title: Heterobimetallic μ-oxido complexes containing discrete V(V)-O-M(III) (M = Mn, Fe) cores: targeted synthesis, structural characterization, and redox studies.
abstract: Heterobimetallic compounds [L'OV(V)(μ-O)M(III)L]n (n = 1, M = Mn, 1-5; n = 2, M = Fe, 6 and 7) containing a discrete unsupported V(V)-O-M(III) bridge have been synthesized through a targeted synthesis route. In the V-O-Mn-type complexes, the vanadium(V) centers have a square-pyramidal geometry, completed by a dithiocarbazate-based tridentate Schiff-base ligand (H2L'), while the manganese(III) centers have either a square-pyramidal (1 and 3) or an octahedral (2 and 5) geometry, made up of a Salen-type tetradentate ligand (H2L) as established by X-ray diffraction analysis. The V-O-Mn bridge angle in these compounds varies systematically from 155.3° to 128.1° in going from 1 to 5 while the corresponding dihedral angle between the basal planes around the metal centers changes from 86.82° to 20.92°, respectively. The V-O-Fe-type complexes (6 and 7) are tetranuclear, in which the two dinuclear V(μ-O)Fe units are connected together by apical iron(III)-aryl oxide interactions, forming a dimeric structure with a pair of Fe-O-Fe bridges. The X-ray data also confirm the V═O → M canonical form to contribute predominantly on the overall V-O-M bridge structure. The molecules in solution also retain their heterobinuclear composition, as established by electrospray ionization mass spectrometry and (51)V NMR spectroscopy. Electrochemically, these complexes are quite interesting; the manganese(III) complexes (1-5) display three successive reductions (processes I-III), each with a monoelectron stoichiometry. Process I is due to a Mn(III)/Mn(II) reduction (E1/2 ranges between -0.32 and -0.05 V), process II is a ligand-based reduction, and process III (E1/2 = ∼1.80 V) owes its origin to a V(V)O/V(IV)O reduction; all potentials are versus Ag/AgCl. The iron(III) compounds (6 and 7), on the other hand, show at least four irreversible processes, appearing at Epc = -0.20, -1.0, -1.58, and -1.68 V in compound 6 (processes IV-VII), together with a reversible process (process VIII) at E1/2 = -1.80 V (ΔEp = 80 mV). While the first two of these are due to Fe(III)/Fe(II) reductions at the two iron(III) centers of these tetranuclear cores, the reversible reduction at a more negative potential (ca. -1.80 V) is due to a V(V)O/V(IV)O-based electron transfer.
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science (IACS) , Jadavpur, Kolkata 700032, India.
authors.forename: Kisholoy
authors.initials: K
authors.lastname: Bhattacharya
authors.forename: Sk Md Towsif
authors.initials: SM
authors.lastname: Abtab
authors.forename: Mithun Chandra
authors.initials: MC
authors.lastname: Majee
authors.forename: Akira
authors.initials: A
authors.lastname: Endo
authors.forename: Muktimoy
authors.initials: M
authors.lastname: Chaudhury
mesh_terms: D007501:Iron / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D014639:Vanadium / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D010087:Oxides; D014639:Vanadium; D008345:Manganese; D007501:Iron; D010100:Oxygen