Construction of 0D to 3D cadmium complexes from different pyridyl diimide ligands

Abstract

Four semirigid ditopic ligands, N,N′-bis(3-pyridylmethyl)-pyromellitic diimide (L¹1), N,N′-bis(4-pyridylmethyl)-pyromellitic diimide (L²2), N,N′-bis(3-pyridylmethyl)-naphthalene diimide (L³3), and N,N′-bis(4-pyridylmethyl)-naphthalene diimide (L⁴4), reacted with Cd(NO₃)₂ to result in four cadmium(II) complexes, namely, {[Cd₂(L¹1)₂(NO₃)₄(CH₃OH)₄]·H₂O} (1), [Cd(L²2)(NO₃)₂(CH₃OH)₂·Cd₂(L²2)₃(NO₃)₄]·{4(HCCl₃)·2H₂O}_n (2), {[Cd(L³3)₂(NO₃)₂]}_n (3), and {[Cd(L⁴4)₂(NO₃)₂]·2(CHCl₃)}_n (4). These complexes have been characterized by elemental analyses, powder X-ray diffraction, thermogravimetric (TG) analyses, IR spectroscopy, and single-crystal X-ray diffraction. Structural analyses show that four types of structures are formed: (1) a discrete M₂L₂ ring with two Cd ions and two cis-L¹1 ligands comprising a zero-dimensional molecular rectangle (0D), (2) an unusual zigzag linear chain and a one-dimensional ladder existing simultaneously in the crystal lattice (1D), (3) a two-dimensional network of the (4,4) net structure (2D), and (4) an unusual chiral three-dimensional framework with 5-fold interpenetrating diamond (dia) topology (3D). In these complexes, the ligands exhibit different coordination modes and construct various architectures by bridging Cd(NO₃)₂ inorganic building blocks. These results suggest that structural diversity of the complexes is tunable by ligand modifications, that is, varying the ligand spacer bulkiness or substituent position of terminal group. Furthermore, gas adsorption measurements indicate that 4 possesses moderate CO₂ uptake and some adsorption selectivity for CO₂ over N₂.