Catena-(bis((1,10-phenanthroline-N,N′)-copper(II)) hydroxy-bis(phosphato)-tris(dioxo-vanadium(v))): A polymorphic phase driven by disorder

In the present paper a copper(II) phosphovanadate is presented and formulated as [Cu₆(phen)₆(V^VO₂) ₆(PO₄)₆(V^VO₂HO) ₃] (1a). This compound was obtained by hydrothermal synthesis and crystallizes in the triclinic group P-1, with a = 10.6290(5), b = 17.4275(8), c = 23.6151(11) Å; α = 92.888(4), β = 98.910(4) and γ = 91.995(4). The leitmotif in (1a) is almost identical to some previously reported ones, viz. [Cu(phen)(V^VO₂)(PO₄)] ₂[V^VO₂(OH)] (2); [Cu(phen)(V^VO ₂)(PO₄)]₂[V^IVO₂(H ₂O)] (3) except for the fact that the small cells found in (2)-(3) are tripled in (1a). The reasons driving to these differences are subtle, and reside in the way in which the disorder in some vanadate groups takes place, viz., completely at random in (2)-(3) thus leading to a small "average" cell, while keeping some systematics in (1a) thus needing for a larger motif to take account of its repetition scheme in the crystal. The magnetic unit in the structure of (1a) is defined by a dinuclear system of Cu^II bonded by a μ₂,η¹-PO₄ bridge. A fit of the corresponding magnetic data of (1a) was done, using the van Vleck equation for two S = centres (H=-JS^_a·S^_b). The parameters obtained by the fit of the experimental data were g = 2.1 and J = -3.5 cm^-1.