Trinuclear units

Oxidative-addition of iodine also was investigated for the complex C -bzimAu]3. This complex behaves like most of the CTCs since it adds iodine at only one gold center to yield [p,-N, C -bzimAu]3l2 [59]. The X-ray structure shows that it consists of discrete trinuclear units with the three gold atoms bridged by 1 -benzylimidazolates. 

In the crystal, most trinuclear carbeniate complexes are known to be stacked with close aurophilic interactions, and organic 7r-acids can be intercalated into these stacks.252 Similar intercalation takes place with the cations of simple silver and thallium(i) salts. The cations become attached to form polymetallic core units through metallophilic bonding. With the trinuclear silver pyrazolates, both metal and ligand exchange have been observed to give new stacks of trinuclear units.254... 

Fig. 2 View of the trinuclear unit of [Fe3(etrz)6(H20)6](CF3S03)6 at 105 K (hydrogen atoms and anions have not been depicted). Shining black, white, black and white small spheres correspond to nitrogen, carbon and oxygen atoms, respectively. The larger black spheres correspond to iron(II) ions... 

The first descriptions of heteronuclear luminescent supramolecular complexes were given by Fackler et al. in 1988 and 1989. In these studies, one gold-thallium and one gold-lead complex were reported. As in the case of the gold-silver dinuclear systems, the extended systems appeared as a result of the unidirectional polymerization of dinuclear or trinuclear units through metal-metal interactions. These were prepared by reaction of the gold precursor [PPN][Au(MTP)2] (PPN = N(PPh3)2 ... 

H2O) 4+ tethers. The unusual cluster is constructed of a trinuclear unit of edgesharing MoOg octahedra, with two diphosphonate ligands decorating the periphery. Both diphosphonate moieties are monoprotonated at the pendant oxygen... 

Type II bioctahedral molybdate unit [Cu(phen)(M02O5)(H2O)(O3PCH2PO3)] 1-D CuN203 Trinuclear unit (Mo205)(03PCH2P03) K2K-... 

Cu(bpy)(Mo205)(H20)(03PCH2P03)]- 2-D CuN203 Trinuclear unit (Mo2015)(H20)(03PCH2P03) 2, ... 

There are few reports of reactions between alkynes and trinuclear clusters of metals other than iron, ruthenium, or osmium. Some rhodium, platinum, and mixed-metal clusters undergo metal-metal bond rupture in reactions with alkynes (54-56), while in other cases the alkyne coordinates to the trinuclear unit without causing any major changes in framework geometry (56-59), as illustrated in Eq. (3). 

A different type of trinuclear unit is formed when a cyanometalate fragment is reacted with an octahedral Mn(III) complex in which the equatorial sites are blocked by a tetradentate Schiff base. Despite the presence of two axial labile hgands, a situation that is conductive to the formation of an infinite chain structure, it was shown that this combination of building blocks often leads to trinuclear complexes (Table III) in which two peripheral Mn(III) ions are linked via the central cyanometalate unit. Consequently, in these structures only one axial site at each Mn (III) center is occupied by a bridging CN ligand, while the other axial site remains occupied by a solvent molecule. 

Substitution at (1) has been investigated extensively from a preparative as well as a mechanistic point of view, and most common substitution techniques, including photochemical activation and electron-transfer catalysis, have been employed. Simple thermal substitution leads to a mixture of products, but with special methods, up to 6 of the 12 CO ligands can be replaced without cleaving the trinuclear unit. 

Manganese is presently absent from this family. Our attempts to make an Mn wheel similar to the cobalt and nickel wheels led to a one-dimensional polymer [Mn2(chp)2(02CMe)2(Me0H)2] [52]. There is in this structure curvature within each trinuclear unit, however, in neighbouring units the structure curves in opposite directions, leading to a zigzag polymer rather than a wheel. There must be a fine balance between these two alternative structures. 

Discovery of the tetranuclear butterfly Cr 4 (p.3-0)2 within [Cr402(02CCH3)7(bipy)2lPFg came some years after those of the Fe and Mn analogues. The synthesis involved use of a mononuclear Cr precursor rather than di- or trinuclear units (93). The core structure, shown in Fig. 15, is similar to the Mn analogue. It has a body Cri "Cr3 distance of 2.783 A and body-wingtip distances of Cri- -Cr4 = 3.316 A and Cr3---Cr4 = 3.427 A. 

The thermal variation of the susceptibility, plotted in Fig. 38 as x-1=f(T), clearly illustrates the antiferromagnetic character of prevailing exchange interactions. When cooling down, the change of slope of x 1 =f(T) around T = 80 K characterizes the increasing influence of the interactions within each trinuclear unit finally, a minimum of x l is observed around 2.5 K, which corresponds to the transition toward a 3d ordering. 

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