Coordination compounds monodentate ligands

Coordination compounds containing bidentate ligands are often thermally more stable than those comprised of related monodentate ligands, e.g. ethylenediamine (en) complexes dissociate at a higher temperature than those of ammonia or pyridine. Compounds containing a ring structure, such as coordinated salicylaldehyde (sal) and acetyl-acetonate (acac), are particularly stable, and may often be sublimed... 

NMR measurements also provide information on the coordination of the ligands in the uranyl polymers. Solid-state I c-NMR confirms the coordination modes of the carboxylate ligands to the uranyl ion that is, both monodentate and bidentate carboxylate coordination modes are evident. The uranyl dicarboxyl ate polymers which possess two moles of coordinated DMSO exhibit two carbon-13 carbonyl resonances, one at about 175 ppm downfield from tetramethylsilane (TMS) and one at about 185 ppm. The polymers which possess only one mole of coordinated DMSO exhibit only the carbonyl peak near 185 ppm. Based on other known coordination compounds, the 175 ppm peak can be assigned to monodentate carboxylate and the 185 ppm peak to bidentate carboxylate. Thus, 7-coordination predominates in the polymers with either one or two moles of solvent coordinated to the uranyl ion, which is consistent with the infrared results reported elsewhere (5). 

Four-coordinate complexes with monodentate ligands have also been reported. The X-ray crystal structures of three modifications of the compound [Au(PPh3)4]BPh4 have been determined, none of which shows the expected simple tetrahedral geometry.2540 Thus, the chloroform solvate... 

The X-ray structures are known of a number of ketone ligands, including hexanedione and 4-methylcyclohexanone, that have bound as monodentate ligands in the fifth coordination site of zinc porphyrin complexes.347,348 Oxaphlorin dimeric compounds are also known where the oxygen from a neighboring porphyrin ring coordinates in the fifth coordination site of a neighboring zinc porphyrin unit.349... 

Hitoshi dedicated his life to Science and to the organization of Science. As a scientist, I remember the studies by X-ray of the coordination compounds in solution of metal ions with monodentate ligands which constituted milestones in the field. Eventually, he started simulating through informatic tools the interaction of solvents and ligands with metal ions. 

Little work has been published on hydrazine adducts the reported compounds InClj-S FL and TnI3-3N2H4 presumably involve monodentate coordination of the ligand.70... 

Names for Mononuclear Coordination Compounds with Monodentate Ligands... 

Chelation sometimes does not take place automatically, as illustrated by the coordination of histamine, 4-(2-aminoethyl)imidazole (19 R = H). It appears to tautomerize and coordinates with the non-chelating nitrogen, whereas the NH2 group is protonated, so that a monodentate ligand (in fact a 4-substituted imidazole) coordinates to the metal, in this case Ni with NCS- anions in the compound [Ni(NCS)4(hamH)2] (hamH = histaminium cation).70... 

---