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

A new alkaline earth metal three-dimensional polar MOF structure in barium carbamoyl­cyano­nitro­somethanide is governed by bridging coordination of the nitroso- and aqua O-atoms, which support a face-sharing connection of coordination polyhedra.

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.