Dative form

The frontier orbitals, and for M and C(lp) and CO(tv ) for CO, dominate the M-CO bonding. As shown in Fig. 4.1a and b, both C and O are sp hybridized in free CO. The singly occupied sp and orbitals on each atom form a a and a tv bond, respectively. This leaves carbon Py empty, and oxygen Py doubly occupied, and so the second tv bond is dative, formed by transfer of the 0 py) lone pair to the empty C py) orbital. This transfer leads to a C -0+ polarization of the molecule, which is almost exactly balanced by a partial C+-0 polarization of all three bonding orbitals because of the higher electronegativity of oxygen. The free CO molecule therefore has a triple bond and a net dipole moment very close to zero. 

The other cases are either the same as the corresponding nominative or formed from it, as follows genitive singular, -en, -ens. -es, -n, -ns, or -s dative and accusative singular and dative plural, -n or -en. 

However, upon terminating chains with thiols, sulphur centered low-molecular weight radicals are formed that are able to start a polymerization of the remaining monomer B. Therefore, formation of homopolymer consisting of B is inevitable if thiols are used. A suitable alternative to the classical transfer additives are degra-dative chain transfer agents, such as allylmalonic acid... 

With eight outer electrons in the formally neutral atom, iron needs to acquire an electron to achieve covalence. Often the ninth electron is obtained from a carbonyl group forming a dative single covalent bond, Fe —CO+. The Fe(CO)3 group then involves five of the nine bonds formed by the iron atom, the bond number of the iron-carbonyl bonds being 1.67, and the iron atom forms four other bonds. If the added electron... 

In contrast, reaction of ligand 72 with 4,4 -biphenyldiboronic acid has been successful and diboronate 73 is obtained in yields of 33%. This complex acts as a receptor for the paraquat dication forming a 1 1 complex with an association constant of 320 in acetone. The intermolecular forces responsible for the complexation are ion-dipole stabilization between the dative N B dipoles and the two cationic centers in paraquat, attractive tz-tz interactions between... 

These d indices for cations and anions relevant to AB cements are shown in Table 2.5. Bases which add on through F or O and do not form i-bonds have similar hardness values they are hard bases. Soft bases form dative 7i-bonds with many cations. They have high-energy-level occupied orbitals with unshared electron pairs. 

Acyclic phosphazenes (phosphazo derivatives, phosphine imines, phosphoranimines) continue to attract interest. A review of the three coordinate materials, RN=PR =X has appeared. " Several molecular orbital calculations have been reported. An ab initio treatment of the PN energy surface suggests that this species is best regarded as having a dative phosphorus-nitrogen double bond rather than a triple bond and the phosphonitrene, once formed,... 

We should note that the formation of this bond confers formal charges on the B and N atoms. In this bond and many similar Lewis acid-base complexes both the electrons forming the bond come from the same atom rather than from different atoms, as in the formation of a bond between two chlorine atoms. This type of bond is often called a donor-acceptor bond, a dative bond, or a coordinate bond, and is sometimes given a special symbol—an arrow denoting the direction in which the electron pair is donated ... 

Reaction of 137 with [NBri4][SCN] leads to formation of the anionic complex [137-SCN]-, which adopts a multidecker structure with the anion sandwiched between successive molecules of 137 (Figure 13).212 The sulfur atoms of the SCN- ion in [ 137-SCN]- interacts unsymmetrically with the mercury atoms of the neighboring molecules of 137 forming four short Hg-S bonds that range from 3.06(1) to 3.36(1) A and two long bonds of 3.74(1) and 3.87(1) A. While the longer Hg-S bonds approach the limit for the involvement of dative interactions, the shorter ones are comparable to those observed in [163-SCN]. ... 

Thiol-containing molecules can interact with metal ions and metal surfaces to form dative bonds. Dative bonds also are known as coordinate covalent bonds. They differ from normal... 

Figure 9.60 Many different thiol-containing linkers can be used to prepare water-soluble QDs. The monothiol compounds suffer from the deficiency of being easily oxidized or displaced off the surface, thus creating holes for potential nonspecific binding. The dithiol linkers are superior in this regard, as they form highly stable dative bonds with the semiconductor metal surface that do not get displaced. The PEG-based linkers are especially effective at creating a biocompatible surface for conjugation with biomolecules.

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