SYNTHESIS, CRYSTAL-STRUCTURE, AND ELECTRONIC PROPERTIES OF (L-METHIONYLGLYCINATO)COPPER(II)

The crystal and molecular structure of (l-methionylglycinato)copper(II) has been determined by single-crystal X-ray diffraction. Crystal data: orthorhombic system, space group P212121, cell data α = 9.889 (2) Å, b = 11.548 (1) Å, c = 9.337 (2) Å, α = β = γ = 90°, Z = 4, V= 1066 Å3, 1369 reflections. The dipeptide serves as a pentadentate ligand to three different Cu atoms with square-pyramidal geometry. The amino nitrogen atom, the ionized amide nitrogen atom, and one of the carboxylate donor atoms are equatorially disposed about one Cu atom, while the free carboxyl oxygen atom bridges to a neighboring copper atom. The peptide oxygen occupies the apical position of yet another Cu atom; the bond angle value of Cu-0(1)-C(2) (152.6°) is unusually high. No hydrogen bonding is observed as intermolecular interaction. The spectroscopic properties, as compared with those of the parent (glycyl-l-tyrosinato)(diaquo)copper(II) dihydrate, show that complex formation starts probably in aqueous solution with the terminal amino group. UV-visible absorption spectra results suggest that the structure found in the crystal does not persist in aqueous solution or in KBr pellets. A cleavage of the carboxylate bridge occurs and one of the carboxyl oxygen atoms is progressively replaced, either by a bromide or by a water molecule. © 1979, American Chemical Society. All rights reserved.