Issue 43, 2023

NaCo7.38(PO4)4Cl4 in a series of homeotype compounds with stable cationic substructures derived from the sulphohalite archetype

Abstract

In this paper, we present the synthesis and characterization of a Cl-bearing member of the phosphate family of compounds with a tetragonal crystal structure and similar topology in the basic projection. The title compound was obtained under hydrothermal conditions and its crystal structure was determined by single crystal low temperature X-ray diffraction. The structure of NaCo7.38(PO4)4Cl4 is formed with CoO4Cl2 octahedra sharing faces and assembled into eight-component ring clusters with a very short Co–Co distance of 3.014 Å. These clusters are linked in a three-periodic network via vertex-bridge contacts of adjacent octahedra and PO4 tetrahedra. Na atoms occupy the open channels of the framework. The structure is discussed as a derivative of cubic sulphohalite, Na6(SO4)2ClF, with the symmetry lowering from the widespread Fm[3 with combining macron]m space group of sulphohalite to the tetragonal acentric space group I[4 with combining macron]2m in our case; these space groups are symmetrically related by subordination “group → subgroup”. Theoretical calculations of possible pathways of Na migration through the framework showed that although the structure contains a sufficient number of voids for sodium ions, their migration is limited by the size of the channels. However, the obtained results indicated that the migration of Li+ ions is very likely through a two-periodic network parallel to the ab plane, which means that Li-containing structural varieties of NaCo7.38(PO4)4Cl4 with possible formulae Li5Co2+Co3+3(PO4)4Cl4 or Li4Co3+4(PO4)4Cl4 can possess ionic conductivity. The angle of intracluster Co–O–Co bonds of 105.4° allows us to assume that there is an antiferromagnetic exchange interaction between the Co atoms, and we assume that the intercluster exchange interactions between Co2+/3+ ions through the intermediate PO4 groups are also probable.

Graphical abstract: NaCo7.38(PO4)4Cl4 in a series of homeotype compounds with stable cationic substructures derived from the sulphohalite archetype

Supplementary files

Article information

Article type
Paper
Submitted
15 Aug 2023
Accepted
30 Sep 2023
First published
02 Oct 2023

CrystEngComm, 2023,25, 6006-6016

NaCo7.38(PO4)4Cl4 in a series of homeotype compounds with stable cationic substructures derived from the sulphohalite archetype

O. Yakubovich, G. Kiriukhina, S. Simonov, A. Volkov and O. Dimitrova, CrystEngComm, 2023, 25, 6006 DOI: 10.1039/D3CE00819C

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