Toward the synthesis of coordination polymers using tetrazolethiones as linkers

Coordination polymers consist of metal ions joined together by organic ligands through coordinate bonds to form arrays extending in one, two, or three dimensions. In order to form polymeric structures, ligands used to construct these materials must be multidentate, containing two or more donor atoms (N, O or S). Tetrazoles, which contain four nitrogen atoms, are widely used to construct coordination polymers, but limited work has been done on tetrazolethiones, the thiol derivatives of tetrazoles. Therefore, the goal of this research was to design tetrazolethionebased coordination polymers and understand how the presence of 5-thio group affects crystal packing compared to the parent tetrazoles. This work focused on generating coordination polymers from the following (hetero)aryl tetrazolethione ligands: 1-(4-bromophenyl)-1,4-dihydro-5H-tetrazole-5-thione, 1-(pyridin-3-yl)- 1,4-dihydro-5H-tetrazole-5-thione, ethyl 4-(5-thioxo-4,5-dihydro-1H-tetrazol-1-yl)benzoate, 1,1'- (1,4-phenylene)bis(1,4-dihydro-5H-tetrazole-5-thione, and 4-(5-thioxo-4,5-dihydro-1H-tetrazol- 1-yl)benzoic acid. Attempts to generate coordination polymers from these ligands have focused on two different methods, (1) solvothermal/hydrothermal reactions (ligand synthesized in situ or independently) and (2) slow diffusion (ligand synthesized independently). Hundreds of reactions were conducted using these methods by varying the ligand, metal ion, solvent, pH, temperature, and reaction stoichiometry, and by adding secondary ligands. Single crystals suitable for X-ray crystallography were obtained in only a few reactions. Hydrothermal reactions involving in situ ligand synthesis proved challenging as the X-ray diffraction analyses revealed the thermal decomposition of 1-(4-bromophenyl)-1,4-dihydro-5Htetrazole- 5-thione ligand to form unanticipated products (e.g., aminotetrazoles and guanidinium salt) during the reaction with cadmium(II) acetate, cadmium(II) nitrate, zinc(II) perchlorate and nickel(II) nitrate. One zinc-based 2D coordination polymer from the reaction of 4-(5-thioxo-4,5- dihydro-1H-tetrazol-1-yl) benzoic acid with zinc(II) acetate in the presence of 4,4′-bipyridine as bridging ligand was obtained, in which the zinc ion assumes a distorted trigonal bipyramidal geometry, associating with two tetrazolethione ligands (via carboxyl group and sulfur) and two bipyridine ligands. Slow diffusion afforded 1D chains of a Zn-based coordination polymer from 1-(4-bromophenyl)-1,4-dihydro-5H-tetrazole-5-thione during the reaction with zinc(II) nitrate. However, the slow diffusion of 4-(5-thioxo-4,5-dihydro-1H-tetrazol-1-yl) benzoic acid to a solution of manganese(II) chloride yielded a disulfide. Lastly, this work also showed that dimethyl 5-isothiocyanatoisophthalate can be obtained in decent yields from dimethyl 5-aminoisophthalate by reaction with CS2 and Et3N (3.3 equiv.) in acetone/THF mixture to generate the dithiocarbamate salt, followed by iodine-mediated desulfurization in a separate pot.