Synthesis and characterization of lanthanum chloranilate complex: Application to spectrophotometric determination of anions

Stacking of metal chelating rings with π-systems in mononuclear complexes of copper(II) with 3,6-dichloro-2,5-dihydroxy-1,4-benzoquinone (chloranilic acid) and 2,2'-bipyridine ligands

A series of four novel mononuclear complexes of copper(II) with chloranilic acid and 2,2'-bipyridine were prepared and structurally characterised by X-ray structure analysis and IR spectroscopy. The complexes exhibit square-planar, square-pyramidal and octahedral coordination. The chloranilate dianion coordinates the Cu(II) atom in a terminal bidentate o-quinone-like mode forming a mononuclear complex species. The crystal packing of the aqua complex and the complexes with crystal water molecules are defined by hydrogen bonds. However, significant contributions are from interactions involving five-membered chelate rings with both types of ligands and intermolecular π-systems (bipyridine and chloranilate rings). The crystal packing of the complex with square planar Cu(II) coordination is dominated by interactions of the chelate rings with π-delocalised bonds and intermolecular π-systems. The occurrence of dimorphism could be related to the different types of these interactions in the stacks. The crystal packing of the octahedral complexes of the mono- and dihydrate solvates reveal 3D-networks with pores occupied by non-coordinated bipyridine molecules.

Structure Modeling of Trivalent Lanthanum and Lutetium Complexes: Sparkle/PM3

The recently defined Sparkle model for the quantum chemical prediction of geometries of lanthanum(III) and lutetium(III) complexes within AM1 (J. Phys. Chem. A 2006, 110, 5897) has been extended to PM3. As training sets, we used the same two groups, one for each lanthanide, of 15 high-crystallographic-quality (R factor < 0.05 A) complexes as was previously chosen to parametrize Sparkle/AM1. Likewise, in the validation procedure, we used the same Sparkle/AM1 validation sets of 60 additional La(III) and 15 additional Lu(III) complexes. The Sparkle/PM3 unsigned mean errors for all interatomic distances between the metal ions and the ligand atoms of the first sphere of coordination proved to be random around the means of 0.068 A for lanthanum(III) and 0.076 A for lutetium(III), thus being comparable to the respective Sparkle/AM1 values of 0.078 and 0.075 A. Furthermore, effective-core-potential ab initio calculations on smaller subsets of such complexes led to similar accuracies. Sparkle/PM3 and Sparkle/AM1 are therefore made available to the researcher who must decide which of the models to use based on considerations of the impact of either PM3 or AM1 on the description of the ligands and the consequence of such a choice on the properties of interest.