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]2CuCl4 (1) and [2-amino-4,6-dimethylpyridinium]2CuBr4 (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 P1¯ with V = 991.2(10) Å3 for (1) and 1059.26(12) Å3 for (2) . There is no significant difference in the non-classical N–H⋯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)°/96.78(6)° for (1) and 139.43(4)°/96.64(3)° 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 π–π interactions exist between cations from different chains with centroid to centroid distance of 4.07 Å in (1) and a long 4.594 Å in (2). The X–π electrostatic interactions are surprisingly stronger in (2) than in (1) with a Br to centroid of pyridinic ring distance of 3.890 Å compared with 3.996 Å for the chloride analogue.

[2-amino-4,6-dimethylpyridinium]2CuCl4 and its Br analogue are isomorphous in P1¯ with Z = 2. The cations are planar, and the anions are distorted tetrahedral with each [CuX4]2− anion hydrogen bonded nonsymmetrically to four cations. The halogen-π electrostatic interaction is stronger in the bromide than the chloride with a shorter Br to centroid of pyridinic ring distance of 3.890 Å compared with 3.996 Å for the chloride analogue.Figure optionsDownload as PowerPoint slide