The structural evolution and tunable photoluminescence of f-element bearing coordination polymers of the 2,4,6-tri-α-pyridyl-1,3,5-triazine ligand

Abstract

The exploration of the family of f-element bearing single-molecule coordination polymers via solvothermal reactions yielded fourteen new rare-earth single-molecule complexes with three distinct phases, Ln(TPTZ)(NO₃)₃CH₃CN (LnTPTZ-1, Ln = Pr and Nd), [Ln(TPTZ)(NO₃)₃(H₂O)]·CH₃CN (LnTPTZ-2, Ln = Pr–Er), and [Ln(TPTZ)(NO₃)₃(H₂O)]·2CH₃CN (LnTPTZ-3, Ln = Tm–Lu), as well as a uranyl coordination polymer UO₂(TPTZ)(NO₃)₂ (UTPTZ). All of the structures exhibited zero-dimensional topologies due to the self-assembly of f-element cations with 2,4,6-tri-α-pyridyl-1,3,5-triazine (TPTZ), a tridentate semiaperture ligand featuring three ortho-N atoms on its pyridine and triazine rings. Due to the effect of lanthanide contraction, the structural evolution of the lanthanide complexes, including decrease in the unit cell dimensions and Ln–O/N bond lengths across the isomorphic structures, and more dramatically, transitions in the overall topology, was observed. In addition, a rather unusually bent O_ylUO_yl unit with a highly distorted hexagonal bipyramid coordination environment was identified in UTPTZ. The homoleptic structures of EuTPTZ-2 and TbTPTZ-2 allowed the fine-tuning of the molar ratio Eu/Tb in a single Eu_xTb_1−xTPTZ-2 complex, concomitantly giving rise to versatile photoluminescent colours in such materials. Explicitly, it exhibited multicolour photoluminescence ranging from green to red under the excitation of UV light, and an excellent linear relationship between chromacity coordinates and colour tunability could be obtained.