Structure tetranuclear species

The dinuclear 2 3 species have been characterized in [Ag20u-dppm)3](OTf)2 and [Ag2(p-dppm)3](N03)2 (92), with the silver centers three coordinate by three phosphorus atoms of different dppm ligands.761,768 A tetranuclear species [Ag2(p-02CMe-0,0 )(p-02CMe-0)(p-dppm)]2 has been obtained by reaction of dppm with two equivalents of AgOAc. 762 The reaction of [Ag(Mes)]4 with dppm gives a trinuclear compound [Ag3(dppm-H)3] (93) in which the dppm ligand has been deprotonated with the formation of mesithylene. In the structure, two of the silver centers are three coordinate to three different phosphorus atoms and the other silver atoms is bonded to two carbon atoms.291,292... 

As mentioned in Section 1.2, the organocopper compound derived from ligand B is a discrete, tetranuclear species. Aggregation of this compound with CuCl or CuBr results in an insoluble material with the composition Cu(C6H4CH2NMe2-2)-CuX (X = Br, Cl) [35]. Because of its insolubility, which hampers structural characterization, a polymeric structure has been proposed for this compound. 

The trinuclear cation Cr,(NH,) 0(OH)45 and the tetranuclear cation Crj(OH),Cr(NH have been prepared similarly by the Cr(II) charcoal catalytic method and were separated by cation-exchange chromatography (40). The trinuclear species was isolated as a bromide salt and has structure 5 in Fig. 1. The tetranuclear species Cr[(0H),Cr(NH,)4[/f has been shown to be a chromium ammonia analog of the so-called Werner s brown salt, Co[(OH)2Co(en),J 3f,f (structure 6 in Fig. 1) (41). 

The structures of the trinuclear species Cr3(OH)45 + and the two tetranuclear species a- and /7-Cr4(OH)6< + have not been established. Linear as well as cyclic trimeric structures (structures 4a, 4b, and 5 in Fig. 1) have been considered (27, 37), as has another cyclic structure such as that shown in Fig. 10. However, the kinetic, thermodynamic, spectroscopic, and magnetic properties appear to provide no evidence to favor the one rather than the other (27). The number of possible... 

This tetranuclear complex was first prepared by Jorgensen (2), and was resolved into optical isomers by Werner (5), who thereby disposed of the vitalist contention that organic carbon is an essential concomitant of optical activity. Werner named the complex hexol after the bridging ligands. The structure of this tetranuclear species has now been established by an X-ray crystal-structure analysis of the racemic salt (52). The complex racemizes fairly readily and rates of racemization depend heavily on pH the first-order rate constants at pH 2.0, 7.0, and 8.1, are respectively, k = 2 x 10 6, 2 x 10 3, and 4 x 10 2 sec-1 at 22"C. Tartrate and selenate decrease the rate of racemization, probably as a result of ion pairing between the hydroxo bridges and the anions (56). 

The tetranuclear complex Co (OH)2Co(en)2 36 + was first prepared by Werner (6) and has subsequently been the subject of several studies (53, 54, 57,156,245 247). Its ammonia analog has already been mentioned in Section IV,A. As mentioned in Section II,B, the en tetranuclear species may exist in eight optically isomeric forms. All eight isomers are formed during the oxidation reaction and have been separated by column chromatography (57). The yields of the isomers decrease in the order A(AAA) > A(AAA) > A(AAA) > A(AAA). The X-ray crystal structures of... 

Intermetallic distances around 2.80 A have been found in analogous complexes of formula trans- [A2Pt(l-MeCyH-,A(3),N(4))2Hg]X2 (X = Cl-, N03 ) [56], where 1-MeCyH binds Pt through N(3) and Hg through N(4) (II, Fig. 5). They will be indicated as 4 2 type complexes. The crystal structures reveal that pairs of dimers are held together by the counterions, Cl- or N03, in such a way as to form tetranuclear species. 

A cyanohydridoborato vanadium(II) complex, tra s-[V(NCBH3)2(thf)4], has been synthesized and structurally characterized (212).858 Additional oligomeric complexes have been prepared complexes that have been characterized include trinuclear vanadium complexes,859-862 dinuclear V-Fe complexes,863 and the first tetranuclear V11 species [V4(/x3-Cl)2(M-Cl)2(M-CF3C02)2(thf)6].864 The addition of tris(pyrazolyl)borate ligand to the tetranuclear species results in the dissociation of the complex to form a neutral dimeric species [V(tpb)-(/x-Cl)(/x-CF3CO2)2V(th03] (213) in which one of the vanadium centers is facially coordinated by tpb.864... 

Reaction of glutonic acid with [Fe2Cl6L] (L = 1 n = 4) in the presence of KPFe results in two forms of the tetranuclear species [Fe20(C5H604)2L]2 (PF6)4, each of which contains two (/i-oxo)bis (p,-carboxylato)diiron(III) cores that are separated from each other by 7.748 A in the solid state. The structure of one form of this dimer of dimers is shown in Fig. 9 the arrangement present is very similar to that found in [Fe402(acetato)4L2](PF6)4 (L = 1 n = 4). Despite this, electrochemical studies indicate that the former complex is more stable toward electrochemical reduction than the latter. 

The tetranuclear clusters are structurally the same as the aforementioned tetranuclear species (Figure 108), but with DBM rather than acac ligands building up the periphery. The pentanuclear clusters have a square pyramidal core (R = Dy, Figure 111). Each triangular face of the... 

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