Supramolecular assembly of a new series of copper-L-arginine Schiff bases

A series of copper-L-arginine complexes has been synthesized and characterized by spectroscopic and single-crystal X-ray diffraction analyses. The L-arginine Schiff bases invariably show [ONO] tridentate coordination on a mononuclear Cu(II) sphere. [Cu(RNap)(OAc)]·2H2O, 1 (RNap = N-(2-hydroxy-1-naphthalidene) L-arginine), obtained from Cu(OAc)2·2H2O and HRNap, gives two stereochemically different molecules in the crystal unit cell, with each of them showing different acetate binding modes. It exhibits a channel structure with disordered water molecules filling the cavity. Complexation of N-(2-hydroxy-5-nitro-1-salicylidene) L-arginine (HRNO2) with Cu(ClO4)2·6H2O yields the intriguing triclinic crystal structure of 2. Its unit cell consists of a neutral molecule [Cu(RNO2)Cl(H2O)], an ion pair [Cu(RNO2)(H2O)2]ClO4 and three water molecules of crystallization. Complexation of HRMe (RMe = N-(2-hydroxy-5-methyl-1-salicylidene) with Cu(OAc)2·2H2O gives [Cu(RMe)(OAc)]·5H2O, 3, whose crystal packing shows a zeolite-like network with a water cluster residing in the hydrophilic channel, thus facilitating the hydrogen bonding interaction.