Syntheses, structures and spectroscopic properties of mixed-ligand chromium(III) complexes containing 1,2-bis(dimethylphosphino)-ethane, 1,3-bis (dimethylphosphino)propane or 1,1,1-tris (dimethylphosphinomethyl)ethane

Mixed-ligand chromium(III) complexes containing di- or tridentate phosphine s, trans-[CrX2(dmpe)(2)](+) (X = Cl, Br, I, CN, NCS or N-3; dmpe = Me2P(CH2 )(2)PMe2), trans-(CrX ' (2)(dmpp)(2)] + (X ' = Cl, Br or I; dmpp = Me2P(CH2 )(3)PMe2), [CrX " (3)(tdmme)] (X " = Cl, Br, CN or NCS; tdmme = MeC(CH2PMe2 )(3)) and [CrCl2(tdmme)(PMe3)](+), have been pre pared and their structures and spectroscopic properties have been investigated. The single-crystal X- ray analyses of trans-[CrI2(dmpp)(2)]I (6) and [Cr(CN)(3)(tdmme)]. 2H(2)O ( 16 . 2H(2)O) have also been reported. The Cr-P bond length in 6 (2.5147(6) Angstrom) is longer than those in trans-[CrCl2(dmpe)(2)]BPh4 (av 2.445 Angs trom) and in 16 . 2H(2)O (av 2.455 Angstrom). In the UV-vis absorption spec tra of trans-[Cr(Cl or Br)(2)(dmpe or dmpp)(2)](+), an intense (epsilon > 1 000 dm(3) mol(-1) cm(-1)) absorption envelope is observed at 20000-30000 cm (-1), in addition to the B-4(1) --> a(4)E d-d transition band at similar to 17000 cm(-2) (epsilon = 44-65 dm(3) mol(-1) cm(-1)). The envelope consists of three d-d transition components: B-4(1) --> (4)A(2), B-4(2) and b(4)E, similar to the corresponding H2N(CH2)2NH(2) (= en) complexes. The magnetic circular dichroism (MCD) spectra of these didentate phosphine complexes sho w a spin-forbidden d-d transition (B-4(1) --> E-2, B-2(2)) component at sim ilar to 19000 cm(-1). The ligand-field and Racah parameters, Delta (d), Del ta (e), Delta (t(2)) and B, of the complexes are estimated. It is found tha t the ligand-field and repulsion parameters of the dmpp complexes are almos t the same as those of the corresponding en complexes. For the dmpe complex es, while Delta (d) is just slightly smaller than those of the dmpp and en complexes, the tetragonal symmetry parameters, Delta (e) and Delta (t(2)), are much reduced. The ligand-field perturbation energies of phosphines are estimated as Delta (dmpp) = 21830 > Delta (tdmme) = 20920 > Delta (dmpe) = 20620 cm(-1), the order of which is strange, since the Cr-P bond lengths in the complexes increase in the order of dmpp > tdmme > dmpe. Furthermore, t he interelectronic repulsion parameter B of [Cr(Cl or Br)(3)(tdmme)] estima ted from the (4)A(2) --> T-4(1) transition energy (B-35) is remarkably much smaller than the parameter estimated from the spin-forbidden (4)A(2) --> T -2(2) transition energy (B-55).