Modeling of the various minima on the potential energy surface of bispidine copper(II) complexes: a further test for ligand field molecular mechanics.
Copper(II) complexes of bispidines (bispidine = tetra-, penta-, or hexadentate ligand, based on the 3,7-diazabicyclo[3.3.1]nonane backbone) display several isomeric forms. Depending on the substitution pattern of the bispidine and the type of coligands used, the structure elongates along one of the three potential Jahn-Teller axes. In an effort to develop a computational tool which can predict which isomer is observed, 23 bispidine-copper(II) complexes with 19 different ligands are analyzed theoretically by ligand field molecular mechanics (LFMM). With two exceptions, the lowest-energy LFMM structure and the experimental solid-state structure agree concerning the Jahn-Teller axis. However, in most cases and especially for six-coordinate complexes, LFMM predicts a second local minimum within a few kilojoules per mole. Although detailed analysis reveals that the current force field is too "stiff", reasonable quantitative reproduction of the structural data is achieved with Cu-L bond length root mean square (rms) deviations for nine complexes of 0.05 A or less and with 20 reproduced to a rms deviation of 0.1 A or less. Across all of the complexes, the Cu-amine and Cu-pyridyl bond length rms deviations are 0.07 and 0.12 A, respectively.
Bentz
Alexander
A
Universität Heidelberg, Anorganisch-Chemisches Institut, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany.
Comba
Peter
P
Deeth
Robert J
RJ
Kerscher
Marion
M
Seibold
Björn
B
Wadepohl
Hubert
H