Transition complexes, dinuclear

Figure l.4 The structural variety of trinuclear ferric hydroxo complexes, Fe3(OH)f i, that could form from Fe2(OH)24+ at low pH. Iron atoms are indicated as full circles, OH as open circles. The arrow indicates a transition from dinuclears to trinuclears (p = 2 to p = 3), which is realistic as an early step in the growth of polynuclears. (From Crichton, 1991.)... 

Carbonyl Complexes of the Transition Metals Cluster Compounds Inorganometalhc Compounds Containing Transition Metal Main Group Elements Cyanide Complexes of the Transition Metals Dinuclear Organometallic Cluster Complexes Gold Inorganic Coordination Chemistry. 

C.M. Grunert, S. Reiman, H. Spiering, J.A. Kitchen, S. Brooker, P. Gutlich, Mixed spin-state [HS-LS] pairs in a dinuclear spin transition complex confirmation by variable-temperature Fe Mossbauer Spectroscopy. Angew. Chem. Inter. Ed. 47, 2997-2999 (2008)... 

The simplest transition metal carbonyls are mononuclear of the type M(CO)x, in other words those with only one metal atom. They are hydrophobic but soluble to some extent in nonpolar liquids, such as n-butane or propane. The dinuclear carbonyls are more complex but have the same general characteristics as the mononuclear carbonyls. The carbonyls, which are or could be used in CVD, are listed in Table 3.4 with some of their properties. 

Oxalamidinate anions represent the most simple type of bis(amidinate) ligands in which two amidinate units are directly connected via a central C-C bond. Oxalamidinate complexes of d-transition metals have recently received increasing attention for their efficient catalytic activity in olefin polymerization reactions. Almost all the oxalamidinate ligands have been synthesized by deprotonation of the corresponding oxalic amidines [pathway (a) in Scheme 190]. More recently, it was found that carbodiimides, RN = C=NR, can be reductively coupled with metallic lithium into the oxalamidinate dianions [(RN)2C-C(NR)2] [route (c)J which are clearly useful for the preparation of dinuclear oxalamidinate complexes. The lithium complex obtained this way from N,N -di(p-tolyl)carbodiimide was crystallized from pyridine/pentane and... 

Examples are tending to be more sophisticated and complex in form. For example, a dinuclear complex featuring a bridging phosphinate and phenolate in addition to peroxide (221) has been reported,966 as a model for phosphodiester systems. Apart from dicobalt(III) systems, a mixed-valence CoII,ni di-/i-superoxo complex (222) has been prepared.967 Transition between the three redox states CoII,n, Co11,111, and Co111111 is electrochemically reversible. 

Dehydrative condensation of transition metal hydroxo complexes is a versatile synthetic method, when the conjugated acid of the incoming ligand (H-A) is a protic compound. There are reports of the synthesis of two types of square-planar hydroxopalladium complexes, mononuclear [TplPr2 x(L)Pd-OH] (X = H, Br) and dinuclear complexes [TplPr2Pd(H20)( -0H)2 (H20)PdTplPr2] (TplPr2 = hydrotris(3,5-diisopropylpyrazolyl)borate), and some dehydrative condensations of them.278... 

Figure 27 Oxidative addition of the organochalcogen compounds to low-valent transition metal centers most often resulting in the cleavage of the chalcogen-chalcogen bond and the formation of mono- or dinuclear complexes with anionic bridging or terminal RE- (E = Se, Te) ligands.

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