New hetero- and homo-metallic dihydroxo-bridged dinuclear complexes of cobalt(III) and chromium(III): synthesis, spectroscopy and crystal structures

Abstract

Sixteen new unsymmetrical hetero- and homo-metallic dinuclear complexes [(nta)Cr(µ-OH)₂ML₄]Cl·nH₂O [M = Co^III or Cr^III; L₄=(NH₃)_4′(en)_2′(tn)_2′{(R,R)chxn}_2′(trien), (amp)_2′(bipy)₂ or (phen)₂; nta = nitrilotriacetate, en = ethane-1,2-diamine, chxn =trans-cyclohexane-1,2-diamine, tn = propane-1,3-diamine, amp = 2-aminomethylpyridine, trien = triethylenetetramine, bipy = 2,2′-bipyridine and phen = 1,10-phenanthroline] were synthesized and characterized by elemental analysis, UV/VIS absorption, circular dichroism and ²H NMR spectra, acid strengths of bridging hydroxide, magnetic properties and crystal structures. The crystals of [(nta)Cr(µ-OH)₂M(tn)₂]Cl·1.5H₂O (M = Co or Cr) are isomorphous and belong to the monoclinic system, space group C2/c, Z= 8, with a= 16.384(2), b= 14.660(2), c= 18.874(2)Å, β= 110.77(1)° and a= 16.465(3), b= 14.727(2), c= 19.057(2)Å, β= 110.28(1) for M = Co and Cr respectively. The crystal structure of [(nta)Cr(µ-OH)₂Cr(phen)₂]Cl·7H₂O was found to be triclinic with space group P, a= 15.79(1), b= 18.04(1), c= 12.77(1)Å, α= 96.39(8)°, β= 102.23(7), γ= 102.83(7)° and Z= 4. The structural parameters of the bridging moiety around each metal ion were almost the same as in the corresponding symmetrical dinuclear species. The ²H NMR spectra of [([²H₆]nta)Cr(µ-OH)₂ML₄]⁺ reflected the stereochemistry of the nta chelate rings and the M–N(of L₄) bond properties.