Crystal structures tetranuclear complexes

Carrell, H. L., dusker, J. P., Job, R., and Bruice, T. C. (1977). A synthetic tetranuclear iron-sulfur complex with ionized side chains The crystal structure of (Fe4S4(S(CH2)aCOO)4) -(Na5-N(C4H9)4) -5C6H9NO./. Am. Chem. Soc. 99, 3683-3690. 

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... 

Reaction of the bis(diphenylphosphino)methane (dppm) complex PdPt-(yi-dppm)2Cl2 (132) with carbonylate anions affords several tri- and tetranuclear clusters. Reactions are outlined in Scheme 7. Treatment of 132 with 2 mol equivalents of [Fe(CO)3(NO)] (796,797), [Co(CO)4] (196,198), or [Mn(CO)5] (196,197) results in the tetranuclear spiked triangular clusters 133,134, or 135. Crystal structures on the dipalladium analogues of 134 and 135 have been reported (797,799). Grossel et al. (136) and Braunstein et al. (200) have independently reported that reaction of 132 with 1 mol equivalent of [Fe(CO)4]2 at ambient temperatures leads to an inseparable 1 1 mixture... 

A fluorescent cationic tetranuclear gold(I) rectangle, [(/v-Ph2PAnPPh2)Au2 (//-4,4,-bpy)2Au2(/i.-Ph2PAnr,Ph2)]X4 (X = PF6, NO3), was assembled using 9,10-bis(diphenylphosphino)anthracene and 4,4/-bipyridyl [124]. The molecular rectangle has a cavity of 7.921(3) x 16.76(3) A as reflected from its crystal structure, and its complexation behavior towards various aromatic molecules at the cavity was demonstrated. 

Schwendt, P., A. Oravcova, J. Tyrselova, and F. Pavelcik. 1996. The first tetranuclear vanadium)V) peroxo complex Preparation, vibrational spectra and x-ray crystal structure of K7[V204(02)8(P04)] 9H20. Polyhedron 15 4507 4511. 

An analysis of the RDF for the acid solution shows that the In3+ ion is bonded to six water molecules at 2.17 A (Fig. 28). The same In—H20 distance is found for octahedrally coordinated In3+ in crystal structures (223, 224). According to the difference curve this coordination is not changed by the hydrolysis. A possible model for a tetranuclear complex with four octahedrally coordinated In atoms occupying the four corners of a regular tetrahedron and joined by single hydroxo bridges is shown in Fig. 28. It is consistent with the experimental data and seems to be a likely model for the hydrolysis complexes formed in solution, but has not yet been found in crystal structures. 

The structures of these materials are as yet unknown. Interestingly, a tetranuclear complex containing four cw-(NH3)2Ptn units and two /t4-car-bonato ligands, [Pt4(NH3)8(C03)2](N03)4, has been isolated from a preparation of a Pt deoxyuridine blue and characterized by X-ray crystal structure analysis [85]. The four Pt ions in this complex form roughly a square of sides of ca. 3.18-3.28 Aand consequently do not form metal-metal bonds. 

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. 

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