Uranyl complexes of p-t-butylcalix[8]arene as H-bond acceptors—subtle effects of the donors

Leaving a mixture of excess N,N,N′,N′-tetramethyl-1,4-butanediamine (Me₄BDA) with p-t-butylcalix[8]arene (L) and [(UO₂)(dmso)₅](ClO₄)₂ in a 1:2 ratio in acetonitrile solution to stand for an extended period resulted in the deposition of a mixture of three different crystalline materials. Single crystal X-ray structural studies were carried out to determine that the three materials were the solvated uncomplexed macrocycle L.1.5MeCN, and two uranyl complexes. These were formulated as (Me₄BDAH₂)²⁺[(HO)(UO₂)₂(L-5H)]^2–·9MeCN·H₂O and (Me₄BDAH₂)²⁺[HO(UO₂)₂{L-5H)]^2–·(Me₃BDAH)⁺[H₂O(UO₂)₂(L-5H)]⁻·Me₄BDA·14MeCN·H₂O·CH₃OH respectively. In contrast to analogous systems based on 1,2-ethanediamine and 1,3-propanediamine derivatives, extension of the chain length separating the N-centres to (CH₂)₄ in the present systems has resulted in the formation of polymeric chains where the calixuranate anions are linked by H-bond acceptance from diammonium units. These links are still not completely direct and pass in part through solvent bridges. Direct double interactions do occur in the inverse situation where the calixarene acts as an H-bond donor to neutral 1,4-butanediamine species but lead only to dimerisation.