Color crystal properties

Most coordination compounds are brilliantly colored, a property that can be explained by the crystal field model. 

An overview of the effect of crystal structure on color application properties of organic pigments was published [7]. 

This section will discuss some important concepts from coloristic practice and the optical properties of pigmented systems. Space considerations permit a treatment of only the most vital concepts. The reader must consult the literature for further details and accounts of special problems [1], A review on the effect of crystal structure on color application properties was published [2],... 

Compoimds of the elements are also presented in similar format. This includes CAS Registry Numbers, formulas, molecular weights and the hydrates they form (if any). This is followed by occurrence (for naturally occurring compounds) and industrial applications. The section on Physical Properties covers the color, crystal structure, density, melting and boiling points and solubihties of the compounds in water, acids, alkalies and organic solvents. 

The physical properties most commonly listed in handbooks of chemical data are color, crystal form (if a solid), refractive index (if a liquid), density (discussed in Experiment 3), solubility in various solvents (discussed in Experiment 17), melting point, sublimation characteristics, and boiling point. When a new compound is isolated or synthesized, these properties almost always accompany the report in the literature. 

Hunger, K. (1999). The effect of crystal structure on color application properties of organic pigments. Rev. Prog. Coloration and Related Topics, 29,11-84. [258,259, 268]... 

Mineralogists, the scientists who study minerals, use various classification schemes to organize the thousands of known minerals. Color crystal structure hardness chemical, magnetic, and electrical properties and numerous other characteristics are used to classify minerals. 

Amin investigated the colored derivatives found on reaction of the acid chloride with primary and secondary amines and with thiols, Ncurath and Doerk prepared and characterized 45 amides derived ftom reaction of the reagent with primary and secondary ninines. The amides have excellent crystallizing properties and absorb at 3)6-337 ro/a with high extinction coefflclanti. 

Properties Light-colored crystals. Insoluble in water. Temperature of dehydration is approximately 140C. 

Properties Colorless, white, and various-colored crystals vitreous to earthy luster good cleavage in three directions. D 2.72, Mohs hardness 2. May contain small amounts of magnesium, iron, manganese, and zinc. Reacts with acids to evolve carbon dioxide. 

Properties Cream-colored crystals. Mp 246.0C. Sodium salt is soluble in water. 

Properties Colored crystals. Mp 32.1C, bp 220C. Hazard Toxic by ingestion and inhalation. 

Properties Rose-colored crystals, almost white when precipitated. D 3.125, mp (decomposes). Soluble in dilute inorganic acids almost insoluble in common organic acids both concentrated and dilute, insoluble in water. 

Properties Rose-colored crystals deliquescent. D (1) 2.98, (2) 1.913 mp (1) 650C, (2) 87.5C bp (1) 1190C. Very soluble in water soluble in alcohol insoluble in ether. Noncombustible. 

Properties Slate-colored crystals. Soluble in alkali. Combustible. 

Properties Buff-colored crystals. Mp 138C. Insoluble in water soluble in acetone and benzene. Combustible. 

Properties Dark-colored crystals (the octahedral form in which the atoms have the diamond arrangement). The amorphous form is a dark-brown powder (see silicon, amorphous). D 2.33, mp 1410C, bp 2355C, Mohs hardness 7, dielectric constant 12, coordination number 6. Soluble in a mixture of nitric and hydrofluoric acids and in alkalies insoluble in water, nitric acid, and hydrochloric acid. Combines with oxygen to form tetrahedral molecules in which one silicon atom is surrounded by four oxygen atoms. In this respect it is similar to carbon. It is also capable of forming -Si=Si- double bonds in orga-nosilicon compounds. 

Impurities give gemstones their color Crystals have fascinating properties. A clear, colorless quartz crystal is pure silicon dioxide (Si02). But a crystal that is colorless in its pure form may exist as a variety of colored gemstones when tiny amounts of transition element compounds, usually oxides, are present. Amethyst (purple), citrine... 

Changes in physicochemical properties of the drug substance (e.g., color, crystal modification) may take place upon irradiation. Efforts should be made to observe such changes during the in vitro assay. The sample absorption spectrum should be recorded before and after irradiation surface color of solid samples should be evaluated by appropriate methods and the identity of the sample crystal modification should be confirmed when the drug is irradiated in the solid state. The humidity in the test chamber can influence the photochemical stability of certain solid samples, as demonstrated for mefloquine. The photoinduced yellowing of uncoated mefloquine tablets is accelerated by an increase in humidity. These tablets are mainly used in tropical countries and the real in-use conditions will include high relative humidity. In such cases, the influence of the humidity on the photostability must be taken into account (Tpnnesen et al., 1997). 

PHYSICAL PROPERTIES black to steel-gray, lustrous crystals or black-brown amorphous powder dark-colored crystals are of the octahedral form, in which the atoms have a diamond arrangement practically insoluble in water, nitric acid, and hydrochloric acid soluble in hydrofluoric acid or in a mixture of nitric and hydrofluoric acids also soluble in molten alkali oxides MP (MIO C, 2570°F) BP (2355 C, 4271 F) DN (2.33 g/cm at 25 C) SG (2.33) CP (20.0 J/K-mol crystal at 25°C) VD (NA) VP (approximately 0 mmHg at 20°C, 1 mmHg at 1724 C) MOHS HARDNESS (7.0). 

Formula ReLmolar mass M) wt.% Ti Color, crystal lattice structure, space group (SG), Pearson symbol, lattice parameters, physical properties... 

Crystal Field Splitting in Octahedral Complexes Color Magnetic Properties Tetrahedral and Square-Planar Complexes... 

Polarizability Crystal habit -potential Color / optical properties... 

For this red perylene, the molecules exhibit slight twisting. Perylenes are not so well understood that complete correlation of structure with color property relationships is yet possible. The best treatment of this topic however is found in a recent review paper on the eftect of crystal structure on the color application properties of organic pig-ments. A number of computer simulations and theoretical studies on the crystal packing of perylene pigments have also been published l... 

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