Molecular Nanocomposites with Lanthanide- and Counter-Cation-Mediated Interfacial Electron Transfer between Phthalocyanine and Polyoxovanadate

A series of {V12}-nuclearity polyoxovanadate cages covalently functionalised with one or sandwiched by two phthalocyaninato (Pc) lanthanide (Ln) moieties via V−O−Ln bonds were prepared and fully characterised for paramagnetic Ln = SmIII–ErIII and diamagnetic Ln = LuIII, including YIII. The LnPc-functionalised {V12O32} cages with fully-oxidised vanadium centres in the ground state were isolated as (nBu4N)3[HV12O32Cl(LnPc)] and (nBu4N)2[HV12O32Cl(LnPc)2] compounds. As corroborated by a combined experimental (EPR, DC and AC SQUID, laser photolysis transient absorption spectroscopy, electrochemistry) and computational methods (DFT, MD, model Hamiltonian approach), the compounds feature intra- and intermolecular electron transfer that is responsible for a partial reduction at V(3d) centres from VV to VIV in the solid state and at high sample concentrations. The effects are generally Ln-dependent and are clearly demonstrated for the (nBu4N)3[HV12O32Cl(LnPc)] representative with Ln= LuIII or DyIII. Intramolecular charge transfer takes place for Ln = LuIII and occurs from a Pc ligand via the Ln centre to the {V12O32} core of the same molecule, whereas for Ln= DyIII only intermolecular charge transfer is allowed, which is realised from Pc in one molecule to {V12O32} core of another molecule usually via the nBu4N+ counter-cation. For all Ln but DyIII two of these phenomena may be present in different proportions. Besides, it is demonstrated that (nBu4N)3[HV12O32Cl(DyPc)] is a field induced single molecule magnet with a maximal relaxation time of order 10–3 s. The obtained results open up the way to further exploration and fine-tuning of these three-modular molecular nanocomposites regarding tailoring and control of their Ln-dependent charge-separated states (induced by intramolecular transfer) and relaxation dynamics as well as of electron hopping between molecules. This should enable to realise ultra-sensitive polyoxometalate powered quasi-superconductors, sensors and data storage/processing materials for quantum technologies.