Synthesis, structure, magnetism, luminescence and DFT analysis of three metal-organic complexes based on 2,5-di(1H-1,2,4-triazol-1-yl)terephthalic acid

Abstract The three multi-dimensional coordination polymers, [Mn2(μ4-dttpa)(μ6-dttpa)(H2O)2]n(1), {[Co(μ4-dttpa)(H2O)2]·2H2O}n(2), and {[Zn3(μ4-dttpa)2(μ2-dttpa)(phen)2(H2O)2]·2H2O}n(3) (H2dttpa ​= ​2,5-di(1H-1,2,4-triazol-1-yl)terephthalic acid; phen ​= ​1,10- phenanthroline), are successfully synthesized and characterized by X-ray single crystal diffraction, powder X-ray diffraction (PXRD), FT-IR spectra, elemental analysis and thermogravimetric analysis. Structurally, complex 1 is a three-dimensional structure with the 3-nodal Schlafli point symbol of {4·63·82}2{42·62·82}{62·84}. Complex 2 displays a two-dimensional network with a 6-connected uninodal net. With the point symbol of {4·62}2·{43·63}2·{44·62}{6}, complex 3 shows the two-dimensional stacking pattern. Temperature-dependent magnetic data of complexes 1 and 2 indicate antiferromagnetic behaviors between adjacent metal ions from 2 ​K to 300 ​K. Further magnetic studies show that the best fitting parameters of comple×1 are obtained using the dinuclear Mn(II) model. From 50K to 300K, complex 2 displays antiferromagnetism over its mononuclear analogue with the zero-field splitting parameter (|D| ​= ​35.2 ​cm−1). The luminescent intensity of complex 3 is much stronger than that of free ligand (H2dttpa) and auxiliary ligand (phen). Moreover, the photoluminescence mechanism of complex 3 has been analyzed by theoretical calculation at ωB97XD/6–311++g(2d,p) level with DFT and TDDFT, which reveals that luminescence emission of 3 is attributed to the ligand-to-ligand charge transfer (π∗phen-πdttpa2-). Compared with the free ligand, the enhancement of the luminescent intensity of compound 3 might occur due to the construction of Zn(II) ion, dttpa2− and phen increases the efficiency of charge transfer between LUMO and HOMO in the solid state.