Synthesis, crystal structures and theoretical study of mixed ligand complexes of lanthanides acetylacetonates with o-phenanthroline and 2,2′-dipyridyl: The unexpected inverted electrostatic trend in stability

Lanthanide Complexes with a Tripodal Nitroxyl Radical Showing Strong Magnetic Coupling

A series of isomorphous mononuclear complexes of Ln(III) ions comprising one stable tripodal oxazolidine nitroxyl radical were obtained in acetonitrile media starting from nitrates. The compounds, [LnRad(NO₃)₃] (Ln = Gd, Tb, Dy, Tm, Y; Rad = 4,4-dimethyl-2,2-bis(pyridin-2-yl)-1,3-oxazolidine-3-oxyl), have a molecular structure. Their coordination polyhedron, LnO₇N₂, can be described as a tricapped trigonal prism with symmetry not far from D_3h. The extracted value of 23 cm^-1 for the antiferromagnetic coupling of Gd-Rad established from the DC magnetic and EPR data is a record strength for the complexes of 4f elements with nitroxyl radicals. The terbium derivative displays frequency-dependent out-of-phase signals in zero field, indicating single-molecule magnetic behavior. With an applied field of 0.1 T, an effective barrier of 57 cm^-1 is found.

The modular synthesis of rare earth-transition metal heterobimetallic complexes utilizing a redox-active ligand

We report a robust and modular synthetic route to heterometallic rare earth-transition metal complexes. We have used the redox-active bridging ligand 1,10-phenathroline-5,6-dione (pd), which has selective N,N' or O,O' binding sites as the template for this synthetic route. The coordination complexes [Ln(hfac)₃(N,N'-pd)] (Ln = Y [1], Gd [2]; hfac = hexafluoroacetylacetonate) were synthesised in high yield. These complexes have been fully characterised using a range of spectroscopic techniques. Solid state molecular structures of 1 and 2 have been determined by X-ray crystallography and display different pd binding modes in coordinating and non-coordinating solvents. Complexes 1 and 2 are unusually highly coloured in coordinating solvents, for example the vis-NIR spectrum of 1 in acetonitrile displays an electronic transition centred at 587 nm with an extinction coefficient consistent with significant charge transfer. The reaction between 1 and 2 and VCp₂ or VCp^t₂ (Cp^t = tetramethylcyclopentadienyl) resulted in the isolation of the heterobimetallic complexes, [Ln(hfac)₃(N,N'-O,O'-pd)VCp₂] (Ln = Y [3], Gd [4]) or [Ln(hfac)₃(N,N'-O,O'-pd)VCp^t₂] (Ln = Y [5], Gd [6]). The solid state molecular structures of 3, 5 and 6 have been determined by X-ray crystallography. The spectroscopic data on 3-6 are consistent with oxidation of V(ii) to V(iv) and reduction of pd to pd^2- in the heterobimetallic complexes. The spin-Hamiltonian parameters from low temperature X-band EPR spectroscopy of 3 and 5 describe a ²A₁ ground state, with a V(iv) centre. DFT calculations on 3 are in good agreement with experimental data and confirm the SOMO as the d_x²-y² orbital localised on vanadium.