Slow magnetic dynamics in a family of mononuclear lanthanide complexes exhibiting the rare cubic coordination geometry.

A new family of mononuclear lanthanide complexes, where the eight coordinate lanthanide ions adopt a very rare cubic coordination geometry is reported. The Dy analogue exhibits SMM behavior with a Ueff value 95.7 K under a 0.02 T applied dc field. Ab initio calculations support the observed magnetic behavior.

Effects of coordination sphere on unusually large zero field splitting and slow magnetic relaxation in trigonally symmetric molecules.

Geometric control in mononuclear complexes has come to the forefront in the field of molecular magnets due to its profound effects on relaxation pathways and blocking temperature in single molecule magnets (SMMs). Herein we report the synthesis and magnetic characterization of six trigonally symmetric, divalent Fe, Co, and Ni molecules, with the rigid geometry enforced via the use of the tris-anionic, tetradentate ligand MST (N,N',N''-[2,2',2''-nitrilotris-(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamide)). A systematic study on the effect of converting between trigonal monopyramidal complexes, (Me4N)[M(MST)], and trigonal bipyramidal complexes, (Me4N)[M(MST)(OH2)] was conducted experimentally and computationally. It was found that (Me4N)[Ni(MST)] exhibits a very large, near record zero-field splitting parameter (D) value of -434 cm-1, owing to an extremely low lying first excited state. The trigonal monopyramidal cobalt and iron complexes exhibit slow magnetic relaxation under applied fields, resulting in barriers of 45 K and 63.9 K respectively. Coordination of a single water molecule in the open axial site of the trigonal monopyramidal complexes exerts drastic dampening effects on the D value as well as slow relaxation. Computations reveal that coordination of water rotates the D zz axis away from the C 3 axis of symmetry resulting in a smaller D value. The aquo species (Me4N)[Co(MST)(OH2)] also exhibits magnetic relaxation under an applied field, but the barrier is reduced to 9.9 K. Water coordination totally quenches the magnetic behavior in the iron complex, and reduces the D value for nickel to -185 cm-1. These results showcase the drastic effect that a small change in the coordination environment can have on magnetic behavior, as well as that trigonal monopyramidal geometry can lead to near record D values.

Titanium(III) Member of the Family of Trigonal Building Blocks with Scorpionate and Cyanide Ligands.

The titanium(III) cyanide compound [Et4N][Tp*Ti(CN)3] ([Et4N] = tetraethylamonium; Tp* = 3,5-dimethyltrispyrazolylhydroborate) is reported, which exhibits a trigonally distorted geometry. Magnetic data and ab initio calculations verified that the molecule is an S = 1/2 paramagnet and that it exhibits significant temperature-independent paramagnetism.

Systematic Study of Open-Shell Trigonal Pyramidal Transition-Metal Complexes with a Rigid-Ligand Scaffold.

A family of distorted trigonal pyramidal transition-metal complexes [MII (N3 N)Li(THF)] (M=Mn, Fe, Co, Ni) have been studied as candidates for mononuclear single-molecule magnets. Magnetic anisotropy of the family depends on the electronic configuration of the central ion, with the Co analogue exhibiting pronounced SMM behavior.

Anion dependence in the spin-crossover properties of a Fe(II) podand complex.

We report the syntheses, characterisations, and spin state behaviours of salts of the tripodal-ligated Fe(II) complex [FeL(6-OH)]X(2) (L(6-OH) = tris{4-[(6-methanol)-2-pyridyl]-3-aza-3-butenyl}amine, X = OTf(-) (1), Br(-) (2), I(-) (3), BPh(4)(-) (4)). Covalent linking of the ligand arms is imperative as a high-spin bis(tridentate) complex (5) is formed when a non-tethered ethyl iminopyridine ligand (L(2) = 4-[(6-methanol)-2-pyridyl]-3-aza-3-butenyl) is used. For salts 1-4, thermally-induced spin-crossover (SCO) is observed in the solid state, with dependence on anion and solvate molecules. Salts with larger anions show more complete SCO centred at higher temperatures (1 > 3 > 2); the triflate salt 1 (T(1/2) = 173 K) also shows the strongest cooperativity of the compounds examined. Hydrogen bonding appears to be critical to SCO in this family of salts: limiting interactions by use of tetraphenylborate produces a high-spin complex down to 5 K. In protic solvents such as methanol, spectra of [FeL(6-OH)](2+) are largely unchanged over a period of three days, but dissociate when interrogated with strong field bidentate ligands. Compounds 1-3, and 5 remain high spin in solution down to 180 K, consistent with the data obtained in the solid state.