Steric Influences on the Ground State of Iron(II) in the Tris(3,3'-dimethyl-2,2'-bipyridine)Iron(II) Ion

Abstract

The tris ( ligand ) complex ions of iron(II) and nickel(II) with 3,3′-dimethyl-2,2′-bipyridine (L) are described. Salts of [FeL₃]²⁺ display anomalously temperature-dependent magnetic and spectroscopic properties which arise from a temperature-induced singlet (¹A₁) ↔ quintet (⁵T₂) spin transition. The structures of [ML₃][ClO₄]₂(M = Fe, Ni) have been determined and these reveal a strong twist (c. 37°) of the pyridine rings about the C-C bridge. This forces the metal atoms out of the bonding planes of the donor nitrogen atoms and effectively reduces the interaction between L and the metal atoms. The average M-N distances are 2.064 Ǻ (M = Fe) and 2.102 Ǻ (M = Ni). Crystal data: the two complex salts are isostructural in monoclinic space group C2/c. [FeL₃][ClO₄]₂: a 12.252(8), b 15.568(5), c 19.288(11) Ǻ, β 93.62(3)°; Z 4; [NiL₃][ClO₄]₂: a 12.255(5), b 15.619(4), c 19.419(9) Ǻ, β 93.23(2); Z 4.