Cover Picture: Heterobimetallic Calix[4]arene Complexes: Interconversion of Dimeric (Ca, Sr or Ba)/TiIV Complexes with a Monomeric K/TiIV Complex (Eur. J. Inorg. Chem. 23/2003)

Abstract

AbstractThe cover picture shows the structures of two new types of calix[4]arene complexes obtained by deprotonating the calixarene with an alkaline earth metal, or potassium metal, followed by reaction with selected titanium(IV) compounds. The alkaline earth metals form dimeric alkaline earth‐titanium(IV) complexes, containing at the core a rhombus of alternating alkaline earth metal and μ3‐oxo centres. Each oxo centre of the rhombic core is the apical ligand of a square‐pyramidal titanium(IV) centre, whose basal plane donors are the four phenolate oxygen atoms from a calix[4]arene arrayed in the symmetrical cone conformation. Terminal methanol ligands surround the alkaline earth centres, and simultaneously hydrogen‐bond to the adjacent phenolate oxygen atoms. Potassium reacts with calix[4]arene and the titanium(IV) source to give a monomeric mixed potassium‐titanium complex. The potassium cation binds within the κ‐basic calix[4]arene cavity, whilst the titanium centre is octahedrally complexed in the exo position by four phenolate and one acetylacetonate ligands. A solution pathway exists for the interconversion between the potassium‐titanium calix[4]arene monomer and the alkaline earth‐titanium dimers, where the product is dictated by the choice of solvent. Details are discussed in the article by R. N. Lamb et al. on p. 4153 ff.