Preparation and Characterization of Calixa [4] rene Complexes with Zinc and Cobalt

The ligand, 5,11,17,23-tetrakis(1,1-dimethylethyl)-25, 26, 27, 28-tetrahydroxycalixa [4] rene (L1H4) was synthesized by condensing 4-tert-butylphenol with formaldehyde using base catalysis and then subjecting the mixture to thermal cyclization. This macro cyclical scaffold was used as a tetra dentate O-donor system for the construction of bimetallic complexes with Co (II) and Zn (II), never reported before, as [M2(L)]. The compounds were fully characterized through 1H NMR spectroscopy and FTIR spectroscopy, and melting point. The formation of metal coordination was confirmed with spectroscopic evidence: deprotonation of the phenolic -OH signal in 1H NMR was observed to indicate the presence of the metal-oxygen bond, and specific M-O stretching bands in the FTIR spectra (Co-O: 430-621 cm-1, Zn-O: 478-597 cm-1) confirmed the formation of a metal-oxygen bond. Comparative analysis showed that the complexes had greater structural rigidity and better thermal stability compared to the free ligand, which favors the existence of stable binuclear structures. This compound is not only an addition to the family of calixarene-based coordination compounds, but also offers clear spectroscopic references to future analysis of Co(II) and Zn(II) interaction with oxygen-donor macrocycles, which can be applied to supramolecular design, molecular recognition and catalysis.