Copper atoms Jahn-Teller effect

In the structure, the copper (or chromium) atom has a greatly distorted octahedral coordination, with two bond distances much longer than the other four (difference = 0.38 A for Cu, 0.36 A for Cr) and small, but significant differences between the pairs of short distances. The major distortion is correlated with the d9, or high-spin d4, electronic configuration of Cu(II) and Cr(II), respectively, giving an uneven occupation of the eg orbitals—the Jahn-Teller effect. The differ-... 

The equal valence rule or loop rule equation (3) is less rigorously obeyed, and does not apply to the enviromnents of atoms with electronically driven anisotropies arising from, for example, lone electron pairs see Lone Pair, Electronic Structure of Main-group Compounds) or Jahn Teller distortions see Jahn-Teller Effect, Copper Inorganic Coordination Chemistry). 

The measurement and interpretation of the d—d spectra of copper(II) complexes have provided a highly fruitful field for coordination chemists in recent years. There are two reasons for this first, copper(II) has a one hole electronic configuration which should render the d—d spectra amenable to theoretical anal3mis. Secondly, the structural chemistry of copper(II) encompasses a remarkable variety of stereochemistries and coordination numbers. This can to some extent be rationalised in terms of the Jahn-Teller effect, and a vast amount of crystallographic data has been accumulated. Indeed, it is probably true to say that more structural parameters have been measured for the coordination compounds of copper(II) than for those of any other transition metal ion. Such data are, of course, a prerequisite for extensive theoretical studies. Moreover, the d—d spectra are sensitive to the detailed geometry about the metal atom, and interest in the ligand field splitting naturally accompanies stmctural studies of copper(II) compounds. 

The structure of [Cu(py)3(N03)2] has been determined and the overall molecular geometry is very similar to that of the Co" and Zn" analogues. The nitrate groups are co-ordinated in an asymmetric bidentate manner in all three compounds, and the large distortions observed in the case of copper are due to a static Jahn-Teller effect. The structure of [Cu BrgOCpy) ] is very similar to that of [Cu OClj ] " shown in (171), the pyridine ligands occupying terminal positions on each metal atom. Structural studies have... 

Discussion. Copper in Krypton. The absorption spectra of copper atoms Isolated in rare gas matrices have been extensively studied (15-25) and the triplet of bands at 310nm attributed to a number of different causes. These include (1) spin orbit splitting and static axial site distortion (17), (2) multiple matrix sites (18), (3) exciplex formation between the metal and a single matrix atom (19), (4) long range metal-metal interactions (2 ), and (5) Jahn-Teller (JT) effect resulting from matrix cage atom vibrations on the excited metal (21,22,23). The MCD of Cu atoms in the rare gas matrices has recently been reported (24,25) and the results interpreted as consistent with either the distorted site or JT hypotheses (39). 

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