This critical review presents a comprehensive study of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) towards construction and synthesis of metal–organic frameworks (MOFs). We describe the geometries of 131 SBUs, their connectivity and composition. This contribution presents a comprehensive list of the wide variety of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) in the construction and synthesis of metal–organic frameworks. The SBUs discussed here were obtained from a search of molecules and extended structures archived in the Cambridge Structure Database (CSD, version 5.28, January 2007) which included only crystals containing metal carboxylate linkages (241 references).

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Secondary building units, nets and bonding in the chemistry of metal–organic frameworks

Double-decker phthalocyanine complexes with Tb3+ or Dy3+ showed slow magnetization relaxation as a single-molecular property. The temperature ranges in which the behavior was observed were far higher than that of the transition-metal-cluster single-molecule magnets (SMMs). The significant temperature rise results from a mechanism in the relaxation process different from that in the transition-metal-cluster SMMs. The effective energy barrier for reversal of the magnetic moment is determined by the ligand field around a lanthanide ion, which gives the lowest degenerate substate a large |Jz| value and large energy separations from the rest of the substates in the ground-state multiplets.

Lanthanide Double-Decker Complexes Functioning as Magnets at the Single-Molecular Level

Synthesis of 3d metallic single-molecule magnets

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.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0883769400027925

Single-Molecule Magnets

6.1.2. Aqueous V(III) Chemistry 877 6.1.3. Oxidation State of Vanadium in Tunicates 878 6.1.4. Uptake of Vanadate into Tunicates 879 6.1.5. Vanadium Binding Proteins: Vanabins 879 6.1.6. Model Complexes and Their Chemistry 880 6.1.7. Catechol-Based Model Chemistry 880 6.1.8. Vanadium Sulfate Complexes 881 6.2. Fan Worm Pseudopotamilla occelata 883 7. Vanadium Nitrogenase 883 7.1. Nitrogenases 883 7.2. Biochemistry of Nitrogenase 884 7.3. Clusters in Nitrogenase and Model Systems: Structure and Reactivity 885

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The chemistry and biochemistry of vanadium and the biological activities exerted by vanadium compounds.

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...

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

Reactions of VCl3(THF)3, bpy, and NaO2CR (R = Et, Ph; bpy = 2,2‘-bipyridine) in a 1:1:3 ratio in Me2CO give [V4O2(O2CR)7(bpy)2](ClO4) (R = Et, 1; R = Ph, 4) following addition of NBun4ClO4. Use of 4,4‘-dimethyl- or 5,5‘-dimethylbipyridine (4,4‘-Me2bpy and 5,5‘-Me2bpy, respectively) and R = Et leads similarly to [V4O2(O2CEt)7(L−L)2](ClO4) (L−L = 4,4‘-Me2bpy, 2; L−L = 5,5‘-Me2bpy, 3). Yields are in the 38−90% range. The cation of 1 is isostructural with previously prepared [M4O2(O2CR)7(bpy)2]+ (M = CrIII, MnIII, FeIII) species and possesses a [V4O2] butterfly core. 1D and 2D COSY 1H NMR spectra of 1 show the solid-state structure is retained on dissolution. The effective magnetic moment (μeff) per V4 for 1 gradually rises from 5.79 μB at 300 K to a maximum of 6.80 μB at 25.0 K and then decreases rapidly to 4.72 μB at 2.00 K. The data in the 7.00−300 K range were fit to the appropriate theoretical expression (based on Ĥ = −2JSi·Sj) to give Jbb = −31.2 cm-1, Jwb = +27.5 cm-1, and g = 1.82, (b = body, w = wing...

Single-Molecule Magnets: Tetranuclear Vanadium(III) Complexes with a Butterfly Structure and an S ) 3 Ground State

Several single-molecule magnets with the composition [Mn12O12(O2CR)16(H2O)x] (x = 3 or 4) exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4−7 K region and the other in the 2−3 K region. New Mn12 complexes were prepared and structurally characterized, and the origin of the two magnetization relaxation processes was systematically examined. Different crystallographic forms of a Mn12 complex with a given R substituent exist where the two forms have different compositions of solvent molecules of crystallization and this results in two different arrangements of bound H2O and carboxylate ligands for the two crystallographically different forms with the same R substituent. The X-ray structure of cubic crystals of [Mn12O12(O2CEt)16(H2O)3]· 4H2O (space group P1) (complex 2a) has been reported previously. The more prevalent needle-form of [Mn12O12(O2CEt)16(H2O)3] (complex 2b) crystallizes in the monoclinic space group P21/c, which at −170 °C has a = 16.462(7) A, b = 22.401(9) A, c = 20.766(...

Single-Molecule Magnets: Jahn−Teller Isomerism and the Origin of Two Magnetization Relaxation Processes in Mn12 Complexes

Two new molecular magnets, the dodecanuclear manganese complexes of the type [Mn12 O12 (O2 CR)16 (H2 O)4 ] (known for R = CH3 , new for R = o-ClC6 H4 , o-BrC6 H4 ) have contributed to a better quantum mechanical understanding of single-molecule magnets. For instance, appreciable differences in the steps seen in the magnetization hysteresis loops of these high-spin clusters are attributed to changes in the rates of magnetization tunneling from one complex to another.

Single-Molecule Magnets: Different Rates of Resonant Magnetization Tunneling in Mn12 Complexes**

Two new single-molecule magnets (SMM), [Mn12O12(O2CCH2C6H5)16(H2O)4] and [Mn12O12(O2CCH2But)16(H2O)4], have been characterized by X-ray diffraction and ac magnetic susceptibility. As indicated by out-of-phase ac susceptibility signals, these two SMM exhibit relaxation processes for the reversal of the direction of magnetization at different temperatures. Possible explanations for why the tert-butyl acetate complex exhibits such a low barrier for magnetization relaxation are given. The figure below shows the potential energy of a SMM with a S = 10 ground state plotted versus the magnetization direction.

Ziming Sun

Papers

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

Single-Molecule Magnets: Tetranuclear Vanadium(III) Complexes with a Butterfly Structure and an S ) 3 Ground State

Single-Molecule Magnets: Jahn−Teller Isomerism and the Origin of Two Magnetization Relaxation Processes in Mn12 Complexes

Single-Molecule Magnets: Different Rates of Resonant Magnetization Tunneling in Mn12 Complexes**

Isomeric Forms of (Mn12O12(O2CR)16(H2O)4) Single-Molecule Magnets