Search for: All records

TCNQ (7,7,8,8-tetracyanoquinodimethane) anion-radical derivatives were used to fine tune the magnetic properties of the [Co II (Fctp) 2 ] 2+ (Fctp = 4′-(2-ferrocenyl)-2,2′:6′2′′-terpyridine) cation in the solid state. The cocrystallization of [Co II (Fctp) 2 ] 2+ with TCNQ˙ − yielded the two pseudo-polymorphic products [Co II (Fctp) 2 ] (TCNQ) 2 ( 1 ) and [Co II (Fctp) 2 ] (TCNQ) 2 ·MeCN ( 2 ) whereas the analogous reaction with TCNQF˙ − (TCNQF = 2-fluoro-7,7,8,8-tetracyanoquinodimethane) exclusively yielded [Co II (Fctp) 2 ] (TCNQF) 2 ·MeCN ( 3 ). Compound 1 exhibits slow relaxation of magnetization under an applied DC field with U eff = 19.1 K and τ 0 = 9.8 × 10 −6 s. Compounds 2 and 3 are isostructural but exhibit different spin-crossover behavior with transition temperatures of T 1/2 = 336 K and 226 K, respectively. Investigations of the solid state structures by DFT calculations indicate that the differences in magnetic properties of the cationic moiety, [Co II (Fctp) 2 ] 2+ , are induced by supramolecular interactions between [Co II (Fctp) 2 ] 2+ and tunable TCNQ˙ − /TCNQF˙ − anion-radical derivatives. 

Structural, magnetic and theoretical studies of three octahedral mononuclear Dy III complexes with triphenylphosphine oxide and halide ligands are reported. The Cl − and Br − analogues exhibit SMM behavior with energy barriers of 49.1 K and 70.9 K, respectively under a small dc field. Ab initio calculations were performed, the results of which predict higher energy barriers for iodide containing SMMs. 

A new family of radical-bridged compounds, (Cp* 2 Co)[M 2 Cl 4 (dpq)] (M = Fe ( 1 ), Co ( 2 ), Zn ( 3 )), (dpq = 2,3-di(2-pyridyl)-quinoxaline) is reported. Magnetic studies, DFT and ab initio calculations reveal strong antiferromagnetic metal–radical interactions with coupling constants of J = −213.1 and −218.8 cm −1 for 1 and 2 , respectively. 

Two new homoleptic Dy III compounds [Dy(Tp Me2 ) 2 ][DyCl 3 (Tp Me2 )]·CH 2 Cl 2 ( 1 ) and [Dy(Tp Me2 ) 2 ]I ( 3 ) as well as a heteroleptic (NMe 4 )[DyCl 3 (Tp Me2 )] ( 2 ) (Tp Me2 = tris(3,5-dimethylpyrazolyl)borate) species are reported. Magnetic studies revealed that 1 is a single-molecule magnet (SMM) with an energy barrier of U eff = 80.7 K with τ 0 = 6.2 × 10 −7 s under a zero applied field. Compound 3 exhibits a U eff of 13.5 K with τ 0 = 1.6 × 10 −6 s under a 0.08 T applied field. Ab initio CASSCF + RASSI-SO calculations were performed to further investigate the magnetic behavior of complexes 1–3 . The results support experimental magnetic data for 1 and 3 and indicate that an intermolecular dipolar interaction of ( zJ = −0.1 cm −1 ) is responsible for the SMM behavior of 1 . 

Two dinuclear lanthanide complexes (Gd and Dy) were prepared and characterized by X-ray, magnetic and computational methods. The Dy analogue shows SMM behavior with an energy barrier of 98.4 K in the absence of an applied dc field. Theoretical calculations were performed on model complexes which support the hypothesis that the energy barrier will increase if the soft-donor atoms S and Se are used in lieu of an O donor. 

A rare disk-like single-molecule magnet (SMM) exclusively bridged by end-on azides with a spin ground state of S = 14 was prepared by the reaction of a divalent Fe II precursor with Me 3 SiN 3 under basic conditions. AC magnetic susceptibility studies revealed unusual, “Janus”-faced SMM behavior for the dried and pristine forms of the compound attributed to solvation/de-solvation effects of the coordinated MeCN ligands which leads to alterations in the crystal field and symmetry of the metal ions. DFT calculations confirmed the ferromagnetic nature of the interactions between the Fe II spin carriers with the zero-field splitting parameters D = −0.2323 cm −1 and E / D = 0.027. The results have important implications for the future study of single-molecule magnets incorporating volatile solvent molecules in the first coordination sphere of the metal ions and their effect on the relaxation dynamics. 

The synthesis, single-crystal structures and magnetic properties of three new cyano-bridged complexes [FeIII4MII2] (M = Fe II , Co II , Ni II ) are reported. Electronic absorption spectroscopy reveals the occurrence of intervalence charge transfer for [FeIII4FeII2]. Field-induced slow magnetic relaxation behavior is exhibited for [FeIII4CoII2] and [FeIII4NiII2] which originates from the ferromagnetic interactions between Fe III and M II spin centers of the square. 

A new cyclic molecule incorporating [Mo III (CN) 7 ] 4− has been characterized by single crystal X-ray methods, SQUID magnetometry and theoretical calculations. The wheel molecule [Mo III (CN) 7 ] 6 [Ni(L)] 12 (H 2 O) 6 exhibits ferromagnetic Mo–Ni coupling which did not exist for the previously reported octacyanometallate analogue [Mo IV (CN) 8 ] 6 [Ni(L)] 12 (H 2 O) 6 . These results indicate that known supramolecular architectures incorporating octacyanometallates can be used as platforms for making new molecules incorporating seven-coordinate cyanide precursors.