Polynuclear complexes units

The demonstration of the formation of a hexanuclear zinc complex with the S-donor ligand 2-aminoethanethiolate, containing Zn3S3 and Zn4S4 cyclic units, contributes to the building up of a pattern of polynuclear complex formation based on coordination preferences of the metal ions involved (320) - reaction of Zn2+ with salicylideneamino ligands and pyrazine can give linear tetranuclear complexes (321). Another hexanuclear zinc complex appears in the section on supramolecular chemistry below (Section VII.D). 

This section summarizes work carried out on polynuclear complexes containing M(bpy)2 units, an area in which there is much interest, in particular with respect to energy transfer. Dendritic systems are excluded from this review, but are covered elsewhere in CCC The complexes-as-ligands strategy is commonly exploited for the controlled construction of multinuclear complexes and examples are seen in this section. 

The study of photoinduced processes in Ir(III)-based arrays has been exploited since facile synthetic methods for the preparation of Ir(III)-polyimine complexes became available. Polynuclear complexes containing, in addition to Ir(III) centers, either Os(II)-, Ru(II)-, Re(II) or Cu(I)-polyimine units linked by different bridging ligands, displayed a rich variety of photoinduced energy transfer processes. In Fig. 22 are reported some representative cases of early studies. 

There are, however, several aspects of contemporary transition metal chemistry whose existence could not have been extrapolated from the Wernerian principles. Among these one could mention considerable areas of metal carbonyl type chemistry, much of the current field of organometallic chemistry and, most unambiguously, the chemistry of compounds containing metal-metal bonds. Although Werner dealt extensively with polynuclear complexes, these were conceived simply as two or more mononuclear complexes united only by the ligands they shared. 

Polynuclear complexes, molecular dyads, triads, and other supermolecules composed of redox- and photo-active metal polypyridine units have a great promise as components of future molecular electronic or photonic devices as optical switches, relays, memories, etc. [38, 46],... 

---