Coordinate covalent bonds formation

Reaction (3.94) is an example of general coordinate-covalent-bond formation... 

The pattern of coordinate covalent bond formation, in which one species provides a lone pair and the other species accepts it, is common. For reasons that will soon be explained, the species that provides the lone pair is called a Lewis base, and the species that accepts it is called a Lewis acid. In other words, a Lewis acid is an electron pair acceptor, and a Lewis base is an electron pair donor. The product of the reaction between a Lewis acid and a Lewis base, BF4 in our first example, is called a complex. The form of the reaction is therefore... 

Hence confirmation by another method is very helpful in determining whether a long metal-donor atom contact actually signifies secondary bonding and involves coordinate covalent bond formation. Most spectroscopic methods caimot reliably detect or interpret such subtle bonding interactions, but halogen NQR spectroscopy offers great promise here. 

The ion has a vacant orbital, which accepts a share in the lone pair on nitrogen. The formation of a covalent bond by the sharing of an electron pair that is provided by one atom is called coordinate covalent bond formation. This type of bond formation is discussed again in Chapters 10 and 25. 

These definitions do not specify that an electron pair must be transferred from one atom to another—only that an electron pair, residing originally on one atom, must be shared between two atoms. Neutralization is defined as coordinate covalent bond formation. This results in a covalent bond in which both electrons were furnished by one atom or ion. 

While nonbonded electron pairs in molecules do not enter into covalent bonding in the usual sense, they may exhibit a secondary kind of valency by being transferred into vacant molecular orbitals in suitable acceptor molecules. This results in the transformation of a coordination complex in which the bond formed between the electron-pair donor and the acceptor is said to be a coordinate covalent or dative bond. Brpnsted basicity is the simplest example of coordinate covalent bond formation. A Brpnsted base donates a pair of nonbonded electrons to a vacant Is orbital of a hydrogen ion to form the conjugate acid. The o-bond formed between the base and the hydrogen ion results in the loss of identity of the nonbonded pair previously localized on the base. The formation of coordination complexes has significance in the interpretation of spectra of compounds having nonbonded electron pairs. 

Site of coordinate covalent bond formation (after the bond has formed, the four N-H bonds are indistinguishable)... 

The boron atom in BF5 can complete its octet if an additional atom or ion with a lone pair of electrons forms a bond by providing both 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 (31), forms when boron trifluoride is passed over a meral fluoride. In this anion, the formation of a coordinate covalent bond with a fluoride ion gives the B atom an octet. Another example of a coordinate covalent bond is that formed when boron trifluoride reacts with ammonia ... 

A proton (H+) is an electron pair acceptor. It is therefore a Lewis acid because it can attach to ( accept") a lone pair of electrons on a Lewis base. In other words, a Bronsted acid is a supplier of one particular Lewis acid, a proton. The Lewis theory is more general than the Bronsted-Lowry theory. For instance, metal atoms and ions can act as Lewis acids, as in the formation of Ni(CO)4 from nickel atoms (the Lewis acid) and carbon monoxide (the Lewis base), but they are not Bronsted acids. Likewise, a Bronsted base is a special kind of Lewis base, one that can use a lone pair of electrons to form a coordinate covalent bond to a proton. For instance, an oxide ion is a Lewis base. It forms a coordinate covalent bond to a proton, a Lewis acid, by supplying both the electrons for the bond ... 

To remove an ion, we can use the fact that many metal cations are Lewis acids (Section 10.2). When a Lewis acid and a Lewis base react, they form a coordinate covalent bond and the product is called a coordination complex. In this section, we consider complexes in which the Lewis acid is a metal cation, such as Ag+. An example is the formation of Ag(NI 1,)2+ when an aqueous solution of the Lewis base ammonia is added to a solution of silver ions ... 

The formation of coordinate covalent bonds is described in Sections 2.11 and 10.2. 

