Inorganic chemistry



  Inorganic chemistry is the branch of organometallic chemistry.

Key concepts

  The bulk of electron affinity (anions) of the parent elements.

Important classes of inorganic compounds are the SiO2) are not.

The simplest inorganic reaction is electrochemistry.

When one reactant contains hydrogen atoms, a reaction can take place by exchanging protons in HSAB theory takes into account polarizability and size of ions.

Inorganic compounds are found in nature as DNA).

The first important man-made inorganic compound was ammonium nitrite for soil fertilization through the lithium aluminium hydride.

Subdivisions of inorganic chemistry are superconductors, and therapies.

Industrial inorganic chemistry

Inorganic chemistry is a highly practical area of science. Traditionally, the scale of a nation's economy could be evaluated by their productivity of sulfuric acid. The top 20 inorganic chemicals manufactured in Canada, China, Europe, Japan, and the US (2005 data):[1] titanium dioxide,

Descriptive inorganic chemistry

Descriptive inorganic chemistry focuses on the classification of compounds based on their properties. Partly the classification focuses on the position in the periodic table of the heaviest element (the element with the highest atomic weight) in the compound, partly by grouping compounds by their structural similarities. When studying inorganic compounds, one often encounters parts of the different classes of inorganic chemistry (an organometallic compound is characterized by its coordination chemistry, and may show interesting solid state properties).

Different classifications are:

Coordination compounds

 

Main article: Coordination chemistry
See also: Werner-type complex

Classical coordination compounds feature metals bound to "actinides, but from a certain perspective, all chemical compounds can be described as coordination complexes.

The stereochemistry of coordination complexes can be quite rich, as hinted at by Werner's separation of two [Co((OH)2Co(NH3)4)3]6+, an early demonstration that chirality is not inherent to organic compounds. A topical theme within this specialization is supramolecular coordination chemistry.[2]

  • Examples: [Co(THF)2.

Main group compounds

  These species feature elements from Hg) are also generally included.[3]

Main group compounds have been known since the beginnings of chemistry, e.g. elemental Fritz Haber in the early 1900’s deeply impacted mankind, demonstrating the significance of inorganic chemical synthesis. Typical main group compounds are SiO2, SnCl4, and N2O. Many main group compounds can also be classed as “organometallic”, as they contain organic groups, e.g. B(buckytubes and binary carbon oxides.

Transition metal compounds

  Compounds containing metals from group 4 to 11 are considered transition metal compounds. Compounds with a metal from group 3 or 12 are sometimes also incorporated into this group, but also often classified as main group compounds.

Transition metal compounds show a rich coordination chemistry, varying from tetrahedral for titanium (e.g. TiCl4) to square planar for some nickel complexes to octahedral for coordination complexes of cobalt. A range of transition metals can be found in biologically important compounds, such as iron in hemoglobin.

Organometallic compounds

 

Main article: Organometallic chemistry

Usually, organometallic compounds are considered to contain the M-C-H group.[4] The metal (M) in these species can either be a main group element or a transition metal. Operationally, the definition of an organometallic compound is more relaxed to include also highly alkoxides.

Organometallic compounds are mainly considered a special category because organic ligands are often sensitive to hydrolysis or oxidation, necessitating that organometallic chemistry employs more specialized preparative methods than was traditional in Werner-type complexes. Synthetic methodology, especially the ability to manipulate complexes in solvents of low coordinating power, enabled the exploration of very weakly coordinating ligands such as hydrocarbons, H2, and N2. Because the ligands are petrochemicals in some sense, the area of organometallic chemistry has greatly benefited from its relevance to industry.

Cluster compounds

   

Main article: Cluster compound

Clusters can be found in all classes of cadmium selenide clusters. Thus, large clusters can be described as an array of bound atoms intermediate in character between a molecule and a solid.


Bioinorganic compounds

 

Main article: Bioinorganic chemistry

See also Bioorganometallic chemistry

These compounds occur (by definition) in nature, but the subfield includes anthropogenic species, such as pollutants and drugs, e.g. gadolinium complexes employed for MRI).

Solid state compounds

Main article: solid-state chemistry

  This important area focuses on materials science.

Theoretical inorganic chemistry

An alternative perspective on the area of inorganic chemistry begins with the density functional theory.

Exceptions to theories, qualitative and quantitative, are extremely important in the development of the field. For example, CuII2(OAc)4(H2O)2 is almost diamagnetic below room temperature whereas Crystal Field Theory predicts that the molecule would have two unpaired electrons. The disagreement between qualitative theory (paramagnetic) and observation (diamagnetic) led to the development of models for "magnetic coupling." These improved models led to the development of new magnetic materials and new technologies.

Qualitative theories

  Inorganic chemistry has greatly benefited from qualitative theories. Such theories are easier to learn as they require little background in quantum theory. Within main group compounds, valence electrons, usually at the central atom in a molecule.

Group Theory

  A central construct in inorganic chemistry is Group Theory.[7] Group Theory provides the language to describe the shapes of molecules according to their "point group symmetry". Group Theory also enables factoring and simplification of theoretical calculations.

Spectroscopic features are analyzed and described with respect to the symmetry properties of the, inter alia, vibrational or electronic states. Knowledge of the symmetry properties of the ground and excited states allows one to predict the numbers and intensities of absorptions in vibrational and electronic spectra. A classic application of Group Theory is the prediction of the number of C-O vibrations in substituted metal carbonyl complexes. The most common applications of symmetry to spectroscopy involve vibrational and electronic spectra.

As an instructional tool, Group Theory highlights commonalities and differences in the bonding of otherwise disparate species, such as NO2.

