A new 3D HoIII-organic framework constructed from 1,3,5-tris(4-carboxyphenyl)benzene and 1,10-phenanthroline: Crystal structure, morphological and solid state luminescence properties

A new polynuclear LnIII coordination compound (1) with the stoichiometric formula {[Ho(BTB)(phen)]·(DMF)}n, (H3BTB ​= ​1,3,5-Tris(4-carboxyphenyl)benzene, phen ​= ​1,10 –phenanthroline monohydrate and DMF ​= ​N, N – dimethylformamide) has been synthesized by the solvothermal method and characterized by the infrared spectroscopy, thermogravimetric analysis, single-crystal X-ray diffraction studies, elemental analysis and solid-state electronic absorption properties and solid-state photoluminescence measurements. The XRD analyses indicate that 1 crystallizes in a monoclinic system with space group P21/c and also each HoIII ion has eight coordination, forming a distorted square antiprismatic geometry. For all the coordinated oxygen atoms, six of them belong to five carboxylate groups from different BTB3−ligands, while two nitrogen atoms from only one phen ligand were involved in the coordination. Two crystallographically equivalent HoIII ions are bridged to a dimeric unit as secondary unit buildings (SUBs) by four carboxyl groups in different directions, which also form typical 1D hexagonal channels with BTB3− ligands, these channels are connected in a three-dimensional (3D) framework. Also, these open channels were occupied by two different BTB3− ligands. According to the 3D Hirshfeld surface and 2D fingerprint plots analysis, H⋯H intermolecular interactions are the dominant interactions in the HoIII. Additionally, the π⋯π stacking information determined by the shape index and curvedness plots coincides with the crystal structure analysis. Moreover, photoluminescence properties of 1 were recorded and investigated at room temperature in the Vis-NIR region. Under the excitation of UV light, 1 exhibited strong yellowish-orange emission with CIE chromaticity coordinates (0.480, 0.430). 1 emits at 521, 575 and 653 ​nm correspond to 5F3 → 5I8, 5S2 +5F4→ 5I8 and 5F5→ 5I8 in the visible region, whereas only one weakly peak at 761 ​nm originated to 5S2 +5F4→ 5I7 in the NIR region. This polymeric complex can potentially be applied to luminescent probes or OLEDs.