Transition metal complexes of 2-amino-3,5-dihalopyridines: Syntheses, structures and magnetic properties of (3,5-diCAPH)₂CuX₄ and (3,5-diBAPH)₂CuX₄

A family of bis(2-amino-3,5-dihalopyridinium)tetrahalocuprate(II) compounds has been synthesized, including (3,5-diCAPH)₂CuCl₄ (1), (3,5-diCAPH)₂CuBr₄ (2), (3,5-diBAPH)₂CuCl₄ (3), and (3,5-diBAPH)₂CuBr₄ (4) [3,5-diCAPH = 2-amino-3,5-dichloropyridinium; 3,5-diBAPH = 2-amino-3,5-dibromopyridinium]. These complexes have been analyzed through single crystal X-ray diffraction and temperature dependent magnetic susceptibility. Compound 1 crystallizes in the P-1 space group and the tetrachlorocuprate ion is best described as possessing a distorted square planar geometry. Compounds 2-4 are structurally similar and crystallized in the P2₁/n, P2₁/c, and P2₁/n space groups respectively. The tetrahalocuprate ions are best described as distorted tetrahedra. All four compounds show antiferromagnetic interactions and were fit to the uniform chain Heisenberg model with resulting 2J/k_B values of -11.71(2) K, -2.21(1) K, -12.43 (2) K, and -1.36(1) K, respectively. The exchange values correlate well with the two-halide exchange pathway parameters. The unusual observation that the chloride complexes show stronger magnetic exchange than the bromide complexes provides strong support that the exchange can be strongly dependent upon the Cu-XX angles and Cu-XX-Cu torsion angles.