Co(II/III) coordinated pyridine alcoholate ligand generated through metal assisted nucleophilic addition to a CO function: Temperature dependent synthesis of a mononuclear complex and a neutral cubane cluster

The synthesis and characterization of pyridine alcoholate ligand coordinated Co(II/III) metal complexes are reported. The characterization includes elemental analysis, spectral, magnetism, and X-ray crystallographic studies. Water readily shows nucleophilic addition to the CO group upon coordination of the 2-pyridyl ring of the ligands, forming a gem-diol form of (2-py)2CO. By coordinating through the two pyridine nitrogen atoms and one oxygen atom from the newly formed gem-diol, the ligand becomes tridentate rather than bidentate, as might be expected. Two spin allowed (1A1g → 1T1g and 1A1g → 1T2g) d ← d transitions are observed in the electronic spectra of the strong field octahedral Co(III) complex and the 1A1g → 1T2g transition is obscured by intense MLCT bands. In [Co{OC(OH)(2-pyridyl)2}2][OAc] · 4H2O (1) the cationic part shows a N4O2 coordinated octahedral geometry for the Co(III) species with two di-(pyridyl)-ketone hydrate (DPKH) moieties coordinated in a tridentate fashion. The tetranuclear cluster molecule of [Co4{OC(OH)(2-pyridyl)2}4[OAc]4] · 7H2O (2) has a cubane core with alternate vertices occupied by Co(II) and oxygen atoms, consisting of two interpenetrating tetrahedra. In complex 2 the 1/χM′versus T   plot fitted with the simple Curie–Weiss law 1/χM′=C/(T-θ), and shows an antiferromagnetic behavior with C = 8.14 and θ = −69.26 ± 0.06 K.

Synthesis of [Co{OC(OH)(2-pyridyl)2}2][OAc] · 4H2O (1) and [Co4{OC(OH)(2-pyridyl)2}4[OAc]4] ·  7H2O (2) are reported along with optical and magnetic studies.Figure optionsDownload as PowerPoint slide