Magnetic and Structural Correlations in [ ( CSHsN ) NH 2 ] 2

The crystal structures of the title compounds, (3-aminOpyridiniUm),cU2cl6 and ( 3-aminopyridinium),Cu2Br6.H20, have been determined. The chloride dimer is monoclinic [a = 7.623 (1) A, b = 14.700 (2) A, c = 8.121 (1) A, j3 = 93.09 (1)O] and crystallizes in the space group PZ,/a, while the bromide dimer is monoclinic [a = 19.096 (5) A, 6 = 6.729 (1) A, c = 19.499 ( 5 ) A, /3 = 126.89 (1)O] and crystallizes in the space group C2/c. The two compounds contain similar species, with each copper ion having a distorted-trigonal-bipyramidal geometry involving four halide ions and the amino nitrogen from the pyridinium ion. Pairs of copper(I1) ions are joined by two Cu-X-Cu (X = CI-, Br-) bridges to form the centrosymmetric dimer structures. The chloride dimer is symmetrically bibridged, while the bromide dimer is of the asymmetrically bibridged type. The latter contains a water of hydration, the structural effects of which are important magnetically. The copper ions in the chloride dimer show principally an angular distortion from trigonal-bipyramidal geometry, and the Cu-CI-Cu bridging angle in the dimer is 94.9 (1)'. In the bromide compound, the coordination is distorted more toward a 4 + 1 coordination eometry around each copper atom, with a Cu-Br-Cu bridging angle of 93.4 (1)" and an interdimer Br-Br distance of 3.728 1. The magnetic susceptibilities of the two compounds were measured between 2.0 and 280 K. The results have been interpreted in terms of ferromagnetic coupling within the chloride dimer (J,-,/k = 30 K). A substantial antiferromagnetic coupling is observed for the bromide salt, and it is concluded that the magnetic dimer consists of copper ions from two adjacent structural dimers. The structural chemistry of five-coordinate copper(I1) chloride species is summarized, and it is concluded that the folded 4 + 1 coordination geometry is the favored geometry.