZn₆P₇O₅₆py₈]⁺ (py = Pyridine)

Abstract

The first examples of extended Mo3 IV-polyoxometalates (Mo3 IV-POMs), 1D-H2 [Ge2Mo6 IVMo4 VIO31Zn­(H2O)­py9]·2Hpy·HOCH2CH2 OH•4H2O­(H2[1]·2Hpy•glycol·H2O) and 2D-[P@Mo3 IVMo9 VIZn6(PO4)6O32py8]­Cl·2py·7H2O ([2]·Cl•2py·7H2O), were prepared through the solvothermal partial oxidation of [Mo3 IVO2(O2CCH3)6(H2O)3]­ZnCl4 in py/H2O containing glycol (for 1) or H3PO4 (for 2). They were characterized by X-ray crystallography and elemental analyses. Their electronic structure and bonding were discussed on the basis of density functional theory (DFT) theoretical calculations. X-ray photoelectron spectroscopy, IR/UV–vis spectra, powder X-ray diffraction, thermal gravimetric analysis, and mass spectrometry were also performed and discussed for 2D-2.

Electron‐Rich MoIV3‐Polyoxomolybdates Resembling the Paratungstic Archetype

“…skeletal conversion [13][14][15] shown in Scheme 1, the oxidation-controllable bioxo-capped precursor [Mo IV 3 O 2 (O 2 CCH 3 ) 6 (H 2 O) 3 ] 2 + was utilized [4] to prepare a series of discrete and extended Mo IV 3 À POMs (9-25, Figure S1), leading to the rapid development of Mo IV À POMs chemistry. [4][5][6][7][8][9][10] However, as commonly encountered in POMs, d 1 -Mo V in the reported Mo IV À POMs was unexceptionally coupled to each other to form diamagnetic Mo V 2 dimer caused by the single metal-metal bond. The previous attempts to incorporate bridging alkoxyl ligands in Mo IV 3 À POMs also failed.…”

“…The top Mo IV 3 traid can be viewed as derived from M VI 3 !M IV 3 6ereduction of the paratungstic archetype concomittant with the substitution of the terminal oxygen atoms with Lewis basic IV 3 O 4 ] clusters [13][14][15]19,20] and reported Mo IV 3 À POMs clusters (2.490-2.545 Å, Table S6). [3][4][5][6][7][8][9][10] The highly strengthened Mo IV -μ 3 -O bonding as indicated by the markedly shorter bond lengths (Mo1-O6, 2.033(3), Mo2-O6, 2.036(3) Å) than Mo V,VI -μ 3 -O (Mo6-O14, 2.231(2), Mo8-O14, 2.249(4) Å) leads to the extremely weak Mo IV -μ 3 -O bonding ability, accounting for the hydrogen transfer from the top μ 3 -OH of [H 2 W 12 O 42 ] 10À to the bottom μ 2 -OH in 1. This is also responsible for the fact that, in contrast to M VI -Keggin POMs, all Mo IV 3 -Keggin species are free of central heteroatoms.…”

“…Electron-rich polyoxometalates (POMs) induced by multiple metal-metal bonds have been received increasing attentions because of their unprecedented versatility in terms of molecular/electronic structures and bonding, unique physicochemical properties and promising applications in catalysis, electron storage, and nanoelectronics (POMtronics) among others. [1,2] Deeply reduced Mo IV 3 À POMs [3][4][5][6][7][8][9][10][11] featuring strong triangular metal-metal Δ-bonds are of special importance in aspects of (a) molecular and crystal structures of POMs are dramatically altered by a varied combination of Mo IV 3 triads and Mo V 2 dimers; (b) robust terminal Mo V,VI =O double bonds are replaced by flexible Mo IV ! :L dative bonds (L=Lewis base ligand), which functionalizes POMs with Mo IV 3 Lewis acidic active sites to form subnano Mo IV 3 •••O x M y Lewis catalysis field (subnano-LCF) with extensive Lewis acid-base synergistic effects; (c) varied number of Δ-Mo IV 3 units remarkably change electronic structures of POMs, especially energy level ones and HOMO-LUMO gaps essential to photoelectric properties; (d) a large number of surface Mo IV 3 and Mo V 2 bonding electrons are available as electronic sponge; (e) peripheral modifiable Lewis base ligands allow for the functionalization of Mo IV 3 À POMs via crystal engineering or ligand substitution; (f) physicochemical proper-ties can be reinforced by efficient Mo IV 3 !O x M VI y electron transfer and incorporating heterometal addenda; (g) X-ray single crystal structural characterization of mixed-valence Mo IV,V,VI À POMs is critical to understand the structural evolution during Mo IV $ Mo VI charging/discharging processes of POM batteries.…”

“…[12] Our recent study indicated that Mo IV 3 -Keggin species are free of central heteroatoms because of the extremely weak μ 3 -O coordinating capability in the [Mo IV 3 O 4 ] triads. [10] However, the synthetic and structural chemistry of Mo IV À POMs have been a long-time uncharted research area, which led to our very limited structural information about the multielectron-reduced states of POMobased molecular cluster batteries or supercapacitors, which involve four type of Mo: Mo VI !d 1 -Mo V /Mo V À Mo V !Mo IV . [2,11,12] In 2013, a synthetic strategy in using partial oxidation of the incomplete cuboidal [Mo IV 3 O 4 ]-type precursor, [Mo IV 3 O 4 (Hnta) 3 ] 2À (Hnta = nitrilotriacetic acid), was developed, producing the first Mo IV À POMs, [Mo IV 6 Mo VI 7 O 32 (OH) 4 py 6 ] 2À .…”

“…3 ) [15][16][17][18] was utilized instead of [Mo IV 3 O 4 ]-type species, [4] leading to the rapid development of Mo IV 3 À POMs chemistry as demonstrated in Figure S1. [5][6][7][8][9][10] However, d 1 -Mo V in the reported Mo IV 3 À POMs is unexceptionally coupled to form diamagnetic Mo O 42 ] 10À that has been wellknown for W VI [21] but never been reported for Mo VI , providing the first example of paratungstic archetype made of Mo. The Cr III -/W VI -substituted allomers anti-[Mo IV 3 Mo V 5 Mo VI 4 Cr III O 31 (μ-OH) 2 py 10 ] (6) /anti-[Mo IV 3 Mo V 6 Mo VI W VI 3 O 32 (μ-OH) 2 py 9 ] (7) and the diamagnetic syn-[Mo IV 3 Mo V 6 W VI 4 O 33 (μ 3 -OH)py 9 ] À (8) resulting from anti!syn conversion concomitant with d 1 -d 1 coupling will also be described.…”