Synthesis, structures and luminescence of several coordination complexes based on β-octamolybdate and Ag/Cu phosphine units†
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Abstract
Four new POM-based coordination complexes [Cu(TPP)2(CH3CN)2]2{[Cu(TPP)2]2(β-Mo8O26)}·2CH3CN (1) (TPP = triphenylphosphine), {[Ag(TPP)]2·[Ag(TPP)2]2·(β-Mo8O26)}·6DMF (2), {[Cu2(DPPM)2(CH3CN)]2(β-Mo8O26)}·2CH3CN·2DCM (3) (DPPM = bis(diphenylphosphino)methane), and {[Ag2(DPPM)2·(CH3CN)]2(β-Mo8O26)}·2CH3CN·2DCM (4) were prepared through the self-assembly of α-octamolybdates and the corresponding Cu/Ag phosphine building blocks. Single crystal X-ray diffraction reveals that compound 1 consists of two cations of [Cu(TPP)2(CH3CN)2]+ and one anion of {[Cu(TPP)2]2(β-Mo8O26)}2−; the anion of {[Cu(TPP)2]2(β-Mo8O26)}2− can be viewed in such a way that the central cluster of β-Mo8O26 are coordinated with two Cu(TPP)2 units via terminal oxygen atoms to form a linear trimer; compound 2 is a neutral cross-like pentamer which is made up of the central β-Mo8O26 coordinated with two equatorial Ag(TPP)2 units and two Ag(TPP) units above and below the β-Mo8O26 cluster via the terminal oxygen atoms; compounds 3 and 4 can be viewed as a trimer consisting of two binuclear metal clusters of {[Cu2(DPPM)2(CH3CN)]2}2+ or {[Ag2(DPPM)2(CH3CN)]2}2+ bridged by one β-Mo8O26 cluster via terminal oxygen atoms. Their structures are further evidenced by FT-IR and PXRD. TGA study indicates that the skeleton of compounds 1–4 is stable up to 250–290 °C and then a rapid weight loss followed. Their band gaps can be calculated (Eg value: 2.27 eV for 1, 3.14 eV for 2, 2.66 eV for 3, and 3.16 eV for 4) using the Tauc's method according to their solid state UV diffuse reflection spectra. Upon irradiation at 211 nm, compounds 1–4 exhibit a series of successive emissions around 360 nm, 380 nm and 400 nm, which demonstrate a similar solid state emission compared to their corresponding Cu/Ag phosphine building blocks.
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