CONSECUTIVE CRYSTALLIZATION OF [CU(MEPPDCL)(2)]BF4 AND [CU(MEPPDCL)(2)CL]BF4-CENTER-DOT-0.5(C2H5)(2)O FROM DICHLOROMETHANE

Treatment of copper(I) with 3-chloro-6-(3,5-dimethylpyrazol-1-yl)pyr ( MeppdCl) in dichloromethane yields firstly red crystals of [Cu(MeppdCl )(2)]BF4 and secondly blue crystals of [Cu(MeppdCl)(2)Cl]BF4]. 0.5(C2H 5)(2)O. The provenance of the chloride anion is uncertain; it may be a ttributed to either copper(I) activation of dichloromethane or minor i mpurities arising during MeppdCl synthesis. In the copper(I) cation, t wo MeppdCl molecules, which are N-donor bidentate chelating ligands, g enerate a squashed tetrahedral coordination geometry [Cu ... N =2.000( 3)-2.052(3) Angstrom] with an open side [N-Cu-N = 140.1(1)degrees]-eff ectively a trigonal bipyramid with a missing equatorial ligand. In the copper(II) cation, a trigonal biypramidal arrangement is formed by tw o MepgdCl ligands, which straddle equatorial [Cu ... N = 2.066(4), 2.1 51(4) Angstrom and axial [Cu ... N= 1.976(4), 1.979(4) Angstrom] sites and an equatorially located chlorine atom [Cu ... Cl = 2.292(1) Angst rom]. Viewing the two coordination geometries as trigonal bipyramidal, the orientation of the MeppdCl molecules reverses on oxidation, the p yrazole nitrogens moving from equatorial to axial sites [N-Cu-N increa ses from 98.9(1)degrees to 168.5(2)degrees] and the pyridazine nitroge ns vice versa [N-Cu-N decreases from 140.1(1)degrees to 110.8(2)degree s]. The copper(I) complex is the most severely distorted, structurally characterised, [Cu(diimine)(2)](+) complex. A novel method of paramet erising the stereochemistry of [Cu(diimine)(2)](+) complexes is propos ed; four readily calculated parameters are used to assess the extent o f distortion of the molecule from D-2d symmetry. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.