ELECTRON DENSITY STUDIES OF METAL SQUARATE COMPLEXES. Chi-Rung Lee, Chih-Chieh Wang, Gene-Hsiang Lee, Yu Wang, Department of Chemistry, National Taiwan University, Taipei, Taiwan

Metal squarate complexes, M(C₄O₄)(H₂O)₄, (M = Fe, Co, Ni, Zn), are known to have a polymeric chain structure with C₄O₄^2- served as a bridge (u-2) ligand, between two metal ions at trans- position. Each metal ion is bonded to two C₄O₄^2- and four water molecules. They are all isostructural with space group C2/c. A complete Ewald sphere of data is measured up to 2[[theta]] of 100deg. by using Mo K[[alpha]] radiation at 110K for Fe and Zn complexes and 130K for Ni and Co complexes. Such carefully measured intensities are used to investigate the detail electron density distribution in order to understand the chemical bonding and the d-orbital splitting subjected in the ligand field. Results on the electron density distribution will be presented in the form of deformation density maps, where indepent isolated spherical atom are substracted from the molecular electron density. Deformation density will be presented in term of [[Delta]][[rho]]x-x, [[Delta]][[rho]]m-a (multipole model) and [[Delta]][[rho]] calculated from the MO calculation.The interesting bent-bond feature on the four-membered-ring ligand C₄O₄^2-can be easily illustrated by the deformation density distributions. The asphericity in electron density distribution around the metal ion is also clearly demonstrated. The comparison on this series of 3d-transition metal complexes will be presented in terms of d-orbital populations and the deformation density distribution. The total number of d-electrons from the experiments are 6.02, 6.82, 7.81, 8.56 respectively for Fe(II), Co(II), Ni(II), Zn(II) ions in these compounds.