Bis(L-N,N-dipropylalaninato)copper(II) - X-ray crystal structure, the crystal structure prediction and conformational analysis with a new force field

The structure of red monoclinic crystals of bis(L-N,N-dipropylalaninato)cop per(rr) was determined by the X-ray diffraction method. Coordination around the copper atom is distorted square-planar, with oxygen and nitrogen atoms in Irans positions. The crystal structure consists of discrete molecules h eld by van der Waals forces. The main conformational feature of the chelate ring systems is the axial position of P-carbon alanine atoms. This paper p roposes a new molecular mechanics model and a new force field derived with the aim to simulate and predict properties of both cis and trans copper(II) amino acid complexes. The force field was optimised on copper(II) coordina tion geometry of three molecules obtained in vacuo by a molecular quantum m echanics method, and on X-ray experimental data of five molecules. Respecti ve equilibrium structures were calculated in the vacuum and condensed phase approximations. This paper examines the efficacy of the new force field FF 1 to reproduce structural properties of 12 tetra-coordinated copper(II) ami no acidates (including the title compound) with various copper(II) coordina tion polyhedron geometry, crystal symmetries, and intermolecular interactio ns. The EF1 force field was used to investigate the influence of N,N-dialky l chain lengthening on stereochemistry of the copper(II) alaninato complexe s. Molecular mechanics calculations suggest that reasons for the prevalence of equatorial and/or axial positions of the alanine CPH, residue in the cr ystal state should be more readily attributed to the crystal packing prefer ences than to intramolecular steric hindrances caused by N-dialkyl groups. (C) 1999 Elsevier Science Ltd. All rights reserved.