Thermal decomposition of [Co(en)3][Fe(CN)6]∙ 2H2O: Topotactic dehydration process, valence and spin exchange mechanism elucidation.

BACKGROUND: The Prussian blue analogues represent well-known and extensively studied group of coordination species which has many remarkable applications due to their ion-exchange, electron transfer or magnetic properties. Among them, Co-Fe Prussian blue analogues have been extensively studied due to the photoinduced magnetization. Surprisingly, their suitability as precursors for solid-state synthesis of magnetic nanoparticles is almost unexplored. In this paper, the mechanism of thermal decomposition of [Co(en)3][Fe(CN)6] ∙∙ 2H2O (1a) is elucidated, including the topotactic dehydration, valence and spins exchange mechanisms suggestion and the formation of a mixture of CoFe2O4-Co3O4 (3:1) as final products of thermal degradation. RESULTS: The course of thermal decomposition of 1a in air atmosphere up to 600°C was monitored by TG/DSC techniques, (57)Fe Mössbauer and IR spectroscopy. As first, the topotactic dehydration of 1a to the hemihydrate [Co(en)3][Fe(CN)6] ∙∙ 1/2H2O (1b) occurred with preserving the single-crystal character as was confirmed by the X-ray diffraction analysis. The consequent thermal decomposition proceeded in further four stages including intermediates varying in valence and spin states of both transition metal ions in their structures, i.e. [Fe(II)(en)2(µ-NC)Co(III)(CN)4], Fe(III)(NH2CH2CH3)2(µ-NC)2Co(II)(CN)3] and Fe(III)[Co(II)(CN)5], which were suggested mainly from (57)Fe Mössbauer, IR spectral and elemental analyses data. Thermal decomposition was completed at 400°C when superparamagnetic phases of CoFe2O4 and Co3O4 in the molar ratio of 3:1 were formed. During further temperature increase (450 and 600°C), the ongoing crystallization process gave a new ferromagnetic phase attributed to the CoFe2O4-Co3O4 nanocomposite particles. Their formation was confirmed by XRD and TEM analyses. In-field (5 K / 5 T) Mössbauer spectrum revealed canting of Fe(III) spin in almost fully inverse spinel structure of CoFe2O4. CONCLUSIONS: It has been found that the thermal decomposition of [Co(en)3][Fe(CN)6] ∙∙ 2H2O in air atmosphere is a gradual multiple process accompanied by the formation of intermediates with different composition, stereochemistry, oxidation as well as spin states of both the central transition metals. The decomposition is finished above 400°C and the ongoing heating to 600°C results in the formation of CoFe2O4-Co3O4 nanocomposite particles as the final decomposition product.

Poly[di-µ(2)-chlorido-dichlorido(µ(3)-di-methyl sulfoxide-κO:O:S)(µ(2)-di-methyl sulfoxide-κO:S)ruthenium(III)sodium].

The structure of the title compound, [NaRuCl(4)(C(2)H(6)OS)(2)](n), comprises centrosymmetric [RuCl(2)(DMSO)Na(DMSO)Cl(2)Ru] units (DMSO is dimethyl sulfoxide, C(2)H(6)OS), with two Ru atoms, each lying on a crystallographic centre of inversion, connected via Na atoms, DMSO and chloride ligands into a two-dimensional (110) array. Both Ru(III) atoms are octa-hedrally coordinated by four chloride ligands in the equatorial plane and by two DMSO mol-ecules in apical positions within a RuCl(4)S(2) donor set. The Na atom is surrounded by three chloride anions and three O atoms derived from three DMSO mol-ecules, with the resulting Cl(3)O(3) donor set defining an octa-hedron. The crystal structure is further stabilized by inter-atomic inter-actions of the types C⋯Cl [C-Cl = 3.284 (2) Å], C-H⋯Cl [C⋯Cl = 3.903 (3) Å] and C-H⋯O [C⋯O = 3.376 (3) Å].

6-(2-Chloro-benzyl-amino)purinium tetra-chlorido(dimethyl sulfoxide-κO)(nitrosyl-κN)ruthenate(III) monohydrate.

The asymmetric unit of the title complex salt, (C(12)H(11)ClN(5))[RuCl(4)(NO)(C(2)H(6)OS)]·H(2)O, contains a 6-(2-chloro-benzyl-amino)purinium cation, a tetra-chlorido(dimethyl sulfoxide)nitro-sylruthenate(III) anion and one solvent water mol-ecule. The Ru(III) atom is octa-hedrally coordinated by four Cl atoms in the equatorial plane, and by a dimethyl sulfoxide O atom and a nitrosyl N atom in axial positions. The cation is an N3-protonated N7 tautomer. Inter-molecular N-H⋯N hydrogen bonds connect two cations into centrosymmetric dimers, with an N⋯N distance of 2.821 (4) Å. The crystal structure also involves N-H⋯O, N-H⋯Cl and O-H⋯Cl hydrogen bonds.

6-(2-Methoxy-benzyl-amino)purine.

The title compound, C(13)H(13)N(5)O, consists of discrete mol-ecules connected by N-H⋯N hydrogen bonds to form infinite chains, with N⋯N separations of 3.0379 (15) and 2.8853 (15) Å. The benzene and purine ring systems make a dihedral angle of 77.58 (3)°. The crystal structure is further stabilized by intra-molecular N⋯O inter-actions [2.9541 (12) Å] and inter-molecular C-H⋯C and C⋯C contacts [3.304 (2), 3.368 (2), 3.667 (2), 3.618 (2) and 3.512 (2) Å] which arrange the mol-ecules into graphite-like layers. The inter-layer separations are 3.248 and 3.256 Å.

Ammonium bis(tetraethylammonium) hexacyanidoferrate(III) trihydrate.

In the structure of the title salt, (NH(4))(C(8)H(20)N)(2)[Fe(CN)(6)].3H2O, the O atom of one of the water molecules shares its crystallographic site with the N atom of the ammonium cation in a 1:1 ratio. The second O atom from the two crystallographically independent water molecules is disordered over two positions separated by 0.551 (1) A. The water molecules and ammonium cations form tetrameric hydrogen-bonded units that, along with the complex anion, form the hydrophilic part of the structure. The hydrophobic part of the structure, represented by the tetraethylammonium cation, is located in cube-like cavities of the hydrophilic framework.