Silver pyrazole complexes with tunable liquid crystals and luminescent properties

Abstract

New silver ionic complexes based on pyrazole ligands of the type [Ag(Hpz^2R(n))₂][A] (Hpz^2R(n) = 3,5-bis(4-alkyloxyphenyl)pyrazole; R = C₆H₄OC_nH_2n+1; [A] = CH₃-p-C₆H₄SO₃⁻ (PTS), CF₃SO₃⁻ (OTf)) (type I) are liquid crystal materials exhibiting photoluminescence in the solid state, in solution and in the mesophase. By way of contrast, the related counterparts [Ag(Hpz^R(n))₂][A] (Hpz^R(n) = 3-(4-alkyloxyphenyl)pyrazole; R = C₆H₄OC_nH_2n+1; [A] = CH₃-p-C₆H₄SO₃⁻ (PTS), CF₃SO₃⁻ (OTf)) (type II), containing monosubstituted pyrazole ligands, are not mesomorphic but also behave as luminescent materials. The crystalline structures of 5 and 10, as representative examples of classes I and II, have been solved. Molecular “H” or “Z” shapes, depending on the cis or trans orientation of the NH groups of the pyrazole ligands, were found, respectively. The first type gave rise to a layer-planar network, while a corrugated layer was found for complex 10, these features being related to the mesomorphic behaviour of both kinds of compounds. The mesomorphic and luminescent properties of complexes I and II were compared with those of related compounds containing the less sterically-demanding counteranions PF₆⁻, NO₃⁻ and BF₄⁻, described in our previous work. In all cases, the effect of the counteranions, as well as the substitution on the pyrazole groups, were analyzed for their corresponding properties.