A tetracobalt(II) cluster with a two vertex truncated dicubane topology endogenously supported by carboxylate-based (2-pyridyl)methylamine ligands: magneto-structural and DFT studies.

A reaction between CoCl and L-(CO) (2 : 1 stoichiometry) in CHOH affords a discrete complex [CoII4-{L-(CO)}(μ-OCH)(CHOH)(HO)Cl] (1) [L-(CO) = 3-[-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)]. The structure of 1 reveals two terminal mononuclear Co{L-(CO)}Cl units connected by a dimeric CoII2(μ-OCH)(CHOH)(HO) unit present in the centre through two methoxo (μ-OCH)- and two carboxylate (μ-1,1-OCO-) bridges affording a tetranuclear coordination cluster of Co(II) with a defective dicubane topology. In 1, Co1 (terminal) has distorted octahedral CoNOCl and the central Co2 has CoO coordination. Such coordination arrangements afford the observed topology. Variable-temperature magnetic studies reveal anti-ferromagnetic coupling in 1. Three magnetic exchange interactions (one anti-ferromagnetic and two ferromagnetic: = +3.3 cm (Co⋯Co 3.176 Å; μ-1,1-OCO- and μ-OCH bridges), = -2.5 cm (Co⋯Co 3.228 Å; μ-1-OCO- and μ-OCH bridges) and = +10.6 cm (Co⋯Co 3.084 Å; two μ-OCH bridges)) have been identified, with the inclusion of the orbital reduction parameter ( = = 1.38), spin-orbit coupling ( = -158 cm) and axial distortion (energy gap = -975 cm between singlet and doublet levels), rationalized by density functional theory (DFT) calculations.