Metallosupramolecular architectures based upon new 2-(1-pyrazolyl)-benzimidazole chelating ligands

Abstract

In this article, we report the synthesis and characterisation of five ligands L1–L5 containing the 2-(pyrazol-1-yl)-benzimidazole chelating group, and investigate their structural chemistry when reacted with either Cu(II) or Zn(II) ions. The mononuclear complexes [Zn(L1)2(NO3)]NO3, 1 and [Cu(L2)2(NO3)]NO3, 2, display similar metal coordination environments although their intermolecular interactions differ through the presence or absence of a benzimidazole N-H group, which allows intermolecular hydrogen bonding to occur in 1, while complex 2 associates purely through π–π interactions. The crystal structure of the dinuclear complex {[Cu2(L3)2(OH2)2]4(ClO4)·PhMe·2MeCN·2H2O}, 3, reveals a series of cyclic units containing internal cavities, within which reside disordered toluene molecules, and which align to form one-dimensional solvent channels throughout the crystal lattice. The structure of the related complex {[Cu2(L4)2(NO3)2]2(NO3)·MeCN}, 4 consists of dimeric units of similar formulation to that of 3, but it contains no internal cavity, and shows a reversal of the relative metal–nitrogen bond length trend observed for the other complexes, due to the steric strain imposed by the backbone group. The structure of complex {[Cu2(L5)2(OH2)2]4(BF4)·0.5(C9H12)}, 5 shows that it forms similar cyclic dimers to those observed in 3, which align throughout the crystal lattice to form much larger (ca. 1 nm diameter) solvent channels.