Chimie Douce Synthesis of Nanostructured Layered Materials

A class of layered ammonium transition-metal molybdate materials were derived by a novel room-temperature chimie douce synthesis technique using calcined layered double hydroxides (LDHs) as precursors. The compounds obtained are highly crystalline, and retain the rhombohedral symmetry of the LDH precursors. The host structure consists of distorted divalent cation octahedra which share edges to form layers perpendicular to the c axis, analogous to the LDH precursor. The tetrahedral molybdate species, however, are not merely intercalated within the interlayer domain, but are bonded to the layers themselves through shared Mo-O-M bonds, where M = Zn²⁺, Co²⁺, Cu²⁺, or Ni²⁺. This arrangement results in the formation of a net negative charge on the host structure, leading to incorporation of ammonium ions between the layers for charge balancing. The applicability of this novel synthesis route is dependent on the composition of the LDH precursor, and it appears that metastability in the calcined LDH favors conversion to this phase.