Coordination compounds coordinate-covalent bonds

Amine—borane adducts have the general formula R3N BX where R = H, alkyl, etc, and X = alkyl, H, halogen, etc. These compounds, characterized by a coordinate covalent bond between boron and nitrogen, form a class of reducing agents having a broad spectmm of reduction potentials (5). 

The hydrated ion [Cu(H20)6]2+ is an example of a complex, a species consisting of a central metal atom or ion to which a number of molecules or ions are attached by coordinate covalent bonds. A coordination compound is an electrically neutral compound in which at least one of the ions present is a complex. However, the terms coordination compound (the overall neutral compound) and complex (one or more of the ions or neutral species present in the compound) are often used interchangeably. Coordination compounds include complexes in which the central metal atom is electrically neutral, such as Ni(CO)4, and ionic compounds, such as K4[Fe(CN)6]. 

In the formation of certain compounds a covalent bond can be formed in which both of the shared electrons come from only one of the atoms. These bonds are called coordinate covalent bonds. Let s examine the formation and bond structure of the NH ion which contains a coordinate covalent bond. 

B) In this case, a lone electron pair on oxygen forms a bond to Ff. A coordinate covalent bond (also known as a dative covalent bond) is a special type of covalent bond in which the shared electrons come from one of the atoms only. After the bond has been formed, its strength is no different from that of a covalent bond. Coordinate covalent bonds are formed when a Lewis base (an electron donor) donates a pair of electrons to a Lewis acid (an electron accepter) the resultant componnd is then called an addnct (a compound formed by the addition reaction between two molecules). The process of forming a dative bond is called coordination. 

Boron can complete its octet if another atom or ion with a lone pair of electrons forms a bond by providing both of the electrons. A bond in which both electrons come from one of the atoms is called a coordinate covalent bond. For example, the tetrafluoroborate anion, BF4 (38), forms when boron trifluoride is passed over a metal fluoride. In this anion, the formation of a coordinate covalent bond gives the B atom an octet. Another example of the formation of a coordinate covalent bond is the compound formed when boron trifluoride reacts with ammonia ... 

Boron trifluoride reacts with dimethyl ether to form a compound with a coordinate covalent bond ... 

The solubility of an ionic compound increases dramatically if the solution contains a Lewis base that can form a coordinate covalent bond (Section 7.5) to the metal cation. Silver chloride, for example, is insoluble in water and in acid, but it dissolves in an excess of aqueous ammonia, forming the complex ion Ag(NH3)2 + (Figure 16.13). A complex ion is an ion that contains a metal cation bonded to one or more small molecules or ions, such as NH3, CN-, or OH-. In accord with Le Chatelier s principle, ammonia shifts the solubility equilibrium to the right by tying up the Ag+ ion in the form of the complex ion ... 

In this chapter, we ll look at the properties and chemical behavior of transition metal compounds, paying special attention to coordination compounds, in which a central metal ion (or atom)—usually a transition metal—is attached to a group of surrounding molecules or ions by coordinate covalent bonds (Section 7.5). 

B is correct. Amines (—NH2) behave as weak Lewis bases and are most similar to ammonia (NH3). A Lewis base is any species that can donate a pair of electrons and form a coordinate covalent bond. Amides contain a carbonyl carbon and therefore are not similar to ammonia. Ether and ethanol are not nitrogen-containing compounds. 

A is correct. Sodium chloride is a protolypic example of an ionic bond. In a coordinate covalent bond, both shared electrons come from the same atom for instance, a Lewis base (i.e., ammonia) or oxygen-containing compound (i.e., water). Although both shared electrons come from the same atom, a coordinate covalent bond is a single bond similar in chemical properties to a covalent bond. 

Dative covalent bonds, or coordinate covalent bonds, are those in which electrons are shared (as in all covalent bonds), but in which both electrons involved in each bond are contributed from the same atom. Such bonds occur in organometallic compounds of transition metals having vacant d orbitals. It is beyond the scope of this book to discuss such bonding in detail the reader needing additional information should refer to works on organometallic compounds.12 The most common organometallic compounds that have dative covalent bonds are carbonyl compounds, which are formed from a transition metal and carbon monoxide, where the metal is usually in the -1, 0, or +1 oxidation state. In these compounds the carbon atom on the carbon monoxide acts as an electron-pair donor ... 

The products of acid-base interactions such as those shown in Equations (5.36) through (5.39) are not properly considered as salts because they are not ionic compounds. Because in many cases these products are formed from two neutral molecules, they are more properly considered as addition compounds or adducts held together by the formation of coordinate covalent bonds. In that connection, they are similar to coordination compounds except that the latter ordinarily involve the formation of coordinate bonds to metal ions by the electron donors ligands). There are some useful generalizations that correlate to the stability of bonds during this type of acid-base interaction, and these are largely summarized by the hard-soft acid-base principle. 

These two compounds have coordinate covalent bonds. 

Hybridization can also help explain the existence and structure of many inorganic molecular ions. Consider, for example, the zinc compounds shown here. At the top is shown the electron configuration of atomic zinc, and just below it, of the divalent zinc ion. Notice that this ion has no electrons at all in its 4-shell. In zinc chloride, shown in the third row, there are two equivalent chlorine atoms bonded to the zinc. The bonding orbitals are of sp character that is, they are hybrids of the 4s and one 4p orbital of the zinc atom. Since these orbitals are empty in the isolated zinc ion, the bonding electrons themselves are all contributed by the chlorine atoms, or rather, the chlor ide ions, for it is these that are the bonded species here. Each chloride ion possesses a complete octet of electrons, and two of these electrons occupy each sp bond orbital in the zinc chloride complex ion. This is an example of a coordinate covalent bond, in which the bonded atom contributes both of the electrons that make up the shared pair. 

The use of transition metals or transition metal clusters to act as nodes for the modular self-assembly of diamondoid networks that are sustained by coordinate covalent bonds is also well established. Such architectures are of more than aesthetic appeal. Indeed, such structures have resulted in a class of compound with very interesting bulk and functional properties. Metal-organic diamondoid structures in which the spacer moiety has no center of inversion are predisposed to generate polar networks since there would not be any inherent center of inversion. Pyridine-4-carboxylic acid is such a ligand and bis(isonicotinato)zinc exists as a three-fold diamondoid structure that is thermally stable and inherently polar.33... 

When a molecular addition compound is formed from BF3 and a Lewis base, energy associated with the 7r-bond in the BF3 molecule is absorbed, and energy associated with the coordinate covalent bond in... 

The name coordination compound comes from the coordinate covalent bond, which historically was considered to form by donation of a pair of electrons from one atom to another. Because these compounds are usually formed by donation of electron pairs of ligands to metals, the name is appropriate. Coordinate covalent bonds are identical to covalent bonds formally formed by combining one electron from each atom only the formal electron counting distinguishes them. Coordination compounds are also acid-base adducts, as described in Chapter 6, and are frequently called complexes or, if charged, complex ions. 

A total of six electrons is shared by the boron atom, which is two less than the number needed for an octet. Such compounds tend to be reactive and can share an entire pair of electrons donated by another atom. When one atom donates a pair of electrons to be shared with an atom or ion that needs two electrons to become stable, a coordinate covalent bond forms, as in Figure 9-12. Atoms or ions with lone pairs often form coordinate covalent bonds with atoms or ions that need two more electrons. 

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