A unique rare-earth cluster within a calixarene sandwich: Parallels in the chemistry of cyclosiloxanes and calixarenes

Determination of the crystal structure of a complex obtained by the reaction of the dimethyl sulfoxide (dmso) solvate of neodymium( III) nitrate with p-t-butyltetrathiacalix[4]arene in dimethylformamide (dmf) in the presence of base showed a regular, planar cluster of four neodymium atoms bridged by a hydroxyl group to be sandwiched between two fully deprotonated calixarene moieties. The sulfur and oxygen donor atoms of the calixarenes are both involved in coordination to the rare-earth atoms. Both dmf and dmso are found as ligands on neodymium but occupation of the calixarene cavity is by dmf only. The proposed overall stoichiometry of the complex is [Nd-4(OH){(p-t-butyltetrathiacalix[4]arene-4H)(dmf)}(2)(dmf)(6)(dmso)(2)](NO3)(3). 3H(2)O.