Aurophilicity
Encyclopedia
In chemistry
, aurophilicity refers to the tendency of gold
complex
es to aggregate via formation of weak gold-gold bonds.
for Au(I) compounds. The aurophilic bond has a length of about 3.0 Å
and a strength of about 7-12 kcal/mol, which is comparable to the strength of a hydrogen bond
. The aurophilic interaction is thought to result from electron correlation of the closed-shell components, which is unusual in light of the fact that closed-shell atoms generally have negligible interaction with one another at distances on the scale of the Au-Au bond. This is somewhat similar to van der Waals interactions, but is unusually strong due to relativistic effects
. Observations and theory show that, on average, 28% of the binding energy in aurophilic interaction can be attributed to relativistic expansion of the gold d orbitals
.
Another important feature of aurophilicity is the propensity of gold atoms to aggregate around nucleation
sites—specifically, though not limited to, ligands that bind through phosphorus
, nitrogen
, and sulfur
centers. While both intra- and inter-molecular aurophilic interactions exist, only intramolecular aggregation has been observed at such nucleation sites.
bonding and aurophilic interaction has proven to be a convenient tool in the field of polymer
chemistry. There has been much research into self-assembling supermolecular structures, both those that aggregate by aurophilicity alone and those that contain both aurophilic and hydrogen-bonding interactions. An important and exploitable property of aurophilic interactions relevant to their supermolecular chemistry is that while both inter- and intramolecular interactions are possible, intermolecular aurophilic linkages are comparatively weak and easily broken by solvation
; most complexes that exhibit intramolecular aurophilic interactions retain such moieties in solution.
....
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, aurophilicity refers to the tendency of gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
complex
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...
es to aggregate via formation of weak gold-gold bonds.
Overview
The phenomenon of aurophilicity is most commonly observed crystallographicallyCrystallography
Crystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.Before the development of...
for Au(I) compounds. The aurophilic bond has a length of about 3.0 Å
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
and a strength of about 7-12 kcal/mol, which is comparable to the strength of a hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
. The aurophilic interaction is thought to result from electron correlation of the closed-shell components, which is unusual in light of the fact that closed-shell atoms generally have negligible interaction with one another at distances on the scale of the Au-Au bond. This is somewhat similar to van der Waals interactions, but is unusually strong due to relativistic effects
Relativistic quantum chemistry
Relativistic quantum chemistry invokes quantum chemical and relativistic mechanical arguments to explain elemental properties and structure, especially for heavy elements of the periodic table....
. Observations and theory show that, on average, 28% of the binding energy in aurophilic interaction can be attributed to relativistic expansion of the gold d orbitals
Electron configuration
In atomic physics and quantum chemistry, electron configuration is the arrangement of electrons of an atom, a molecule, or other physical structure...
.
Another important feature of aurophilicity is the propensity of gold atoms to aggregate around nucleation
Nucleation
Nucleation is the extremely localized budding of a distinct thermodynamic phase. Some examples of phases that may form by way of nucleation in liquids are gaseous bubbles, crystals or glassy regions. Creation of liquid droplets in saturated vapor is also characterized by nucleation...
sites—specifically, though not limited to, ligands that bind through phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, and sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
centers. While both intra- and inter-molecular aurophilic interactions exist, only intramolecular aggregation has been observed at such nucleation sites.
Applications
The similarity in strength between hydrogenHydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
bonding and aurophilic interaction has proven to be a convenient tool in the field of polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
chemistry. There has been much research into self-assembling supermolecular structures, both those that aggregate by aurophilicity alone and those that contain both aurophilic and hydrogen-bonding interactions. An important and exploitable property of aurophilic interactions relevant to their supermolecular chemistry is that while both inter- and intramolecular interactions are possible, intermolecular aurophilic linkages are comparatively weak and easily broken by solvation
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
; most complexes that exhibit intramolecular aurophilic interactions retain such moieties in solution.
....