Syntheses and crystal structures of cis - and trans -copper(II) complexes of L-arginine

Two copper(II) complexes of L-arginine, trans-[Cu(l-Arg)2(NO3)]NO3 · 3H2O (1) and {cis-[Cu(l-Arg)2](NO3)2 · 3H2O} n (2) (Arg = arginine) were prepared by reaction of Cu(NO3)2 · 3H2O and L-arginine in acetone and aqueous solution, respectively. X-ray analysis reveals 1 crystallizes in a monoclinic system, P21 with a = 10.3857(15), b = 16.885(3), c = 15.9586(19) Å, β = 15.9586(19)°, Z = 4, V = 2654.2(6) Å3. The copper(II) centers lie in a distorted N2O3 square-pyramidal environment. While 1 adopts a mononuclear structure, and the axial position occupied by a nitrate with Cu1–O9 = 2.535 Å and Cu2–O20 = 2.581 Å, 2 features a 1-D infinite chain structure. In 1, adjacent monomeric units connect with each other to give a 2-D layer structure of (4, 4) nets through hydrogen bonds between the guanidinium and carboxylic groups of arginine, and 2-D layers further assemble to a 3-D supermolecular structure via a series of inter-layer hydrogen bonds.