The single-molecule magnet (SMM) properties of the isocarbonyl-ligated dysprosium metallocene [Cp*2 Dy{μ-(OC)2 FeCp}]2 (1Dy ), which contains a rhombus-shaped Dy2 Fe2 core, are described. Combining a strong axial [Cp*](-) ligand field with a weak equatorial field consisting of the isocarbonyl ligands leads to an anisotropy barrier of 662 cm(-1) in zero applied field. The dominant thermal relaxation pathways in 1Dy involves at least the fourth-excited Kramers doublet, thus demonstrating that prominent SMM behavior can be observed for dysprosium in low-symmetry environments.

The 'normal' three-coordinate iron-NHC complex [(IPr)Fe(N'')2] (N″ = N(SiMe3)2) rearranges to its abnormal NHC analogue [(aIPr)Fe(N″)2] (6) on heating, providing a rare abnormal iron-aNHC complex, and the first such three-coordinate complex. The tert-butyl-substituted complex [(I(t)Bu)Fe(N″)2] (4) undergoes a thermal decomposition that has not previously been observed in iron-NHC chemistry, resulting in the bis(imidazole) complex [((t)BuIm)2Fe(N″)2] (7). A mechanism that involves consecutive C-H and C-N activation is proposed to account for the formation of 7.

Single-molecule magnets are a type of coordination compound that can retain magnetic information at low temperatures. Single-molecule magnets based on lanthanides have accounted for many important advances, including systems with very large energy barriers to reversal of the magnetization, and a di-terbium complex that displays magnetic hysteresis up to 14 K and shows strong coercivity. Ligand design is crucial for the development of new single-molecule magnets: organometallic chemistry presents possibilities for using unconventional ligands, particularly those with soft donor groups. Here we report dysprosium single-molecule magnets with neutral and anionic phosphorus donor ligands, and show that their properties change dramatically when varying the ligand from phosphine to phosphide to phosphinidene. A phosphide-ligated, trimetallic dysprosium single-molecule magnet relaxes via the second-excited Kramers' doublet, and, when doped into a diamagnetic matrix at the single-ion level, produces a large energy barrier of 256 cm−1 and magnetic hysteresis up to 4.4 K.

The synthesis of antimony-ligated dysprosium SMMs is described in addition to the unexpected reactivity of the SMMs in stibine dehydrocoupling catalysis.

It had previously been found in this laboratory that flexible polymer molecules adsorbed at colloidal particles most likely extend with many segments into the interior of the surrounding medium. This led one to expect a possible “steric protection” of colloidal particles by adsorption of flexible polymers of sufficiently high molecular weight since the merely slight interpenetration of polymer chains protruding from two colliding particles should keep them at distances too large to give a van der Waals interaction energy sufficient for coherence. This new type of stabilization was now proved using gold hydrosols as test systems and polyethylene glycols as adsorptives. The stabilization was found to increase with polymer concentration and, particularly, with the molecular weight of the polymer. In analogy with the previous finding, that the adsorption equilibrium is being approached very slowly if the molecular weight of the polymer exceeds several thousand, it was found that the degree of stabilization achieved by addition of polymer to the gold sols increases with the time elapsed before the subsequent addition of coagulating electrolyte. This increase is particularly strong during the first hour following addition of the polymer. The potential significance of the results for stabilization of organosols is discussed.