The role of non-classical supramolecular interactions in the structures of 2-amino-4,6-dimethylpyridinium tetrahalocuprate(II) salts

The compounds [2-amino-4,6-dimethylpyridinium](2)CuCl4 (1) and [2-amino-4,6-dimethylpyridinium](2)CuBr4 (2) were prepared from acidic ethanolic media containing CuX2 and [2-amino-4,6-dimethylpyridine] in the molar ratio 1:1. The compounds were characterized by IR and single-crystal X-ray diffraction and found to be isomorphous in the space group P (1) over bar with V = 991.2(10) angstrom(3) for (1) and 1059.26(12) angstrom(3) for (2). There is no significant difference in the non-classical N-H center dot center dot center dot X hydrogen bonding between (1) and (2). The [CuX42-] anions show essentially the same extent of distortion from tetrahedral geometry with max./min. values for the X-Cu-X bond angles of 139.72(6)degrees/96.78(6)degrees for (1) and 139.43(4)degrees/96.64(3)degrees for (2). Each [CuX4](2-) anion is hydrogen bonded nonsymmetrically to four cations. In this manner, ladder chains are formed that run along the b-axis, with planar cations falling parallel to the (2, 0, 1) plane. Weaker pi-pi interactions exist between cations from different chains with centroid to centroid distance of 4.07 angstrom in (1) and a long 4.594 angstrom in (2). The X-pi electrostatic interactions are surprisingly stronger in (2) than in (1) with a Br to centroid of pyridinic ring distance of 3.890 angstrom compared with 3.996 angstrom for the chloride analogue. (c) 2005 Elsevier B.V. All rights reserved.