Topology of metallacalix[4]arenes with uracil and cytosine ligands: favorable and unfavorable assemblies

Abstract

Synthetic procedures reported for metallacalix[n]arenes result in the isolation of a single isomer of many topologically possible ones. We performed quantum chemical calculations (M11L, SMD) in order to understand this selective formation. An evaluation of all the feasible metallacalix[4]arene isomers, based on pyrimidine nucleobases cis-[M(a)₂(N)]₄ⁿ⁺ (M = Pd, Pt; a = NH₃; N = cytosinate, uracilate), indicates that their relative energy depends on steric factors and attractive/repulsive intramolecular interactions. Our theoretical approximation confirms that the experimentally isolated isomers are the energetically more favorable.