First outer-sphere 1,3-diethyl-2-thiobarbituric compounds [M(H2O)6](1,3-diethyl-2-thiobarbiturate)2·2H2O (M=Co2+, Ni2+): Crystal structure, spectroscopic and thermal properties

Highlights: • Two new compounds [(Co,Ni)(H₂O)₆](Detba)₂·2H₂O with outer-sphere Detba⁻ were prepared. • XRD, XRPD, DSM, TG and IR spectroscopy were used for the compound characterization. • The comparison of Ni(H₂O)₆X₂ (X = Htba and Detba) showed different supramolecular interactions. • The structures are stabilized by the π–π interactions. Two new d-element compounds, [Co(H₂O)₆](Detba)₂·2H₂O (1) and [Ni(H₂O)₆](Detba)₂·2H₂O (2) (HDetba – 1,3-diethyl-2-thiobarbituric acid) were synthesized and characterized by single-crystal and powder X-ray diffraction analysis, TG–DSC and FT-IR. Structural analysis revealed that (1) and (2) are discrete structures, in which M²⁺ ion (M = Co, Ni) is six-coordinated by water molecules and it forms an octahedron. The outer-sphere Detba⁻ ions and H₂O molecules participate in OH⋯(O/S) intermolecular hydrogen bonds which form the 2D layer. Thermal decomposition includes the stage of dehydration and the following stage of oxidation of Detba⁻ with a release of CO₂, SO₂, H₂O, NH₃ and isocyanate gases.