Inorganic Complexes and Coordination Compounds

An inorganic molecule that contains several atoms, including one or more metal atoms, is called an inorganic complex or coordination compound. An example is nickel tetracarbonyl, Ni(CO)4. An inorganic complex with an electric charge is called a complex ion. Familiar examples of complex ions are the ferrocyanide ion, Fe(CN)e - the ferricyanide ion, Fe(CN)e the hydrated aluminum ion, A1(H20)6, and the deep blue cupric ammonia complex ion, Cu(NH3)4 +, which is formed by adding ammonium hydroxide to a solution of cupric salt. Complex ions are important in the methods of separation used in qualitative and quantitative chemical analysis and in various industrial processes. 

Nakamoto K. Complexes of alkoxides, alcohols, ethers, ketones, aldehydes, esters and carboxylic groups, in Infrared and Raman spectra of inorganic and coordination compounds, Wiley, 2009, 62-67. 

Tt is well-known that Werner determined the structure of a number of metal complexes by skillfully combining his famous coordination theory with chemical methods (30). Modern physico-chemical methods such as x-ray diffraction and infrared spectroscopy, used in the study of Werner complexes, have paralleled the development of these techniques. The results of these investigations have not only confirmed the validity of Werner s coordination theory but have also provided more detailed structural and bonding information. In early 1932, Damaschun (13) measured the Raman spectra of seven complex ions, such as [Cu(NH3)4]" and [Zn(CN)4j and these may be the first vibrational spectra ever obtained for Werner complexes. In these early days, vibrational spectra were mainly observed as Raman spectra because they were technically much easier to obtain than infrared spectra. In 1939, Wilson 35, 36) developed a new theory, the GF method," which enabled him to analyze the normal vibrations of complex molecules. This theoretical revolution, coupled with rapid developments of commercial infrared and Raman instruments after World War II, ushered in the most fruitful period in the history of vibrational studies of inorganic and coordination compounds. 

In unidentate complexes the separation between the two vibrations is larger than that in the Tree ion. where Ar,( , = 200cm, whereas the opposite trend is seen in bidenlate complexes. See, for example. Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 3rd ed., Wiley-Interscience, New York, 1977. 

The correlation method developed by Fateley et al. is simpler than facioi group analysis and gives the same results. A complete normal coordinate analysis on the whole Bravais cell of calcite-type crystals was carried out by Nakagawa and Walter. Similar treatments have been extended to nitro and aquo complexes. For a review of lattice vibrations of inorganic and coordination compounds, see Ref. lOl. 

SPECTRA OF INORGANIC AND COORDINATION COMPOUNDS 1 -18. DINiTROGENCNz), NITRlDO(N), AND HYDRiDO(H) COMPLEXES... 

A very important use of XRD is in the determination of the structure of single crystals, that is, identifying the exact position in 3D space of every atom (molecules, ion) in the crystal. Single crystal XRD was a major tool in elucidating the structure of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA), insulin, vitamins, and proteins. Single crystal diffractometry is used for structural determination of biomolecules, natural products, pharmaceuticals, inorganic coordination complexes, and organometallic compounds. 

While the largest success of the unconventional aromaticity is certainly in the realm of bare metal clusters, the synthesis and characterization of the compounds containing [Pd4(p4-C9 H 9) (P4 -Cg H g) ] complex clearly demonstrated the importance of the delocalized 5-bonding and 5-aromaticity in inorganic, organometaUic, and coordination chemistry. 

Figure 5.6 Infrared spectra of metal hexamine complexes. From Nakamoto, K., Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B, Applications in Coordination, Organometallic and Bioinorganic Chemistry, 5th Edn. Copyright (1997 John Wiley Sons, Inc.). This material is used by permission of John WUey Sons, Inc.

COTTON, F.A., "The Infrared Spectra of Transition Metal Complexes" in LEWIS, J., and WILKINS, R. G., "Modern Coordination Chemistry", Inter -science, 1960 NAKAMOTO, K., "Infrared Spectra of Inorganic and Coordination Compounds", Wiley, 1963. 

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