Tuning structures and emissive properties in a series of Zn(ii) and Cd(ii) coordination polymers containing dicarboxylic acids and nicotinamide pillars

Abstract

New coordination polymers are reported. All polymers were prepared from a blend of four dicarboxylic acids, three neutral nicotinamide ligands, and Zn(II) or Cd(II) salts. The acids included: malonic (H₂mal), succinic (H₂suc), adipic (H₂adi), and 1,4-benzenedicarboxylic (H₂bdc) acids, with all of them varying in length and rigidity of the carbon skeletons. The neutral ligands included two positional isomers, isonicotinamide (iso-nia) and nicotinamide (nia), and a nia thio-analogue, thionicotinamide (S-nia). The preparation resulted in eight Cd(II) and four Zn(II) coordination polymers: [Cd₂(suc)(sucH)₂(nia)₄]_n (1), {[Cd(suc)(nia)₃]·H₂O·dmf}_n (2), {[Cd(adi)(iso-nia)₂]·dmf}_n (3), [Cd(adi)(iso-nia)₂]_n, (4), {[Zn(mal)(iso-nia)(H₂O)]·dmf}_n (5), {[Cd(mal)(iso-nia)(H₂O)]·dmf}_n (6), {[Zn(mal)(nia)(H₂O)]·dmf}_n (7), {[Cd(mal)(nia)(H₂O)]·dmf}_n (8), {[Zn(mal)(S-nia)(H₂O)]·dmf}_n (9), {[Zn(bdc)(nia)₂]·dmf}_n (10), {[Cd(bdc)(nia)₂]·dmf}_n (11), and nicotinamide-free {[Cd(bdc)(H₂O)₂(dmf)]·dmf}_n (12). Compounds 1–4 and 12 consist of one-dimensional arrays, while compounds 5–11 are two-dimensional coordination arrays. The coordination cores in 1, 3, 4, 10, and 11 present {M₂(COO)₂} (M = Zn, Cd) binuclear clusters, while the networks of 2, 5–9 and 12 are built on mononuclear metal nodes with nicotinamide ligands acting as double or single pillars. The structure-confirmed single crystal to single crystal transformation of 3 into 4 was detected and reported. While 1 and 4 are solvent-free apohosts, the remaining solids acted as hosts of water and dmf solvent which are accommodated in the crystal lattices as coordinated ligands or lattice solvents. The new solids were characterized by IR spectroscopy, thermogravimetric analysis, and single-crystal and powder X-ray diffraction methods. The luminescence properties of six as-synthesized coordination polymers and of some activated products are reported. The influence of the metal, ligand, and solvent on tuning the structures and emission properties was monitored, and the most impressive effects were interpreted with the help of TD-DFT computations.