A 6-Connected {Cu₂O₅} Cluster-Based Metal-Organic Framework Based on Tetrabromoterephthalate: Synthesis, Crystal Structure and Fluorescent Properties

An interseting Cu(II)-based organic framework containing a Cu₂O₅ cluster, [Cu (TBA)(CH₃OH)]_n (1) has been hydrothermally synthesized with tetrabromoterephthalate (H₂TBA) ligand, and characterized through infrared spectroscopy (IR), elemental and thermal analysis (EA), power X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD) analyses. The X-ray single-crystal diffraction analysis shows that the Cu^II center is hexa-coordinated and situated on perfect octahedral geometry formed by four carboxyl oxygen atoms of four symmetry-related TBA²⁻ anions and two O-donors of two reverse µ₂-CH₃OH bridges. Each TBA²⁻ ligand plays as a µ₄ tetra-monodentate linker and connect four Cu²⁺ cations together to form the three dimensional structure of 1. Surprisingly, there are no significant hydrogen bonds and π-stack interactions in 1, but the Br···Br halogen bonds interactions. Detailed topology analysis found that the 3D cluster-based metal-organic framework of 1 can be simplified to 4 topological types: a 4-c 1-nodal net dia with point symbol {6⁶}, a 6,6-c 2-nodal net htp with point symbol {4¹³·6²}{4⁸·6⁶·8}, a 4,6-c 2-nodal net bpq with point symbol {3²·6²·7²}{3⁴·4²·6⁴·7⁵}, and a 6,8-c 2-nodal net 6,8T902 with point symbol {3⁴·4⁴·5⁴·6³}{3⁸·4¹⁴·5⁴·6²}, respectively. Moreover, 1 exhibits intense solid-state luminescence emissions centered at 478 nm at room temperature, which mainly originates from the intraligand π→ π* transitions of TBA²⁻. The CCDC number of 1 is 2,355,788.