New architectures from the self-assembly of MIISO4 salts with bis(4-pyridyl) ligands. The first case of polycatenation involving three distinct sets of 2D polymeric (4,4)-layers parallel to a common axis

Abstract

New network structures and topologies have been obtained from the reactions of different metal(II) sulfates with three bis(4-pyridyl) spacer ligands, that illustrate the influence of the SO₄²⁻ anions in the self-assembly of polymeric coordination architectures. The products include [Fe(bpp)₂(SO₄)] [bpp = bis(4-pyridyl)propane] (1), [Cd(bpethy)(SO₄)] [bpethy = bis(4-pyridyl)ethyne] (2), [Cu(bpe)(SO₄)(H₂O)]·2H₂O [bpe = bis(4-pyridyl)ethane] (3), [Co₂(bpe)₃(SO₄)₂(MeOH)₂]·xSolv (4) and [Ni₆(bpe)₁₀(H₂O)₁₆](SO₄)₆·xH₂O (5). In compounds 1–4 the SO₄²⁻ anions are directly involved in the polymeric frameworks, forming bridges that connect different metal centres. Compound 1 contains one-dimensional ribbons of rings joined by the anions to give a 3D array with the CdSO₄-type topology. In compound 2 the Cd²⁺ cations are connected by μ₄–η⁴-bridging anions to give 2D layers of linked octahedra and tetrahedra, that are joined by the bpethy ligands into a 3D array. The structure of compound 3 consists of simple Cu(bpe) chains linked by the anions into 2D sheets. Compound 4 is a complex polymer comprised of highly undulated 2D layers of folded quadrilateral meshes; the layers are deeply interdigitated and joined together by the anions, thus resulting in an unique 3D architecture containining 6- and 4-connected cobalt centres. Compound 5 is the more interesting species in that it is an entangled array of three distinct sets of layers. It contains two different types of 4-connected 2D motifs, i.e. undulated layers of rectangular meshes and square grid layers, in a ratio of 2 ∶ 1. The three sets are parallel to a common axis but show a relative rotation of ca. 120° about it, giving a common axis, giving inclined interweaving in an unprecedented ‘parallel/parallel/parallel’ fashion, to generate a unique 3D architecture.