Synthesis, structure, and theoretical studies of a calcium complex of a unique dianion derived from 1-methyl­pyrrolidin-2-one

The title compound, catena-poly[[tetra­kis­(1-methyl­pyrrolidin-2-one-κO)calcium(II)]-μ-(E)-1,1′-dimethyl-2,2′-dioxo-1,1′,2,2′-tetra­hydro-[3,3′-bipyrrolyl­idene]-5,5′-bis­(thiol­ato)-κ(2) O:O′], [Ca(C(10)H(8)N(2)O(2)S(2))(C(5)H(9)NO)(4)](n), 1, crystallizes in the triclinic space group P [Image: see text]. The crystal studied was twinned by non-merohedry via two different twofold operations, about the normals to (001) and (1[Image: see text]0), giving four twin domains with refined occupancies of 0.412 (4), 0.366 (4), 0.055 (1), 0.167 (4). The Ca atoms are located on centers of inversion. Each Ca is surrounded by four 1-methyl­pyrrolidin-2-one (NMP) ligands and coordinated through one of the two O atoms to two (E)-1,1′-dimethyl-2,2′-dioxo-1,1′,2,2′-tetra­hydro-[3,3′-bipyrrolyl­idene]-5,5′-bis­(thiol­ate), [C(10)H(8)N(2)O(2)S(2)](2−), dianions (abbreviation: DMTBT). This dianion thus facilitates the formation of a 1-D polymer, which propagates in the [011] direction. These ribbons are linked by inter­molecular C—H⋯S inter­actions. Each Ca atom is in an octa­hedral CaO(6) six-coordinate environment with Ca—O bond lengths ranging from 2.308 (6) to 2.341 (6) Å, cis bond angles ranging from 88.2 (2) to 91.8 (2)° and the trans angles all 180° due to the Ca atoms being located on centers of inversion. Theoretical calculations were carried out using density functional theory (DFT) and the results showed that although the central DMTBT dianion is planar there is likely some resonance across the central bond between both aza­pentyl rings, but this is not sufficient to establish a ring current. The calculated UV–vis spectrum shows a peak at 625 nm, which accounts for the deep blue–purple color of solutions of the complex.