New Coordination Polymers of Copper(I) and Silver(I) with Pyrazine and Piperazine: A Step Toward "Green" Chemistry and Optoelectronic Applications.

Abstract

Five coordination polymers and one hexanuclear cluster have been obtained, and their crystal structures were determined upon reaction of Cu(I) or Ag(I) precursors with pyrazine (Pyz) or piperazine (Ppz). Five complexes are mixed-imine-ligand with anionic-fluorinated pyrazolate [3,5-(CF3)2Pz]- ([PzF]-) besides Pyz or Ppz, whereas the sixth had the neutral diimine as a single chromophore. Complexes 1-3 are isomers of the same Cu/PzF/Pyz composition with the same or different unit cell stoichiometry, namely, {Cu6[3,5-(CF3)2Pz]6(Pyz)3(CH2Cl2)}∞ (1·CH2Cl2), {Cu2[3,5-(CF3)2Pz]}2(Pyz)2·toluene}∞ (2·toluene), and {Cu3[3,5-(CF3)2Pz]3(Pyz)1.5·1.5benzene}∞ (3·1.5benzene), respectively. Altering only the metal attains {Ag6[3,5-(CF3)2Pz]6(Pyz)2·2benzene} (4·2benzene), while also changing the neutral diimine attains {Ag2[3,5-(CF3)2Pz]2(Ppz)}∞ (5). Using Pyz without an anionic imine yields {[Cu(Pyz)(MeCN)2][BF4]}∞ (6). The crystal structure of 1 shows two trimers linked together with two pyrazine ligands. Crystals of 2 represent a metal-organic framework (MOF-TW1) with significant surface area (1278 m2/g) and porosity (23.7% void volume) without considering toluene adsorbates in channels. MOF-TW1 was obtained serendipitously upon a reaction attempt to attain a mixed-metal product, instead attaining a Cu(I)-only product with interconnected four-coordinate dinuclear units. Likewise, 3 was obtained through a transmetalation of all Ag atoms in 4 to replace them by Cu atoms. Three reactions (to obtain 1, 4, and 5) were successfully carried out by both solvent-mediated and solventless transformations, whereas 2 and 3 were obtained only by solvent-mediated reactions, while 6 was attainable only by solventless transformations. The solventless transformations occurred either by sublimation and vapor diffusion or by mechanical grinding at ambient laboratory conditions-without the aid of heating, high pressure, vacuum, or any automated equipment. All transformations could be monitored by the human eye as the reaction progresses, as evidenced by progressive discoloration and/or luminescence changes. All crystal structures were obtained with the aid of conventional crystal growth methods from organic solvents for bulk products obtained from both solvelntless and solvent-mediated reactions. Powder X-ray diffraction was used to compare bulk products with one another and the crystallographic products. All Cu(I) products are colored and nonluminescent; the progress of their vapor diffusion-based solventless reactions can be followed by gradual discoloration of white solid reactants and/or quenching precursor's phosphorescence. Both Ag(I) products were colorless with 4 being luminescent but not 5.