Transition-metal complexes, electron

This article is an attempt to review possibilities in a quantum chemical treatment of open-shell systems. In order to cut down the extent of this review, we disregard some problems, especially those concerning macromolecules, polymerization reactions, and open-shell transition-metal complexes. Electron spin resonance is mentioned only briefly, because it has been a topic of many reviews. 

Ru and Os tetranuclear clusters, 6, 874 in transition metal complex electron counting, 1, 2-3 Eight-membered rings, via ring-closing diene metathesis,... 

Neutral ligand method, for transition metal complex electron counting, 1, 4... 

Keywords TDDFT Excitation energies Excited states Transition metal complexes Electronic spectra Metallotetrapyrroles Metallocarbonyls a-diimine complexes Porphyrins Porphyrazines Phthalocyanines Werner complexes Sandwich complexes... 

In contrast to the later transition metal complexes, electron-deficient complexes of the earlier transition metals, e.g., CpV(CO)2 (RC=CR) (94), are mostly inert to acetylene cyclization. Thus, bis- or trisacetylene com-... 

B. Mechanisms of Redox Catalysis by Transition Metal Complexes-Electron and Ligand Transfer Processes... 

Crystallographic studies of transition metal hydride complexes Stereochemistry of six-coordination Five-coordinate structures Stereochemistry of five-coordinate Co complexes Absolute stereochemistry of chelate complexes Stereochemistry of optically-active transition metal complexes Electron density distributions in inorganic compounds... 

Zeta with polarization functions for the second-row atoms and Triple-Zeta for the metal atoms. Highly correlated methods such as the CCSD theory are even more demanding in term of basis sets quality and this is one of the limiting steps for further applications in the field of transition metal complexes electronic spectroscopy [12]. 

Glatzel JPS, Bergmann U (2005) High resolution 1 s core hole X-ray spectroscopy in 3d transition metal complexes - electronic and structural information. Coord Chem Rev 249 (l-2) 65-95... 

Many transition metal complexes including Ni(CO)4 obey the 18 electron rule, which IS to transition metal complexes as the octet rule is to mam group elements like carbon and oxygen It states that... 

Eor transition metal complexes the number of ligands that can be attached to a metal will be such that the sum of the electrons brought by the ligands plus the valence electrons of the metal equals 18... 

With an atomic number of 28 nickel has the electron conflguration [Ar]4s 3c (ten valence electrons) The 18 electron rule is satisfied by adding to these ten the eight elec Irons from four carbon monoxide ligands A useful point to remember about the 18 electron rule when we discuss some reactions of transition metal complexes is that if the number is less than 18 the metal is considered coordinatively unsaturated and can accept additional ligands... 

The 18 electron rule is a general but not universal guide for assessing whether a certain transition metal complex is stable or not Both of the following are stable compounds but only one obeys the 18 electron rule Which one" ... 

Polyatomic molecules cover such a wide range of different types that it is not possible here to discuss the MOs and electron configurations of more than a very few. The molecules that we shall discuss are those of the general type AFI2, where A is a first-row element, formaldehyde (FI2CO), benzene and some regular octahedral transition metal complexes. 

Flowever, transition metal complexes do absorb in the visible region, giving them a characteristic colour. Flow can this happen if the transitions are forbidden The answer is that interaction may occur between the motion of the electrons and vibrational motions so that some vibronic transitions are allowed (see Section 7.3.4.2b). 

All the forbidden electronic transitions of regular octahedral transition metal complexes, mentioned in Section 7.3.1.4, are induced by non-totally symmetric vibrations. 

Because the electron-counting paradigm incorporates the 18-electron rule when appHed to transition-metal complexes, exceptions can be expected as found for classical coordination complexes. Relatively minor exceptions are found in (Tj -C H )2Fe2C2BgHg [54854-86-3] (52) and [Ni(B2QH22)2] A [11141-32-5] (53). The former Q,n electrons) is noticeably distorted from an idealized stmcture, and the latter is reminiscent of the and complexes discussed above. An extremely deficient electron count is obtained for complexes such as P7036-06-9] which have essentially undistorted... 

The alkaline and rare-earth metals, and positive actinide ions, generally have greater affinity for —0 groups as electron donors. Many transition metals complex preferentially with enoHc —0 and some nitrogen functions. PolarizabiUty of the donor atoms correlates with stabiUty of complexes of the heavier transition metals and the more noble metal ions. 

For many species the effective atomic number (FAN) or 18- electron rule is helpful. Low spin transition-metal complexes having the FAN of the next noble gas (Table 5), which have 18 valence electrons, are usually inert, and normally react by dissociation. Fach normal donor is considered to contribute two electrons the remainder are metal valence electrons. Sixteen-electron complexes are often inert, if these are low spin and square-planar, but can undergo associative substitution and oxidative-addition reactions. 

W. A. Nugent and J. M. Mayer, Metal-Eigand Multiple Bonds The Chemistry of Transition Metal Complexes Containing Oxo, Nitrido, Imido, Jilkylidene, orJilkylidyne Eigands,Jolm. Wiley Sons, Inc., New York, 1988. Contains electronic and molecular stmcture, nmr, and ir spectroscopy, reactions, and catalysis. 

The electron transfer rates in biological systems differ from those between small transition metal complexes in solution because the electron transfer is generally long-range, often greater than 10 A [1]. For long-range transfer (the nonadiabatic limit), the rate constant is... 

J Li, L Noodleman, DA Case. Electronic structure calculations Density functional methods with applications to transition metal complexes. In EIS Lever, ABP Lever, eds. Inorganic Electronic Structure and Spectroscopy, Vol. 1. Methodology. New York Wiley, 1999, pp 661-724. 

---