Crystal Structure of fac-Tris(pivaloylcyanoximato)Cobalt(III), [Co(PiCO)3]

• Published in: Crystallography reports 2023-12, Vol.68 (7), p.1134-1141
• Main Authors: van Dyk, H., Mokolokolo, P. P., Brink, A., Gerasimchuk, N.
• Format: Article
• Language: English
• Subjects: Angles (geometry); Cobalt; Cobalt compounds; Crystal structure; Crystallography; Crystallography and Scattering Methods; Ligands; NMR; Nuclear magnetic resonance; Physics; Physics and Astronomy; Silver; Single crystals; Spectrum analysis; Structure of Organic Compounds; Unit cell
• ISSN: 1063-7745; 1562-689X
• DOI: 10.1134/S1063774523600813

The absolute configuration of the title compound, fac -tris(pivaloylcyanoximato)cobalt(III) [Co(PiCO) 3 ], was determined by single-crystal X-ray diffraction, while the solution state was analyzed in detail by NMR and UV–Vis spectroscopy. The complex crystallizes as a fac -isomer in the monoclinic crystal system with space group P 2 1 / c and unit cell parameters a = 7.085(1), b = 12.067(2), c = 30.015(6) Å, β = 90.209(7)°, Z = 4. The final R -factor is 0.049 ( wR ( F 2 ) = 0.084) for 6375 observed reflections. The molecule has an octahedral geometry defined by three N , O -donor, one from each of the three coordinating pivaloylcyanoxime ligands coordinated to the Co(III) metal centre. The bite angles for the three N , O- bidentate ligands with the Co centre are 83.80(8)°, 84.26(7)°, and 84.22(7)°, respectively. The dihedral angles between the planes defined by cobalt and N , O -donor atoms of each of the ligands are 88.683(7)°, 89.565(8)°, and 88.494(8)°, which confirms the near-perfect octahedral geometry of the compound. The geometric isomerism exhibited by the cyanoximato ligands is cis- anti. UV–Vis studies were conducted on the protonated ligand, HPiCO, its potassium cyanoximate salt (K + PiCO – ), its silver(I)-cyanoximato, [AgPiCO], and its cobalt(III)-cyanoximato complexes, [Co(PiCO) 3 ]: the results show a negative solvatochromic characteristic of cyanoxime ligands. The 1 H and 13 C NMR spectra show the disorder (occupancy 60:40%) of the one tert -butyl group, which is also indicated by the crystallographic data.