Croconate violet
Encyclopedia
Croconate violet or 1,3-bis(dicyanomethylene)croconate is a divalent
anion with chemical formula
or ((N≡C-)2C=)2(C5O3)2−. It is one of the pseudo-oxocarbon anion
s, as it can be described as a derivative of the croconate
oxocarbon anion
through the replacement of two oxygen
atoms by dicyanomethylene group
s =C(-C≡N)2. Its systematic name is 3,5-bis(dicyanomethylene)-1,2,4-trionate. The term croconate violet as a dye name specifically refers to the dipotassium
salt .
in 1978. He obtained the potassium salt by treating dipotassium croconate with malononitrile
in water solution at 80–90 °C. The dipotassium salt crystallyzes from water as a dihydrate
in deep blue metallic needles. The water solutions have an intense violet color and strongly stain the skin.
. It is an orange crystalline solid that melts at 260–270°C and dissolves in water to give violet skin-staining solutions. It strongly acidic (pK1 = 0.32 ± 0.02, pK2 = 1.02 ± 0.02). From this acid other alkali metal
salts can be prepared. The acid cannot be prepared directly from croconic acid
and malononitrile; croconate blue
is obtained instead.
s with strong absorptions in the UV-Vis region. Solutions of the acid or of the dipotassium salt strongly stain the skin. It retains the aromatic character and some other properties of the croconate anion.
Croconate violet salts also have interesting electrochemical, semiconducting and photophysical properties, and have been the subject of research in supramolecular chemistry
. The dipotassium salt for example is a semiconductor with electrical conductivity 0.0002 Ω
-1 cm-1.
The lithium
salt is very soluble in water. The rubidium
salt and the mixed rubidium-potassium
salt crystallyze as deep blue dihydrates
in the triclinic space group
, with the same structure. In these solids the croconate violet anion is almost planar, with the dicyano methylene groups slightly twisted out of the mean plane. The aromatic character of the croconate core is retained or even enhanced, with strongly delocalized π electrons
. The tetra-n-butylammonium salt (N4)2 is an anhydrous metallic green solid, stable to 225°C, that is highly soluble in organic solvents (in contrast to the dipotassium salt).
The mixed salts of potassium and of certain trivalent lanthanide
s cations (lanthanum
, neodymium
, gadolinium
, and holmium
) exhibit some degree of π-stacking interactions; namely, the π electrons of the croconate rings in one layer form weak bonds with those in the adjacent layers. In the anhydrous tetrabutylammonium salt the anions are separated by more than 12 Å and no π-stacking occurs.
Valence (chemistry)
In chemistry, valence, also known as valency or valence number, is a measure of the number of bonds formed by an atom of a given element. "Valence" can be defined as the number of valence bonds...
anion with chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
or ((N≡C-)2C=)2(C5O3)2−. It is one of the pseudo-oxocarbon anion
Pseudo-oxocarbon anion
In chemistry, the term pseudo-oxocarbon anion is used to refer to a negative ion that is conceptually derived from an oxocarbon anion through replacement of one or more of the basic oxygen atoms by chemically similar elements or functional groups, such as sulfur , selenium , or dicyanomethylene...
s, as it can be described as a derivative of the croconate
Croconic acid
Croconic acid or 4,5-dihydroxycyclopentenetrione is a chemical compound with formula C5H2O5 or 32. It has a cyclopentene backbone with two hydroxyl groups adjacent to the double bond and three ketone groups on the remaining carbon atoms...
oxocarbon anion
Oxocarbon anion
In chemistry, an oxocarbon anion is a negative ion consisting solely of carbon and oxygen atoms, and therefore having the general formula CxOyn− for some integers x, y, and n....
through the replacement of two oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
atoms by dicyanomethylene group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...
s =C(-C≡N)2. Its systematic name is 3,5-bis(dicyanomethylene)-1,2,4-trionate. The term croconate violet as a dye name specifically refers to the dipotassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
salt .
History and synthesis
The anion was syntesized and characterized by A. FatiadiAlexander J. Fatiadi
Alexander J. Fatiadi is a chemist.He obtained his masters from the George Washington University, Washington DC . He has worked at the National Bureau of Standards.-Selected publications:...
in 1978. He obtained the potassium salt by treating dipotassium croconate with malononitrile
Malononitrile
Malononitrile, also propanedinitrile, is a nitrile, with formula CH22. Malononitrile is relatively acidic, with an pKa of 11 in water...
in water solution at 80–90 °C. The dipotassium salt crystallyzes from water as a dihydrate
Hydrate
Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
in deep blue metallic needles. The water solutions have an intense violet color and strongly stain the skin.
