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The leading European journal for inorganic and organometallic chemistry
Paper
Dalton Trans., 2004, 327 - 333, DOI: 10.1039/b312919e
A paradigm shift in the construction of heterobimetallic complexes: Synthesis of group 2 & 4 metal–calix[6]arene complexes
Antonella J. Petrella, Donald C. Craig, Robert N. Lamb, Colin L. Raston and Nicholas K. Roberts
Deprotonation of calix[6]arenes with barium in methanol followed by the addition of [Ti(OPri)4] or [Zr(OBun)4] is effective in the formation of novel dimeric 2
1 barium–titanium(IV)/zirconium(IV) calix[6]arene complexes. In these complexes a central Ti(IV)/Zr(IV) coordinated in the exo-position connects the two calix[6]arenes in the 1,3-alternate conformation, each with an endo-barium sharing common phenolate groups with the titanium/zirconium centre and participating in cation–
interactions. A homometallic barium calix[6]arene dimer was also prepared wherein the calix[6]arenes are in the 1,3-alternate conformation with each coordinating one endo- and one exo-barium centre. The exo-barium cations connect the two calix[6]arenes through bridging methanol ligands. In this and the heterometallic complexes, cation– complexation of the Ba2+ ion within the 1,3 alternate conformation of calix[6]arene facilitates the formation of the dimeric complexes in methanol. In contrast, the smaller Sr2+ ion did not form similar complexes in methanol, and the formation of an analogous 2 1 strontium–titanium calixarene complex required the use of the more sterically demanding donor alcohol, isopropanol, the resulting complex being devoid of cation– interaction. The results show (i) that a subtle interplay of solvation strength, coordination array type and cavity/cation size influences the accessibility of heterobimetallic complexes based on calix[6]arenes, and (ii) a synergistic endo–exo binding behaviour.
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