Octahedral complexes Octahedron, tetragonal

The electronic configuration of a nickel(III) complex is d1. In a tetragonal ligand field3034 the ground configuration will be (dXzdyz)4(dxy)2(dziy(dx2 yi)° for a square planar or elongated octahedral complex and (dJ idyi)4(dj y)2(dx2 y2)1(d )0 f°r a compressed octahedron. In the first case the EPR spectra will show g > 11 = 2.00 while in the latter situation the pattern gy 2.00 will be observed.3035,3036... 

Fig. 15 Effective magnetic moment for nearly-octahedral d1 complexes. Left Figgis theory for 2T2g reference (k = 1, X > 0) solid line - v = 0 (octahedron) dashed - v = -10 (compressed bipyramid, Aax < 0) dot-dashed - v = +10 (elongated bipyramid, Aax > 0). Right calculation in a complete d1 space (level-6) for a Ti(III) complex on tetragonal distortion with F4(xy) = 5000 cm-1 dashed - compressed bipyramid with F4(z) = 6000 cnr1 solid - octahedron with F4(z) = 5000 cm-1 dot-dashed - elongated bipyramid with F4(z) = 4000 cm-1...

Copper is markedly different in its reactivity compared to iron. In porphyrins copper is totally buried. Due to the rigid structure of the porphyrins, where no twisting of the ligands is possible no reactivity with oxygen is seen. Hence, copper porphyrin-complexes display no superoxide dismutase activity In biological systems copper is essentially coordinated to nitrogen or sulphur. In octahedral Jahn-Teller distorted Cu(II) complexes a tetragonal distortion of the octahedron, usually an extension... 

In fact the vast majority of 6-coordinate complexes are indeed octahedral or distorted octahedral. In addition to the twist distortion just considered distortions can be of two other types trigonal and tetragonal distortions which mean compression or elongation along a threefold and a fourfold axis of the octahedron respectively (Fig. 19.8). 

Fig. 36 Modeling the magnetic functions (level-6) for a nearly-octahedral Mo(IV) complex. Left F4(xy) = 5000 cm 1, F4(z) = 6000 cm-1 (compressed tetragonal bipyramid) centre F4(xy) = F4(z) = 5000 cm 1 (octahedron) right F4(xy) = 5000 cm"1, F4(z) = 4000 cm 1 (elongated tetragonal bipyramid) dot-dashed - the parallel (z) component, dashed - the perpendicular (xy) component, solid - averaged...

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