Croconic acid violet
The croconate violet anion is the conjugate base of the acid croconic acid violet , also obtained by Fatiadi in 1978 by treating the potassium salt with hydrochloric acidHydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
. It is an orange crystalline solid that melts at 260–270°C and dissolves in water to give violet skin-staining solutions. It strongly acidic (pK1 = 0.32 ± 0.02, pK2 = 1.02 ± 0.02). From this acid other alkali metal
Alkali metal
The alkali metals are a series of chemical elements in the periodic table. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, along with hydrogen. The alkali metals are lithium , sodium , potassium , rubidium , caesium , and francium...
salts can be prepared. The acid cannot be prepared directly from croconic acid
Croconic acid
Croconic acid or 4,5-dihydroxycyclopentenetrione is a chemical compound with formula C5H2O5 or 32. It has a cyclopentene backbone with two hydroxyl groups adjacent to the double bond and three ketone groups on the remaining carbon atoms...
and malononitrile; croconate blue
Croconate blue
Croconate blue or 1,2,3-triscroconate is a divalent anion with chemical formula or 32−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the croconate oxocarbon anion through the replacement of three oxygen atoms by dicyanomethylene groups =C2...
is obtained instead.
Properties
Croconate violet salts are dyeDye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
s with strong absorptions in the UV-Vis region. Solutions of the acid or of the dipotassium salt strongly stain the skin. It retains the aromatic character and some other properties of the croconate anion.
Croconate violet salts also have interesting electrochemical, semiconducting and photophysical properties, and have been the subject of research in supramolecular chemistry
Supramolecular chemistry
Supramolecular chemistry refers to the area of chemistry beyond the molecules and focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components...
. The dipotassium salt for example is a semiconductor with electrical conductivity 0.0002 Ω
Ohm
The ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...
-1 cm-1.
The lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
salt is very soluble in water. The rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...
salt and the mixed rubidium-potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
salt crystallyze as deep blue dihydrates
Hydrate
Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
in the triclinic space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
, with the same structure. In these solids the croconate violet anion is almost planar, with the dicyano methylene groups slightly twisted out of the mean plane. The aromatic character of the croconate core is retained or even enhanced, with strongly delocalized π electrons
Pi bond
In chemistry, pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital...
. The tetra-n-butylammonium salt (N4)2 is an anhydrous metallic green solid, stable to 225°C, that is highly soluble in organic solvents (in contrast to the dipotassium salt).
The mixed salts of potassium and of certain trivalent lanthanide
Lanthanide
The lanthanide or lanthanoid series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium...
s cations (lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
, neodymium
Neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
, gadolinium
Gadolinium
Gadolinium is a chemical element with the symbol Gd and atomic number 64. It is a silvery-white, malleable and ductile rare-earth metal. It is found in nature only in combined form. Gadolinium was first detected spectroscopically in 1880 by de Marignac who separated its oxide and is credited with...
, and holmium
Holmium
Holmium is a chemical element with the symbol Ho and atomic number 67. Part of the lanthanide series, holmium is a rare earth element. Its oxide was first isolated from rare earth ores in 1878 and the element was named after the city of Stockholm....
) exhibit some degree of π-stacking interactions; namely, the π electrons of the croconate rings in one layer form weak bonds with those in the adjacent layers. In the anhydrous tetrabutylammonium salt the anions are separated by more than 12 Å and no π-stacking occurs.
See also
- 2-(dicyanomethylene)croconate2-(Dicyanomethylene)croconate2-croconate is a divalent anion with chemical formula or 2−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the croconate oxocarbon anion through the replacement of one oxygen atom by a dicyanomethylene group =C2.The anion was syntesized and...
- Croconate blueCroconate blueCroconate blue or 1,2,3-triscroconate is a divalent anion with chemical formula or 32−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the croconate oxocarbon anion through the replacement of three oxygen atoms by dicyanomethylene groups =C2...
, 1,2,3-tris(dicyanomethylene)croconate - 1,2-bis(dicyanomethylene)squarate1,2-Bis(dicyanomethylene)squarate1,2-Bissquarate is a divalent anion with chemical formula or 22−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the squarate oxocarbon anion through the replacement of two adjacent oxygen atoms by dicyanomethylene groups =C2.The anion can be obtained...
- 1,3-bis(dicyanomethylene)squarate1,3-Bis(dicyanomethylene)squarate1,3-Bissquarate is a divalent anion with chemical formula or 22−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the squarate oxocarbon anion through the replacement of two opposite oxygen atoms by dicyanomethylene groups =C2.The anion can be obtained...