American Chemical Society
ic501411w_si_003.cif (36.22 kB)

Relationships between Electron Density and Magnetic Properties in Water-Bridged Dimetal Complexes

Download (36.22 kB)
posted on 2014-11-03, 00:00 authored by Jacob Overgaard, James P. S. Walsh, Venkatesha R. Hathwar, Mads R. V. Jørgensen, Christina Hoffman, Jamie A. Platts, Ross Piltz, Richard E. P. Winpenny
The electron densities in two analogous dimetallic transition metal compounds, namely, [M2(μ-OH2)­(tBuCOO)4(tBuCOOH)2(C5H5N)2] (M = Co­(1), Ni­(2)), were determined from combined X-ray and neutron single-crystal diffraction at 100 K. Excellent correspondence between the thermal parameters from X- and N-derived atomic displacement parameters is found, indicating high-quality X-ray data and a successful separation of thermal and electronic effects. Topological analysis of electron densities derived from high-resolution X-ray diffraction, as well as density functional theory calculations, shows no direct metal–metal bonding in either compound, while the total energy density at the bond critical points suggests stronger metal–oxygen interactions for the Ni system, in correspondence with its shorter bond distances. The analysis also allows for estimation of the relative strength of binding of terminal and bridging ligands to the metals, showing that the bridging water molecule is more strongly bound than terminal carboxylic acid, but less so than bridging carboxylates. Recently, modeling of magnetic and spectroscopic data in both of these systems has shown weak ferromagnetic interactions between the metal atoms. Factors related to large zero-field splitting effects complicate the magnetic analysis in both compounds, albeit to a much greater degree in 1. The current results support the conclusion drawn from previous magnetic and spectroscopic measurements that there is no appreciable direct communication between metal centers.