Tetra­sodium hepta­(cobalt/aluminium) hexa­(arsenate/phosphate) is a new member of the isostructural family of compounds with the general formula A 4 M 7(XO4)6 (A: Na, K; M: Ni, Co; X: P, As). The proposed structural model is based both on a careful investigation of the crystal data, as well as validation tools by means of bond-valence-sum (BVS) and charge-distribution (CHARDI) calculations.

To investigate the influence of P/As substitution on structures and electrical properties, e.g. the effect on material densities, two new solid P/As-doped solutions, NaCoPAsO (disodium cobalt diphosphorus arsenic heptaoxide) and NaCoPAsO (disodium cobalt phosphorus arsenic heptaoxide), with melilite-like structures have been synthesized by solid-state reactions. Their unit-cell parameters are in agreement with Vegard's law. The obtained structural models were investigated by the bond valence sum (BVS) and charge distribution (CHARDI) validation tools and, for the latter, the structures are described as being built on anion-centred polyhedra. The frameworks can be described as layered and formed by {[Co(P,As)O]} slabs, with alkali cations sandwiched between the layers and with the interlayer spaces increased due to P/As substitution. The BVS model was extended to a preliminary simulation of the sodium conduction properties in the studied structural type and suggests that the most probable sodium conduction pathways are bidimensional, at the (002) planes.

A new cyclo­diphosphazane, [EtNP(S)NMe2]2, was synthesized and characterized by NMR and EDX spectroscopy and single-crystal XRD. The stability of the structure is ensured only by van der Waals inter­actions and the their prevalence is confirmed by an analysis of the three-dimensional Hirshfeld surface (HS) and two-dimensional fingerprint plots (FP).

No abstract

No abstract