Preparation, crystal structures and spectroscopic properties of chloro(pentane-2,4-dionato) {1,1,1-tris(dimethylphosphinomethyl)ethane}chromium(III), -cobalt(III) and -rhodium(III) hexafluorophosphate: comparison of the M-P, M-Cl and M-O (M = Cr, Co

摘要

Three metal(III)-tripodal tridentate phosphine complexes of the formula [MCl(acac)(tdmme)]PF6, where M = Cr, Co or Rh; acac = pentane-2,4-dionate; tdmme = 1,1,1-tris(dimethylphosphinomethyl)ethane, were prepared and their molecular and crystal structures and spectroscopic properties examined. All the complexes crystallized in an isomorphous space group P2(1)2(1)2(1), which is indicative of spontaneous resolution of the enantiomeric pair. The Cr-P bond lengths in [CrCl(acac)(tdmme)]PF6 (average 2.437 Angstrom) are remarkably longer than the corresponding Co-P (average 2.201 Angstrom) and Rh-P (average 2.252 Angstrom) ones. The longer and therefore the weaker Cr-P bonds may explain the relatively weak trans influence of the -PMe2 group in [CrCl(acac)(tdmme)]PF6; among the three Mill complexes, the elongation of M-O bond lengths in [MCl(acac)(tdmme)]PF6 from those in [M(acac)(3)] has been found to be Cr(III) (0.016 Angstrom) < Co-III (0.059 &ANGS;) < Rh-III (0.096 Angstrom), indicating a much weaker trans influence of the -PMe2 group in the Cr-III complex than in the Co-III and Rh-III, complexes. The first d-d transition band of [CrCl(acac)(tdmme)](+) was observed at 18590 cm(-1). This is appreciably smaller than the corresponding band of the Coin complex at 20960 cm(-1), suggesting the ligand-field strength of tdmme is fairly weak in the Cr-III complex. The ligand-field strength Delta and the Racah's B parameters of [CrCl(acac)(tdmme)](+) were also discussed. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 37]