LIGAND-FIELD PHOTOCHEMISTRY OF PENTACYANOFERRATE(II) COMPLEXES WITH DIAMINE LIGANDS - INFLUENCE OF THE CHELATING LIGANDS AND THE ROLE OF NEIGHBORING GROUP EFFECTS ON THE PHOTOINDUCED RING-CLOSURE PROCESS

A series of pentacyanoferrate(II) complexes with bidentate diamine ligands, [Fe(CN)5(N N)]3-, where N N is 1,2-diaminoethane, N,N-diethyl-1,2-diaminoethane, 2-((2-aminoethyl)amino)ethanol, 1,2-diaminopropane, 1,2-diamino-2-methylpropane, 1,3-diaminopropaane, 2-amino-5-(diethylamino)pentane, 1,6-diaminohexane, or 1,2-diaminobenzene, was studied in the presence of an excess of the free ligand in solution. In this condition, the photodissociation of L becomes ineffective, and only the photolabilization of a cyanide can be observed, yielding the corresponding tetracyanoferrate(II) complexes. The quantum yields for photosubstitution of cyanide range from 0.11 to 0.025 for photolyses at 365 nm and are dependent on the N N chain length of the aliphatic diamines. The presence of bulky substituents in one of the amine groups has little influence on the photoinduced ring closure efficiency. However, methyl substituents on the carbon chain of the chelating ligand cause an increase in the quantum yield. The variation of the quantum yield with the different ligands permits comparison of several effects such as metric, topological, chelating, and neighboring group effects on the photoreactivity of the series.