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.

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.

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.

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. The L*, a*, and b* values of the specimens against simulated tetracycline tooth and black-and-white backgrounds were measured by a spectrophotometer, and color differences ΔE001 between specimens on simulated tetracycline backgrounds and the backgrounds themselves and ΔE002 between specimens on simulated tetracycline backgrounds and the white background were calculated. The translucent parameter (TP) was also evaluated. RESULTS: The ΔE001 of feldspathic specimens (IPS d.SIGN) with the opaque layer was significantly greater than that of glass ceramic specimens (IPS e.max Press LT), and the ΔE001 of group B4 was consistently greater than those of the other color groups (P<0.05). The ΔE002 values of all feldspathic specimens with the opaque layer were less than 1.25, and the ΔE002 values of the glass ceramic specimens were greater than 2.23. However, no significant difference was observed among the different color groups (P>0.05). The TP values of feldspathic specimens with the opaque layer were significantly lower than those of glass ceramic specimens(P<0.05), but no significant difference was observed among different color groups (P>0.05). CONCLUSIONS: When changing the color of tetracycline-stained teeth, 0.50 mm-thick IPS d.SIGN feldspathic veneers with an opaque layer provide better chromatic properties than IPS e.max Press LT glass ceramic veneers. However, the translucency of feldspathic veneers is generally poorer than that of glass ceramic veneers.

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.

2-(Dihydroxy-meth-yl)pyridinium chloride.

In the title compound, C(6)H(8)NO(2) (+)·Cl(-), inter-molecular O-H⋯Cl and N-H⋯Cl hydrogen bonds are observed in which each chloride anion links three adjacent cations into a hydrogen-bond network.

2,4-Diamino-6-methyl-1,3,5-triazin-1-ium chloride.

In the title compound, C(4)H(8)N(5) (+)·Cl(-), a two-dimensional layer packing network is observed in which every chloride anion links three adjacent 2,4-diamino-6-methyl-1,3,5-triazin-1-ium cations by N-H⋯Cl hydrogen-bonding inter-actions, forming 12-membered and eight-membered hydrogen-bonded rings with graph-set motifs R(4) (4)(12) and R(3) (3)(8), respectively. In addition, N-H⋯N hydrogen bonds are found between adjacent cations, forming another type of eight-membered [R(2) (2)(8)] hydrogen-bonded ring.

4-Amino-pyridinium azide 4-amino-pyridine solvate.

In the title compound, C(5)H(7)N(2) (+)·N(3) (-)·C(5)H(6)N(2), all N atoms of the azide anion are situated on a twofold rotational axis, so the 4-amino-pyridinium cation and 4-amino-pyridine mol-ecule, being related by symmetry, occupy one position in the asymmetric unit. Inter-molecular N-H⋯N hydrogen bonds generate a three-dimensional hydrogen-bonding network which consolidates the crystal packing.

[Effect of porcelain thickness and substrate on optical properties of porcelain veneers for tetracycline stained teeth].

PURPOSE: To analyze the effect of porcelain layer thicknesses and substrates on color properties and translucency of IPS e.max LT porcelain laminate veneers used to restore tetracycline stained teeth. METHODS: Porcelain specimens with different core and veneer thickness (veneer/core thickness: 0.25 mm/0.25 mm, 0.50 mm/0.25 mm, 0.25 mm/0.50 mm, 0.50 mm/0.50 mm, and 0.25 mm/0.75 mm) were fabricated by heat-press layering technique. CIE L*a*b* parameters were measured under simulated tetracycline backgrounds and black and white backgrounds by a spectrophotometer, color differences ΔE001 between specimens on simulated tetracycline backgrounds and backgrounds themselves and ΔE002 between specimens on simulated tetracycline backgrounds and white background were calculated. The translucent parameter(TP) was also calculated. The data were submitted to statistical analysis with SPSS 17.0 software package. RESULTS: ΔE001 increased with increase of thickness of the core and veneer layer, but there was no significant difference between 0.25 mm and 0.50 mm core thickness groups with 0.50 mm veneer in thickness (P>0.01). Except for light grey, ΔE002 decreased over other substrates with increase of thickness of the core and veneer layer, but there was no significant difference between 0.50 mm and 0.75 mm core thickness groups with 0.25 mm veneer in thickness (P>0.01). Both ΔE001 and ΔE002 were significantly different over different substrates（P<0.01）. TP decreased as the increase of core and veneer thickness and TP was significantly different with different core and veneer thickness（P<0.01）. CONCLUSIONS: Both the core/veneer thickness and the substrate have significant influence on color matching and masking ability of IPS e.max LT porcelain laminate veneers used to restore tetracycline stained teeth. As for IPS e.max LT porcelain veneers, the color property was the best when yellowish tetracycline stained teeth were restored, while the light grey was worst. The thickness of core and veneer has significant influence on the translucency of porcelain laminate veneers.

