SPECTROSCOPIC STUDIES OF THE TRANS-[VOCL2(H2O)(2)] CHROMOPHORE IN ITS HYDROGEN-BONDING ADDUCT WITH 18-CROWN-6

An electron paramagnetic resonance (EPR) study has been carried out on a single crystal of trans-[VOCl2(H2O)(2)](18-crown-6).2H(2)O or adduct of trans-diaquadichlorooxovanadium(IV) with 1,4,7,10,13,16-hexaoxacyclooctadecane (abbr. 18C6) at ambient temperature. This crystal belongs to a centric triclinic space group, and the chromophore and crown ether alternate to form a magnetically diluted vanadyl system. The EPR study has revealed the rhombic spin Hamiltonian parameters g(x)=1.952(1), g(x)=1.985(2), g(y)=1.990(3), \A(z)\=18.8(3), \A(x)\=7.6(3) and \A(y)\>5.5 mT, where the z, x and y principal axes are along the V=O and nearly along the V-OH2 and V-Cl bonds, respectively. Errors of these parameters are large, especially in A(y), owing to many broad hyperfine linewidths resulting in overlapping. A negative sign is suggested for all the principal A values. Three d-d* transitions, d(xy)-->d(xz) (12.9 kcm(-1)), d(xy)-->d(yz) (15.2) and d(xy)-->d(x2y2) (17.0), and a charge-transfer transition, a(1)(related to d(x2y2))-->a(2)(d(xy)) (27-28 kcm(-1)) from the acetone solution, were assigned. The trans-[VOCl2(H2O)(2)] species is not dissociated in acetone and 2-propanol solution, but the chloro ligands are substituted with aqua ligands when there is a lot of water in the solution.