Steric effects on the electronic and molecular structures of nickel(II) and cobalt(II) 2,6-dipyrazol-1-ylpyridine complexes

• Published in: Polyhedron Vol. 20; no. 22; pp. 2829 - 2840
• Main Authors: Holland, Joanne M., Kilner, Colin A., Thornton-Pett, Mark, Halcrow, Malcolm A.
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 15.10.2001; Elsevier
• Subjects: 2,6-Dipyrazol-1-ylpyridine complexes; Chemistry; Chemistry, Inorganic & Nuclear; Crystallography; Donor ligands; Electronic structures; Molecular structures; Physical Sciences; Science & Technology; 2,6-Dipyrazol-1-ylpyridine complexes; Donor ligands; Electronic structures; Molecular structures; SINGLE; GROUND-STATE; CRYSTAL-STRUCTURE; X-RAY STRUCTURE; LUMINESCENCE PROPERTIES; electronic structures; molecular structures; PERCHLORATE; donor ligands; LIGANDS; SPIN-STATE; 2,6-dipyrazol-1-ylpyridine complexes; CHEMISTRY; METAL-COMPLEXES
• ISSN: 0277-5387
• DOI: 10.1016/S0277-5387(01)00892-0

The complexes [M(L 1R) 2](BF 4) 2 (M=Ni, Co; L 1R=2,6-dipyrazol-1-ylpyridine [L 1H], 2,6-bis-{3-iso-propylpyrazol-1-yl}pyridine [L 1Pr i ], 2,6-bis-{3-phenylpyrazol-1-yl}pyridine [L 1Ph], 2,6-bis-{3-[2,4,6-trimethylphenyl]pyrazol-1-yl}pyridine [L 1Mes]) and [M(L 2) 2](BF 4) 2 (M=Ni, Co; L 2=2-{3-[2,4,6-trimethylphenyl]pyrazol-1-yl}-6-{5-[2,4,6-trimethylphenyl]pyrazol-1-yl}pyridine) have been prepared. Single crystal structure determinations of [M(L 1H) 2](BF 4) 2 (M=Ni, Co) and solvates of [Ni(L 1Mes) 2](BF 4) 2, [Co(L 1Mes) 2](ClO 4) 2 and [Co(L 2) 2](BF 4) 2 all show six-coordinate metal centres with local near- D 2 d symmetry. The L 1Mes and L 2 mesityl substituents have only a small effect on the MN{pyrazole} (M=Ni, Co) bond lengths in these compounds. The d– d spectra of the complexes show that L 1Mes is a significantly better donor ligand than L 1H, L 1Pr i or L 1Ph, and that L 1Pr i is a weaker ligand than might be expected purely on inductive grounds. A combination of UV–Vis/NIR, EPR, NMR and magnetic measurements have demonstrated that all the Co(II) compounds are high-spin in the solid state and in solution at 290 K. The complexes [NiL 2] 2+ and [CoL 2] 2+ (L=L 1R, L 2) have been prepared. All the Co(II) compounds are high-spin at 290 K and, probably, at 150 K. UV–Vis measurements imply that the relative donating power of L 1R obeys the following order in ‘R’: Mes>H>Pr i >Ph. This is not the ranking predicted purely on inductive grounds.