Polytypism of Ln(SeO)(HSeO)·2HO compounds: synthesis and crystal structure of the first monoclinic modification of Nd(SeO)(HSeO)·2HO, DFT calculations and order/disorder description.

Compounds with the general formula Ln(SeO)(HSeO)·2HO, where Ln = Sm, Tb, Nd and Lu, are characterized by orthorhombic symmetry with space group P222 and unit-cell parameters in the ranges a ∼ 6.473-6.999, b ∼ 6.

Polymorphism, polytypism and modular aspect of compounds with the general formula AM(TO) (A = Na, Rb, Cs, Ca; M = Mg, Mn, Fe, Cu; T = S, P): order-disorder, topological description and DFT calculations.

The crystal structure of NaMn(SO) [unit-cell parameters a = 14.8307 (18), b = 9.9107 (18), c = 8.

Order-disorder character and twinning in the structure of a new synthetic titanosilicate: (Ba,Sr)4Ti6Si4O24 x H2O.

Prismatic crystals of the title compound, up to 100 microm long and {001} twinned by metric merohedry, were obtained as a side-product of a hydrothermal run devoted to synthesizing the heterophyllosilicate lamprophyllite. Single-crystal X-ray diffraction data were collected on a Bruker-AXS Smart Apex diffractometer from a crystal with approximate composition (Ba(0.80)Sr(0.