Hexacyano octahedral metallic clusters as versatile building blocks in the design of extended polymeric framework and clustomesogens

Abstract

Using self-assembling processes to generate hybrid organic inorganic materials allows the control of their structuration at the nanometric scale. We describe in this work the synthesis, liquid crystal and photo-physical properties of [M₆Qⁱ₈(CN)^a₆]ⁿ⁻ (M = Mo, Re; Qⁱ = Br, Se; n = 2, 3 or 4) cluster anionic units containing clustomesogens. A new and efficient synthetic route was developed to synthesize the [Mo₆Brⁱ₈(CN)^a₆]²⁻ building block that is stable in water solution and that could be crystallized as the porous [trans-Cd(H₂O)₂][Mo₆Brⁱ₈(CN)^a₆]. Hybrids were obtained by a metathesis reaction with a specifically designed organic cation. Their self-assembling abilities can be tailored by playing with the charge of the inorganic building blocks going from a nematogenic behaviour, which is particularly rare for ionic mesomorphic material, to the formation of layered structures. The intrinsic properties (luminescence or magnetism) of transition metal clusters are well retained in the hybrid matrices. The nanostructuration of the material influences its ability to emit light despite the isotropy of the emissive nanocluster. Finally, we demonstrate that the magnetic [Re₆Se₈CN₆]³⁻ can be reduced into the luminescent [Re₆Se₈CN₆]⁴⁻ upon heating at 150 °C. These hybrid materials show promising prospects in the field of luminescent material.