Two unusual metal-organic frameworks based on W/S/Cu clusters and Tetrakis(4-pyridyl)benzene: Enhanced nonlinear optics and efficient luminescence sensing

Tetradentate organic ligand 1,2,4,5-tetrakis (4-pyridyl)benzene (tpb) is firstly developed to build cluster-containing metal-organic frameworks (C-MOFs). Two unusual W/S/Cu C-MOFs {[WS₄Cu₄I₂(TPB)]·DMF}_n (1) and {[WS₄Cu₃Cl(TPB)]·2DMF}_n (2) have been synthesized and structurally characterized. 1 is fabricated by 8-connected pentanuclear planar open-shaped cluster [WS₄Cu₄]²⁺, 4-connected tetrakis-pyridine TPB unit and I⁻ bridge to form a three-dimensional (3-D) pillar-layered framework. Its (4,8)-connected topology firstly appears in W(Mo)/S/Cu C-MOFs. 2 is constructed by 4-connected T-shaped cluster [WS₄Cu₃]⁺, 4-connected TPB unit and terminal Cl⁻ ligand, and possesses a 2-D wave-like (4,4) network. Z-scan experiment reveals that 1–2 have third-order nonlinear optical (NLO) properties. Particularly, 1 exhibits significantly enhanced NLO performance. Moreover, 2 displays strong luminescence, highly sensitive and selective sensing of 2,4,6-trinitrophenol (TNP) in aqueous medium. The efficient emission quenching mechanism of 2 towards TNP is studied as well.