Cyanide bonding molecular orbitals

It is important to establish the main similarities and differences in the electronic spectra of isoelectronic metal carbonyls and cyanides and to relate these spectral comparisons to the nature of the M-CN and M—CO bonds. In this paper the electronic spectra of d6 metal carbonyls and cyanides are assigned on the basis of a derived molecular orbital energy level scheme. The differences in the energies erf the single electron molecular orbitals for representative metal hexa-carbonyls and hexacyanides are obtained and a general discussion erf electronic structure is presented. 

E20.19 NHj and CN ligands are quite different with respect to the types of bonds they form with metal ions. Ammonia and cyanide ion are both a-bases, but cyanide is also a ii-acid. This difference means that NH3 can form molecular orbitals only with the metal e orbitals, while CN can form molecular orbitals with the metal and t2g orbitals. The formation of molecular orbitals is the way that ligands expand the clouds of the metal d orbitals— the bonding betw een and the ligand has more covalent character in [Co(CN)g) than in [Co(NH3)6]. ... 

Problem 16.1 Hydrogen cyanide, HCN, is isoelectronic with the N2 molecule. The Lewis structure would presumably be H-C=N . Do you expect the molecule to he linear or bent Give a description of the bonding in terms of 2c molecular orbitals. 

The cyanide anion is a weak base, but a good nucleophile. The pfC of HCN is 9.0 and the H-CN bond dissociation energy is 125.5 kcal mol"l CN" is isoelectronic with N and CO and has a C-N bond order of 3. The molecular orbital diagram of CN" is qualitatively similar to that of CO or Nj. This similarity in bond order between CN", N, and CO is supported by infrared and Raman spectroscopic data. The fundamental stretching frequency of a dimethyl-formamide solution of [Etp] [CN]" is 2070 cm"h These values can be compared to the fundamental stretclring frequencies of 2143 and 2330 cm" for CO and N respectively. ... 

Molecular Orbitals for Octahedral Metal Carixmyls and Cyanides.— The coordinate stem adopted for tiie case of full metal valence orbitals are d, ( -h l)s, and ( + l)p. The carbon 2s mid 2pr orbitals will be used for ff-bonding for x-bonding, both the ligand x-bonding (x ) and x-antibonding (x ) molecidar orbitals will be combined urith the d, and p, metal orbitals to form the x-molecular orbital system for the complex. The sin e electron molecular orbitals all are assumed to have the form... 

Assume that the cyanide ion, CN, has molecular orbitals similar to those of a homonuclear diatomic molecule. Write the configuration and bond order of CN . Is a substance of the ion diamagnetic or paramagnetic ... 

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