Synthesis, spectroscopic and structural properties of bis (N-acetyl-DL-tryptophanato)copper(II) complex and its amine adducts: effect of amines on the amino acid coordination. Crystal and molecular structure of diaqua bis(N-acetyl-DL-tryptophanato)bis(pyridine)copper(II).

A green compound of the type Cu(Ac t rp)xH2O( ctrp = N-acetyl-DL-tryptophanate ion) and its aromatic and aliphaticheterocyclic amine adducts, Cu(Actrp)2B2 (B = pyridine (py), 3- and 4-methylpyridine (3- and 4-pic), N-methylpiperazine(NCHjpipz), morpholine (morph), and piperidine (pipd)), Cu(Actrp)2(py)2(H20)2, and Cu(Actrp)2.pipz (pipz = piperazine),were prepared and characterized by means of low- and room-temperature magnetic and EPR measurements androom-temperature electronic and infrared spectroscopy. While Cu(Actrp)2 xH2O shows physical properties indicating a binuclearconfiguration, all the aromatic heterocyclic amine adducts appear to possess a tetragonal configuration with CUOJN~chromophore. For one of the latter complexes, diaquabis(N-acetyl-DL-tryptophanato)bis(pyridine)copper(Il), the crystalstructure was also determined by single-crystal X-ray diffraction methods. The complex crystallizes in the monoclinic spacegroup P21/c with two molecules in a unit cell of dimensions a = 9.377 (6) A, b = 19.341 (14) A, c = 11.615 (7) beta = 123.2(2)°, .The geometry about the copper atom,which is coordinated to two carboxylic oxygens and two pyridine nitrogen atoms. is completed to an elongated tetragonal bipyramidby two weak interactions with two water molecules. The Cu-N, Cu-O(amino acid), and Cu-O(water) distances are 1.95(l), 2.02 ( I ) , and 2.61 (1) A, respectively, and the O(amino acid)-Cu-N angle is 87.9 (6)’. For the adducts of the aliphaticheterocyclic amines a square-planar geometry with CuO2N2 chromophore may be suggested. In all the complexes reportedin this work the amino acid appears to coordinate the copper(II) ion only toward the carboxylate group. For the assignmentof the way in which the carboxylate group coordinates, we suggest that the observation of the position of the v(OCO), is particularlyrelevant