A coordination complex consists of a central atom or ion, which is usually metallic and is called the coordination centre, and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents. Many metal-containing compounds, especially those that include transition metals, are coordination complexes.
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs, often through Lewis bases. The nature of metal–ligand bonding can range from covalent to ionic. Furthermore, the metal–ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligands".
In coordination chemistry, a coordinate covalent bond, also known as a dative bond, dipolar bond, or coordinate bond is a kind of two-center, two-electron covalent bond in which the two electrons derive from the same atom. The bonding of metal ions to ligands involves this kind of interaction. This type of interaction is central to Lewis acid–base theory.
In chemistry, a hydride is formally the anion of hydrogen (H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride of nitrogen, etc. For inorganic chemists, hydrides refer to compounds and ions in which hydrogen is covalently attached to a less electronegative element. In such cases, the H centre has nucleophilic character, which contrasts with the protic character of acids. The hydride anion is very rarely observed.
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any species that has a filled orbital containing an electron pair which is not involved in bonding but may form a dative bond with a Lewis acid to form a Lewis adduct. For example, NH3 is a Lewis base, because it can donate its lone pair of electrons. Trimethylborane (Me3B) is a Lewis acid as it is capable of accepting a lone pair. In a Lewis adduct, the Lewis acid and base share an electron pair furnished by the Lewis base, forming a dative bond. In the context of a specific chemical reaction between NH3 and Me3B, a lone pair from NH3 will form a dative bond with the empty orbital of Me3B to form an adduct NH3•BMe3. The terminology refers to the contributions of Gilbert N. Lewis.
In coordination chemistry, the term scorpionate ligand refers to a tridentate (three-donor-site) ligand which would bind to a metal in a fac manner. The most popular class of scorpionates are the hydrotris(pyrazolyl)borates or Tp ligands. These were also the first to become popular. These ligands first appeared in journals in 1966 from the then little-known DuPont chemist of Ukrainian descent, Swiatoslaw Trofimenko. Trofimenko called this discovery "a new and fertile field of remarkable scope".
A three-center two-electron (3c–2e) bond is an electron-deficient chemical bond where three atoms share two electrons. The combination of three atomic orbitals form three molecular orbitals: one bonding, one non-bonding, and one anti-bonding. The two electrons go into the bonding orbital, resulting in a net bonding effect and constituting a chemical bond among all three atoms. In many common bonds of this type, the bonding orbital is shifted towards two of the three atoms instead of being spread equally among all three. Example molecules with 3c–2e bonds are the trihydrogen cation and diborane. In these two structures, the three atoms in each 3c-2e bond form an angular geometry, leading to a bent bond.
Anions that interact weakly with cations are termed non-coordinating anions, although a more accurate term is weakly coordinating anion. Non-coordinating anions are useful in studying the reactivity of electrophilic cations. They are commonly found as counterions for cationic metal complexes with an unsaturated coordination sphere. These special anions are essential components of homogeneous alkene polymerisation catalysts, where the active catalyst is a coordinatively unsaturated, cationic transition metal complex. For example, they are employed as counterions for the 14 valence electron cations [(C5H5)2ZrR]+ (R = methyl or a growing polyethylene chain). Complexes derived from non-coordinating anions have been used to catalyze hydrogenation, hydrosilylation, oligomerization, and the living polymerization of alkenes. The popularization of non-coordinating anions has contributed to increased understanding of agostic complexes wherein hydrocarbons and hydrogen serve as ligands. Non-coordinating anions are important components of many superacids, which result from the combination of Brønsted acids and Lewis acids.
Organoboron chemistry or organoborane chemistry is the chemistry of organoboron compounds or organoboranes, which are chemical compounds of boron and carbon that are organic derivatives of borane (BH3), for example trialkyl boranes..
In chemistry, a dihydrogen bond is a kind of hydrogen bond, an interaction between a metal hydride bond and an OH or NH group or other proton donor. With a van der Waals radius of 1.2 Å, hydrogen atoms do not usually approach other hydrogen atoms closer than 2.4 Å. Close approaches near 1.8 Å, are, however, characteristic of dihydrogen bonding.
Boron compounds are compounds containing the element boron. In the most familiar compounds, boron has the formal oxidation state +3. These include oxides, sulfides, nitrides, and halides.
In chemistry, an ate complex is a salt formed by the reaction of a Lewis acid with a Lewis base whereby the central atom increases its valence and gains a negative formal charge..
The covalent bond classification (CBC) method is also referred to as the LXZ notation. It was published by M. L. H. Green in 1995 as a solution for the need to describe covalent compounds such as organometallic complexes in a way that is not prone to limitations resulting from the definition of oxidation state. Instead of simply assigning a charge to an atom in the molecule, the covalent bond classification method analyzes the nature of the ligands surrounding the atom of interest, which is often a transition metal. According to this method, there are three basic types of interactions that allow for coordination of the ligand. The three types of interaction are classified according to whether the ligating group donates two, one, or zero electrons. These three classes of ligands are respectively given the symbols L, X, and Z.
