Sulfidation of single molecular sheets of MoO3 pillared by bipyridine in nanohybrid MoO3(4,4′-bipyridyl)0.5

Abstract

Individual sheets of MoO3 in MoO3(4,4′-bipyridyl)0.5 (basal spacing d002 = 1.12 nm) can be considered as two-dimensional (2D) inorganic "macromolecules" while the interlayer organic ligands can be viewed as "pillars" to support or as "threads" to suspend these 2D host planes. This work concerns a sulfidation investigation of single molecular sheets of MoO3 in the single crystals of the above compound under a H2S/H2 stream with various characterization methods. It is found that at a temperature as low as 100 °C, formation of surface HxMoO3-(4,4′-bipyridyl)0.5 commences. A surface product of MoO2-xSx is also observed throughout 100-200 °C. At 250 °C, all these intermediate phases are transformed completely to a final phase MoS2(4,4′-bipyridyl)0.2 (basal spacing d001, = 1.02 nm) accompanying a partial deintercalation (from 0.5 down to 0.2) of 4,4′-bipyridine molecules from the interlayer space. In this connection, 4,4′-bipyridine molecules change from a standing configuration to a lying one after this sulfidation process. Although this new phase is thermally stable at its formation temperature (250 °C), inter-slab condensation of MoS2 (basal spacing d002 = 0.62 nm) can also be observed in the topmost surface region. A mechanism based on these findings is also proposed. As demonstrated in this work, sulfurizing single molecular sheets of MoO3 in existing MoO3-containing layered compounds would also serve as a new means for synthesis of lamellar organic-inorganic nanohybrids comprising building units of transition metal dichalcogenides.