UNEXPECTED 5-COORDINATION IN (1,3-DIAMINOPROPANE)-3,5-DINITROBENZOATOCOPPER(II) 3,5-DINITROBENZOATE - COMPARISON BETWEEN THE COORDINATED AND NONCOORDINATED ANIONS

The crystal and molecular structure of (1,3-diaminopropane)-3,5-dinitr obenzoatocopper(II) 3,5-dinitrobenzoate (C13H23CuN6O6) + (C7H3N2O6)- w as determined by single crystal X-ray methods. The compound crystalliz es in the monoclinic system, space group P2(1)/c, a = 19.378(9), b = 6 .358(2), c = 22.549(9) angstrom, beta = 107.48(3)-degrees, Z = 4, D(c) = 1.59, D(m) = 1.60(1) g/cm3. The final R value for 2746 reflections was 0.037 (R(w) = 0.035, 1/sigma2 weights). Only one of the two 3,5-di nitrobenzoate anions is coordinated via one carboxylate oxygen with th e bond length of 2.252(3) angstrom. Thus the coordination around the c entral Cu(II) ion is 4 + 1 and the site symmetry approximately C2v. Th e coordination mode 4 + 1 is the first reported among the series consi sting of variously substituted benzoates and bis(1,3-diaminopropane) c opper(II) cations. The non-coordinated 3,5-dinitrobenzoate anion is bo nded by hydrogen bonds to the neighbouring amines. The nu(as)(CO2) vib rations for both anions appear at about 1609 cm-1 whereas the nu(s)(CO 2) is seen at 1335 and 1527 cm-1 for the coordinated and non-coordinat ed anions, respectively. Ab initio calculations with the 3-21G basis set for 3,5-dibitrobenzoic acid and its anion reveal elongation of the bond between the carboxylate group and aromatic ring upon deprotonati on of the acid. The complexation of the anion does not cause any clear difference in the bond length. The charge densities obtained by the S TO-3G basis set show that the oxygen coordinated to the copper(II) ca tion carries more negative charge than the non-coordinated oxygen. In the non-coordinated anion the charge densities are more evenly distrib uted.