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 2 and L 3 -(CO 2 - ) 2 (2 : 1 stoichiometry) in CH 3 OH affords a discrete complex [CoII4-{L 3 -(CO 2 - ) 2 } 2 (μ 3 -OCH 3 ) 2 (CH 3 OH) 2 (H 2 O) 2 Cl 2 ] (1) [L 3 -(CO 2 - ) 2 = 3-[ N -{2-(pyridin-2-yl)methyl}amino]-bis(propionate)]. The structure of 1 reveals two terminal mononuclear Co II {L 3 -(CO 2 - ) 2 }Cl units connected by a dimeric CoII2(μ 3 -OCH 3 ) 2 (CH 3 OH) 2 (H 2 O) unit present in the centre through two methoxo (μ 3 -OCH 3 )- 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 Co II N 2 O 3 Cl and the central Co2 has Co II O 6 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: J 1 = +3.3 cm -1 (Co⋯Co 3.176 Å; μ-1,1-OCO- and μ 3 -OCH 3 bridges), J 2 = -2.5 cm -1 (Co⋯Co 3.228 Å; μ-1-OCO- and μ 3 -OCH 3 bridges) and J 3 = +10.6 cm -1 (Co⋯Co 3.084 Å; two μ 3 -OCH 3 bridges)) have been identified, with the inclusion of the orbital reduction parameter ( α = Aκ = 1.38), spin-orbit coupling ( λ = -158 cm -1 ) and axial distortion (energy gap Δ = -975 cm -1 between singlet and doublet levels), rationalized by density functional theory (DFT) calculations.