Energetics of transition-metal ions in low-coordination environments

An Angular Overlap Model for Cu(II) Ion in the AMOEBA Polarizable Force Field

“…This gives a direct measurement to the LF effect since it is known that 4-coordinated Cu 2+ complexes do not adopt the tetrahedral geometry for small ligands, which minimizes water-water repulsion. 8,12,36 …”

“…Total BSSE-corrected interaction energies for the complexes were also computed. The potential energy difference between square-planar and tetrahedral [Cu­(H 2 O) 4 ] 2+ is plotted as a function of copper–oxygen separations, with water–water interactions removed. This gives a direct measurement to the LF effect since it is known that four-coordinated Cu 2+ complexes do not adopt the tetrahedral geometry for small ligands, which minimizes water–water repulsion. ,, One hundred complex structures were generated by introducing small geometric perturbations to the optimized square-planar [Cu­(H 2 O) 4 ] 2+ and octahedral [Cu­(H 2 O) 6 ] 2+ . This process involves randomly perturbing copper–oxygen distance by a maximum of ±0.35 Å deviation from optimal value as well as rotating each of the water molecules around the copper–oxygen vector and two orthogonal axes between 0 and 10°.…”

“…The potential energy difference between square-planar and tetrahedral [Cu­(H 2 O) 4 ] 2+ is plotted as a function of copper–oxygen separations, with water–water interactions removed. This gives a direct measurement to the LF effect since it is known that four-coordinated Cu 2+ complexes do not adopt the tetrahedral geometry for small ligands, which minimizes water–water repulsion. ,, …”

“…Models such as VALBOND − are based on a simplified version of the VB theory, in which TM ions are treated as hypervalent resonance centers and L-M-L interactions are described by geometric overlap between sd n hybridized bonding metal–ligand orbitals. On the other hand, models proposed by Deeth et al − and Carlsson et al − are developed from the AOM and the ligand field (LF) effects are handled through explicit diagonalization of a perturbed d-orbital matrix due to the presence of ligands. These methods have demonstrated satisfactory agreements with experiments and ab initio calculations when used to study a range of TM systems with different coordination geometries and ligation states.…”

Stability of Different Zinc(II)−Diamine Complexes in Aqueous Solution with Respect to Structure and Dynamics: A QM/MM MD Study

“…To our knowledge, no experimental/theoretical data for the zinc(II)−diamine complex in aqueous solution are available discussing the structure and, in particular, the dynamics of the system. According to common models the preferred arrangement of ligands in ions with filled d shells is mostly due to electrostatic and steric ligand−ligand interactions. , Kinetic instability of the cis isomer might be attributed to the “trans-effect” and the steric NH 3 −NH 3 interactions. A similar kinetic trans effect has been observed in methanol exchange of the Co(CH 3 OH) 5 Py 2+ complex studied by NMR, influence of the imidazole group on the Co−S bond length in the [Co(C 2 N 2 H 8 ) 2 (C 3 N 2 H 4 )(SO 3 )]ClO 4 ·2H 2 O complex recorded by X-ray diffraction, and the trans effect of triphenylstibine and triphenylphosphine in Pt(II) complexes studied by stopped-flow spectrophotometry .…”