A mononuclear hexacoordinate Cu(II) complex shows a field induced slow magnetic relaxation that is not facilitated by an energy barrier to spin reversal due to the zero-field splitting. Two relaxation channels were found: the magnetic field strongly supports the low-frequency relaxation path with a relaxation time as long as τ = 0.8 s at T = 1.9 K and B = 1.5 T. The mechanism of the relaxation at low temperature involves the dominant Raman process for this S = 1/2 spin system along with a temperature-independent term belonging to a quantum tunneling.

An unprecedentedr eversible dynamic transformation is reported in am etal-organic framework involving bond formation, which is accompanied by two important structural changes;achiral to chiral and two-to three-dimensions. Using two bent organic ligands (diimpym = 4,6-di(1H-imidazol-1-yl)pyrimidine;H 2 npta = 5-nitroisophthalic acid) and Co II (NO 3 ) 2 ·6H 2 Ot he coordination polymer Co(diimpym)(npta)·CH 3 OH, (1·CH 3 OH), was obtained solvothermally. Its structure consists of knitted pairs of square layers (4 4 -sql net) of five-coordinated Co and disordered methanol, and it crystallizedi nt he achiral Pbca space group at room temperature. It undergoes as ingle crystal to single crystal (SC-SC) transformation to a3 Di nterpenetrated framework (a-polonium-type net, pcu)o fs ix-coordinated Co and ordered methanol in the chiral P2 1 2 1 2 1 space group below 220 K. Most unusual is the dynamic temperature-dependent shortening of aC o···O connection from an on-bonded 2.640 (298 K) to ab onded2 .347 distance (100 K) transforming the square pyramidal cobalt polyhedron to ad istorted octahedron. The desolvated crystals( 1)o btained at 480 Kr etain the full crystallinitya nd crystallize in the achiral Pbca space group between 100 and 298 Kb ut the dynamic shorteningo ft he Co···O distance connecting the layers into the 3D pcu framework structure is observed. Following post-synthetic insertion of ethanol (1·CH 3 CH 2 OH)i td oes not exhibit the transformation and retains the knitted2 Da chiral Pbca structure for all temperatures (100-298 K) and the ethanol is always disordered. The structurala nalyses thusc oncludet hat the ordering of the methanol induces the chirality while the availables pace controlst he dynamic motion of the knitted 2D networks into the 3D interpenetrated framework. Consequently, 1 selectively adsorbs CO 2 to N 2 and exhibits Type-III isotherms indicating dynamic motion of the 2D networks to accommodate the CO 2 at 273 and 298 Ki nc ontrast to the rigidity of the 3D framework at 77 Kp reventing N 2 from penetrating the solid. The magnetic properties are also reported.

Abrupt room temperature switching (T(c) = 295 K with a 5 K hysteresis) was achieved in a neutral Fe(II) complex based on a 2-(1H-pyrazol-1-yl)-6-(1H-tetrazol-5-yl)pyridine ligand. Structural characterization and spin crossover study (via SQUID magnetometry, photoexcitation and X-ray absorption spectroscopy) in the solid state are described.

Pentacoordinate complex [CoL(3)Cl2] with a tridentate antenna-like ligand L(3) forms a dimer held by short π-π stacking with head-to-head contacts at 3.4 Å. The direct-current (dc) magnetic susceptibility and magnetization data confirm weak ferromagnetic interaction and a large-magnetic anisotropy, D/hc = 150 cm(-1) and E/hc = 11.6 cm(-1). The system shows superparamagnetic behavior at low temperature that depends upon the applied magnetic field. At Bdc = 0.2 T, a low-frequency peak at the out-of-phase susceptibility is seen (ν ∼ 0.3 Hz), whereas the onset of the second peak appears at ν > 1500 Hz, indicating the existence of two slow relaxation processes.

Herein, we have synthesised and characterised a novel organic–inorganic hybrid crystal, [CH3NH3]2KCr(CN)6 (MACr).