Homochiral 1D Helical Chain Based on an Achiral Cu(II) Complex

Self-assembly of an achiral [Cu­(L)] complex produced a homochiral helical chain [Cu­(L)]₃·2H₂O (<b>1</b>) (L = 2-dimethylaminoethyl­(oxamato)). Interestingly, complex <b>1</b> obtained in our laboratory exhibits only a left-handed helical chain without any chiral source. Single-crystal X-ray analysis revealed the absolute structure and homochirality of its helical chain structure in the space group of <i>P</i>3₂. Solid-state circular dichroism (CD) spectra confirmed the high enantio excess of the crystals obtained in different synthesis batches. Magnetic susceptibility measurements reveal a relatively strong intrachain antiferromagnetic interaction between Cu­(II) centers via an oxamato bridge (<i>J</i> = −74.4 cm^–1)

Homochiral 1D Helical Chain Based on an Achiral Cu(II) Complex

Self-assembly of an achiral [Cu­(L)] complex produced a homochiral helical chain [Cu­(L)]₃·2H₂O (<b>1</b>) (L = 2-dimethylaminoethyl­(oxamato)). Interestingly, complex <b>1</b> obtained in our laboratory exhibits only a left-handed helical chain without any chiral source. Single-crystal X-ray analysis revealed the absolute structure and homochirality of its helical chain structure in the space group of <i>P</i>3₂. Solid-state circular dichroism (CD) spectra confirmed the high enantio excess of the crystals obtained in different synthesis batches. Magnetic susceptibility measurements reveal a relatively strong intrachain antiferromagnetic interaction between Cu­(II) centers via an oxamato bridge (<i>J</i> = −74.4 cm^–1)

Ferromagnetic Exchange Coupling in a Family of Mn^III Salen-Type Schiff-Base Out-of-Plane Dimers

A series of Mn^III saltmen dimers, [Mn₂(5-Rsaltmen)₂(X)₂]­(A)_2<i>n</i> (saltmen^2– = <i>N</i>,<i>N</i>′-(1,1,2,2-tetramethylethylene)­bis­(salicylideneiminate); R = H, Cl, Br, MeO, Me; X = H₂O, ReO₄^–, NO₃^–, N₃^–, NCS^–, A^– = ClO₄^–, PF₆^–, CF₃SO₃^– for X = H₂O) were synthesized and structurally and magnetically investigated to understand the correlation between their intradimer ferromagnetic (FM) interaction and single-molecule magnet (SMM) behavior. All complexes had a similar di-μ-phenolate-bridged out-of-plane dimer structure but displayed different bridging Mn–O_ph* distances depending on the R substituents of the saltmen ligand and axial X ligand. Magnetic susceptibility studies revealed intradimer FM coupling (<i>J</i>_Mn–Mn*), resulting in an <i>S</i>_T = 4 ground state for all dimers. However, the magnitude of FM coupling strongly depended on R and X. <i>J</i>_Mn–Mn* increased with decreasing Mn–O_ph* distance but decreased with decreasing Mn–X distance with a relation of H₂O ≈ ReO₄^– > NO₃^– > N₃^– ≈ NCS^– with a linear trend for R = H, Cl, Me but not for R = Br, MeO. Theoretical investigations revealed that a larger orbital overlap stabilized a FM spin configuration through competition between the orbital degeneracy and on-site Coulomb repulsion of out-of-phase and in-phase orbitals. Most dimers showed typical SMM behavior. The dimers with larger <i>J</i>_Mn–Mn* tended to have higher blocking temperatures