A new family of tetranuclear nickel cube complexes [Ni(4)L(4)(solv)(4)] (1, solv = MeOH; 2, solv = H(2)O; H(2)L = pyrazole-based tridentate {ONO} ligand) has been studied in detail, in particular by X-ray diffraction and superconducting quantum interference device (SQUID) magnetometry. Different solvates 1·H(2)O, 2·4C(3)H(6)O, 2·CH(2)Cl(2), and 2·H(2)O were obtained in crystalline form. Only small structural variations were found for the Ni-O-Ni angles of the [Ni(4)O(4)] cores of those compounds, but these slight variations have dramatic consequences for the magnetic properties. [Ni(4)L(4)(MeOH)(4)]·H(2)O (1·H(2)O) and [Ni(4)L(4)(H(2)O)(4)]·H(2)O (2·H(2)O) can be reversibly interconverted in the solid state by exposure to the respective solvent, MeOH or H(2)O, and this goes along with a switching of the spin ground state from magnetic (S(T) = 4) to diamagnetic (S(T) = 0). Likewise the (irreversible) loss of lattice solvent in [Ni(4)L(4)(H(2)O)(4)]·4C(3)H(6)O (2·4C(3)H(6)O) to give 2·2C(3)H(6)O changes the ground state from S(T) = 4 to S(T) = 0. In view of these dramatic solvatomagnetic effects for the present [Ni(4)L(4)(solv)(4)] complexes, which occur upon extrusion of lattice solvent or facile exchange of coordinated solvent molecules while keeping the robust [Ni(4)O(4)] core intact, a note of care is issued: whenever magnetic data are obtained for powdered material or for crystals that easily loose lattice solvent molecules, the magnetic properties may not necessarily reflect the situation observed in the corresponding single crystal diffraction study. Finally, a thorough analysis of the present series of complexes as well as other {Ni(4)(μ(3)-OR)(4)} cubes reported in the literature confirms that a correlation between the (Ni-O-Ni)(av) bond angle and J in [Ni(4)O(4)] cubane complexes does indeed exist.
The pyrazole-based tridentate diol ligand 2-(1-(2-hydroxyethyl)-1H-pyrazol-3-yl)phenol (H2L) forms a cubane-type complex [Co4L4(MeOH)4] (1) that features a {Co4O4} core and four exogenous MeOH ligands. Electrospray ionization mass spectrometry suggests that the MeOH ligands are easily lost, and thermogravimetric analysis evinces a thermally induced release of those methanol molecules from solid material in the temperature range from 380 to 440 K. Desolvation was found to give rise to a pronounced solvatomagnetic effect that causes a switching of the spin ground state of the {Co4O4} core from diamagnetic to magnetic. Furthermore, the desolvated "naked" [Co4L4] cube (1*) shows slow relaxation of the magnetization and butterfly-like magnetic hysteresis at 2 K. A comparatively high relaxation barrier Ueff/kB = 64.4 K and a characteristic relaxation time τ0 = 3.8 × 10(-9) s for 1* have been derived from an Arrhenius plot. These findings thus demonstrate that the emergence of interesting magnetic properties in molecule-based materials can be triggered via a solvatomagnetic process, even for materials that in their solvated form have a diamagnetic (ST = 0) ground state.
Agents. -A simple procedure using urea-hydrogen peroxide affords symmetrical and unsymmetrical title compounds. The method is insensitive to moisture and air and only para-substituted products are formed.
Synthesis of diaryliodonium triflates using environmentally benign oxidizing agents. Abstract: A range of symmetric and unsymmetric diaryliodonium triflates have been prepared employing urea-hydrogen peroxide as the oxidizing agent. The use of aqueous hydrogen peroxide and catalytic systems with MTO in the oxidation of iodoarenes has also been investigated.
Synlett: Accounts and Rapid Communications in Synthetic Organic
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