Cyclotriphosphazenes as Scaffolds for the Synthesis of Metallomesogens.

Abstract

(Amino)cyclotriphosphazenes have been used as new scaffolds for the synthesis of silver(I) metallomesogens. Two cyclotriphosphazenes, [N3P3(NHCy)6] (phos-1) and nongem-trans-[N3P3(NHCy)3(NMe2)3] (phos-2), were reacted with the silver complex having a pro-mesogenic ligand, [Ag(OTf)L] (L = CNC6H4{OC(O)C6H2(3,4,5-(OC10H21)3)}-4; OTf = OSO2CF3), in different molar ratios, 1:1, 1:2, or 1:3, to give two series of cationic metallophosphazenes, [N3P3(NHCy)6{AgL}n](TfO)n (phos-1.n) and nongem-trans-[N3P3(NHCy)3(NMe2)3{AgL}n](TfO)n (phos-2.n) with n = 1, 2, or 3. The chemical structure of these compounds, deduced from spectroscopic techniques, was in accordance with coordination of the silver fragments "AgL" to nitrogen atoms of the phosphazene ring, whereby their number n depends on the molar ratio used. Despite the presence of the bulky substituents on the core N atoms, cyclotriphosphazenes coordinated to three "AgL" units exhibited mesomorphism at room temperature. The mesophase was characterized as columnar hexagonal according to the optical microscopy and X-ray diffraction studies. A model based on an intermolecular association in pairs of the metallocyclotriphosphazenes having three AgL units has been proposed in order to explain the mesomorphic columnar arrangement in these materials. Starting silver complex, [Ag(OTf)L], also exhibited a columnar hexagonal mesophase at room temperature.