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A novel approach for the direct synthesis of a 1,2,4-triazine core starting from eight azo conjugated aromatic compounds, 5-azo-(1,2,4-triazolyl) salicylic acid, 5-azo-(3-methyl-1,2,4-triazolyl) salicylic acid, 5-azo-(3-carboxyl-1,2,4-triazolyl) salicylic acid, 5-azo-(1,2-pyrazolyl) salicylic acid, 4-azo-(1,2,4-triazolyl) phenol, 4-azo-(3-carboxyl-1,2,4-triazolyl) phenol, 4-azo-(1,2-pyrazolyl) phenol, and 5-azo-(1,2,4-triazolyl) acetylsalicylic acid, via transition or lanthanide metal catalyzed intramolecular C–H/N–H functionalization and C–N bond formation has been developed under one-step hydrothermal synthetic conditions. [ABSTRACT FROM AUTHOR]

Two hydrated 5-azotetrazolyl salicylic acid (H3ASA) of [(H3ASA)·H2O] (1) and [(H3ASA)·4H2O] (2) and five H3ASA based dinuclear Ln(3+) complexes of {[Ln2(H1.5ASA)4(H2O)8]·6H2O} [Ln = Dy (3), Tb(4)], {[Gd2(H1.5ASA)4 (H2O)8]·5H2O} (5), {[Sm2(H1.5ASA)4(H2O)8]·6H2O} (6) and {[Eu4(H1.5ASA)8(H2O)18]·10H2O} (7) have been synthesized and characterized by single crystal X-ray diffraction analysis. In 1 and 2, the neutral H3ASA molecules show a trans-enol-E isomer but display two different dihedral angles. Complexes 3-7 exhibit three types of dinuclear structures in which the anionic ligands show two trans-enol-E/Z isomers. The photochromic and photoluminescent properties of 1, 3-7 and the magnetic properties for 3-7 were investigated.