The crystal structures of the title complexes, Cu(L-leu)2 and Cu(D,L-but)2, have been determined by single-crystal three-dimensional X-ray techniques. Crystal data for the two complexes are as follows. Cu(L-leu)2, Cu(H2NCH-(CO2)CH2CH(CH3)2)2: space group P21, a=9.725 (4), b=5.127 (1), c=14.689 (6) Å; β=105.79 (3)°; dobsd=1.532 (5), dcalcd=1-525 g/cm3; Z=2. Cu(D,L-but)2, Cu(H2NCH(CO2)CH2CH3)2: space group P21/c; a=11.138 (6), b=5.066 (1), c=9.487 (6) Å; β=92.15 (6)°; dobsd=1.66 (2), dcalcd=1.662 g/cm3; Z=2. Full-matrix least-squares refinement of 1683 and 1552 reflections with F2≥3σ(F2) gave final values for RF of 0.032 and 0.037 for Cu(L-leu)2 and Cu(D,L-but)2, respectively. Both structures consist of tetragonally coordinated Cu(II) ions arranged in isolated sheets. Equatorial N2O2 ligation is provided by trans coordination of two amino acids, while axial Cu-O ligation by two neighboring amino acids completes the metal coordination and links the CuL2 units to form carboxylate-bridged sheets of Cu(II) ions. Intermolecular N-H—O hydrogen bonds further link the CuL2 units within each sheet. Coordination of the polar ends of the amino acids with Cu(II) allows the nonpolar side chains to align, creating hydrophobic regions which are slightly different in both structures. Bond distances and angles within the coordination spheres are typical, while C-C-C bond angles at the hydrophilic-hydrophobic juncture are ~6° larger than the remaining C-C-C angles. These large angles are attributed to modest steric strain between the carboxylate, amino, and alkyl groups attached to the α carbon atom. The structures are compared with those of their free amino acids and those of other Cu(II) amino acid complexes.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry