Field sweep rate dependence of the coercive field of single-molecule magnets: a classical approach with applications to the quantum regime

A method, based on the Neel-Brown model of thermally activated magnetization reversal of a magnetic single-domain particle, is proposed to study the field sweep rate dependence of the coercive field of single-molecule magnets (SMMs). The application to Mn12 and Mn84 SMMs allows the determination of the important parameters that characterize the magnetic properties: the energy barrier, the magnetic anisotropy constant, the spin, tau_0, and the crossover temperature from the classical to the quantum regime. The method may be particularly valuable for large SMMs that do not show quantum tunneling steps in the hysteresis loops.Comment: 6 pages, 6 figure

Zinc(II) and Nickel(II) Benzoate Complexes from the Use of 1-methyl-4,5-diphenylimidazole

Two new complexes, [Zn(O2CPh)2(L)2]⋅2MeOH  (⋅2MeOH) and [Ni2(O2CPh))4(L)2]⋅2MeCN  (⋅2MeCN), have been synthesized and characterized by X-ray analysis in the course of an ongoing investigation of the MII/X−/L[MII=Co,Ni,Cu,Zn; X−=Cl−,Br−,I−,NCS−,NO−3,N−3,PhCO−2; L=1-methyl-4,5-diphenylimidazole] reaction system, aiming at understanding and assessing the relative strength and the way in which the intermolecular interactions control the supramolecular organization of these compounds. In the mononuclear complex ⋅2MeOH, the benzoate ion acts as a monodentate ligand resulting in a distorted tetrahedral N2O2 coordination environment. Complex ⋅2MeCN exhibits a dinuclear paddle-wheel structure; each NiII has a square pyramidal NiNO4 chromophore with four benzoate oxygens in the basal plane and the pyridine-type nitrogen atom of one ligand L at the apex. The structure of ⋅2MeOH is stabilized by intramolecular - interactions between aromatic rings of adjacent 4,5-diphenylimidazole moieties; it is a feature also evidenced in similar compounds of the type [MX2L2]

Symmetric and asymmetric dinuclear manganese(IV) complexes possessing a [Mn<SUP>IV</SUP><SUB>2</SUB>(&#956;-O)<SUB>2</SUB>(&#956;-O<SUB>2</SUB>CMe)]<SUP>3+</SUP> core and terminal Cl<SUP>-</SUP> ligands

The synthesis of new dinuclear manganese(IV) complexes possessing the [Mn<SUP>IV</SUP><SUB>2</SUB>(&#956;-O)<SUB>2</SUB>(&#956;-O<SUB>2</SUB>CMe)]<SUP>3+</SUP> core and containing halide ions as terminal ligands is reported. [Mn<SUB>2</SUB>O<SUB>2</SUB>(O<SUB>2</SUB>CMe)Cl<SUB>2</SUB>(bpy)<SUB>2</SUB>]<SUB>2</SUB>[MnCl<SUB>4</SUB>] (1; bpy = 2,2'-bipyridine) was prepared by sequential addition of [MnCl<SUB>3</SUB>(bpy)(H<SUB>2</SUB>O)] and (NBzEt<SUB>3</SUB>)<SUB>2</SUB>[MnCl<SUB>4</SUB>] to a CH<SUB>2</SUB>Cl<SUB>2</SUB> solution of [Mn<SUB>3</SUB>O<SUB>4</SUB>(O<SUB>2</SUB>CMe)<SUB>4</SUB>(bpy)<SUB>2</SUB>]. The complex [Mn<SUP>IV</SUP><SUB>2</SUB>O<SUB>2</SUB>(O<SUB>2</SUB>CMe)Cl(bpy)<SUB>2</SUB>(H<SUB>2</SUB>O)](NO<SUB>3</SUB>)<SUB>2</SUB> (2) was obtained from a water/acetic acid solution of MnCl<SUB>2</SUB>&#183;4H<SUB>2</SUB>O, bpy, and (NH<SUB>4</SUB>)<SUB>2</SUB>[Ce(NO<SUB>3</SUB>)<SUB>6</SUB>], whereas the [Mn<SUP>IV</SUP><SUB>2</SUB>O<SUB>2</SUB>(O<SUB>2</SUB>CR)X(bpy)<SUB>2</SUB>(H<SUB>2</SUB>O)](ClO<SUB>4</SUB>)<SUB>2</SUB> [X = Cl<SUP>-</SUP> and R = Me (3), Et (5), or C<SUB>2</SUB>H<SUB>4</SUB>Cl (6); and X = F<SUP>-</SUP>, R = Me (4)] were prepared by a slightly modified procedure that includes the addition of HClO<SUB>4</SUB>. For the preparation of 4, MnF<SUB>2</SUB> was employed instead of MnCl<SUB>2</SUB>&#183;4H<SUB>2</SUB>O. [Mn<SUB>2</SUB>O<SUB>2</SUB>(O<SUB>2</SUB>CMe)Cl<SUB>2</SUB>(bpy)<SUB>2</SUB>]<SUB>2</SUB>[MnCl<SUB>4</SUB>]&#183;2CH<SUB>2</SUB>Cl<SUB>2</SUB> (1&#183;2CH<SUB>2</SUB>Cl<SUB>2</SUB>) crystallizes in the monoclinic space group C2/c with a = 21.756(2) &#197;, b = 12.0587(7) &#197;, c = 26.192(2) &#197;, &#945; = 90&#176;, &#946;= 111.443(2)&#176;,&#947; = 90&#176;, V = 6395.8(6) &#197;<SUP>3</SUP>, and Z = 4. [Mn<SUB>2</SUB>O<SUB>2</SUB>(O<SUB>2</SUB>CMe)Cl(H<SUB>2</SUB>O)(bpy)<SUB>2</SUB>](NO<SUB>3</SUB>)<SUB>2</SUB>&#183;H<SUB>2</SUB>O (2&#183;H<SUB>2</SUB>O) crystallizes in the triclinic space group P&#8593; with a = 11.907(2) &#197;, b = 12.376(2) &#197;, c = 10.986(2) &#197;, &#945;= 108.24(1)&#176;, &#946;= 105.85(2)&#176;, &#947;= 106.57(1)&#176;, V = 1351.98(2) &#197;<SUP>3</SUP>, and Z = 2. [Mn<SUB>2</SUB>O<SUB>2</SUB>(O<SUB>2</SUB>CMe)Cl(H<SUB>2</SUB>O)(bpy)<SUB>2</SUB>](ClO<SUB>4</SUB>)<SUB>2</SUB>&#183;MeCN (3&#183;MeCN) crystallizes in the triclinic space group P with a = 11.7817(7) &#197;, b = 12.2400(7) &#197;, c = 13.1672(7) &#197;, &#945;= 65.537(2)&#176;, &#946;= 67.407(2)&#176;, &#947;= 88.638(2)&#176;, V = 1574.9(2) &#197;<SUP>3</SUP>, and Z = 2. The cyclic voltammogram (CV) of 1 exhibits two processes, an irreversible oxidation of the [MnCl<SUB>4</SUB>]<SUP>2-</SUP> at E<SUB>&#189;</SUB> ~0.69 V vs ferrocene and a reversible reduction at E<SUB>&#189;</SUB>= 0.30 V assigned to the [Mn<SUB>2</SUB>O<SUB>2</SUB>(O<SUB>2</SUB>CMe)Cl<SUB>2</SUB>(bpy)<SUB>2</SUB>]<SUP>+/0</SUP> couple (2Mn<SUP>IV</SUP> to Mn<SUP>IV</SUP>Mn<SUP>III</SUP>). In contrast, the CVs of 2 and 3 show only irreversible reduction features. Solid-state magnetic susceptibility (X<SUB>M</SUB>) data were collected for complexes 1&#183;1.5H<SUB>2</SUB>O, 2&#183;H<SUB>2</SUB>O, and 3&#183;H<SUB>2</SUB>O in the temperature range 2.00-300 K. The resulting data were fit to the theoretical X<SUB>M</SUB> T vs T expression for a Mn<SUP>IV</SUP><SUB>2</SUB> complex derived by use of the isotropic Heisenberg spin Hamiltonian (&#951;= -2JS<SUB>1</SUB>S<SUB>2</SUB>) and the Van Vleck equation. The obtained fit parameters were (in the format J/g) -45.0(4) cm<SUP>-1</SUP>/2.00(2), -36.6(4) cm<SUP>-1</SUP>/1.97(1), and -39.3(4) cm<SUP>-1</SUP>/1.92(1), respectively, where J is the exchange interaction parameter between the two Mn<SUP>IV</SUP> ions. Thus, all three complexes are antiferromagnetically coupled

Fine Tuning the Hydrophobicity of a New Three-Dimensional Cu²⁺ MOF through Single Crystal Coordinating Ligand Exchange Transformations

The synthesis, characterization, and single–crystal–to–single–crystal (SCSC) exchange reactions of a new 3D Cu2+ MOF based on 5-aminoisophthalic acid (H2AIP), [Cu6(μ3-ΟΗ)3(ΑΙΡ)4(HΑΙΡ)]n·6nDMF·nH2O - UCY-16·6nDMF·nH2O, are reported. It exhibits a 3D structure based on two [Cu4(μ3–OH)2]6+ butterfly–like secondary building units, differing in their peripheral ligation, bridged through HAIP–/AIP2– ligands. This compound displays the capability to exchange the coordinating ligand(s) and/or guest solvent molecules through SCSC reactions. Interestingly, heterogeneous reactions of single crystals of UCY-16·6nDMF·nH2O with primary alcohols resulted not only in the removal of the lattice DMF molecules but also in an unprecedented structural alteration that involved the complete or partial replacement of the monoatomic bridging μ3–OH– anion(s) of the [Cu4(μ3–OH)2]6+ butterfly structural core by various alkoxy groups. Similar crystal-to-crystal exchange reactions of UCY-16·6nDMF·nH2O with long-chain aliphatic alcohols (CxH2x+1OH, x = 8–10, 12, 14, and 16) led to analogues containing fatty alcohols. Notably, the exchanged products with the bulkier alcohols UCY-16/n-CxH2x+1OH·S′ (x = 6–10, 12, 14, and 16) do not mix with H2O being quite stable in this solvent, in contrast to the pristine MOF, and exhibit a hydrophobic/superhydrophobic surface as confirmed from the investigation of their water contact angles and capability to remove hydrophobic pollutants from aqueous media

Fine Tuning the Hydrophobicity of a New Three-Dimensional Cu²⁺ MOF through Single Crystal Coordinating Ligand Exchange Transformations

The synthesis, characterization, and single–crystal–to–single–crystal (SCSC) exchange reactions of a new 3D Cu2+ MOF based on 5-aminoisophthalic acid (H2AIP), [Cu6(μ3-ΟΗ)3(ΑΙΡ)4(HΑΙΡ)]n·6nDMF·nH2O - UCY-16·6nDMF·nH2O, are reported. It exhibits a 3D structure based on two [Cu4(μ3–OH)2]6+ butterfly–like secondary building units, differing in their peripheral ligation, bridged through HAIP–/AIP2– ligands. This compound displays the capability to exchange the coordinating ligand(s) and/or guest solvent molecules through SCSC reactions. Interestingly, heterogeneous reactions of single crystals of UCY-16·6nDMF·nH2O with primary alcohols resulted not only in the removal of the lattice DMF molecules but also in an unprecedented structural alteration that involved the complete or partial replacement of the monoatomic bridging μ3–OH– anion(s) of the [Cu4(μ3–OH)2]6+ butterfly structural core by various alkoxy groups. Similar crystal-to-crystal exchange reactions of UCY-16·6nDMF·nH2O with long-chain aliphatic alcohols (CxH2x+1OH, x = 8–10, 12, 14, and 16) led to analogues containing fatty alcohols. Notably, the exchanged products with the bulkier alcohols UCY-16/n-CxH2x+1OH·S′ (x = 6–10, 12, 14, and 16) do not mix with H2O being quite stable in this solvent, in contrast to the pristine MOF, and exhibit a hydrophobic/superhydrophobic surface as confirmed from the investigation of their water contact angles and capability to remove hydrophobic pollutants from aqueous media