*Article* **A Mero-Plesiotype Series of Vanadates, Arsenates, and Phosphates with Blocks Based on Densely Packed Octahedral Layers as Repeating Modules**

**Olga Yakubovich 1,\* and Galina Kiriukhina 1,2**


**Abstract:** The family of layered vanadates, arsenates, and phosphates is discussed in terms of a modular concept. The group includes minerals vésignéite and bayldonite, and a number of synthetic analogous and modifications which are not isotypic, but their crystal structures comprise similar blocks (modules) consisting of a central octahedral layer filled by atoms of *d* elements (Mn, Ni, Cu, or Co) and adjacent [VO<sup>4</sup> ], [AsO<sup>4</sup> ], or [PO<sup>4</sup> ] tetrahedra. The octahedral layers are based on the close-packing of oxygen atoms. Within these layers having the same anionic substructure, the number and distribution of octahedral voids are different. In the crystal structures of compounds participating in the polysomatic series, these blocks alternate with various other structural fragments. These circumstances define the row of structurally-related vanadates, arsenates, and phosphates as a mero-plesiotype series. Most of the series members exhibit magnetic properties, representing two-dimensional antiferromagnets or frustrated magnets.

**Keywords:** modular structures; polysomes (series); synthetic analogues of minerals; transition metal phosphates; X-ray diffraction; antiferromagnets; frustrated magnets; kagomé lattice
