Study on (Et4N)[VFe3S4(R(2)dtc)(4)] complexes with cubane-type cores - Syntheses, structure, spectral and magnetic properties and chemical behaviors in solution

A series of cubane-type cluster compounds (Et4N)[VFe3S4(R(2)dtc)(4)] (R-2 = OC4H8 (1), C5H10 (2), C4H8 and Et-2) and (Ph4P)[VFe3S4(Bz(2)dtc)(4)] have been synthesized from a self-assembly reaction system VS43-/FeCl2/R(2)dtc(- )/PhS- in DMF and characterized. A formation mechanism of the VFe3S4 cubane was suggested to contain a possible process in which linear intermediate [ VS4(FeL2)(2)](3-) was converted to incomplete cubane-type intermediate. The dynamic study on the H-1 NMR for 1 and (Et4N)[VFe3S4(Et(2)dtc)(4)] exhibit s a possible metal exchange in DMSO solution, accompanying the formation of Fe4S4(R(2)dtc)(4). Cyclic voltammograms show similar electrochemical behav iors between 1 and 2 indicated by an quasi-reversible redox couple at +0.35 to +0.66 V and two reduced peaks at -0.35 to -0.42 V and -0.75 to -0.86 V, respectively. The chemical shifts of 0.51 to 0.57 mm s(-1) in Mossbauer eff ect of the VFe3S4 cubanes exhibit the equivalence of the three Fe atoms sho wing that the VFe3 skeleton can be treated as a valence-delocalized system. The metal formal oxidation states were deduced as intermediate between V-( II) + 3Fe((III)) and V-(III) + Fe-(II) + 2Fe((III)). A magnetic exchange mo del based on the former valence system of V-(II)/3Fe((III)) was used for th e fitting of variable-temperature magnetic susceptibilities, revealing an a ntiferromagnetic interaction in the VFe3 coupling system. (C) 1999 Elsevier Science Ltd. All rights reserved.