Intramolecular Electron Transfer in (BzImH)[(LOV)₂O] (H₂L =S-Methyl 3-((2-Hydroxyphenyl)methyl)dithiocarbazate):  A Novel μ-Oxo Dinuclear Oxovanadium(IV/V) Compound with a Trapped-Valence (V₂O₃)³⁺Core

Abstract

The mononuclear oxovanadium complexes [V V OL(OR)] (R: Me, 1a; Et, 1b; Pr i , 1c) and [V IV OLB] (B: Im, 2a; BzIm, 2b) of the tridentate ONS donor ligand S-methyl 3-((2-hydroxyphenyl)methyl)dithiocarbazate (H 2 L) are reported. The novel mixed-valence (µ-oxo)divanadium(IV,V) complex (BzImH)[(LVO) 2 O] (3) was synthesized using 1a and 2b as precursors. All of the complexes were characterized by various physical techniques, including 1 H NMR, EPR, and cyclic voltammetry. The X-ray structures of 1a and 3 were determined. Crystals of 1a are triclinic, of space group P1 h, with a ) 11.045(1) Å, b ) 13.429(4) Å, c ) 9.611(1) Å, R ) 100.00(1)°, β ) 114.33(1)°, γ ) 81.00(1)°, and Z ) 4. The asymmetric unit of 1a contains two independent molecules with minor conformational differences. Crystals of 3 are monoclinic, of space group P2 1 /n, with a ) 10.10(1) Å, b ) 20.594(9) Å, c ) 14.679(8) Å, β ) 95.28(6)°, and Z ) 4. 3 is a bent molecule, with a V-O-V bridge angle of 144.0(6)°. It has a trapped-valence structure in the solid state with a rare syn-dioxo-µ-oxo [OV-O-VO] 3+ core and reveals a 15-line EPR spectrum ( 51 V, I ) 7 / 2 ) in solution (CH 3 CN) at room temperature, indicating delocalization of the odd electron. The spectrum gradually changes its profile with the lowering of temperature and ultimately collapses into an 8-line pattern at 225 K due to thermal trapping of the odd electron (k th ∼ 7.3 × 10 9 s -1 ). 3 also exhibits an intervalence transfer (IT) band in solution with features (λ max 970 nm, 1670 M -1 cm -1 in CH 3 CN) remaining practically unaffected by the change of solvents. The IT band was analyzed by Gaussian curve fitting, and the electron exchange integral H AB was estimated as 2210 cm -1 . Thus, 3 appears to be an interesting mixed-oxidation-state (µ-oxo)divanadium(IV,V) complex that exhibits a trapped-valence structure in the solid state and undergoes valence delocalization in solution.

Vanadium(Ⅳ) Complexes with N,N,S-Donor Systems

“…10 Each of the acetyl pyridine nitrogen and imine nitrogen distance to the vanadium was consistent with values -2.099-2.121 Å for acetyl pyridine nitrogen and 2.054-2.118 Å for imine nitrogen found in other oxovanadium(IV) complexes.…”

“…In addition, the complexes 1 and 2 exhibited a strong band in the 952 cm −1 range due to the terminal V=O stretching, 10 along with a medium-intensity band in the high-frequency region (3374 cm −1 for 2), associated with the N-H stretch of phenyl amine. 4,10,11 The electronic absorption spectra of the complexes exhibited two bands of moderate intensity (log ε = 1.…”

“…4,10,11 The electronic absorption spectra of the complexes exhibited two bands of moderate intensity (log ε = 1. ).…”

A journey into the electrochemistry of vanadium compounds

“…A mixed-valence divanadium(IV,V) complex, [V 2 O 3 (mphtc) 2 ] − was prepared from mononuclear V(IV) and V(V) precursors [137] (electrochemical data in Table 4, entry 7) and exhibited a trappedvalence structure in the solid state, while undergoing valence delocalization in solution.…”

“…The mononuclear oxido-V(V) alkoxy complexes of S-methyl-3-(5-bromo-2-hydroxyphenyl)dithiocarbazate, VO(bmphtc)OR with R = methyl, ethyl, isopropyl [137], gave cyclic voltammograms with identical features, due to a reduction process corresponding to a V(V) → V(IV) electron transfer ( Table 5, [157]. The cyclic voltammogram in DMSO showed a cathodic reversible process (Table 6, entry 7).…”