Coordinate covalent bonds structure

The Lewis structure of the product, a white molecular solid, is shown in (32). In this reaction, the lone pair on the nitrogen atom of ammonia, H3N , can be regarded as completing boron s octet in BF3 by forming a coordinate covalent bond. 

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. 

In the NHaCI structure while the NHt ion contains four covalent bonds (1 coordinate covalent bond and 3 polar covalent bonds) there is an ionic bond between the NH and Cl ions. 

FIGURE 5.16 The electron dot structure of a nitrogen atom (left) and an ammonia molecule (right). The pair of electrons above the nitrogen is the nonbonding pair available for coordinate covalent bonding. 

PROBLEM 7.5 Draw an electron-dot structure for the hydronium ion, H30 +, and show how a coordinate covalent bond is formed by the reaction of H20 with H +. 

The electrons of an electron-pair bond need not be contributed by both of the bonding atoms, as is demonstrated in the formation of the ammonium ion by the addition of a proton to ammonia. The Lewis structures for these two entities are shown in Fig. 9-13 recall that H+ has no electrons. Such a bond is often called a coordinate covalent bond, but is essentially no different from any other covalent bond. The special name indicates that one of the members of the bond brings to the process of bonding any electrons. In this particular case, once the bond has formed, it becomes indistinguishable from the other three N—H bonds in the molecule with the structure being a regular tetrahedron. 

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... 

We shall now focus upon 2D and 3D structures that will be oiganized by dimensionality of architecture and chemical components and draw mineralomimetic analogies. In terms of chemical composition, we shall focus upon purely organic networks, which are typically sustained by hydrogen bonds and stacking interactions, and metal-oiganic structures that are based upon coordinate covalent bonds. 

Since Cu ions on the zeolite surface exist in an isolated environment, they may interact with the sulfate species on the catalysts deactivated by SOj. The sulfate groups might partially surround the copper ions, as previously supested by Choi et al. [37] and Hamada et al. [38]. The sulfate may also have some characteristics of a coordinate covdent bond, where Cu ions and sulfate species may act as a Lewis acid and base, respectively [39], Ligands such as HjO, NHj, (C2Hj)3P, CO molecules and Cf, CN, OH , NOj, and C204 ions should at least contain a lone pair of electron to form a coordinate covalent bond between metal ions [40]. It should be noted that the sulfate catalyst species formed on the catalysts deactivated by SO2 contains lone electron pairs on O atoms which surround S atom of SO4 groups. Therefore, it is expected that the electrostatic interaction between Cu ions and sulfate species probably influences the local structure of Cu ions on the zeolite catalyst surface. 

In Section 8-5 we found that gaseous BeCb is linear. The Be atoms in BeC molecules, however, act as Lewis acids. In the solid state, the Cl atoms form coordinate covalent bonds to Be, resulting in a polymeric structure. In such compounds. Be follows the octet rule. 

Structure of the cobalamin family of compounds. A through D are the four rings in the corrinoid ring system. The B ring is important for cobalamin binding to intrinsic factor. If R = -CN, the molecule is cyanocobalamin (vitamin B12) if R = 5 -deoxyadenosine, the molecule is adenosylcobalamin if R = -CH3, the molecule is methylcobalamin. Arrows pointing toward the cobalt ion represent coordinate-covalent bonds. 

Complete the Lewis structure and indicate the coordinate covalent bonds in the molecule. 

Simplified structures of the porphine molecule and the Fe porphyrin complex. The dashed lines represent coordinate covalent bonds. 

The porphyrin structure in chlorophyll. The dotted lines indicate the coordinate covalent bonds. The electron-delocalized portion of the molecule is shown in color. 

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