David N. Hendrickson

Bio: David N. Hendrickson is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Magnetization & Magnetic susceptibility. The author has an hindex of 85, co-authored 510 publications receiving 27715 citations. Previous affiliations of David N. Hendrickson include University of California, Los Angeles & Sun Yat-sen University.

High-spin molecules: [Mn12O12(O2CR)16(H2O)4]

Abstract: The syntheses and electrochemical and magnetochemical properties of [Mn 12 O 12 (O 2 CPh) 16 (H 2 O) 4 ] (3), its solvate 3.PhCOOH-CH 2 Cl 2 , and [Mn 12 O 12 (O 2 CMe) 16 (H 2 O) 4 ].MeCOOH-3H 2 O (4) are reported. Complex 3 can be prepared either by reaction of Mn(OAc) 2 .4H 4 O, benzoic acid, and NBu n 4 MnO 4 in pyridine or by reaction of PhCOOH with complex 4 slurried in CH 2 Cl 2 .

Single-Molecule Magnets

Abstract: Magnets are widely used in a large number of applications, and their market is larger than that of semiconductors. Information storage is certainly one of the most important uses of magnets, and the lower limit to the size of the memory elements is provided by the superparamagnetic size, below which information cannot be permanently stored because the magnetization freely fluctuates. This occurs at room temperature for particles in the range of 10–100 nm, owing to the nature of the material. However, even smaller particles can in principle be used either by working at lower temperatures or by taking advantage of the onset of quantum size effects, which can make nanomagnets candidates for the construction of quantum computers.

Exchange-biased quantum tunnelling in a supramolecular dimer of single-molecule magnets

Abstract: Various present and future specialized applications of magnets require monodisperse, small magnetic particles, and the discovery of molecules that can function as nanoscale magnets was an important development in this regard. These molecules act as single-domain magnetic particles that, below their blocking temperature, exhibit magnetization hysteresis, a classical property of macroscopic magnets. Such 'single-molecule magnets' (SMMs) straddle the interface between classical and quantum mechanical behaviour because they also display quantum tunnelling of magnetization and quantum phase interference. Quantum tunnelling of magnetization can be advantageous for some potential applications of SMMs, for example, in providing the quantum superposition of states required for quantum computing. However, it is a disadvantage in other applications, such as information storage, where it would lead to information loss. Thus it is important to both understand and control the quantum properties of SMMs. Here we report a supramolecular SMM dimer in which antiferromagnetic coupling between the two components results in quantum behaviour different from that of the individual SMMs. Our experimental observations and theoretical analysis suggest a means of tuning the quantum tunnelling of magnetization in SMMs. This system may also prove useful for studying quantum tunnelling of relevance to mesoscopic antiferromagnets.

Reduced Anionic Mn12 Molecules with Half-Integer Ground States as Single-Molecule Magnets

Abstract: The preparation, characterization, and X-ray structure are reported for the single-molecule magnet (PPh4)[Mn12O12(O2CPh)16(H2O)4]·8(CH2Cl2) (2). Complex 2 crystallizes in the triclinic space group P1, which at 213 K has a = 17.2329(2), b = 17.8347(2), c = 26.8052(2) A, α = 90.515(2), β = 94.242(2), γ = 101.437(2)°, and Z = 2. The salt consists of PPh4+ cations and [Mn12O12(O2CPh)16(H2O)4]- anions. The (Mn12O12)15+ core of the anion is formed by an external ring of eight Mn atoms bridged by μ3−O2- ions to an internal tetrahedron of four Mn atoms. Because of disorder in both phenyl rings and solvate molecules, it was difficult to use bond valence sum values to determine definitively the oxidation state of each Mn atom. There is a Mn4O4 cubane unit in the internal part of the molecule and these Mn atoms are all MnIV ions. For the eight “external” Mn atoms the bond valence sum values did not define well their oxidation states. For these eight Mn atoms, it was not possible to determine whether a trapped-valen...

Chemical Redox Agents for Organometallic Chemistry

Abstract: 1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

Magnetic bistability in a metal-ion cluster

Abstract: MAGNETIC materials of mesoscopic dimensions (a few to many thousands of atoms) may exhibit novel and useful properties such as giant magnetostriction, magnetoresistivity and magnetocaloric effects1–4. Such materials also allow one to study the transition from molecular to bulk-like magnetic behaviour. One approach for preparing mesoscopic magnetic materials is to fragment bulk ferromagnets; a more controllable method is to take a 'bottom-up' approach, using chemistry to grow well defined clusters of metal ions5,6. Lis7 has described a twelve-ion manganese cluster in which eight of the Mn ions are in the +3 oxidation state (spin S=2) and four are in the +4 state (S=3/2). These ions are magnetically coupled to give an S=10 ground state8, giving rise to unusual magnetic relaxation properties8,9. Here we report that the magnetization of the Mn12 cluster is highly anisotropic and that the magnetization relaxation time becomes very long below a temperature of 4 K, giving rise to pronounced hysteresis. This behaviour is not, however, strictly analogous to that of a bulk ferromagnet, in which magnetization hysteresis results from the motion of domain walls. In principle, a bistable magnetic unit of this sort could act as a data storage device.

Molecular spintronics using single-molecule magnets

Abstract: A revolution in electronics is in view, with the contemporary evolution of the two novel disciplines of spintronics and molecular electronics. A fundamental link between these two fields can be established using molecular magnetic materials and, in particular, single-molecule magnets. Here, we review the first progress in the resulting field, molecular spintronics, which will enable the manipulation of spin and charges in electronic devices containing one or more molecules. We discuss the advantages over more conventional materials, and the potential applications in information storage and processing. We also outline current challenges in the field, and propose convenient schemes to overcome them.

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

Abstract: The chemistry of heterocyclic carbenes has experienced a rapid development over the last years. In addition to the imidazolin-2-ylidenes, a large number of cyclic diaminocarbenes with different ring sizes have been described. Aside from diaminocarbenes, P-heterocyclic carbenes, and derivatives with only one, or even no heteroatom within the carbene ring are known. New methods for the synthesis of complexes with N-heterocyclic carbene ligands such as the oxidative addition or the metal atom template controlled cyclization of β-functionalized isocyanides have been developed recently. This review summarizes the new developments regarding the synthesis of N-heterocyclic carbenes and their metal complexes.