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The asymmetric unit of the title compound, C(15)H(18)N(2)O(2), contains two independent mol-ecules with essentially identical geometries and conformations. The dihedral angles between the benzene and pyrimidine rings in the two mol-ecules are 89.96 (11) and 73.91 (11)°. The six methyl groups are disordered over two sets of sites, with site occupancies of 0.545 (4):0.455 (4) and 0.542 (7):0.458 (7) in the two mol-ecules. The crystal structure is stabilized by N-H⋯O hydrogen bonds.

In the crystal structure of the title mol-ecule, C(26)H(32)N(2)O(2), the six methyl groups are disordered over two positions, with site-occupancy ratios of 0.665 (8):0.335 (8) and 0.639 (8):0.361 (8). The central pyrimidine ring is almost planar with an r.m.s. deviation of 0.009 Å. The dihedral angles formed by the two benzene rings with the pyrimidine ring are 70.70 (8) and 88.02 (9)°. The dihedral angle between two benzene rings is 46.67 (10)°.

The title compound, C(16)H(12)F(3)N(3)O(5)S·H(2)O, was prepared by reaction of 4-nitro-benzaldehyde, 4,4,4-trifluoro-1-(thio-phen-2-yl)butane-1,3-dione and urea. The asymmetric unit contains two independent mol-ecules, with essentially identical geom-etries and conformations. The dihydro-pyrimidine rings adopt a half-chair conformation. The dihedral angles between the benzene ring and the thio-phene ring are 54.82 (8) and 58.72 (8)° in the two mol-ecules. The mol-ecular conformation of one of the mol-ecules is stabilized by two intra-molecular O-H⋯O hydrogen bonds, generating an S(6) ring. The crystal structure is stabilized by inter-molecular O-H⋯O and N-H⋯O hydrogen bonds.

In the title compound, C(15)H(12)F(3)N(3)O(3)S, the pyrimidine ring adopts a half-chair conformation with the mean plane formed by the ring atoms excluding the C atom bonded to thio-phene-2-carbonyl group lying nearly perpendicular to the pyridine and thio-phene rings, making dihedral angles of 84.91 (4) and 87.40 (5)°, respectively. The dihedral angle between the pyridine and thio-phene rings is 54.44 (5)°. The crystal structure is stabilized by inter-molecular O-H⋯O and N-H⋯N hydrogen bonds and weak C-H⋯O inter-actions further consolidate the structure.

The title compound, C(5)H(3)F(3)N(2)O(2)·H(2)O, was prepared by the reaction of ethyl 4,4,4-trifluoro-3-oxobutano-ate with urea. In the crystal, the 6-(trifluoro-meth-yl)pyrimidine-2,4(1H,3H)-dione and water mol-ecules are linked by N-H⋯O and O-H⋯O hydrogen bonds. A ring dimer structure is formed by additional inter-molecular N-H⋯O hydrogen bonds.

The title compound, {[Gd(C(8)H(2)NO(6))(H(2)O)(3)]·H(2)O}(n), was obtained in water under hydro-thermal conditions. The Gd(III) ions are nine-coordinated by two O and one N atoms from one pyridine-2,4,6-tricarboxyl-ate ligand, two O atoms from another ligand, one O atom from a third ligand and three coordinated water mol-ecules. Each ligand binds three metal centers. Two-dimensional layers are formed through the Gd-O bonds and the layers are linked by O-H⋯O hydrogen bonds, forming a three-dimensional network.

The title compound, C(36)H(36)N(4)O(4), was prepared as a spiro-lactam ring formation of the rhodamine dye for comparison with a ring-opened form. The xanthene ring system is approximately planar [r.m.s. deviations from planarity = 0.023 (9) Å for the xanthene ring]. The dihedral angles formed by the spiro-lactam and 1,3-benzodioxole rings with the xanthene ring system are 86.8 (1) and 74.3 (1)°, respectively.