Reactivity of the Asymmetric Wells-Dawson Ion: Lanthanide-Containing 34-Tungsto-2-Phosphates [Ln(P(H$_4$)W$_{17}$O$_{61}$)$_2$]$^{19–}$ (Ln = La$^{3+}$, Ce$^{3+}$, Eu$^{3+}$, Gd$^{3+}$, Yb$^{3+}$, Lu$^{3+}$, Y$^{3+}$)

We report on the synthesis of the lanthanide-containing 17-tungsto-1-phosphates [Ln(P(H$_4$)W$_{17}$O$_{61}$)$_2$]$^{19–}$ (Ln = La$^{3+}$, Ce$^{3+}$, Eu$^{3+}$, Gd$^{3+}$, Yb$^{3+}$, Lu$^{3+}$, Y$^{3+}$), comprising a lanthanide ion connecting two [P(H$_4$)W$_{17}$O$_{61}$]$^{11–}$ units in a syn-configuration. The compounds were characterized in the solid state by IR, powder XRD, and TGA, and in solution by $^{31}$P and $^{183}$W NMR. Alternating current magnetic susceptibility investigations revealed the Ce$^{3+}$ and Yb$^{3+}$ analogues to be single-molecule magnets (SMM), which was further corroborated by sub-kelvin temperature μSQUID studies. For the Eu$^{3+}$ analogue, we have observed a strong $^5$D$_0$ → $^7$F$_J$ (J = 0–4) emission along with a weaker $^5$D$_J$ (J = 1, 2, or 3) → $^7$F$_J$ emission arising from higher excited state manifolds, upon excitation via the $^7$F$_0$ → $^5$L$_6$ transition at 395 nm. Analysis of the steady-state and time-resolved data suggests a distorted square-antiprismatic coordination geometry around the Eu$^{3+}$ center. The presence of water molecules residing in the outer coordination sphere appears to decrease the intrinsic quantum yield (φ$_{Eu}$) by providing O–H oscillators as a nonradiative relaxation channel. ... mehrThe observed branching ratio of about 41% for the $^5$D$_0$ → $^7$F$_4$ transition highlights that [Eu(P(H$_4$)W$_{17}$O$_{61}$)$_2$]$^{19–}$ exhibits a pronounced $^5$D$_0$ → $^7$F$_4$ emission.