Crystal structure of the inverse crown ether tetra-kis-[μ2-bis-(tri-methyl-sil-yl)amido]-μ4-oxido-dicobalt(II)disodium, [Co2Na2{μ2-N(SiMe3)2}4](μ4-O).

Christopher B Hansen,Alexander S Filatov,Gregory L Hillhouse

doi:10.1107/s2056989016006861

Christopher B Hansen, Alexander S Filatov + Show 1 more

Open Access

https://doi.org/10.1107/s2056989016006861

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Abstract

The title compound, [Co2Na2{μ2-N(SiMe3)2}4](μ4-O), (I), represents a new entry in the class of inverse crown ethers. In the mol-ecule, each Co atom is formally in the oxidation state +II. The structure contains one half of a unique mol-ecule per asymmetric unit with the central μ4-oxido ligand residing on an inversion center, leading to a planar coordination to the Na and Co atoms. In the crystal, bulky tri-methyl-silyl substituents prevent additional inter-actions with cobalt. However, weak inter-molecular Na⋯H3C-Si inter-actions form an infinite chain along [010]. The structure is isotypic with its Mg, Mn and Zn analogues.

Highlights

The title compound, [Co2Na2{2-N(SiMe3)2}4](4-O), (I), represents a new entry in the class of inverse crown ethers
The structure contains one half of a unique molecule per asymmetric unit with the central 4-oxido ligand residing on an inversion center, leading to a planar coordination to the Na and Co atoms
The asymmetric unit contains half of a unique molecule comprised of an oxygen atom located on an inversion center, one cobalt atom, one sodium atom, and two –N(SiMe3)2 ligands with the remainder of the molecule being completed by application of inversion symmetry

Summary

Chemical context

Compounds that feature oxido-bridged cobalt clusters have been of great interest in recent years as active homogeneous (Blakemore et al, 2015) and heterogeneous (Kärkäs et al., 2014) oxygen-evolution catalysts. In the course of studies of compounds with low-coordinate cobalt atoms (Hansen et al, 2015), we have isolated and structurally characterized a cobalt-containing tetranuclear compound featuring a central 4-bridging oxido ligand,. Schematic representation of inverse crown ethers that have previously been structurally characterized. Compound (I) is the first cobalt-based inverse crown ether. The majority of examples contain magnesium or zinc as M0, though manganese (Kennedy et al, 2008; Mulvey et al, 2010), aluminum (Wu et al, 2010), and ytterbium (Lu et al, 2010).

Structural commentary

Supramolecular features

Database survey

Synthesis and crystallization

Refinement