Hard Single-Molecule Magnet Behavior by a Linear Trinuclear Lanthanide–[1]Metallocenophane Complex

A synthetic protocol was developed that involves the transmetalation of a mono-dysprosium–[1]­ferro­cenophane complex with DyX₃ (X = Cl^– or I^–) to afford [Dy₃Fc₆Li₂­(THF)₂]⁻, featuring a rare linear arrangement of magnetically anisotropic Dy³⁺ ions. The close spatial inter-lanthanide proximity, in combination with μ₂-bridging sp²-hybridized C_Cp groups, enforces significant magnetic coupling and results in hard single-molecule magnet (SMM) behavior, with an effective barrier to magnetization reversal of up to 268 cm^–1. Our results highlight the versatility of lanthanide metallo­cenophane architectures toward the development of novel multi­nuclear SMM frameworks

Slow Magnetic Relaxation in a Lanthanide-[1]Metallocenophane Complex

The first example of a lanthanide metallocenophane complex has been isolated as [Li­(THF)₄]­[DyFc₃Li₂(THF)₂] (<b>1</b>). The molecular structure of complex <b>1</b> differs dramatically from those of main group and transition metal ferrocenophane complexes and features a distorted trigonal prismatic geometry around the Dy­(III) ion and close intramolecular Dy···Fe distances. Furthermore, complex <b>1</b> exhibits all characteristics of a soft single-molecule magnet

Slow Magnetic Relaxation in a Lanthanide-[1]Metallocenophane Complex

The first example of a lanthanide metallocenophane complex has been isolated as [Li­(THF)₄]­[DyFc₃Li₂(THF)₂] (<b>1</b>). The molecular structure of complex <b>1</b> differs dramatically from those of main group and transition metal ferrocenophane complexes and features a distorted trigonal prismatic geometry around the Dy­(III) ion and close intramolecular Dy···Fe distances. Furthermore, complex <b>1</b> exhibits all characteristics of a soft single-molecule magnet

Electrocatalytic CO₂ Reduction by Imidazolium-Functionalized Molecular Catalysts

We present the first examples of CO₂ electro-reduction catalysts that feature charged imidazolium groups in the secondary coordination sphere. The functionalized Lehn-type catalysts display significant differences in their redox properties and improved catalytic activities as compared to the conventional reference catalyst. Our results suggest that the incorporated imidazolium moieties do not solely function as a charged tag but also alter mechanistic aspects of catalysis

Exchange Coupling and Magnetic Blocking in Bipyrimidyl Radical-Bridged Dilanthanide Complexes

The synthesis and magnetic properties of three new bipyrimidyl radical-bridged dilanthanide complexes, [(Cp*₂Ln)₂(μ-bpym^•)]⁺ (Ln = Gd, Tb, Dy), are reported. Strong Ln^III-bpym^•– exchange coupling is observed for all species, as indicated by the increases in χ_M<i>T</i> at low temperatures. For the Gd^III-containing complex, a fit to the data reveals antiferromagnetic coupling with <i>J</i> = −10 cm^–1 to give an <i>S</i> = ¹³/₂ ground state. The Tb^III and Dy^III congeners show single-molecule magnet behavior with relaxation barriers of <i>U</i>_eff = 44(2) and 87.8(3) cm^–1, respectively, a consequence of the large magnetic anisotropies imparted by these ions. Significantly, the latter complex exhibits a divergence of the field-cooled and zero-field-cooled dc susceptibility data at 6.5 K and magnetic hysteresis below this temperature

Exchange Coupling and Magnetic Blocking in Bipyrimidyl Radical-Bridged Dilanthanide Complexes

The synthesis and magnetic properties of three new bipyrimidyl radical-bridged dilanthanide complexes, [(Cp*₂Ln)₂(μ-bpym^•)]⁺ (Ln = Gd, Tb, Dy), are reported. Strong Ln^III-bpym^•– exchange coupling is observed for all species, as indicated by the increases in χ_M<i>T</i> at low temperatures. For the Gd^III-containing complex, a fit to the data reveals antiferromagnetic coupling with <i>J</i> = −10 cm^–1 to give an <i>S</i> = ¹³/₂ ground state. The Tb^III and Dy^III congeners show single-molecule magnet behavior with relaxation barriers of <i>U</i>_eff = 44(2) and 87.8(3) cm^–1, respectively, a consequence of the large magnetic anisotropies imparted by these ions. Significantly, the latter complex exhibits a divergence of the field-cooled and zero-field-cooled dc susceptibility data at 6.5 K and magnetic hysteresis below this temperature

Exchange Coupling and Magnetic Blocking in Bipyrimidyl Radical-Bridged Dilanthanide Complexes

The synthesis and magnetic properties of three new bipyrimidyl radical-bridged dilanthanide complexes, [(Cp*₂Ln)₂(μ-bpym^•)]⁺ (Ln = Gd, Tb, Dy), are reported. Strong Ln^III-bpym^•– exchange coupling is observed for all species, as indicated by the increases in χ_M<i>T</i> at low temperatures. For the Gd^III-containing complex, a fit to the data reveals antiferromagnetic coupling with <i>J</i> = −10 cm^–1 to give an <i>S</i> = ¹³/₂ ground state. The Tb^III and Dy^III congeners show single-molecule magnet behavior with relaxation barriers of <i>U</i>_eff = 44(2) and 87.8(3) cm^–1, respectively, a consequence of the large magnetic anisotropies imparted by these ions. Significantly, the latter complex exhibits a divergence of the field-cooled and zero-field-cooled dc susceptibility data at 6.5 K and magnetic hysteresis below this temperature

