Assembly of a Series of Trinuclear Zinc(II) Compounds with N2O2 Donor Tetradentate Symmetrical Schiff Base Ligand

Self-assembly of the symmetrical tetradentate N2O2 donor Schiff base ligand, that is, bis(salicylidene)trimethyl-enediamine (sy-H2L3), with different zinc salts has led to six anion-dependent complexes, namely, [Zn-3(sy-L-3)(2)(mu(2)-Cl)Cl(C2H5OH)]center dot C2H5OH (1), Zn[Zn(sy-L-3)(mu(2)-NO2)(C2H5OH)](2)center dot 2H(2)O (2), Zn[Zn(sy-L-3)(mu(2)-CH3COO)](2) (3), Zn(DMF)(2)[Zn(sy-L-3)(H2O)(SCN)](2) (4), Zn[Zn(sy-L-3)(mu(2)-HCOO)(DMF)](2)center dot H2O (5) and Zn[Zn(sy-L-3)(mu(2)-HCOO)](2) (6), respectively. Six compounds were characterized by elemental analyses, 1R spectra, mass spectrometry and thermogravimetric analyses, of which five structures 1, 2, 4, 5, and 6 were further determined by single-crystal X-ray diffraction analyses, and compound 3 was previously reported in the literature. It was observed that mu(2)-bridges in these trinuclear complexes were formed through the phenolic oxygens of the ligand or the anions in the medium. In the presence of nitrite (for 2), acetate (for 3), thiocyanate (for 4), or formate (for 5-6), mu(2)-bridges formed between a pair of adjacent zinc atoms resulting in linear trinuclear complexes with one symmetrical center. However, mu(2)-bridges involving chloride and the phenolic oxygens of ligand sy-H2L3 led to the formation of a V-shaped trinuclear complex 1. It is noteworthy that in the assembling process of complexes 4-6, when the appropriate amount of DMF was added to the reaction mixture, thiocyanate anion coordinated to the terminal Zn2+ ion in a,eta(1)-N coordination manner and gave compound 4 with a coordination of water molecules and DMF molecules to the terminal and the middle zinc ions in a range from room temperature to 70 degrees C. Above similar to 70 degrees C, C-N bond cleavage of part of the solvent DMF molecules induced the formation of compounds with coordination of formate and DMF to Zn2+. Upon increasing the temperature higher than 110 degrees C, because of the decomposition of a large number of DMF molecules, the same reaction produced trinuclear complex 6, in which only formate coordinated to a pair of the adjacent zinc atoms in a mu(2)-bridging coordination fashion. In addition, photoluminescent properties and biological activities of ligand sy-H2L3 and six corresponding compounds were also studied.