In the polyatomic ion the formation of a coordinate covalent bond between nitrogen and hydrogen involves —... 

The basis for the toxicological activity of this substance is the reaction of cobalt ion with cyanide ion to form a relatively nontoxic and stable ion complex. The hexacyanocobaltate ion contains a Co2+ central metal ion with six cyanide ions as ligands. This coordination complex involves six coordinate covalent bonds whereby each cyanide ion supplies a pair of electrons to form each covalent bond with the central cobalt ion. The formation constant for the hexacyanocobaltate ion is even larger than for dicobalt EDTA,3 and thus the cobalt ion preferentially exchanges an EDTA ligand for six cyano ligands ... 

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. 

Define monodentate, bidentate, hexadentate, ligand, complex ion, chelate, chelating agent, masking, masking agent, formation constant, coordinate covalent bond, water hardness, aliquot. 

Lewis (1923) put forward another definition of acids and bases solely dependent on giving or taking of an electron pair. According to Lewis— an add is an electron pair acceptor, whereas a base is an electron pair donor . Therefore, it is obvious that whenever any neutralization occurs the formation of an altogether new coordinate covalent bond between the electron pair donor and acceptor atoms take place. 

Base In chemistry, the nonadd part of a salt a substance that combines with adds to form salts a substance that dissociates to give hydroxide ions in aqueous solutions a substance whose molecule or ion can combine with a proton (hydrogen ion) a substance capable of donating a pair of electrons (to an acid) for the formation of a coordinate covalent bond. [EU]... 

The process of formation of a coordinate-covalent bond the reverse of unimolecular heterolysis. 3. The number of ligands surrounding a central atom. See also... 

The radius ratio is considered important because the central ion must be prevented from rattling around in a cavity (see Orgel, 1966). However, the radius ratio is not a rigorous prognosticator, since the concept applies to hard spheres. It has already been noted that ions may be polarizable and deformable, sometimes with a tendency to directional covalent bond formation. These properties affect models based on hard spheres and the extent to which the radius ratio determines the coordination number of a particular ligand. Thus, .. . we can accept the radius ratio rule as a useful, if imperfect, tool in our arsenal for predicting and understanding the behavior of ionic compounds. (Huheey, 1983). 

Problem 1.11 Each of the following molecules and ions can be thought to arise by coordinate covalent bonding. Write an equation for the formation of each one and indicate the donor and acceptor molecule or ion. (a) NH (6) be, (c) (CH,),OMgCI, (d) Fe(CO), ... 

Salt and chelate formation with edetate (ethylenediaminetetraacetate, EDTA). A In a solution of calcium disodium salt of EDTA, the sodium and hydrogen ions are chemically and biologically available. B In solutions of calcium disodium edetate, calcium is bound by coordinate-covalent bonds with nitrogens as well as by the usual ionic bonds. C In the lead-edetate chelate, lead is incorporated into five heterocyclic rings. 

Association was first thought of as a reversible reaction between like molecules that distinguished it from polymerization, which is not reversible. Association is characterized by reversibility or ease of disassocialion, low energy of formation (usually about 5 and not more than 10 kcal per mole), and the coordinate covalent bond which Lewis called the acid-basc bond. Association takes place between like and unlike species. The most common type of this phenomenon is hydrogen bonding. Association of like species is demonstrable by one or more of the several molecular weight methods. Association between unlike species is demonstrable by deviation of the system from Raoult s law. 

The product elimination step proceeds with cleavage of the catalyst-substrate bonds. This may occur by dissociation, solvolysis, or a coupling of substrate moieties to form the product. The last of these involves covalent bond formation within the product, and corresponds to the microscopic reverse of oxidative addition. Upon reductive elimination both the coordination number and formal oxidation state of the metal complex decrease. In most homogeneous catalytic processes, the product elimination step, while essential, is usually not rate determining. The larger kinetic barriers are more frequently encountered in substrate activation and/or transformation. 

---