Exchange Coupling and Magnetic Blocking in Bipyrimidyl Radical-Bridged Dilanthanide Complexes

The synthesis and magnetic properties of three new bipyrimidyl radical-bridged dilanthanide complexes, [(Cp*₂Ln)₂(μ-bpym^•)]⁺ (Ln = Gd, Tb, Dy), are reported. Strong Ln^III-bpym^•– exchange coupling is observed for all species, as indicated by the increases in χ_M<i>T</i> at low temperatures. For the Gd^III-containing complex, a fit to the data reveals antiferromagnetic coupling with <i>J</i> = −10 cm^–1 to give an <i>S</i> = ¹³/₂ ground state. The Tb^III and Dy^III congeners show single-molecule magnet behavior with relaxation barriers of <i>U</i>_eff = 44(2) and 87.8(3) cm^–1, respectively, a consequence of the large magnetic anisotropies imparted by these ions. Significantly, the latter complex exhibits a divergence of the field-cooled and zero-field-cooled dc susceptibility data at 6.5 K and magnetic hysteresis below this temperature

Oxidative Stretching of Metal–Metal Bonds to Their Limits

Oxidation of quadruply bonded Cr₂(dpa)₄, Mo₂(dpa)₄, MoW­(dpa)₄, and W₂(dpa)₄ (dpa = 2,2′-dipyridylamido) with 2 equiv of silver­(I) triflate or ferrocenium triflate results in the formation of the two-electron-oxidized products [Cr₂(dpa)₄]²⁺ (<b>1</b>), [Mo₂(dpa)₄]²⁺ (<b>2</b>), [MoW­(dpa)₄]²⁺ (<b>3</b>), and [W₂(dpa)₄]²⁺ (<b>4</b>). Additional two-electron oxidation and oxygen atom transfer by <i>m</i>-chloroperoxybenzoic acid results in the formation of the corresponding metal–oxo compounds [Mo₂O­(dpa)₄]²⁺ (<b>5</b>), [WMoO­(dpa)₄]²⁺ (<b>6</b>), and [W₂O­(dpa)₄]²⁺ (<b>7</b>), which feature an unusual linear M···MO structure. Crystallographic studies of the two-electron-oxidized products <b>2</b>, <b>3</b>, and <b>4</b>, which have the appropriate number of orbitals and electrons to form metal–metal triple bonds, show bond distances much longer (by >0.5 Å) than those in established triply bonded compounds, but these compounds are nonetheless diamagnetic. In contrast, the Cr–Cr bond is completely severed in <b>1</b>, and the resulting two isolated Cr³⁺ magnetic centers couple antiferromagnetically with <i>J</i>/<i>k</i>_B= −108(3) K [−75(2) cm^–1], as determined by modeling of the temperature dependence of the magnetic susceptibility. Density functional theory (DFT) and multiconfigurational methods (CASSCF/CASPT2) provide support for “stretched” and weak metal–metal triple bonds in <b>2</b>, <b>3</b>, and <b>4</b>. The metal–metal distances in the metal–oxo compounds <b>5</b>, <b>6</b>, and <b>7</b> are elongated beyond the single-bond covalent radii of the metal atoms. DFT and CASSCF/CASPT2 calculations suggest that the metal atoms have minimal interaction; the electronic structure of these complexes is used to rationalize their multielectron redox reactivity

A Well-Defined Terminal Vanadium(III) Oxo Complex

The ubiquity of vanadium oxo complexes in the V+ and IV+ oxidation states has contributed to a comprehensive understanding of their electronic structure and reactivity. However, despite being predicted to be stable by ligand-field theory, the isolation and characterization of a well-defined terminal mononuclear vanadium­(III) oxo complex has remained elusive. We present the synthesis and characterization of a unique terminal mononuclear vanadium­(III) oxo species supported by the pentadentate polypyridyl ligand 2,6-bis­[1,1-bis­(2-pyridyl)­ethyl]­pyridine (PY5Me₂). Exposure of [V^II(NCCH₃)­(PY5Me₂)]²⁺ (<b>1</b>) to either dioxygen or selected O-atom-transfer reagents yields [V^IV(O)­(PY5Me₂)]²⁺ (<b>2</b>). The metal-centered one-electron reduction of this vanadium­(IV) oxo complex furnishes a stable, diamagnetic [V^III(O)­(PY5Me₂)]⁺ (<b>3</b>) species. The vanadium­(III) oxo species is unreactive toward H- and O-atom transfer but readily reacts with protons to form a putative vanadium hydroxo complex. Computational results predict that further one-electron reduction of the vanadium­(III) oxo species will result in ligand-based reduction, even though pyridine is generally considered to be a poor π-accepting ligand. These results have implications for future efforts toward low-valent vanadyl chemistry, particularly with regard to the isolation and study of formal vanadium­(II) oxo species