In chemistry, a boranylium ion is an inorganic cation with the chemical formula BR+
2, where R represents a non-specific substituent. Being electron-deficient, boranylium ions form adducts with Lewis bases. Boranylium ions have historical names that depend on the number of coordinated ligands:
Trihydridoboron, also known as borane or borine, is an unstable and highly reactive molecule with the chemical formula BH
3. The preparation of borane carbonyl, BH3(CO), played an important role in exploring the chemistry of boranes, as it indicated the likely existence of the borane molecule. However, the molecular species BH3 is a very strong Lewis acid. Consequently, it is highly reactive and can only be observed directly as a continuously produced, transitory, product in a flow system or from the reaction of laser ablated atomic boron with hydrogen.
A borylene is the boron analogue of a carbene. The general structure is R-B: with R an organic residue and B a boron atom with two unshared electrons. Borylenes are of academic interest in organoboron chemistry. A singlet ground state is predominant with boron having two vacant sp2 orbitals and one doubly occupied one. With just one additional substituent the boron is more electron deficient than the carbon atom in a carbene. For this reason stable borylenes are more uncommon than stable carbenes. Some borylenes such as boron monofluoride (BF) and boron monohydride (BH) the parent compound also known simply as borylene, have been detected in microwave spectroscopy and may exist in stars. Other borylenes exist as reactive intermediates and can only be inferred by chemical trapping.
The triboracyclopropenyl fragment is a cyclic structural motif in boron chemistry, named for its geometric similarity to cyclopropene. In contrast to nonplanar borane clusters that exhibit higher coordination numbers at boron (e.g., through 3-center 2-electron bonds to bridging hydrides or cations), triboracyclopropenyl-type structures are rings of three boron atoms where substituents at each boron are also coplanar to the ring. Triboracyclopropenyl-containing compounds are extreme cases of inorganic aromaticity. They are the lightest and smallest cyclic structures known to display the bonding and magnetic properties that originate from fully delocalized electrons in orbitals of σ and π symmetry. Although three-membered rings of boron are frequently so highly strained as to be experimentally inaccessible, academic interest in their distinctive aromaticity and possible role as intermediates of borane pyrolysis motivated extensive computational studies by theoretical chemists. Beginning in the late 1980s with mass spectrometry work by Anderson et al. on all-boron clusters, experimental studies of triboracyclopropenyls were for decades exclusively limited to gas-phase investigations of the simplest rings (ions of B3). However, more recent work has stabilized the triboracyclopropenyl moiety via coordination to donor ligands or transition metals, dramatically expanding the scope of its chemistry.
9-borafluorenes are a class of boron-containing heterocycles consisting of a tricyclic system with a central BC4 ring with two fused arene groups. 9-borafluorenes can be thought of as a borole with two fused arene rings, or as a trigonal planar boron atom with an empty p orbital bridging two biphenyl rings. However, 9-borafluorenes are generally less reactive than boroles due to less antiaromatic character and Lewis acidity. Containing highly conjugated π systems, 9-borafluorenes possess interesting photophysical properties. In addition, 9-borafluorenes are good Lewis acids. This combination of properties enables potential uses such as in light-emitting materials, solar cells, and sensors for some molecules.
An N-heterocyclic carbene boryl anion is an isoelectronic structure of an N-heterocyclic carbene (NHC), where the carbene carbon is replaced with a boron atom that has a -1 charge. NHC boryl anions have a planar geometry, and the boron atom is considered to be sp2-hybridized. They serve as extremely strong bases, as they are very nucleophilic. They also have a very strong trans influence, due to the σ-donation coming from the boron atom. NHC boryl anions have stronger electron-releasing character when compared to normal NHCs. These characteristics make NHC boryl anions key ligands in many applications, such as polycyclic aromatic hydrocarbons, and more commonly low oxidation state main group element bonding.
Bismuthinidenes are a class of organobismuth compounds, analogous to carbenes. These compounds have the general form R-Bi, with two lone pairs of electrons on the central bismuth(I) atom. Due to the unusually low valency and oxidation state of +1, most bismuthinidenes are reactive and unstable, though in recent decades, both transition metals and polydentate chelating Lewis base ligands have been employed to stabilize the low-valent bismuth(I) center through steric protection and π donation either in solution or in crystal structures. Lewis base-stabilized bismuthinidenes adopt a singlet ground state with an inert lone pair of electrons in the 6s orbital. A second lone pair in a 6p orbital and a single empty 6p orbital make Lewis base-stabilized bismuthinidenes ambiphilic.
