How robust is the N-H•••Cl2-Cu synthon?: Crystal structures of some perchlorocuprates

A series of perchlorocuprate salts, namely, [4,4'-H(2)diazastilbene][CuCl4] 1, [H-2-N-(4-pyridyl)isonicotinamide] [CUCl4] 2, [H-2-N-(3-pyridyl)isonicotinamide][CuCl4] 3, [H2-N-(4-pyridyl)nicotinamide] [CuCl4] 4, [H-2-N,N'-bis(4-pyridyl)urea][CuCl4] 5, [H-isonicotinic acid](2) [CuCl4] 2H(2)O 6, [2-aminopyridinium]2[CuCl4] 7, and [3-aminopyridinium](2)[CuCl4] 8 have been synthesized and analyzed by single-crystal X-ray diffraction. The results indicate that N-H center dot center dot center dot Cl-Cu hydrogen-bonding interaction is important in supramolecular syntheses of these solids. However, occurrence of bifurcated hydrogen bonding of the type N-H center dot center dot center dot Cl2Cu (synthon A) appears to be dependent on the topology of the cations, geometry of the anions, and other weak interactions such as C-H center dot center dot center dot Cl-Cu. Salts of isomeric cations such as 2, 3 and 4, and 7 and 8 are crystallographically isostructural in their respective groups despite having different hydrogen-bonding site topologies. The hydrogen-bonding-capable backbones (amide and urea moieties) in 2, 3, 4, and 5 do not display the typical hydrogen-bonding network involving these moieties.