Ferromagnetic Polarization: The Quantum Picture of Switching On/Off Single-Molecule Magnetism

The mixed 3d–4f pentanuclear complex (Bu₄N)­[Mn^III₄Y^III(shi)₄(OAc)₄(CH₃OH)₄]·CH₃OH·H₂O (<b>1</b>) (H₃shi = salicylhydroxamic acid) was synthesized by the direct reaction of Y­(NO₃)₃·6H₂O, Mn­(OAc)₂·4H₂O, and H₃shi. When an additional ligand, (NHBu₃)₃[W­(CN)₈]·2H₂O, was added, the mixed 3d–4f–5d hexanuclear complex (Et₄N)₅[Mn^III₄Y^III(shi)₄(OAc)₄W^V(CN)₈]­(WO₄)_0.5 (<b>2</b>) was obtained. X-ray crystallographic analysis shows that the 3d–4f complex <b>1</b> represents a 12-metallacrown-4 (12-MC-4) structure, in which the metallacrown ring [Mn–N–O]₄ connection captures one Y^III ion with four bridging acetate anions, completing the eight-coordinated environment around Y^III ion, while four methanol molecules each coordinate to the Mn^III ions on the other side of the Y^III ion. After octacyanotungstate is introduced, the [W^V(CN)₈] group substitutes for four methanol molecules of <b>1</b> to form complex <b>2</b>. Magnetic studies indicate the overall antiferromagnetic coupling present within the MC ring of complex <b>1</b>. However, interestingly, the dominant ferromagnetic coupling between Mn^III ions was observed in complex <b>2</b>. A susceptibility analysis shows that the natural spin alignments in 12-MC-4 metallacrowns are tuned from overall antiferromagnetic to dominant ferromagnetic fashions by magnetic coupling between Mn^III ions and the W^V ion. Complex <b>1</b> [Mn^III₄Y^III] retains an <i>S</i> = 0 ground state, and complex <b>2</b> [Mn^III₄Y^IIIW^V] shows obvious single-molecule magnet (SMM) behavior with an <i>S</i>_T = 11/2 ground state, respectively, before and after introduction of the octacyanotungstate group. The spin frustration geometrical structure constructed by four Mn^III ions and one W^V ion was considered as the key factor for switching on the SMM properties of the 12-MC-4 system

Di-, tri-, and tetranuclear cobalt, copper, and manganese complexes bridged by <i>μ</i>-hydroxyl groups of tetradentate Schiff base ligands: structures, magnetic properties, and antitumor activities

<div><p>[Co₂(HL^<b>1</b>)₂(H₂O)₂](NO₃) (<b>1</b>), [Cu₂(H_<b>2</b>L^<b>1</b>)(HL^<b>1</b>) (CH₃COO)]·H₂O (<b>2</b>), [Cu₄(HL^<b>1</b>)₄(C₂H₅OH)]·C₂H₅OH·H₂O (<b>3</b>), and [Mn₃(HL^<b>2</b>)₂(CH₃OH)₂(CH₃COO)₄]·2(CH₃OH)·H₂O (<b>4</b>) {<b>H</b>_<b>3</b><b>L</b>^<b>1</b><b> </b>= 2-ethyl-2-(2-hydroxybenzylideneamino)propane-1,3-diol, <b>H</b>_<b>3</b><b>L</b>^<b>2</b><b> </b>= 2-ethyl-2-[(2-hydroxynaphthalene-1-yl)methyleneamino]propane-1,3-diol} have been synthesized and characterized by IR spectra, elemental analyses, single-crystal X-ray diffraction, TGA, XRD, and magnetic measurements. Compound <b>1</b> possesses mixed-valence dinuclear {Co₂(<i>μ</i>₂-O)₂} with Co(II) and Co(III) ions linked through <i>μ</i>₂-hydroxyl of Schiff base ligands. Compound <b>2</b> displays a binuclear structure with {Cu₂(<i>μ</i>₂-O)(<i>η</i>²-COO)} containing one <i>μ</i>₂-hydroxyl and a single <i>syn–syn</i> acetate bridge. Compound <b>3</b> is tetranuclear with a cube-shaped {Cu₄(<i>μ</i>₃-O)₄} core constructed by four Cu(II) centers and four <i>μ</i>₃-hydroxyls of Schiff base ligands. Compound <b>4</b> displays a linear trinuclear {Mn₃(<i>μ</i>₂-O)₂(<i>η</i>²-COO)₂} structure in which the terminal Mn(III) and the central Mn(II) ions are linked by a <i>μ</i>₂-hydroxyl of Schiff base and two <i>syn–syn</i> acetate bridges. The results show that terminal hydroxyl groups of Schiff base ligands play an important role in assembling polynuclear compounds. Magnetic properties and antitumor activities of these compounds were investigated. The antitumor activities reveal that <b>1</b> and <b>2</b> are more effective antitumor agents for K-562 and HL-60, respectively.</p></div

One-Pot Construction of Heteroarylation/Esterification Products of Acrylic Acids via Iridium(III)-Catalyzed C–H Activation

A carboxylate-assisted iridium(III)-catalyzed regioselective C(sp2)–H heteroarylation/esterification reaction of acrylic acid is disclosed herein for the first time. This catalytic protocol tolerates various α-substituted, β-substituted, and α, β-disubstituted acrylic acids as well as heteroaromatic boronates well. The resulting 3,4-dihydro-2H-pyran-6-carboxylic acid derivative 3r highlighted the AIE-active luminophore with multiple emission signal properties and a high quantum yield of 28%, exhibiting the potential application of this methodology for the synthesis of nitrogen-containing organic functional materials