Polynuclear complexes octahedral

Polynuclear complexes based on octahedral building blocks may be structurally not well defined because of stereogenic problems [8]. However, clever synthetic strategies have recently been devised to obtain chirally pure species [61-65]. Synthesis and, of course, photophysical and photochemical studies of stereochemically pure metal-based dendrimers are still in their infancy. 

The coordination chemistry of chromium(III) was first seriously investigated by Pfeiffer at the turn of the century in many ways his studies parallel the work of Werner on cobalt(III). The complexes of chromium(III) are almost exclusively six-coordinate with an octahedral disposition of the ligands. Many are monomeric ((Jeff 3.6 BM), although hydroxy-bridged and other polynuclear complexes are known in which spins on neighbouring chromiums are coupled. 

In preparation of a Co(XII) complex by oxidation of an ammoniacai solution of CoCl2, there are three possible coordinating groups present in solution, Cl, H20, and NH3. Ignoring the possibility of hydroxo complexes, peroxo complexes, and polynuclear complexes, show that there arc 57 possible octahedral complexes which could be formed using these ligands alone. (Don t try to draw all of them )... 

The compound [VCl3(terpy)] is a paramagnetic, octahedral complex formed in the reaction of VCI3 (100) or [VCl3( BuNC)3] (408) with terpy. A bis(terpy)vanadium(III) complex is presumably the product of oxidation of [V(terpy)2] (49). A red polynuclear complex is formed from the reaction of aqueous vanadium(III) solutions with one equivalent of terpy (49). 

In the previous sections we have concentrated on complexes where the ligands were highly structured, and thereby enabled a degree of control over the formation of the polynuclear species. However, many polynuclear complexes may be formed upon condensation of very simple ligands, and in this section we will discuss some examples of these. One of the oldest examples is to be found in the acetylacetonates. Dehydration of the octahedral complex [Ni(acac)2(OH2)2] leads to [Ni(acac)2]3- The structure of the trimer [100] is shown in Figure 36. 

Classical or Werner complexes have a metal in a positive oxidation state coordinated by donor ligands. The coordination number and geometry are determined by size and bonding factors, octahedral and tetrahedral being common for 3d ions, and square-planar coordination for some (ft ions. Polynuclear complexes can have bridging ligands and/or metal-metal bonding. 

The d electron configuration is frequently stabilized by a metal-metal interaction in polynuclear complexes. The luminescence of such clusters will be discussed below. However, d ions in solid matrices are known to emit. For example, octahedral [Os Cl6] " in various host lattices shows an LF emission. A NIR VIS upconversion was achieved with Os in CsjZrClg [29]. 

From electrochemical data it may be concluded that the solvates are composed of complex ions formed by halide ion transfer thus the system SbClg-SeOClj gives rise to SeOCl and SbCl ions. Polynuclear complexes are also possible. However, a structure determination has shown that crystals of the solvates SbCl. SeOCl comprise discrete SbCl. SeOCl molecules with an octahedral configuration in which five chlorine atoms and one oxygen atom coordinate the antimony atom. The coordination of the selenium atom is approximately pyramidal. The Sb-0 distance corresponds to a single bond distance indicating that the interaction between the solute and the solvent molecule is strong. 

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