Stephanie L. Castro

Single-Molecule Magnets: Characterization of Complexes Exhibiting Out-of-Phase AC Susceptibility Signals

Abstract The structures and characterization are described of complexes that exhibit an out-of-phase AC magnetic susceptibility x m” The dodecanuclear complexes [Mn12O12(O2CR)16(H2O)4]z contain 8MnIII, 4MnIV or MnII, 7MnIII, 4MnIV and possess ground state spins of S = 9 or 10 (z = 0) or S = 19/2 (z = −1). The distorted-cubane complexes [Mn4O3X(O2CR)3(dbm)3] contain 3MnIII, MnIV and have been prepared with a variety of X groups; in every case, the ground state is S = 9/2. The anion [Mn11O10X6(O2CPh)11(H2O)4]2− (9MnIII, 2MnIV; X = NCO−, N3 −) contains two [Mn4O3X] distorted-cubanes linked by a [Mn3O4]+ unit; the ground state is S = 5. The cation [V4O2(O2CEt)7(bpy)2]+ (4VIII) has a [V4O2]8+ butterfly core and a S = 3 ground state. All these complexes exhibit out-of-phase AC magnetic susceptibility signals at low temperatures (<8 K). These signals are indicative of slow relaxation of the magnetization, unable to keep in phase with the oscillating AC magnetic field, and are taken as evidence for single-molecul...

Single-molecule magnets: out-of-phase ac susceptibility signals from tetranuclear vanadium(III) complexes with an S = 3 ground state

The salts of the tetranuclear vanadium(III) ions [V4O2(O2- CEt)7(L–L)2]z (L–L = bpy, z = +1; L–L = pic–, z = –1) with a V4 butterfly topology and a S = 3 ground state have been found to exhibit out-of-phase ac susceptibility signals, a signature of single-molecule magnets.

Tetranuclear vanadium(III) carboxylate chemistry, and a new example of a metal butterfly complex exhibiting spin frustration: structure and properties of [V4O2(O2CEt)7(bpy)2](ClO4)

Treatment of [VCl3(thf)3](thf = tetrahydrofuran) with bpy (bpy = 2,2′-bipyridine) and NaO2CEt in a 1 : 1 : 3 molar ratio in Me2CO followed by addition of ClO4– allows isolation of [V4O2(O2CEt)7(bpy)2](ClO4)[4(ClO4)], which contains a butterfly-like V4 unit; variable-temperature magnetic susceptibility studies show 1 to possess both ferro- and antiferro-magnetic exchange interactions leading to spin-frustration effects and an S= 3 ground state.

A mixed-valence (TiIIITiIV) carboxylate complex: crystal structures and properties of [Ti2OCl3(O2CPh)2(thf)3] and [NEt4]3[Ti2Cl9]

The reaction of [TiCl3(thf)3] with 4 equiv. PhCO2H in refluxing thf or 3 equiv. of Cl– in CH2Cl2 gives [Ti2OCl3(O2CPh)2(thf)3]a and [NEt4]3[Ti2Cl9]2, respectively: crystallography shows them to possess trapped-valence [Ti2(µ-O)(µ-O2CPh)2]3+(TiIIITiIV) and [Ti2(µl)3]3+ cores, respectively, the former with an unusual asymmetrically bridging O2– displaying triple/single bond distances to the metal ions.