Chemistry of [Co(triamine)(diamine)Cl]2þ complexes: the X-ray crystal structures and ab initio calculations for five [Co(dien)(ampy)Cl]2þ isomersq

The structures of five of the seven possible isomeric forms in the [Co(dien)(ampy)Cl]2þ system (three mer- and two fac-) have been determined by single crystal X-ray diffraction: (1) m1·Cl2·H2O, triclinic P1¯, a ¼ 7:3757ð12Þ; b ¼ 9:9250ð16Þ; c ¼ 11:5002ð19Þ A ° , a ¼ 100:242ð3Þ8; b ¼ 100:832ð3Þ8; g ¼ 94:615ð3Þ8; Z ¼ 2; (2) m3·ZnCl4, monoclinic P21/c, a ¼ 11:057ð3Þ; b ¼ 9:581ð2Þ; c ¼ 17:568ð4Þ A ° , b ¼ 95:560ð5Þ8; Z ¼ 4; (3) m4·ZnCl4 monoclinic P21/n, a ¼ 8:4464ð14Þ; b ¼ 24:398ð4Þ; c ¼ 10:0645ð17Þ A ° , b ¼ 112:510ð3Þ8; Z ¼ 4; (4) f1·ZnCl4, triclinic P1¯ , a ¼ 10:318ð1Þ; b ¼ 12:706ð3Þ; c ¼ 7:578ð1Þ A ° , a ¼ 107:01ð2Þ8; b ¼ 94:90ð1Þ8; g ¼ 99:07ð1Þ8; Z ¼ 2; (5) f2·(ZnCl4)0.5·Cl·H2O, triclinic P1, a¼7:7225ð18Þ; b¼8:359ð2Þ; c¼15:898ð4Þ A ° , a¼96:025ð4Þ8; b¼93:298ð5Þ8; g ¼ 116:191ð4Þ8; Z ¼ 1: The last structure provides an example of spontaneous resolution. Two additional and independently determined structures are reported, in excellent agreement with these results. The structural work confirms the results of the detailed 2D NMR study. The agreement between the single crystal data and the calculated ab initio molecular parameters is excellent (within ^3%). The calculated total energies have been computed for the gas phase and aqueous solution, and are been used to explain the relative abundances of the seven isomers observed experimentally. The modes of isomer rearrangement are discussed. q 2004 Elsevier B.V. All rights reserved.