Novel coordination of a hydroxamic acid : Crystal structures of bis(glycinohydroxamoto)nickel(II) and tris(glycinohydroxamoto)cobalt(III)

The structures of two glycinohydroxamoto (GHA) complexes of Ni(II) and Co(III) have been determined by single-crystal X-ray diffraction methods. The crystals of Ni(GHA)₂ are monoclinic with a = 5.360(1), b = 7.315(4), c = 10.194(4) Å, β = 96.57(3), Z = 2, and space group P2₁/c. The crystals of Co(GHA)₃•1/2 H₂O are monoclinic with a = 22.467(19), b = 8.041(4), c = 13.700(11) Å, β = 116.01(7), Z = 8, and space group C2/c. The values of the final residuals R for Ni(GHA)₂ and Co(GHA)₃•1/2 H₂O are 0.0275 and 0.032, respectvely. The molecular structures of Ni(GHA)₂ and Co(GHA)₃ consist of a square planar and an octahedral coordination, respectively, with the glycinohydroxamato (NH₂CH₂CONOH⁻) ligands coordinating to the metal ion via the N (amino) and the N (NOH⁻). These two complexes are the first well-established cases of coordination of the NHO⁻ group of a hydroxamic acid to a transition metal via the nitrogen atom.