Structural and Electronic Properties of Bis[2-(pyrazin-2-ylamino)-4-(pyridin-2-yl)thiazolato]iron(II) and Its Solvated Derivatives

Abstract

The uncharged complex [Fe( pzapt )₂] [ pzapt is the deprotonated form of 2-(pyrazin-2-ylamino)-4-(pyridin-2-yl) thiazole ] crystallizes with varying degrees of solvation , depending on the solvent. The electronic properties of the solvates differ. For all of them temperature dependence of the magnetic moment is observed, associated with a continuous temperature-induced singlet (¹A₁) ↔ quintet (⁵T₂) transition. The transition is centred below room temperature for the benzene solvates but the unsolvated and chloroform solvate complexes exist predominantly in a singlet low-spin state. Overall the stabilization of the singlet state is greater in this system than in the previously studied [Fe( papt )₂] [ paptH = 2-(pyridin-2-ylamino)-4-(pyridin-2-yl) thiazole ]. A spin equilibrium has been characterized for both [Fe( pzapt )₂] and [Fe( papt )₂] in methanol solution. The crystal structure of [Fe( pzapt )₂].3/2C₆H₆ reveals Fe-N bond lengths consistent with both singlet and quintet state iron(II) being present. The benzene molecules are incorporated into the lattice as groups of three by occupying channels created by the packing of the complex molecules. Bis [2-(pyrazin-2-ylamino)-4-(pyridin-2-yl) thiazole ]iron(II) sesquibenzene solvate: monoclinic, space group P 2₁/c, a 14.894(7), b 12.601(2), c 16.777(8) Ǻ, β 94.57(2)°, Z 4.