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

Abstract

Abstract Mixed-ligand chromium(III) complexes containing di- or tridentate phosphines, trans-[CrX2(dmpe)2]+ (X = Cl, Br, I, CN, NCS or N3; dmpe = Me2P(CH2)2PMe2), trans-[CrX′2(dmpp)2]+ (X′ = Cl, Br or I; dmpp = Me2P(CH2)3PMe2), [CrX′′3(tdmme)] (X′′ = Cl, Br, CN or NCS; tdmme = MeC(CH2PMe2)3) and [CrCl2(tdmme)(PMe3)]+, have been prepared 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)]·2H2O (16·2H2O) have also been reported. The Cr–P bond length in 6 (2.5147(6) Å) is longer than those in trans-[CrCl2(dmpe)2]BPh4 (av 2.445 Å) and in 16·2H2O (av 2.455 Å). In the UV-vis absorption spectra of trans-[Cr(Cl or Br)2(dmpe or dmpp)2]+, an intense (ε > 1000 dm3 mol−1 cm−1) absorption envelope is observed at 20000–30000 cm−1, in addition to the 4B1 → a4E d–d transition band at ∼17000 cm−1 (ε = 44–65 dm3 mol−1 cm−1). The envelope consists of three d–d transition components: 4B1 → 4A2, 4B2 and b4E, similar to the corresponding H2N(CH2)2NH2 (= en) complexes. The magnetic circular dichroism (MCD) spectra of these didentate phosphine complexes show a spin-forbidden d–d transition (4B1 → 2E, 2B2) component at ∼19000 cm−1. The ligand-field and Racah parameters, Δ(d), Δ(e), Δ(t2) and B, of the complexes are estimated. It is found that the ligand-field and repulsion parameters of the dmpp complexes are almost the same as those of the corresponding en complexes. For the dmpe complexes, while Δ(d) is just slightly smaller than those of the dmpp and en complexes, the tetragonal symmetry parameters, Δ(e) and Δ(t2), are much reduced. The ligand-field perturbation energies of phosphines are estimated as Δdmpp = 21830 > Δtdmme = 20920 > Δdmpe = 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, the interelectronic repulsion parameter B of [Cr(Cl or Br)3(tdmme)] estimated from the 4A2 → 4T1 transition energy (B35) is remarkably much smaller than the parameter estimated from the spin-forbidden 4A2 → 2T2 transition energy (B55).