Covalent bonds, dative

A dative covalent bond, or co-ordinate bond, is a covalent bond in which both of the shared pair of electrons come from the same atom. 

Examples The following compounds and species are examples of dative covalent bonding. 

The water molecules are bonded to the central Mn2+ cation via dative covalent bonds from the lone pair on the oxygen atom into empty orbitals in the metal ion. 

The original concepts of metal-ligand bonding were essentially related to the dative covalent bond the development of organometallic chemistry has revealed a further way in which ligands can supply more than one electron pair to a central atom. This is exemplified by the classical cases of bis(benzene)chromium and bis(cyclopentadienyl)iron, trivial name ferrocene. These molecules are characterised by the bonding of a formally unsaturated system (in the organic chemistry sense, but expanded to include aromatic systems) to a central atom, usually a metal atom. 

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. 

Classical coordination chemistry has been developed in terms of the traditional ligands1,2 such as water, ammonia and the chloride anion, all of which contain at least one lone pair of electrons which may be used in the coordination of the ligand to a metal by the formation of a dative covalent bond. 

Organometallic Compounds with Dative Covalent Bonds... 

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 ... 

A dative covalent bond Is just an ordinary 0 bond whose electrons happen to come from one atom. Most bands are formed by electron donation from one atom to another and a classification that makes it neosssary to know the history of the molecule is not useful. Forget dative bonds and stick to o bonds qr it bonds. 

The kind of bond formed in these two reactions used to be called a dative covalent bond because both electrons in the bond were donated by the same atom. We no longer classify bonds in this way, but call them o bonds or it bonds as these are the fundamentally different types of bonds in organic compounds. Most new bonds are formed by donation of both electrons from one atom to another. 

A neutron diffraction study of this compound has also been made. Since OH or Cl together provide 5 electrons (one normal and two dative covalent bonds) Pt acquires the same electronic structure as in PtCll... 

In this addition compound, the N to B bond is referred to as a dative covalent bond, as although the two-electron pair bond is indistinguishable for a normal shared electron pair bond, the source of the electron pair is from one of the atoms of the bond and not equally from both. 

This donor function of a lone pair of electrons is quite common and occurs in coordination complexes of the transition metal ions, such as [Ni(NH3)JS04, [Mn(0H2)6]S04 and [Fe(0H2)JS04. In such complexes the NH3 and OH2 ligands share their lone pairs with the respective metal cations by dative covalent bond formation, a function in which they are said to act as ligands. In both of these complexes, the six-coordinated metal cations are referred to as coordination complexes, which are significantly stabilised by this process and can maintain their identity, even when dissolved in water. 

Dative covalent bonding wherein a similar electron shared bond occurs but all of the electrons are provided by the atom at one end of the bond. 

The bonding to transition metal ions has been described in the previous section as being predominantly that of dative covalent bonding whereby lone pairs of electrons are donated into vacant orbitals of the transition series metal ions. It was established by Werner that these bonds are directional in nature and have certain preferred angles subtended at the central metal ion. 

Figure 7.1 Complex formed between hexadentate EDTA anion and an octahedral six-coordinate metal ion". The six dative covalent bonds point towards the comers of a regular octahedron. The complex ion formed will, in all probability, be water soluble because of the residual negative charge left on the complex, i.e. (4-n) , becoming aquated...

Coordination chemistry is the study of coordination compounds or, as they are often defined, coordination complexes. These entities are distinguished by the involvement, in terms of simple bonding concepts, of one or more coordinate (or dative) covalent bonds, which differ from the traditional covalent bond mainly in the way that we envisage they are formed. Although we are most likely to meet coordination complexes as compounds featuring a metal ion or set of metal ions at their core (and indeed this is where we will overwhelmingly meet examples herein), this is not strictly a requirement, as metalloids may also form such compounds. One of the simplest examples of formation of a coordination compound comes from a now venerable observation - when BF3 gas is passed into a liquid trialkylamine, the two react exothermally to generate a solid which contains... 

In hydrated cations, such as [Mg(H20)6] , the water molecules are bonded to the magnesium ion by dative covalent bonds. Each oxygen atom bonds with its lone pair into empty s and p orbitals in the Mg ion. 

Bonding in complex ions. The simplest view is that the ligands form dative covalent bonds by donating a lone pair of electrons into empty orbitals of the transition metal ion. These could be empty 3d, 4s, 4p or 4d orbitals in the ion (e.g. see the arrangement of electrons in boxes in Figure 5.3). 

An L-function ligand is one which interacts with a metal center via a dative covalent bond (i.e. a coordinate bond), in which both electrons are donated by the L ligand. As such, an L-function ligand donates two electrons to a metal center. Since the metal uses no electrons in forming the M-L bond, an L-function ligand does not influence the valence of a metal center. Simple examples of L-type ligands include R3P, R2O, and CO, i.e. donor molecules that have lone pairs (Lewis bases). 

In a further generalization, Lewis [4] advanced a definition that was no longer restricted to proton-exchange reactions. An acid was defined as any substance that can accept a pair of electrons from a donor substance, and a base as any substance able to donate an electron pair and form a "dative" covalent bond. In these more general terms, the acid-base interaction includes the formation of covalent bonds and applies to any chemical reaction in which an addition compound (adduct) is formed through a coordinative bond ... 

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