Spin state dependence of electrical conductivity of spin crossover materials

We studied the spin state dependence of the electrical conductivity of the spin crossover compound [Fe(Htrz)2(trz)](BF4) (Htrz = 1H-1,2,4-triazole) by means of dc electrical measurements. The low spin state is characterized by higher conductance and lower thermal activation energy of the conductivity, when compared to the high spin state

Pyridinium bis(pyridine-κN)tetrakis(thiocyanato-κN)ferrate(III)

In the title compound, (C5H6N)[Fe(NCS)4(C5H5N)2], the FeIII ion is coordinated by four thiocyanate N atoms and two pyridine N atoms in a trans arrangement, forming an FeN6 polyhedron with a slightly distorted octahedral geometry. Charge balance is achieved by one pyridinium cation bound to the complex anion via N—H...S hydrogen bonding. The asymmetric unit consists of one FeIII cation, four thiocyanate anions, two coordinated pyridine molecules and one pyridinium cation. The structure exhibits π–π interactions between pyridine rings [centroid–centroid distances = 3.7267 (2), 3.7811 (2) and 3.8924 (2) Å]. The N atom and a neighboring C atom of the pyridinium cation are statistically disordered with an occupancy ratio of 0.58 (2):0.42 (2)

Crystal structure of poly[bis(μ-2-bromopyrazine)tetra-μ2-cyanido-dicopper(I)iron(II)]: a bimetallic metal-organic framework

In the title metal-organic framework, [Fe(C4H3BrN2)2{Cu(CN)2}2]n, the FeII cation is located on an inversion center and has a slightly elongated octahedral coordination environment [FeN6], ligated by two pyrazine N atoms of symmetry-related bridging 2-bromopyrazine molecules in the axial positions and by four N atoms of pairs of symmetry-related cyanido groups in the equatorial positions. The CuI center has a fourfold coordination environment [CuC3N], with an almost perfect trigonal–pyramidal geometry, formed by three cyanido C atoms and an N atom of a bridging 2-bromopyrazine molecule. Copper(I) centers related by a twofold rotation axis are bridged by two carbon atoms from a pair of μ-CN groups, resulting in Cu2(CN)2 units. Each Cu2(CN)2 unit is linked to six FeII cations via a pair of linear CN units, the pair of μ-CN groups and two bridging 2-bromopyrazine ligands, resulting in the formation of a metal–organic framework, which is additionally stabilized by the short Cu...Cu contacts of 2.4450 (7) Å

1D iron(ii)-1,2,4-triazolic chains with spin crossover assembled from discrete trinuclear complexes

Temperature-induced spin crossover has been found in a molecular ferrous complex of 4-amino-1,2,4-triazole for the FeN6 centres, while the FeN3O3 centres are always HS

1,2,4,5-Tetrazine: an unprecedented mu4-coordination that enhances ability for anion···pi interactions

[eng] A series of framework coordination polymers reveals the use of 1,2,4,5-tetrazines as efficient bridging ligands towards silver(I) and copper(I) ions. All four nitrogen atoms were functional as lone pair donors leading to an unprecedented m4-coordination of the ligands (1,2,4,5-tetrazine, ttz; 3,6-dimethyl-1,2,4,5-tetrazine, Me2ttz) in [Ag(ttz)(X)] (X = NO3, 1; ClO4, 2), [Ag2(Me2ttz)(NO3)2] (3), [Ag2(Me2ttz)(H2O)2(ClO4)2] (4), [Ag3(Me2ttz)(H2O)2(CF3SO3)3] (5) and [Cu4Cl4(Me2ttz)] (6). In 1 and 2, m4-tetrazines and silver ions (AgN4, Ag-N 2.42-2.53A˚ ) compose a 3D framework of {42;84} topology. Structures 3 and 4 were based on disilver-tetrazine ribbons, while in 5 m4-tetrazines interconnect silver-triflate chains. In 6, m4-ligands connect inorganic layers sustained by copper-chloride squares, hexa- and octagons (1.974(2) and 1.981(2)A˚ ). Multiple N-coordination to metal ions enhances the ability of the electron deficient tetrazine system for anion ◊ ◊ ◊ p binding. Compounds 1 and 2 exhibit very short interactions of this type with corresponding O◊ ◊ ◊ C(N) separations down to a record value of 2.78A˚ and O◊ ◊ ◊ p 2.61A˚ . For 6, p-acidity of tetrazine was reflected by contacts Cl ◊ ◊ ◊ p of 3.30A˚ . Results of high level ab initio calculations (RI-MP2/aug-cc-pVTZ) were in good agreement with experimental results, and were suggestive of the progressive enhancement of the p-acidity by increasing the number of Ag(I) ions N-coordinated to tetrazine