The role of inner- and outer-sphere ligands in pivalate and cymantrenecarboxylate complexes of transition metals

The formation of transition metal complexes with pivalate and cymantrenecarboxylate ligands in the presence of axial cyclopentadienyl and alpha-substituted pyridine ligands is discussed. The latter present steric hindrances due to repulsion from the O atoms of the carboxylate bridges. Particular emphasis is placed on the role of outer-sphere ammonium cations: their hydrogen bonding to fluoride bridges limits the growth of cyclic chromium(III) complexes with the pivalate and fluoride ligands that possess the properties of molecular magnets.