Two Pseudopolymorphic Star-Shaped Tetranuclear Co(3+) Compounds with Disulfide Anions Exhibiting Two Different Connection Modes and Promising Photocatalytic Properties

Abstract

The compound [Co4(C6H14N2)4(μ4-S2)2(μ2-S2)4] (I) and the pseudo-polymorph [Co4(C6H14N2)4(μ4-S2)2(μ2-S2)4]⋅4 H2O (II) were obtained under solvothermal conditions (C6H14N2=trans-1,2-diaminocyclohexane). The structures feature S2(2-) ions exhibiting two different coordination modes. Terminal S2(2-) entities join two Co(3+) centres in a μ2 fashion, whereas the central S2(2-) groups connect four Co(3+) cations in a μ4-coordination mode. Compound II can be transformed into compound I by heat and storage over P2O5 and storing compound I in humid air yields in the formation of compound II. The intermolecular interactions investigated through Hirshfeld surface analysis reveal that besides S⋅⋅⋅H bonding close contacts are associated with relatively weak H⋅⋅⋅H interactions. A detailed DFT analysis of the bonding situation explains the long S-S bonds in the μ4-bridging S2(2-) units and the short bonds for the S2(2-) moieties in the μ2-connecting mode. Photocatalytic hydrogen evolution experiments demonstrate the potential of compound II as catalyst.

Keywords: Hirshfeld surface; cobalt; density functional calculations; disulfide bridges; photocatalysis.