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 3.724 (2) and 3.767 (3) Å.

2,4-Diamino-6-methyl-1,3,5-triazin-1-ium nitrate.

In the title salt, C(4)H(8)N(5) (+)·NO(3) (-), a ring N atom of 2,6-diamino-4-methyl-triazine is protonated. Each anion is connected to three neighbouring cations by multiple N-H⋯O hydrogen bonds which, together with N-H⋯N contacts, generate a layer structure.

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.

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]. Mol-ecules in each layer are linked by inter-molecular O-H⋯O hydrogen bonding and Br⋯Br inter-actions [3.772 (4) Å]. There are two mol-ecules in the asymmetric unit.

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

The title compound, C(7)H(4)Cl(2)O(2), exhibits a layer crystal structure; mol-ecules within each layer are linked by weak C-H⋯O inter-molecular hydrogen bonds. There is also an intramolecular O-H⋯O hydrogen bond.

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.

Structure-performance relationship for a family of disperse azo dyes having the same D-π-A 4-nitro-4'-amino-azobenzene skeleton: structures, solvatochromism and DFT computations.

A combinational study of structural chemistry and dyestuff chemistry has been carried out to reveal the structure-performance relationship for eight disperse azo dyes by comparing their structures, electronic spectra, solvatochromism and theoretic computations. All eight structural analogues have the same 4-nitro-4'-amino-azobenzene donor-π-acceptor skeleton but different substituted groups, namely, R1 and R2 in ring A, R3, R4 and R5 in Ring B. X-ray single-crystal diffraction analyses indicate that four azo dyes have severely twisted aminoazobenzene structures because of the steric hindrance of ortho dichloro/dibromo radicals of 4-nitrobenzene moiety, while the other four dyes show essentially planar conformation due to the ortho monosubstituted 4-nitrobenzene amine and 4'-amino-azobenzene units. It is noted that the electronic spectra are closely related to their molecular structures, where the presence of different auxochrome groups and the spatial crowding effects in the aminoazobenzene backbone lead to significant alterations of the bathochromic and hypsochromic shifts.

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. More importantly, the simultaneous DSC/TG-MS-FTIR method has been used to explore the thermal stability of four neutral metal-complex dyes 1-4, where the two axially coordinated DMF molecules in Ni(II) and Cu(II) complexes exhibit distinguishable decomposition behavior because of their different M-O bond lengths originating from the Jahn-Teller distortions.

Azo-hydrazone tautomerism observed from UV-vis spectra by pH control and metal-ion complexation for two heterocyclic disperse yellow dyes.

The azo-hydrazone tautomerism of two pyridine-2,6-dione based Disperse Yellow dyes has been achieved by pH control and metal-ion complexation, respectively, which is evidenced by UV-visible spectra using pH-titration, (1)H NMR and X-ray single-crystal diffraction techniques for two dyes and one neutral dinuclear dye-metal complex. pH-titration experiments under strong and weak acidic conditions (HCl and HOAc) as well as strong and weak alkaline conditions (NaOH and ammonia) demonstrate that there is an equilibrium between the azo (HL(1-A) and HL(2-A)) and hydrazone (HL(1-H) and HL(2-H)) tautomers for two dyes in solution but the hydrazone form is dominant under conventional conditions. The hydrazone proton is also observed in the (1)H NMR spectra of HL(1-H) and HL(2-H) which can be verified by the hydrogen-deuterium exchange and the presence of cooperative six-membered intramolecular hydrogen rings involving the hydrazone proton in their X-ray single-crystal structures. Moreover, the azo-hydrazone tautomerism is evidenced by the formation of a novel neutral dinuclear dye-metal complex Cu(2)(L(2-A))(4), where all the ligands are in the azo form and two types of coordination modes are present for four L(2-A) ligands. Namely, the side two ligands serve as the bidentate capping ligands, while the middle ones act as the quadridentate bridging ligands linking adjacent Cu(II) centers in a reverse fashion.

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.O hydrogen-bonding interactions between their carboxylic acid and carbamoyl groups.