Bifunctional dipyridylpyrazole silver complexes with tunable thermotropic liquid crystal and luminescent behaviour

Five new series of alkyloxyphenyl-substituted dipyridylpyrazole silver(I) complexes [Ag(pypz^R(n)py)]₂[A]₂ (R(n) = C₆H₄OC_nH_2n+1, n = 1, 12, 14, 16, 18; [A] = NO₃⁻, BF₄⁻, ReO₄⁻, PF₆⁻, CH₃-p-C₆H₄SO₃⁻) have been prepared by reaction of the corresponding pyrazoles pypz^R(n)py with different silver salts AgA. The coordination of the non-mesomorphic ligands to the silver(I) metal ion induces mesomorphism in the new complexes. Most of them show smectic A mesophases in accordance with the textures observed by polarised light optical microscopy, and the lamellar arrangements established by temperature-dependent powder X-ray diffraction experiments. Additionally, all compounds behave as fluorescent materials in dichloromethane solution at room temperature. The ability of the pyrazole ligands as chemosensors for the detection of toxic and heavy metal ions such as Hg²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ has also been proved. On the other hand, the luminescence properties of the silver compounds are improved through the in situ formation of polymetallic derivatives in solution. The effect of the counter-ions on both the liquid crystal and the luminescence behaviour is discussed.