Single-chain magnet features in 1D [MnR₄TPP][TCNE] compounds

Molecular chains of antiferrimagnetically coupled MnIII-ion (S = 2) and TCNE (tetracyanoethylene) radical moments (s = ½) show different behaviour depending on group R substituted to TPP (tetraphenylporphyrin) and on the substitution site. The compound with R = F in Ortho position is a Single-Chain Magnet (SCM) with blocking temperature Tb = 6.6K, while that with R = F in Meta position shows both blocking (Tb = 5.4 K) and magnetic ordering transition (Tc = 10 K). For bulky groups R = OCnH2n+1, the magnetically ordered phase is observed (Tc ≈ 22 K), which does not however prevent slow relaxation at T <8 K. Magnetic hysteresis with coercive field Hc of 2 T at 2.3 K is like that of SCM. The frequency dependent AC susceptibility in the superimposed DC field reveals common features of all systems. The energy of intrachain ferromagnetic coupling between effective spin units 3/2, relevant at low temperatures, is determined for all compounds and the interchain dipolar coupling is estimated. It is concluded that slow relaxation is inherent for all quasi one-dimensional compounds and for the magnetically ordered ones shows up in the high enough magnetic field

Magnetooptical and structural investigations of five dimeric cobalt(II) complexes mimicking metalloenzyme active sites

Four novel cobalt(II) complexes mimicking metalloenzyme active sites, novel C 14H 22Cl 12Co 2O 132C 3H 8O (1), C 28H 36Cl 24Co 4O 284C 4H 8O 2 (2), C 16H 22Cl 12Co 2O 13C 2HCl 3O 2 (3), C 16H 22Cl 12Co 2O 13 (4), and one known C 40H 78Cl 8Co 2O 17 (5) are composed of the same core of two high-spin cobalt(II) centers triply bridged by water and two trichloroacetato (1-4) or two pivalate (5) groups but differ in terminal ligands. The crystal structures of new compounds 1-4 belong to the space groups P1̄, P2 1/c, P1̄, and Pbcn, respectively. All five investigated complexes contain Co atoms in distorted octahedral coordination. The complexes were characterized by magnetic susceptibility and magnetization measurements and by variable-temperature variable-field magnetic circular dichroism spectroscopy. Experimental data were analyzed in the frame of the theoretical model, which includes an unquenched orbital moment of the Co II ions. All investigated compounds are antiferromagnetically coup

Synthesis, crystal structure, and magnetic properties of the coordination polymer [Fe(NCS)2[Fe(NCS)_{2}(1,2-bis(4-pyridyl)-ethylene)]n_{n} showing a two step metamagnetic transition.

Reaction of iron(II) thiocyanate with an excess of trans-1,2-bis(4-pyridyl)-ethylene (bpe) in acetonitrile at room temperature leads to the formation of $[Fe(NCS)_{2}(bpe)_{2} \cdot (bpe)]$ (1), which is isotypic to its Co(II) analogue. Using slightly different reaction conditions the literature known compound $[Fe(NCS)_{2}(bpe)_{2}(H_{2}O)_{2}]$ (2) was obtained as a phase pure material. Simultaneous differential thermoanalysis and thermogravimetry prove that the hydrate 2 transforms into the anhydrate $[Fe(NCS)_{2}(bpe)_{2}]$ (3), that decomposes on further heating into the new ligand-deficient 1:1 compound of composition $[Fe(NCS)_{2}(bpe)]_{N}$ (4), which can also be obtained directly by thermal decomposition of 1. Further investigations reveal that 4 can also be prepared under solvothermal conditions, and single crystal structure analysis shows that the iron(II) cations are linked via $\mu$ -1,3 bridging thiocyanato anions into chains, that are further connected into layers by the bpe ligands. Magnetic measurements, performed on powder samples, prove that 1 and 2 show only Curie–Weiss behavior, whereas in 4 antiferromagnetic ordering with a Néel temperature of 5.0 K is observed. At T < 4.0 K a two-step metamagnetic transition occurs at applied magnetic fields of 1300 and 1775 Oe. The magnetic properties are discussed and compared with those of related compounds