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

Abstract

A series of perchlorocuprate salts, namely, [4,4'-H₂diazastilbene][CuCl₄] 1, [H₂-N-(4-pyridyl)isonicotinamide][CuCl₄] 2, [H₂-N-(3-pyridyl)isonicotinamide][CuCl₄] 3, [H₂-N-(4-pyridyl)nicotinamide][CuCl₄] 4, [H₂-N,N'-bis(4-pyridyl)urea][CuCl₄] 5, [H-isonicotinic acid]₂[CuCl₄]2H₂O 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· · · Cl-Cu hydrogen-bonding interaction is important in supramolecular syntheses of these solids. However, occurrence of bifurcated hydrogen bonding of the type N-H· · · 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· · · 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.