Coordination Polymers Based on Heterohexanuclear Rare Earth Complexes: Toward Independent Luminescence Brightness and Color Tuning

Reactions in solvothermal conditions between hexanuclear rare earth complexes and H<sub>2</sub>bdc, where H<sub>2</sub>bdc symbolizes terephthalic acid, lead to a family of monodimensional coordination polymers in which hexanuclear complexes act as metallic nodes. The hexanuclear cores can be either homometallic with general chemical formula [Ln<sub>6</sub>O­(OH)<sub>8</sub>(NO<sub>3</sub>)<sub>6</sub>]<sup>2+</sup> (Ln = Pr–Lu plus Y) or heterometallic with general chemical formula [Ln<sub>6<i>x</i></sub>Ln′<sub>6–6<i>x</i></sub>O­(OH)<sub>8</sub>(NO<sub>3</sub>)<sub>6</sub>]<sup>2+</sup> (Ln and Ln′ = Pr–Lu plus Y). Whatever the hexanuclear entity is, the resulting coordination polymer is iso-structural to [Y<sub>6</sub>O­(OH)<sub>8</sub>(NO<sub>3</sub>)<sub>2</sub>(bdc)­(Hbdc)<sub>2</sub>·2NO<sub>3</sub>·H<sub>2</sub>bdc]<sub>∞</sub>, a coordination polymer that we have previously reported. The random distribution of the lanthanide ions over the six metallic sites of the hexanuclear entities is demonstrated by <sup>89</sup>Y solid state NMR, X-ray diffraction (XRD), and luminescent measurements. The luminescent and colorimetric properties of selected compounds that belong to this family have been studied. These studies demonstrate that some of these compounds exhibit very promising optical properties and that there are two ways of modulating the luminescent properties: (i) playing with the composition of the heterohexanuclear entities or (ii) playing with the relative ratio between two different hexanuclear entities. This enables the independent tuning of luminescence intensity and color.