Reaction pathways

The theory of chemical reactions is more challenging than the theory for a static molecule. Marcus theory provides a powerful linkage between bonding, mechanism, and reactivity. The relative strengths of metal-ligand bonds, which can be calculated theoretically, anticipates the kinetically accessible pathways.

Thermodynamics and inorganic chemistry

An alternative quantitative approach to inorganic chemistry focuses on energies of reactions. This approach is highly traditional and empirical, but it is also useful. Broad concepts that are couched in thermodynamic terms include electron affinity, some of which cannot be observed directly.

Mechanistic inorganic chemistry

An important and increasingly popular aspect of inorganic chemistry focuses on reaction pathways. The mechanisms of reactions are discussed differently for different classes of compounds.

Main group elements and lanthanides

The mechanisms of main group compounds of groups 13-18 are usually discussed in the context of organic chemistry (organic compounds are main group compounds, after all). Elements heavier than C, N, O, and F often form compounds with more electrons than predicted by the carbocations. Such electron-deficient species tend ro react via associative pathways. The chemistry of the lanthanides mirrors many aspects of chemistry seen for aluminium.

Transition metal complexes

Mechanisms for the reactions of transition metals are discussed differently from main group compounds.[8] The important role of d-orbitals in bonding strongly influences the pathways and rates of ligand substitution and dissociation. These themes are covered in articles on coordination chemistry and ligand. Both associative and dissociative pathways are observed.

An overarching aspect of mechanistic transition metal chemistry is the kinetic lability of the complex illustrated by the exchange of free and bound water in the prototypical complexes [M(H2O)6]n+:

[M(H2O)6]n+ + 6 H2O* → [M(H2O*)6]n+ + 6 H2O
where H2O* denotes isotopically enriched water, e.g. H217O

The rates of water exchange varies by 20 orders of magnitude across the periodic table, with lanthanide complexes at one extreme and Ir(III) species being the slowest.

Redox reactions

Redox reactions are prevalent for the transition elements. Two classes of redox reaction are considered: atom-transfer reactions, such as oxidative addition/reductive elimination, and manganate exchange one electron:

[MnO4]− + [Mn*O4]2− → [MnO4]2− + [Mn*O4]−

Reactions at ligands

Coordinated ligands display reactivity distinct from the free ligands. For example, the acidity of the ammonia ligands in surface science, a subfield of solid state chemistry. But the basic inorganic chemical principles are the same. Transition metals, almost uniquely, react with small molecules such as CO, H2, O2, and C2H4. The industrial significance of these feedstocks drives the active area of catalysis.

Characterization of inorganic compounds

Because of the diverse range of elements and the correspondingly diverse properties of the resulting derivatives, inorganic chemistry is closely associated with many methods of analysis. Older methods tended to examine bulk properties such as the electrical conductivity of solutions, molecular orbital theory as fully delocalised orbitals are a more appropriate simple description of electron removal and electron excitation.

Commonly encountered techniques are:

  • molecular structures.
  • Various forms of spectroscopy
    • Ultraviolet-visible spectroscopy: Historically, this has been an important tool, since many inorganic compounds are strongly colored
    • Pt) give important information on compound properties and structure. Also the NMR of paramagnetic species can result in important structural information. Proton NMR is also important because the light hydrogen nucleus is not easily detected by X-ray crystallography.
    • carbonyl ligands
    • Electron-nuclear double resonance (ENDOR) spectroscopy
    • Mössbauer spectroscopy
    • Electron-spin resonance: ESR (or EPR) allows for the measurement of the environment of paramagnetic metal centres.
  • Cyclic voltammetry and related techniques probe the redox characteristics of compounds.

Synthetic inorganic chemistry

Although some inorganic species can be obtained in pure form from nature, most are synthesized in chemical plants and in the laboratory.

Inorganic synthetic methods can be classified roughly according the volatility or solubility of the component reactants.[9] Soluble inorganic compounds are prepared using methods of cryogens. Solids are typically prepared using tube furnaces, the reactants and products being sealed in containers, often made of fused silica (amorphous SiO2) but sometimes more specialized materials such as welded Ta tubes or Pt “boats”. Products and reactants are transported between temperature zones to drive reactions.

References

At Wikiversity you can learn more and teach others about Inorganic chemistry at:
The Department of Inorganic chemistry
  1. ^ "Facts & Figures Of The Chemical Industry” Chemical and Engineering News, July 10, 2006.
  2. ^ Lehn, J. M., Supramolecular Chemistry: Concepts and Perspectives, VCH: Weinhiem, 1995
  3. ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
  4. ^ C. Elschenbroich, A. Salzer ”Organometallics : A Concise Introduction” (2nd Ed) (1992); Wiley-VCH: Weinheim. ISBN 3-527-28165-7
  5. ^ S. J. Lippard, J. M. Berg “Principles of Bioinorganic Chemistry” University Science Books: Mill Valley, CA; 1994. ISBN 0-935702-73-3.
  6. ^ Wells, A.F. (1984). Structural Inorganic Chemistry, Oxford: Clarendon Press.
  7. ^ Cotton, F. A., Chemical Applications of Group Theory, John Wiley & Sons: New York, 1990
  8. ^ R. G. Wilkins "Kinetics and Mechanism of Reactions of Transition Metal Complexes" Wiley-VCH Verlag; 2nd, 1991) ISBN 3-527-28389-7
  9. ^ Girolami, G. S.; Rauchfuss, T. B. and Angelici, R. J., Synthesis and Technique in Inorganic Chemistry, University Science Books: Mill Valley, CA, 1999

See also
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Inorganic_chemistry". A list of authors is available in Wikipedia.