Framework dimensionality of copper(i) coordination polymers of 4,4′-bipyrimidine controlled by anions and solvents

Abstract

The reaction of [Cu(C₂H₄)_n]NO₃ with 4,4′-bipyrimidine (bpm) in Me₂CO under C₂H₄ afforded a polymeric Cu(I)–bpm/C₂H₄ adduct [Cu₂(bpm)(C₂H₄)(NO₃)₂]_n (1) with an infinite 1-D zigzag chain structure. Similar reactions of [Cu(C₂H₄)_n]ClO₄ or [Cu(MeCN)₄]BF₄ with bpm in Me₂CO under C₂H₄ afforded Cu(I)–bpm/C₂H₄ adducts {[Cu₃(bpm)₂(C₂H₄)₂](ClO₄)₃}_n (2) and {[Cu₃(bpm)₂(C₂H₄)₂]–(BF₄)₃}_n (3), respectively, which have an infinite 1-D zigzag ladder structure. It is interesting that two disordered ClO₄⁻ or BF₄⁻ anions are accommodated in the inside cavity of the ladder chains. In contrast, the reaction of [Cu(MeCN)₄]BF₄ with bpm in MeOH under C₂H₄ afforded a Cu(I)–bpm/C₂H₄ adduct {[Cu₄(bpm)₃(C₂H₄)₃(MeOH)](BF₄)₄·2H₂O·3MeOH}_n (4). Three Cu atoms are bridged by three bpm ligands to form a metallacalix[3]arene structure with three legs of C₂H₄. Furthermore, these metallacalix[3]arenes are linked through another Cu atom in the terminal N atom of bpm to produce a chiral 2-D sheet structure with space groupP6₃. One BF₄⁻ anion is accommodated in the small triangular Cu₃ cavities, whereas three disordered BF₄⁻ anions are encapsulated in the large triangular Cu₃ cavities. In contrast to complex 4, [Cu(MeCN)₄]BF₄ was reacted with bpm in MeOH under Ar, and C₂H₄ gas was then bubbled into the resultant brown suspensions. The reaction solution was allowed to come to room temperature, and Cu(I)–bpm complex {[Cu₃(bpm)₃](SiF₆)_1.5}_n (5) was collected. The tetrahedral Cu atom is coordinated by two N atoms in the chelate site of bpm and two N atoms in the terminal sites of two other bpm ligands to form two racemic metallacalix[3]arene structures. It is noteworthy that these metallacalix[3]arenes are joined through the bpm ligands to afford a 3-D cage structure consisting of two right-handed and left-handed helix networks. One disordered SiF₆²⁻ anion is accommodated in the inside cavity between two opposite metallacalix[3]arene structures. On the basis of these results, it has been concluded that BF₄⁻, PF₆⁻, ClO₄⁻ and SiF₆²⁻ anions can serve as anion templates to self-assemble polymeric Cu(I) C₂H₄ adducts and a cage compound in complexes 2–5. The NO₃⁻ anion is ineffective as an anion template, as indicated by the higher coordination ability of the NO₃⁻ anion in complex 1. Additionally, solvent-dependent effects have been observed in the formation process: Me₂CO can preferentially induce polymeric 1-D chain and 1-D ladder structures in complexes 1–3, whereas MeOH can produce 2-D sheet and 3-D cage structures by the linkage of metallacalix[3]–arene structures in complexes 4 and 5.