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)]center dot 2H(2)O, 1 (RNap N-(2-hydroxy-1-naphthalidene) L-arginine), obtained from Cu(OAc)(2)center dot 2H(2)O 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)center dot H2O 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)center dot H2O gives [Cu(RMe)(OAc)]center dot 5H(2)O, 3, whose crystal packing shows a zeolite-like network with a water cluster residing in the hydrophilic channel, thus facilitating the hydrogen bonding interaction.