Atomically Precise Bismuth Oxido Nanoclusters as Hosts for Ln3+: Effects of Doping on Optical and Magnetic Properties of a Soluble Metal Oxide

Lanthanide doping in bismuth-based oxides and coordination polymers is known to modify the materials properties significantly while preserving their principal structure. Herein we report a series of lanthanide doped bismuth oxido nanoclusters (BiO-NCs) of the type [Bi38O45(NO3)24(dmso)y]:Ln (C-1:Ln; Ln3+ = La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; y = 26–28) including isostructural host and doped structures. The dopants are statistically distributed on the lattice position of Bi3+ and changing the optical and magnetic properties of the BiO-NCs host material. Successful doping of the BiO-NCs was demonstrated by electrospray ionization mass spectrometry (ESI-MS) and exemplarily by single crystal X-ray diffraction (SC XRD) analysis for C-1:Gd and C-1:Dy. The respective amount of doping (≈ 1 ω%) was determined using inductive coupled plasma optical emission spectroscopy (ICP-OES). Altered optical properties in the UV–vis absorption and photoluminescence (PL) emission were demonstrated with special focus on C-1:Er, C-1:Yb and C-2d:Dy. PL emission studies showed dual emission based on Bi3+ and the Ln3+ specific emissions, resulting in characteristic emission combinations over a wide wavelength range from visible to the NIR region. Starting from C-1:Gd and C-1:Dy the methacrylate substituted BiO-NCs [Bi38O45(OMc)24(EtOH)14]:Gd (C-2E:Dy) and [Bi38O45(OMc)24(EtOH)14]:Dy (C-2E:Dy) were synthesized to finally give solvent-free [Bi38O45(OMc)24]:Ln (C-2d:Gd, C-2d:Dy) after drying. The introduction of paramagnetic behavior in the BiO-NC diamagnetic host structure was confirmed by superconducting quantum interference device (SQUID) measurements, with molar susceptibilities of χmolT = 5.10 cm3·K·mol–1 for C-2d:Gd and χmolT = 10.00 cm3·K·mol–1 for C-2d:Dy. The core composition aligns well with the data obtained by ICP-OES analysis. We further investigated the suitability of Gd3+ in C‑2d:Gd as polarization agent (PA) for dynamic nuclear polarization (DNP)-enhanced magic-angle spinning nuclear magnetic resonance (MAS-NMR) experiments, which resulted in a proton enhancement of approximately 10.