Three-dimensional alkaline earth metal–organic framework poly[[μ-aqua-aquabis(μ3-carbamoylcyanonitrosomethanido)barium] monohydrate] and its thermal decomposition

In the structure of the title salt, {[Ba(μ3-C3H2N3O2)2(μ-H2O)(H2O)]·H2O}n, the barium ion and all three oxygen atoms of the water molecules reside on a mirror plane. The hydrogen atoms of the bridging water and the solvate water molecules are arranged across a mirror plane whereas all atoms of the monodentate aqua ligand are situated on this mirror plane. The distorted ninefold coordination of the Ba ions is completed with four nitroso-, two carbonyl- and three aqua-O atoms at the distances of 2.763 (3)–2.961 (4) Å and it is best described as tricapped trigonal prism. The three-dimensional framework structure is formed by face-sharing of the trigonal prisms, via μ-nitroso- and μ-aqua-O atoms, and also by the bridging coordination of the anions via carbonyl-O atoms occupying two out of the three cap positions. The solvate water molecules populate the crystal channels and facilitate a set of four directional hydrogen bonds. The principal Ba–carbamoylcyanonitrosomethanido linkage reveals a rare example of the inherently polar binodal six- and three-coordinated bipartite topology (three-letter notation sit). It suggests that small resonance-stabilized cyanonitroso anions can be utilized as bridging ligands for the supramolecular synthesis of MOF solids. Such an outcome may be anticipated for a broader range of hard Lewis acidic alkaline earth metal ions, which perfectly match the coordination preferences of highly nucleophilic nitroso-O atoms. Thermal analysis reveals two-stage dehydration of the title compound (383 and 473 K) followed by decomposition with release of CO2, HCN and H2O at 558 K.