Coordination of 2,2'-Bithiazole. Spectral, Magnetic and Structural Studies of the Iron(II) and Nickel(II) Complexes

Abstract

Iron(II) and nickel(II) complexes of 2,2′bithiazole (2bt) have been prepared. Salts of [Fe(2bt)₃]²⁺ have spectral properties typical of iron(II) diimine systems. Their magnetic and Mossbauer spectral properties show an anomalous temperature-dependence which is associated with a temperature-induced singlet (¹A₁) ↔ quintet (⁵T₂) transition. The manifestation of the spin transition is complicated by the existence of two modifications of the complex perchlorate. In one of these there is a relatively small fraction of quintet state species in an essentially low-spin lattice. This fraction increases only slightly at elevated temperatures within the range 89-343 K. The other modification is essentially high-spin at high temperatures and low-spin at low temperatures. The quadrupole splitting values for the two high-spin species are quite different, arising from different lattice contributions. The structures of 2bt and the related 4,4′-bithiazole and of [Ni(2bt)₃][ClO₄]₂ have been determined by single-crystal X-ray diffactometry. These afford a comparison of the coordination features of the isomeric bithiazoles. 2,2′-Bithiazole, orthorhombic with space group P bca , Z = 8, α 9.284(1), b 14.564(1), c 10.802(1) Ǻ; 4,4′-Bithiazole, monoclinic with space group P2₁/c, Z = 2, a 5.528(2), b 6.288(2), c 11.316(4)Ǻ. The nickel complex, orthorhombic with non-centrosymmetric space group Pna2₁, four molecules per unit cell, a 16.709(3), b 9.511(4), c 17.491(2)Ǻ, has a stacking fault which reduces the intensity of h = 2n+1 data. Pseudosymmetry enables data with h = 2n to be described by a disordered structure in the centrosymmetric space group Pnmn.