The versatility of the dihydrogenobis(1-pyrazolyl)borate ligand, H2B(pz)2–: novel anionic complexes with chromium(II), chromium(III), and manganese(II). X-Ray structure of [AsPh4][MnCl{H2B(pz)2}2]

Abstract

New five-co-ordinate chromium(II) and manganese(II) complexes with the ligand dihydrogenobis(1-pyrazolyl)borate, H₂B(pz)₂, have been prepared and characterized. The complexes have the general formula A[MX{H₂B(pz)₂}₂](M = Cr^II or Mn^II; A = NEt₄, PPh₄, or AsPh₄; X = halides or pseudohalides). All of the complexes are high spin. The structure of [AsPh₄][MnCl-{H₂B(pz)₂}₂] has been determined by single-crystal X-ray diffraction methods. The compound crystallizes in the space group P2₁/n with a= 16.952(4), b= 13.039(3), c= 17.331(4)Å, β= 105.53(2)°, and Z= 4. The structure was solved by heavy-atom methods and refined to R= 0.058. The co-ordination geometry about manganese(II) is square pyramidal with the four donor N atoms of the two H₂B(pz)₂ ligands forming the basal plane and the Cl atom occupying the apical position. The Mn atom is displaced by 0.52 Å from the base of the pyramid toward the Cl atom. Slow oxidation of [NEt₄][Cr{H₂B(pz)₂}₂(NCS)] in solution yields the chromium(III) complex [NEt₄][Cr₂(EtO)₃{H₂B(pz)₂}₂(NCS)₂] with co-ordinated ethoxo groups.