Using long bis(4-pyridyl) ligands designed for the self-assembly of coordination frameworks and architectures

Abstract

Five long bis(4-pyridyl) ligands with different tether groups, namely 1,4-phenylenebis(4-pyridylmethanone) (L¹), bis(4-pyridyl)terephthalate (L²), 1,5-bis(pyridin-4-ylmethoxy)naphthalene (L³), 1,4-bis[2-(4-pyridyl)ethenyl]benzene (L⁴) and 4,4′-bis(pyridin-4-ylmethoxy)biphenyl (L⁵), have been synthesized and employed for the self-assembly of coordination polymers and architectures, with the aim of obtaining structural motifs characterized by long metal–metal separations. Six coordination products (compounds 1–6) have been obtained by reacting the ligands with cobalt(II) nitrate in all cases but one, in which zinc(II) triflate was used. The crystal structures show a variety of structural motifs. [Co(L²)(NO₃)₂(MeCN)]·MeCN (2) and [Co(L⁵)(NO₃)₂] (5) contain one-dimensional polymeric chains (linear, with a period of 19.64 Å in 2; zigzag, with a period of 38.65 Å in 5). [Zn(L¹)(H₂O)₄](CF₃SO₃)₂·(L¹)₂·H₂O (1) and [Co(L⁴)₂(H₂O)₄](NO₃)₂·(L⁴)₄·(H₂O)₈ (4) exhibit extended three-dimensional and two-dimensional arrays, respectively, sustained both by coordinative and hydrogen bonds. Compound 3, [Co(L³)₂(NO₃)₂]·(CH₂Cl₂)₂, consists of two-dimensional layers of large rhombic meshes (diagonals of the rhombus 15.43 and 35.74 Å), while compound 6, [Co₂(L⁵)₄(NO₃)₄]·(Me₂CO)₂, contains discrete dinuclear molecules, consisting of large rings with appendages, which exhibit an exceptionally long dimension of 62.84 Å and form columnar supramolecular arrays.