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(dimethyl-phosphinomethyl)ethane

摘要

Mixed-ligand chromium(III) complexes containing di- or tridentate phosphines,trans-[CrX_2(dmpe)_2]~+ (X = Cl,Br,I.CN,NCS or N_3;dmpe = Me_2P(CH_2)_2PMe_2),trans-[CrX'_2(dmpp)_2]~+ (X' = Cl,Br or I;dmpp = Me_2P(CH_2)_3PMe_2),[CrX"_3(tdmme)] (X" = Cl,Br,CN or NCS;tdmme = MeC(CH_2PMe_2)_3 and [CrCl_2(tdmme)(PMe_3)]~+,have been prepared and their structures and spectroscopic properties have been investigated.The single-crystal X-ray analyses of trans-[CrI_2(dmpp)_2]I (6) and [Cr(CN)_3 (tdmme)]·2H_2O (16·2H_2O) have also been reported.The Cr-P bond length in 6 (2.5147(6) A) is longer than those in trans-[CrCl_2(dmpe)_2]BPh_4 (av 2.445 A) and in 16·2H_2O(av 2.455A).In the UV-vis absorption spectra of trans-[Cr(Cl or Br)_2(dmpe or dmpp)_2]~+,an intense (#epsilon#> 1000 dm~3 mol~(-1) cm~(-1)) absorption envelope is observed at 20000-30000 cm~(-1),in addition to the ~4B_1 —>a~4E d-d transition band at approx 17000 cm~(-1) (#epsilon# = 44-65 dm~3 mol~(-1) cm~(-1)).The envelope consits of three d-d transition components:~4B_1 —>~4A_2,~4B_2 and b~4B_2 and b~4E,similar to the corre-sponding H_2N(CN_2)_2NH_2 (= Een) complexes.The magnetic circular dichroism (MCD) spectra of these didentate phosphine complexes show a spin-forbidden d-d transition (~4B_1 —>~2E,~2B_2) component at approx 19000 cm~(-1).RThe ligand-field and Racah parameters, #DELTA#(d),#DELTA#(e),#DELTA#(t_2) 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 thoseof the corresponding en complexes.For the dmpe com-plexes,while #DELTA#(d) is just slightly smaller than those of the dmpp and en complexes,the tetragonal symmetry parameters,#DELTA#(i) 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 te compelxes in-crease in the order of dmpp > tdmme > dmpe.Furthermore,the interelectronic repulsion parameter B of [Cr(Cl or Br)_3(tdmme)] estimated from the ~4A_2 —>~4T_1 transition energy (B_(35) is remarkably much smaller than the parameter esti-mated from the spin-forbidden ~4A_2 —>~2T_2 transition energy (B_(55).