A series of myoglobin active site analogues (1-6) has been synthesized and characterized. These synthetic models differ in their cavity dimensions, and have been designed to demonstrate the effects of steric factors on O-2 and CO binding affinities. Quantitative gas titrations were employed to measure these affinities, yielding M values that are strikingly lower than those reported for hemoglobin and myoglobin. The 1,4,7-triazacyclononane-capped porphyrin 1 has about 1200 times the CO affinity but only about 10 times the O-2 affinity of the cyclam-capped porphyrin 2, suggesting a more open gas binding cavity for 1. The cavity dimensions and conformation of 2 were determined by single-crystal X-ray structural analysis of the Zn analogue 7. This paper unequivocally demonstrates that steric effects can control the ratio of O-2/CO binding constants.

An account of the strategies for the synthesis of coordination compounds with interesting photophysical and photochemical properties is given. Ru(II)-diimine complexes have been developed with various absorption and emission characteristics and for special chemical stability of the excited state species. The isomer problem, encountered in the synthesis of polynuclear complexes, which are candidates for Photochemical Molecular Devices (PMD), is attacked by using enantiomerically pure chiral building blocks or chiragen ligands, which form metal complexes with predetermined helical chirality. Cyclometallating ligands with Pt(II) and Pd(II) can be designed, so that the photochemically induced oxidative addition reactions lead to compounds of special interest, especially from the stereochemical point of view.

Alfred Werner conjectured as early as 1899 that octahedrally coordinated metal complexes should occur in nonidentical mirror image isomers. For such objects, Lord Kelvin, in 1893, had coined the adjective "chiral", a term never used by Werner. It can be proved by examination of the original sample of [Co(NO2)(2)(en)(2)]Br, prepared by Edith Humphrey, a Ph.D. student of Werner's, that crystals of optically pure samples were obtained in Werner's laboratory as early as 1899 or 1900. However, Werner did not publish the first successful resolution of an octahedral metal complex until 1911. Presently, interest in chirality in coordination compounds is booming, mainly because of the importance of coordination compounds in enantioselective homogeneous catalysis. Other interesting applications are enantioselective interactions of chiral coordination species with biomolecules, and the stereoselective synthesis of multicenter systems.

Facile stereoselective synthesis of an enantiomerically pure DELTA-Ru-trisbipyridine type complex is accomplished by using a new chiral and conformationally rigid ligand, which completely predetermines the helical chirality of the metal, yielding exclusively DELTA-configuration in the present case. The ligand, abbreviated chiragen[6] is a bisbipyridine compound, where two pinene substituted bipyridine units are linked through an aliphatic C6-chain. The two remaining coordination sites of the complex are occupied by 4,4'-dimethylbipyridine. The structure of the DELTA-[Ru(chiragen-[6])(4,4'-dimethylbipyridine)](CF3SO3)2 complex has been determined by X-ray crystallography. Metal complexes formed by chiragen ligands have potential applications in enantioselective catalysis and as chiral building blocks for polynuclear species.

Short and efficient syntheses of two new optically active bipyridines have been accomplished using alpha-pinene as source of chirality. The new bipyridines allow easy access to chiral helicating and caging ligands of sterically well defined shapes and properties.