A Novel Mineral-like Copper Phosphate Chloride with a Disordered Guest Structure: Crystal Chemistry and Magnetic Properties

Novel copper phosphate chloride has been obtained under middle-temperature hydrothermal conditions. Its crystal structure was established based on the low-temperature X-ray diffraction data: Na₂Li_0.75(Cs,K)_0.5[Cu₅(PO₄)₄Cl]·3.5(H₂O,OH), sp. gr. C2/m, a = 19.3951(8) Å, b = 9.7627(3) Å, c = 9.7383(4) Å, β = 99.329(4)°, T = 150 K, MoK_α (λ = 0.71073 Å), R = 0.049. The crystal structure includes tetrameric copper clusters as the main building blocks, which are built of four CuO₄Cl pyramids sharing apical Cl vertices. The clusters are combined through phosphate groups and additional copper-centered polyhedra to form two mostly ordered periodic layers. Between the layers and inside the framework channels, alkali ions, H₂O molecules, or OH groups are statistically distributed. Na₂Li_0.75(Cs,K)_0.5[Cu₅(PO₄)₄Cl]·3.5(H₂O,OH) is a synthetic modification of a sampleite-polymorph of the lavendulan mineral group and represents a new member in a mero-plesiotype series of copper phosphates and arsenates, for which the crystal structures contain two-periodic [Cu₄X(TO₄)₄]_∞ modules (T = As, P; X = Cl, O). Magnetically, this phase exhibits the phase transition at T_C = 6.5 K, below which it possesses a weak ferromagnetic moment.

Na3Sm(PO4)2: (3+1)-dimensional commensurately modulated structure model and photoluminescence properties

For the first time, we determined the detailed crystal structure of Na3Sm(PO4)2 using single crystal X-ray diffraction and established the commensurately modulated structure model using the superspace formalism. The structure adopts a (3+1)-dimensional superspace group Pca21(0β0)000 with the modulation vector q=1/3b*. At the same time, the photoluminescent properties of Na3Sm(PO4)2 sintered at different temperatures between 800 and 1200°C were studied. Under near-UV excitation (402 nm), Na3Sm(PO4)2 shows intense characteristic emission bands of Sm3+ (561, 596, 642 nm) with the CIE coordinate of (0.5709, 0.4282), corresponding to orange color. The excitation spectrum covers a wide range from 350 nm to 470 nm, which indicates that Na3Sm(PO4)2 can be efficiently activated by near-UV or visuable LED ship.

One-dimensional decavanadate chains in the crystal structure of Rb4[Na(H2O)6][HV10O28]·4H2O

New decavanadate minerals, the products of the leaching or metasomatic processes, are possible in natureviaNa/Rb removal/inclusion reactions. As part of our search for novel vanadate phases with varying functionalities, a new phase, tetrarubidium hexaaquasodium hydrogen decavanadate tetrahydrate, Rb4[Na(H2O)6][HV10O28]·4H2O, has been synthesized by the hydrothermal technique at 553 K. Ten shared edges of V-centred octahedra form monoprotonated decavanadate cages, which are joined togetherviahydrogen bonds into one-dimensional chains parallel to the [101] direction. Within these chains, H atoms are sandwiched between neighbouring polyanions. Na and Rb atoms and H2O molecules occupy interstices flanked by the anionic chains providing additional crosslinking in the structure. This compound is the second decavanadate withP2/nsymmetry. Structural relationships among protonated and deprotonated decavanadates with inorganic cations, including minerals of the pascoite group, are discussed.