K2MIII2(MVIO4)(PO4)2 (MIII = Fe, Sc; MVI = Mo, W), Novel Members of the Lagbeinite-Related Family: Synthesis, Structure, and Magnetic Properties

The possibility of PO43– for MoO42– partial substitution in the langbeinite framework has been studied by exploration of the K–Fe­(Sc)–Mo­(W)–P–O systems using the high-temperature solution method. It was shown that 1/3PO43– for MoO42– substitution leads to formation of three novel compounds K2Fe­(MoO4)­(PO4)2, K2Sc­(MoO4)­(PO4)2, and K2Sc­(WO4)­(PO4)2 with slightly increased lattice parameters and significant distortion of the anion tetrahedra without structure changes. In contrast, the antiferromagnetic structure is modified by substitution in the low-temperature region. The structural peculiarities are discussed in light of bond-valence sums calculations.