Dimeric structures rhenium complexes

Attempts to prepare fluoro derivatives of (102) failed and resulted in the formation of the unusual /i-pyrazolyl fi-oxo dimer [ ReO HBF(pz)2-A,A 2(/i-pz)2(M-0)] (105)." An X-ray structural analysis shows that one pyrazolyl residue of each tridentate ligand has been substituted by fluoride. With the analogous complex containing hydridotris(3,5-dimethyl-l-pyrazolylborate), however, mixed Cl/F, I/F, or OSO2CF3/F derivatives of (102) are readily formed. The different reactivity of the hydridotris(pyrazolyl)borato rhenium complexes has been attributed to the greater steric protection of the boron atom afforded by the dimethyl-substituted ligand. 

The correct crystal structure of the rhenium chloride complex of stoichiometry KReCL "H20 revealed a dimeric structure (Fig. 1) with three outstanding features (82). The rhenium-rhenium separation was extremely short (2.24 0.01 A), no bridging chloride ligands were present, and the two sets of four chlorides were eclipsed relative to one another when viewed down the Re—Re axis. 

Rhenium ions, and especially tricarbonylrhenium(l)chloro fragments, have been used to organize and link pyridine-functionalized porphyrins as molecular squares, rectangles, planar dimers, and more complex structures. 

Of course, sometimes the geometry of the spacer is not sufficient to fully control the behavior of the scaffold and the chromophores flexibility can be responsible for unusual behavior. For example. Hupp has reported the properties of two collapsed dimers showing a compact structures due to ethynyl-pyridyl side arms used for binding rhenium complexes that act as spacers (Fig ure 13.72)128,... 

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