Heteroleptic molecule

A number of general features in Table 1-3 is apparent. Complexes may be cationic, neutral or anionic. Ligands may be simple monatomic ions, or larger molecules or ions. Many ligands are found as related neutral and anionic species (for example, water, hydroxide and oxide). Complexes may contain all of the same type of ligand, in which case they are termed homoleptic, or they may contain a variety of ligand types, whereby they are described as heteroleptic. Some ligands such as nitrite or thiocyanate can coordinate to a metal ion in more than one way. This is described as ambidentate behaviour. In such cases, we commonly indicate... 

Although most of the structurally characterized gold clusters are phosphine-based systems, in recent years some studies have focused on the synthesis of gold clusters with other stabilizers coexisting with phosphines such as thiols, arsines and boranes. Certain heteroleptic gold clusters stabilized with these ligands and arylphosphines in the same molecule have been structurally characterized. 

It should be mentioned that in many cases it turns out to be impossible to isolate the bimetallic mixed-ligand complex. The isolable reaction products appear to be homometallic heteroleptic species. The composition of the reaction products is often dependent on the polarity and donor properties of the solvent as the molecules of the latter compete with the bridging alkoxo-, car-boxylato-, or p-diketonatoligands for the place in the coordination sphere of metal atoms. Thus if the reaction of Pb(OAc)2 with Sn(OBu )4 mentioned above is carried out in pyridine, it gives Sn(OBu )3(OAc)Py and Pb(OAc)(OBu ) as the major products and not the bimetallic complex [298]. Sn(OBu )3(OAc)Py turns also to be the major product of the reaction of Sn(OBu )4with Me3SiOAc... 

The TijC OPr ) molecule is, according to the NMR data, formed in solution on hydrolysis at h = 0.05-0.2, but only a heteroleptic complex of Ti(p3-0)( A3-0Me)(0Pri)9 composition could be obtained in the crystalline form [454],... 

Oxidation of the metal-metal bond. The most frequently studied redox processes are those of oxidative addition to the multiple metal-metal bonds in the molecules of low-valent derivatives. They lead very often to the formation of heteroleptic derivatives that keep, however, a metal-metal bond in their structure. That happens, for example, on the interaction of M2(OR)6 with alcohols (for M = W only) [17, 314, 368], halogenes [367, 870], or alkyl or acylperoxides [370] ... 

Among the heteroleptic derivatives of special interest is the decanuclear cyclic molecule of [Fe( i-OMe)2 (C1CH2COO)]io —the iron ring with the effective diameter of 12 A. All the 10 iron atoms are situated in the same plane and connected with each other by pairs of (OMe)2-bridges [1554]. Hydrolysis of Fe(OR)3 and application in sol-gel method discussed in Chapters 9 and 10. 

Fig. 5.7 Luminescence of homoleptic and heteroleptic [Ru(bipy)3]2+ complexes as a function of the number of oxygen atoms in the molecule - and hence of the steric shielding of the central ion (according to Balzani, Vogtle et al.)...

X-ray structure analysis revealed a 7-coordinate rare-earth metal center with two asymmetrically / -coordinating tetramethylaluminate ligands, an asymmetrically / -coordinating siloxide ligand and one methyl group of a trimethylaluminum donor molecule (Fig. 28). Such heteroleptic complexes can be regarded as molecular models of covalently bonded alkylated silica surface species. Moreover, isoprene was polymerized in the presence of 1-3 equivalents of diethylaluminum chloride, with highest activities observed for (Cl) (Ln) ratios of 2 1 (Table 12) (Fischbach et al., 2006, personal communication) [150]. 

Another class of heteroleptic alkyl complexes contains 7t-donating ancillary ligands such as RU[N(Si(CH3)3)2]3 (R = CH3, H, BH ). The hydride species can be converted into the methyl species via reaction with BuLi and CH3Br. The methyl compound has exhibited insertion chemistry with small molecules including aldehydes, ketones, nitriles, and isocyanides (206). Stable metallacyde compounds are also known, ie,... 

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