New hydrated phases of potassium orthovanadate: K ₃ (VO ₄ )(H ₂ O) _0.56 and K ₃ (VO ₄ )(H ₂ O) ₄

Single crystals of the hydrated potassium orthovanadate phases K₃(VO₄)·0.56H₂O, tripotassium orthovanadate 0.56-hydrate, and K₃(VO₄)·4H₂O, tripotassium orthovanadate tetra-hydrate, were isolated during the processing of products obtained under hydro-flux conditions. The asymmetric unit of K₃(VO₄)(H₂O)_0.56 (space group <i>P</i>1, <i>Z</i> = 12) comprises six formula units of K₃(VO₄) and five water mol-ecules of crystallization. The complex crystal structure is made up of isolated [VO₄]^3- tetra-hedra connected <i>via</i> K⁺ cations exhibiting coordination numbers between 6 and 8. The structure is consolidated by the formation of a finite hydrogen-bonded network between the water mol-ecules and [VO₄]^3- tetra-hedra. Two of the K⁺ cations are positionally disordered, and three of the water mol-ecules of crystallization are occupationally and/or positionally disordered. The asymmetric unit of K₃(VO₄)(H₂O)₄ (space group <i>Pmn</i>2₁, <i>Z</i> = 2) comprises two K⁺ cations, one V^V atom, three O atoms and two water mol-ecules. The crystal structure is also made up from isolated [VO₄]^3- tetra-hedra inter-linked by K⁺ cations (coordination numbers 7 and 8). In comparison with the less-hydrated phase, the higher water content of this compound results in an infinite network of O-H⋯O hydrogen bonds between the water mol-ecules and [VO₄]^3- tetra-hedra.