Zn-O Bonding in the Coordination Polymer Zn(HCOO)2(H2O)2 - a Combined Experimental and Theoretical Charge Density Study

We present a combined experimental and theoretical charge density study of the coordination polymer, Zn(HCOO)2(H2O)2, which serves as a non-magnetic reference for the isostructural magnetic compounds containing 3d transition metals [1]. The charge density has been modeled using the multipole formalism against a high resolution single crystal X-ray diffraction dataset collected at 100 K. The theoretical model is based on periodic DFT calculations at the experimental geometry. Both models show that the Zn atom densities are highly spherical, but show small accumulations of charge towards the negative ligands. These VSCCs are present in both the experimental and theoretical densities. The metal-ligand interactions are found to be primarily ionic, but there are subtle topological indications of covalent contributions to the bonds [2-4]. The Source Function calculated at the bond critical points reveals a rather delocalized picture of the density in the bridging carboxylates, and this presumably reflects the exchange pathway in the magnetic analogs [5]. References [1] R. D. Poulsen, M. R. V. Joergensen, J. Overgaard, F. K. Larsen, W. G. Morgenroth, T. Graber, Y.-S. Chen, B. B. Iversen, Chem. Eur. J. 13 (2007) 9775-9790. [2] E. Espinosa, I. Alkorta, J. Elguero, E. Molins, J. Chem. Phys. 117 (2002) 5529-5542. [3] P. Macchi, A. Sironi, Coord. Chem. Rev. 238-239 (2003) 383-412. [4] C. Gatti, Z. Kristallogr. 220 (2005) 399-457. [5] P. Radhakrishna, B. Gillon, G. Chevrier, J. Phys.: Condens. Matter 5 (1993) 6447-6460.