title: Synthesis and magnetic properties of a new family of macrocyclic M(II)3Ln(III) complexes: insights into the effect of subtle chemical modification on single-molecule magnet behavior.
abstract: Thirteen tetranuclear mixed-metal complexes of the hexaimine macrocycle (L(Pr))(6-) have been prepared in a one-pot 3:1:3:3 reaction of copper(II) acetate hydrate, the appropriate lanthanide(III) nitrate hydrate, 1,4-diformyl-2,3-dihydroxybenzene (1), and 1,3-diaminopropane. The resulting family of copper(II)-lanthanide(III) macrocyclic complexes has the general formula Cu(II)(3)Ln(III)(L(Pr))(NO(3))(3)·solvents (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Tb, Ho, Er, Tm, or Yb). X-ray crystal structure determinations carried out on [Cu(3)Ce(L(Pr))(NO(3))(3)(MeOH)(3)] and [Cu(3)Dy(L(Pr))(NO(3))(3)(MeOH)(3)] confirmed that the large Ln(III) ion is bound in the central O(6) site and the three square pyramidal Cu(II) ions in the outer N(2)O(2) sites (apical donor either nitrate anion or methanol molecule) of the Schiff base macrocycle. Only the structurally characterized Cu(3)Tb complex, reported earlier, is a single-molecule magnet (SMM): the other 12 complexes do not exhibit an out-of-phase ac susceptibility signal or hysteresis of magnetization in a dc field. Ab initio calculations allowed us to rationalize the observed magnetic properties, including the significant impact of subtle chemical modification on SMM behavior. Broken-symmetry density functional theory (BS-DFT) calculations show there is a subtle structural balance as to whether the Cu···Cu exchange coupling is ferro- or antiferromagnetic. Of the family of 13 magnetically characterized tetranuclear Cu(II)(3)Ln(III) macrocyclic complexes prepared, only the Tb(III) complex is an SMM: the theoretical reasons for this are discussed.
authors.affiliation: Department of Chemistry and the MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, P.O. Box 56, Dunedin, New Zealand.
authors.forename: Humphrey L C
authors.initials: HL
authors.lastname: Feltham
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Clérac
authors.forename: Liviu
authors.initials: L
authors.lastname: Ungur
authors.forename: Veacheslav
authors.initials: V
authors.lastname: Vieru
authors.forename: Liviu F
authors.initials: LF
authors.lastname: Chibotaru
authors.forename: Annie K
authors.initials: AK
authors.lastname: Powell
authors.forename: Sally
authors.initials: S
authors.lastname: Brooker