Cyclotriphosphazenes as Scaffolds for the Synthesis of Metallomesogens

• Published in: Inorganic chemistry 2020-04, Vol.59 (7), p.4842-4857
• Main Authors: Jiménez, Josefina, Sanz, José Antonio, Serrano, José Luis, Barberá, Joaquín, Oriol, Luis
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.0c00124

(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.