Photoinduced Single-Molecule Magnet Properties in a Four-Coordinate Iron(II) Spin Crossover Complex

The four-coordinate Fe­(II) complex, PhB­(MesIm)₃Fe-NPPh₃ (<b>1</b>) has been previously reported to undergo a thermal spin-crossover (SCO) between high-spin (HS, <i>S</i> = 2) and low-spin (LS, <i>S</i> = 0) states. This complex is photoactive below 20 K, undergoing a photoinduced LS to HS spin state change, as determined by optical reflectivity and photomagnetic measurements. With continuous white light irradiation, <b>1</b> displays slow relaxation of the magnetization, i.e. single-molecule magnet (SMM) properties, at temperatures below 5 K. This complex provides a structural template for the design of new photoinduced mononuclear SMMs based on the SCO phenomenon

Tris(carbene)borate Ligands Featuring Imidazole-2-ylidene, Benzimidazol-2-ylidene, and 1,3,4-Triazol-2-ylidene Donors. Evaluation of Donor Properties in Four-Coordinate {NiNO}¹⁰ Complexes

The synthesis and characterization of new tris­(carbene)­borate ligand precursors containing substituted benzimidazol-2-ylidene and 1,3,4-triazol-2-ylidene donor groups, as well as a new tris­(imidazol-2-ylidene)­borate ligand precursor are reported. The relative donor strengths of the tris­(carbene)­borate ligands have been evaluated by the position of ν­(NO) in four-coordinate {NiNO}¹⁰ complexes, and follow the order: imidazol-2-ylidene > benzimidazol-2-ylidene > 1,3,4-triazol-2-ylidene. There is a large variation in ν­(NO), suggesting these ligands to have a wide range of donor strengths while maintaining a consistent ligand topology. All ligands are stronger donors than Tp* and Cp*

Cyanide Ligand Assembly by Carbon Atom Transfer to an Iron Nitride

The new iron­(IV) nitride complex PhB­(ⁱPr₂Im)₃FeN reacts with 2 equiv of bis­(diisopropyl­amino)­cyclo­propenylidene (BAC) to provide PhB­(ⁱPr₂Im)₃­Fe­(CN)­(N₂)­(BAC). This unusual example of a four-electron reaction involves carbon atom transfer from BAC to create a cyanide ligand along with the alkyne ⁱPr₂N–CC–NⁱPr₂. The iron complex is in equilibrium with an N₂-free species. Further reaction with CO leads to formation of a CO analogue, which can be independently prepared using NaCN as the cyanide source, while reaction with B­(C₆F₅)₃ provides the cyanoborane derivative

Steric and Electronic Control of the Spin State in Three-Fold Symmetric, Four-Coordinate Iron(II) Complexes

The three-fold symmetric, four-coordinate iron­(II) phosphoraminimato complexes PhB­(MesIm)₃Fe–NPRR′R″ (PRR′R″ = PMePh₂, PMe₂Ph, PMe₃, and PⁿPr₃) undergo a thermally induced <i>S</i> = 0 to <i>S</i> = 2 spin-crossover in fluid solution. Smaller phosphoraminimato ligands stabilize the low-spin state, and an excellent correlation is observed between the characteristic temperature of the spin-crossover (<i>T</i>_1/2) and the Tolman cone angle (θ). Complexes with <i>para</i>-substituted triaryl phosphoraminimato ligands (<i>p</i>-XC₆H₄)₃PN^– (X = H, Me and OMe) also undergo spin-crossover in solution. These isosteric phosphoraminimato ligands reveal that the low-spin state is stabilized by more strongly donating ligands. This control over the spin state provides important insights for modulating the magnetic properties of four-coordinate iron­(II) complexes