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

Highlights: • The luminescence mechanism of Zinc(II) compound has been elaborated by DFT and TDDFT analysis. • Summary and comparison of dttpa²⁻ complexes in this paper and published in literature. • A new coordination mode μ₂-(η¹)-(η¹) of dttpa²⁻ in the solid state is first published. 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 Schläfli 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 2K to 300K. 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|=35.2cm⁻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-π_dttpa2-). 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.