Single-molecule magnets: a family of MnIII/CeIV complexes with a [Mn8CeO8]12+ core

Four heterometallic, enneanuclear Mn8Ce clusters [Mn8CeO8(O2CMe)12(H2O)4] (4), [Mn8CeO8(O2CMe)12(py)4] (5), [Mn8CeO8(O2CPh)12(MeCN)4] [Mn8CeO8(O2CPh)12(dioxane)4] (6), and [Mn8CeO8(O2CCHPh2)12(H2O)4] (7) have been prepared by various methods. Their cores are essentially isostructural and comprise a nonplanar, saddlelike [MnIII8O8]8+ loop containing a central CeIV ion attached to the eight micro3-O2- ions. Peripheral ligation around the [Mn8CeO8]12+ core is provided by eight micro- and four micro3-O2CR- groups. Terminal ligation on four MnIII atoms is provided by H2O in 4 and 7, pyridine in 5, and MeCN/dioxane in 6. Solid-state magnetic susceptibility studies, fits of dc magnetization vs field and temperature data, and in-phase ac susceptibility studies in a zero dc field have established that complexes 4, 5, and 7 possess S=16, S=4 or 5, and S=6+/-1 spin ground states, respectively, but in all cases there are very low-lying excited states. The large variation in the ground-state spins for this isostructural family is rationalized as due to a combination of weak exchange interactions between the constituent MnIII atoms, and the presence of both nearest-neighbor and next-nearest-interactions of comparable magnitudes. Magnetization vs applied dc field sweeps on single crystals of 4.4H2O and 7.4H2O.3MeCN.2CH2Cl2 down to 0.04 K have established that these two complexes are new single-molecule magnets (SMMs). The former also shows an exchange-bias, a perturbation of its single-molecule properties from very weak intermolecular interactions mediated by hydrogen-bonding interactions with lattice-water molecules of crystallization.     

Insertion of functional groups into a Nd3+ metal-organic framework via single-crystal-to-single-crystal coordinating solvent exchange

Single-crystal-to-single-crystal (SCSC) transformations represent some of the most fascinating phenomena in chemistry. They are not only intriguing from a basic science point of view but also provide a means to modify or tune the properties of the materials via the postsynthetic introduction of suitable guest molecules or organic functional groups into their structures. Here, we describe UCY-2, a new flexible Nd(3+) metal-organic framework (MOF), which exhibits a unique capability to undergo a plethora of SCSC transformations with some of them being very uncommon. These structural alterations involve the replacement of coordinating solvent molecules of UCY-2 by terminally ligating solvents and organic ligands with multiple functional groups including -OH, -SH, -NH-, and -NH(2) or their combinations, chelating ligands, anions, and two different organic compounds. The SCSC coordinating solvent exchange is thus demonstrated as a powerful method for the functionalization of MOFs.     

Metal ion-assisted transformations of 2-pyridinealdoxime and hexafluorophosphate

Metal-ion mediated reactions of 2-pyridinealdoxime and hexafluorophosphate lead to Zn(II) complexes containing picolinic acid, picolinamide and monofluorophosphate (-2) as ligands.     

A new family of octanuclear Mn complexes with a rod-like topology

Three new octanuclear compounds were prepared from reactions of [Mn(O₂CR)₂]·2H₂O (R = Et or Ph) with the diols 1,3-propanediol (pdH₂) or 2-methyl-1,3-propanediol (mpdH₂) in the presence of NaN₃. All three compounds [Mn₈(N₃)₄(O₂CR)₆(L)₄(py)₆] (L = pd²⁻, R = Et 1; L = mpd²⁻, R = Et 2; L = pd²⁻, R = Ph 3) (py = pyridine) possess a novel near-planar, rod-like topology. Dc and ac magnetic susceptibility studies in the 2–300 K range for complexes 1 and 2 revealed the presence of dominant antiferromagnetic exchange interactions, leading to diamagnetic ground spin states.     

A Mn36Ni4 'loop-of-loops-and-supertetrahedra' aggregate possessing a high S(T) = 26 ± 1 spin ground state

The initial use of 1,3-propanediol in mixed Mn/3d cluster chemistry has led to a Mn(III)(28)Mn(II)(8)Ni(II)(4) molecular aggregate which consists of two Mn(III)(8)Ni(2) loops and two Mn(III)(6)Mn(II)(4) supertetrahedral units and displays a high ground spin state value S(T) = 26 ± 1.     

Characterization and magnetic properties of a "super stable" radical 1,3-diphenyl-7-trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl

1,3-Diphenyl-7-trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (4), prepared in high yield via the catalytic oxidation of the corresponding amidrazone 5 by using Pd/C (1.6 mol %) and 1,8-diazabicyclo[5.4.0]undec-7-ene (0.1 equiv) in air, is stable in dichloromethane solutions in the presence of MnO(2) and KMnO(4). Furthermore, radical 4 is thermally stable well past its melting point (160-161 °C) with a decomposition onset temperature of 288 °C. X-ray studies show that radical 4 packs in equidistant slipped π-stacks along the a axis. Cyclic voltammetry shows two fully reversible waves, corresponding to the -1/0, 0/+1 processes. EPR studies indicate that the spin density is mainly delocalized on the triazinyl fragment of the heterocycle. Magnetic susceptibility measurements in the 5-300 K region showed that the radical obeys Curie-Weiss behavior down to 10 K (C = 0.376 emu·K·mol(-1) and θ = +1.41 K) consistent with weak ferromagnetic interactions between S = 1/2 radicals. Subsequent fitting of the magnetic data to a 1D ferromagnetic chain model provided an excellent fit (g = 2.00, J/k = +1.49 K) down to 10 K but failed to reproduce the subsequent decrease in χT at lower temperatures, which has been ascribed to the onset of weaker antiferromagnetic interactions between ferromagnetic chains.     

New type dithiolene complex based on 4,5-(1,4-dioxane-2,3-diyldithio)-1,3-dithiol ligand: Synthesis,experimental and theoretical investigation

A new Nickel complex with an extended multisulfur dithiolene ligand Ni(edodddt)₂ (edodddt = 2,3,4α,8α-tetrahydro-dithiine [2,3-b] [1,4] dioxo-6,7-dithiolene) has been synthesized and characterized by electrochemical measurements, IR, UV–Vis and NMR spectroscopy. Its crystal structure was resolved by X-ray diffraction on a single crystal. DFT calculations were made in order to compare the results with the experimental findings and gain an insight of the properties of this new dithiolene complex.