A Ni8 metallacalix[4]arene and a Cu4 molecular rhomboid: limiting the nuclearity of carboxysalen-like metal complexes

Abstract

Octanuclear [Ni₂(L)(H₂O)₂]₄·7CH₃OH·12H₂O (1·7CH₃OH·12H₂O) and tetranuclear [Cu₂(HL)(CH₃OH)_1.5(H₂O)_1.5]₂(ClO₄)₂·2CH₃OH (2·2CH₃OH) (H₄L = 4-carboxysalpn or N,N′-bis(4-carboxysalicylidene)-1,3-propylenediamine) are obtained from similar reactions, the main difference coming from the slightly higher pH of the medium for the nickel reaction vessel. This small disparity of the pH leads to full deprotonation of the ligand in 1 while one of the carboxylic functions remains protonated in 2, making it unable to act as a donor and, therefore, justifying the different nuclearity of both compounds. In any case, the isolation of complexes of H₄L with limited nuclearity is remarkable, given that similar carboxysalen-based ligands lead to coordination polymers when the carboxylic functions are partially or fully deprotonated. This indicates that not only the pH of the medium but also the longer propylene spacer of the Schiff base have a fundamental role in the nuclearity of the isolated products. 1·7CH₃OH·12H₂O is an odd Ni₈ 1,3-alternate metallacalix[4]arene, formed from four symmetry-related [Ni₂(L)(H₂O)₂] metalloligands, joined through the fully deprotonated carboxylic functions. 2·2CH₃OH is a molecular rhomboid, built from two [Cu₂(HL)(CH₃OH)_1.5(H₂O)_1.5]⁺ metallotectons, linked through the only deprotonated carboxylic group of the ligand, the protonated carboxylic moiety remaining uncoordinated. In addition, the magnetic analysis of both polynuclear compounds shows that they are antiferromagnetic in nature and that the magnetic interaction between dinuclear metallotectons is negligible.