INTRAMOLECULAR MAGNETIC AND ELECTROSTATIC INTERACTIONS IN STEPWISE STACKED TRINUCLEAR PARAMAGNETIC METALLOCENES WITH THE METAL SEQUENCES FEM'FE AND NIM'NI(M'=V, CR, CO, NI) AND COCRCO

A building block concept was used for the synthesis of paramagnetic tr inuclear metallocenes which are Cp-bridged by two adjacent Me(2)Si gro ups. The series of compounds abbreviated by the metal sequence FeM'Fe contained one central paramagnetic metallocene with M' = V, Cr, Co, an d Ni and two terminal ferrocenes, while three paramagnetic metallocene s were assembled in CoCrCo and the series NiM'Ni with M' = V, Cr, Co, and Ni. Two paramagnetic centers were present in NiFeNi. The X-ray cry stal structure analysis of FeVFe showed a folding of the bridging liga nd so that the axes of adjacent metallocenes are inclined by 39.9 degr ees and the CH3 groups are not equivalent (triclinic, space group P ($ ) over bar 1, a = 10.075(2) Angstrom, b = 10.268(1) Angstrom, c = 9.01 9(1) Angstrom, alpha = 96.93(1)degrees, beta = 95.78(1)degrees, gamma = 95.15(1)degrees, Z = 1). Seven species MM'M were investigated by cyc lic voltammetry. They underwent up to five oxidations and two reductio ns. From the potential splittings Coulomb interactions of 140 and 40 m V were estimated between next-neighbor and terminal metallocenes, resp ectively. H-1 and C-13 NMR studies of the series FeM'Fe established th e orbital which is preferred by the unpaired spin and that appreciable spin density is transferred within the bridging ligand from the param agnetic to the diamagnetic metallocene depending on the folding angle. In the series NiM'Ni and in CoCrCo the spin densities add and subtrac t depending on the metals. From temperature-dependent H-1 NMR studies of NiVNi and NiNiNi it was concluded that in solution the bending of t he molecules decreased with increasing temperature. The H-1 NMR signal widths disclosed magnetic interactions in NiM'Ni. Solid state magneti c measurements on NiVNi, NiCrNi, and NiNiNi showed that the interactio n is antiferromagnetic with J = -3.08, -1.95, and -10.5 cm(-1), respec tively; the Hamiltonian describing the interaction between two local s pins is written in the form -JS(A)S(B). The ground state of these mole cules was discussed in terms of a model which relates them to localize d trimethylenediyl diradicals.