Crystal and molecular structure of a cobalt(III) ammine complex of 2-Amino-4-imino-2-methylpentanoic acid

Abstract

The crystal and molecular structure of a cobalt(III) ammine complex of 2-amino-4-imino-2-methyl-pentanoic acid, [Co(NH₃)₃{HN=C(CH₃)CH₂C(CH₃)(NH₂)(CO₂)}]S₂O₆, has been determined from three-dimensional X-ray data collected by counter methods. The complex crystallizes in the monoclinic space group P2₁/c (C⁵_2h, No. 14), with a = 7.576(4), b = 18.209(7), c = 14.068(6) Ǻ, β = 125.25(2)°, Z = 4. The structure was solved by conventional Patterson and Fourier methods, and was refined by block-diagonal least-squares methods to weighted and unweighted 12-factors of 0.041 and 0.040 respectively, for the 1479 unique reflections having I/σ(I) ≥ 3.0. All hydrogen atoms have been located and refined. The complex cation is essentially octahedral about the central cobalt atom with three amine groups occupying mutually cis coordination sites; the three remaining sites at the cobalt atom are occupied by the tridentate 2-amino-4-imino-2-methylpentanoic acid ligand. The Co-O distance is 1.914(4) Ǻ, while the Co-N(imine) distance is 1.924(5) Ǻ. The Co-N(NH₃) distances range from 1.968(5) to 1.979(5) Ǻ, and are equal within experimental error. Within the tridentate 2- amino-4-imino-2-methylpentanoic acid ligand, the C=N distance is 1.252(7) Ǻ, while at the carboxyl group the ?free? C-O distance [1.233(6) Ǻ] is significantly shorter than the distance from the carbon to the coordinated oxygen atom [1.270(7) Ǻ]. In the S₂O₆ counter anion, the S-S distance is 2.112(2) Ǻ, and the S-O distances range from 1.434(6) to 1.457(4) Ǻ, averaging 1.439 Ǻ.