Effect of ceramic materials on the optical properties of porcelain veneers for tetracycline-stained teeth.

Objectives: To analyze the chromatic properties and translucency of porcelain veneers made from different ceramic materials against the background of tetracycline-stained teeth.

Methods: Porcelain specimens (A1, A3, B2, B4) measuring 0.50 mm in thickness were prepared by heat-press casting and layering.

Two pairs of 1 : 2 nickel(II) and copper(II) metal-complex dyes showing the same trans configuration and azo-hydrazone transformation but different thermal properties.

Two pairs of 1: 2 neutral trans mononuclear transition-metal (M = Ni(II) and Cu(II)) complexes of pyridine-2,4-dione and quinoline-2,4-dione based heterocyclic dyes have been structurally and spectrally characterized and compared herein. X-ray single-crystal diffraction analyses of four complexes, namely trans-[Ni(La)2(DMF)2] (1), trans-[Cu(La)2(DMF)2] (2), trans-[Ni(Lb)2(DMF)2] (3) and trans-[Cu(Lb)2(DMF)2] (4), reveal that they have the same trans configuration between the bidentate chelating dianionic ligands and two axially coordinated DMF molecules. Furthermore, a transformation from the hydrazone to azo configuration has been observed for both bidentate chelating ligands La(-) and Lb(-) after metal-ion complexation.

3,3'-Dichloro-biphenyl-4,4'-diaminium sulfate.

In the title compound, C(12)H(12)Cl(2)N(2) (2+)·SO(4) (2-), the two rings are not coplanar [dihedral angle = 48.7 (2)°]. In the crystal, multiple N-H⋯O hydrogen-bond inter-actions are found between the ammonium and sulfate groups.

2-Amino-6-nitro-1,3-benzothia-zol-3-ium hydrogen sulfate.

In the title molecular salt, C(7)H(6)N(3)O(2)S(+)·HSO(4) (-), the 2-amino-6-nitro-1,3-benzothia-zole ring system is essentially planar [mean deviation = 0.0605 (4) Å]. In the crystal, N-H⋯O and O-H⋯O hydrogen-bonding inter-actions result in a layer motif.

4,4'-(Cyclo-hexane-1,1-di-yl)dianilinium dichloride monohydrate.

In the title compound, C(18)H(24)N(2) (2+)·2Cl(-)·H(2)O, both the cation and the water mol-ecule lie on a twofold crystallographic axis. In the cation, the two benzene rings are perpendicular to each other, making a symmetry-constrained dihedral angle of 90°. In the crystal, N-H⋯Cl, O-H⋯Cl and N-H⋯O hydrogen bonds result in the formation of a three-dimensional network.

Biphenyl-3,3',4,4'-tetra-amine.

The title compound, C(12)H(14)N(4), has a crystallographically imposed centre of symmetry. Inter-molecular N-H⋯N hydrogen bonds between amino groups link adjacent mol-ecules into a three-dimensional network where ten-membered hydrogen-bonded rings are observed.

Tetra-kis(2,2'-bipyrid-yl)dichlorido-di-μ(3)-hydroxido-di-μ(2)-hydroxido-tetra-copper(II) dinitrate hexa-hydrate.

The tetra-nuclear copper(II) title complex, [Cu(4)Cl(2)(OH)(4)(C(10)H(8)N(2))(4)](NO(3))(2)·6H(2)O, has a crystallographically imposed centre of symmetry. The metal atoms display a distorted tetragonal-pyramidal coordination geometry, and are linked by two μ(2)- and two μ(3)-hydroxo groups, assuming a chair-like conformation for the Cu(4)O(2) core. In the crystal, the complex mol-ecules are linked into a three-dimensional network by inter-molecular O-H⋯O, O-H⋯Cl, C-H⋯O and C-H⋯Cl hydrogen bonds and π-π stacking inter-actions with centroid-centroid separations of 3.

2-Amino-benzimidazolium hydrogen sulfate.

In the title salt, C(7)H(8)N(3) (+)·HSO(4) (-), the benzimdazole ring system is planar [mean deviation 0.0086 (1) Å]. In the crystal, N-H⋯O and O-H⋯O hydrogen-bond inter-actions give rise to a layer motif.

catena-Poly[copper(II)-bis(μ-2,4-dichloro-6-formyl-phenolato)-κO,O':Cl;κCl:O,O'].

In the title compound, [Cu(C(7)H(3)Cl(2)O(2))(2)](n), the Cu(II) atom lies on a centre of inversion and adopts a [4+2] coordination mode, with two long axial Cu-Cl coordinative bonds complementing four Cu-O bonds from two 2,4-dichloro-6-formyl-phenolate ligands in a distorted square plane. π-π stacking inter-actions are also formed between neighbouring aromatic rings, with a centroid-centroid separation of 3.624 (2) Å.

3,5-Dibromo-2-hydroxy-benzaldehyde.

The title compound, C(7)H(4)Br(2)O(2), exhibits a layer packing structure via weak π-π stacking inter-actions [centroid-centroid distances between adjacent aromatic rings are 4.040 (8) and 3.776 (7) Å].

An azo dye molecule having a pyridine-2,6-dione backbone.

The title azo dye, 2-(2-methoxyethoxy)ethyl 4-[(5-cyano-1-ethyl-4-methyl-2,6-dioxo-1,2,3,6-tetrahydropyridin-3-ylidene)hydrazino]benzoate, C21H24N4O6, with a 1-ethyl-5-cyano-2-hydroxy-4-methyl-6-pyridone component, crystallizes in the hydrazone form. Hydrogen bonding mediates the formation of four-molecule aggregates, which are further grouped into an extended structure by pi-pi stacking interactions between the aromatic rings of adjacent molecules, with a centroid-centroid separation of 3.697 (2) A.

(1R,3S)-1-Monoamidocamphoric acid.

The title compound, (1S,3R)-3-carbamoyl-2,2,3-trimethylcyclopentane-1-carboxylic acid, C(10)H(17)NO(3), was synthesized and characterized by IR, EA, ES-MS (electrospray ionization mass spectra), (1)H NMR, (13)C NMR and X-ray diffraction techniques. The two independent molecules form a two-dimensional network via O-H.O and N-H.