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The sodium cyclobutadienyl (Cb) reagent [Na2{η4-C4(SiMe3)4}(THF)]2(2) reacts with rare-earth halides [MCl3(THF)x], where M = Y, Dy (x= 3.5) and Lu (x= 3), giving the sandwich coordination polymers [M{η3-C4(SiMe3)4H}{η4-C4(SiMe3)3-κ-(CH2SiMe2}Na]∞(3M, M = Y, Dy, Lu). The coordination environments of the rare-earth metals in 3Mfeature an η4-cyclobutadienyl ligand, with additional coordination by a tuck-in trimethylsilyl group and an η3-cyclobutenyl ligand. The ligand activation is thought to be a consequence of deprotonation of the Cb ligand by 2. The axial nature of the crystal field in 3Mis reflected in the single-molecule magnet properties of 3Dy, which has an anisotropy barrier of 309 cm–1in zero applied magnetic field.

The discovery of materials capable of storing magnetic information at the level of single molecules and even single atoms has fueled renewed interest in the slow magnetic relaxation properties of single-molecule magnets (SMMs). The lanthanide elements, especially dysprosium, continue to play a pivotal role in the development of potential nanoscale applications of SMMs, including, for example, in molecular spintronics and quantum computing. Aside from their fundamentally fascinating physics, the realization of functional materials based on SMMs requires significant scientific and technical challenges to be overcome. In particular, extremely low temperatures are needed to observe slow magnetic relaxation, and while many SMMs possess a measurable energy barrier to reversal of the magnetization (Ueff), very few such materials display the important properties of magnetic hysteresis with remanence and coercivity.

Bicyclic guanidine 1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidine (hppH) was investigated as a source of anionic or neutral ligand at antimony. Reaction of the in situ generated lithium guanidinate with SbCl3in a 1:1 or 2:1 ratio forms the expected metathesis products Sb(hpp)nCl3–n(1, n= 1; 2, n= 2). The molecular structures of 1and 2were determined by X‐ray diffraction, which shows chelating guanidinates and suggests the presence of a stereochemically active lone pair of electrons. The reaction of two equivalents of the neutral guanidine hppH with SbCl3proceeds via proton transfer between the hpp fragments, affording the ion pair [hppH2][Sb(hpp)Cl3] (3), where [Sb(hpp)Cl3]–is an unusual example of a monometallic antimonate(III) anion. The molecular structure of 3shows hydrogen bonding between two of the chlorides and the NHfunctionalities of the guanidinium cation.

A novel magnesium guanidinate complex is prepared and used as a catalyst in the Tishchenko reaction of aldehydes (I).