Mikołaj F. Rudolf

Cobalt(II) triazene 1-oxide bis(chelates). A case of planar (low spin)–tetrahedral (high spin) isomerism

High- and low-spin cobalt(II) trizene 1-oxide bis(chelates) have been isolated. The low-spin complexes possess square-planar structure whilst the high-spin complexes are tetrahedral. The molecular structure of high-spin [Co(OMeN3C6H4Me-4)2] has been determined: triclinic, space group P, Z= 2, a= 7.970(5), b= 10.174(5), c= 11.676(5)A, α= 87.18(4), β= 74.31(4) and γ= 74.06(4)°. For some complexes the isolation of both planar (low-spin) and tetrahedral (high-spin) isomers or of their conglomerates is possible depending on the synthesis conditions. The crystal structure of square-planar [Ni(OMeN3C6H4-Me-4)2], which is isomorphous with the low-spin isomer of [Co(OMeN3C6H4Me-4)2], has been determined: triclinic, space group P, Z= 1, with a= 7.495(2), b= 7.694(5), c= 8.612(3)A, α= 64.64(5), β= 87.84(2) and γ= 78.64(3)°. The complexes exhibit a planar-tetrahedral equilibrium in non-co-ordinating solvents, the ΔH⊖ and ΔS⊖ values of which, determined from solution magnetic susceptibility measurements, are in the range 1–15 kJ mol–1 and 5–30 J K–1 mol–1, respectively. The electrochemical properties of the complexes are given.

ESR studies of low-spin [N1,N4-bis(salicylidene)-S-alkyl-isothiosemicarbazonato]cobalt(II) complexes doped into the lattices of corresponding zinc(II) chelates

Abstract Direct template reaction of salicylaldehyde S-alkyl-isothiosemicarbazone with salicylaldehyde and its derivatives, in the presence of cobalt(II) [or zinc(II)] acetate, triethylamine and triethyl orthoformate yields the aqua-adducts of the corresponding N 1 ,N 4 -bis(salicylidene)-S-alkyl-isothiosemicarbazone complexes. ESR measurements of cobalt doped zinc complexes were performed. The spectra are typical for the z 2 > 1 ground state. The energies of the two excited doublet states were estimated on the basis of spin Hamiltonian parameters. A six-coordinate structure with coordination of the phenolic oxygen of an adjacent molecule has been proposed for the CoL·H 2 O complexes. The formation of low-spin pyridine adducts of the title complexes in the solid was shown.

The synthesis and electronic structure of Oxoisothiocyanatomolybdates(V) and -tungstates(V)

Abstract A number of complex salts containing the [MoO(NCS) 5 ] 2− and [WO(NCS) 5 ] 2− anions have been synthesized. The structure of these complex anions have been investigated by electronic, vibrational, and ESR spectra; magnetic studies were also carried out over a temperature range. The data obtained indicate that the complex anions are mononuclear with C 4v symmetry, and contain N-bonded NCS − ligands.

Synthesis and spin-crossover characteristics of polynuclear 4-(2´-hydroxy-ethyl)-1,2,4-triazole Fe(II) molecular materials

A new series of Fe(II) spin-crossover materials of formula [Fe(hyetrz)3](Anion)2•xH2O, where hyetrz = 4-(2′-hydroxy-ethyl)-1,2,4-triazole and Anion = Cl−, NO3−, Br−, I−, BF4−, ClO4−, PF6−, have been prepared and the spin transition characteristics studied. The structure of these compounds consists of linear chains in which the Fe(II) ions are linked by triple N1,N2-1,2,4-triazole bridges. Most of the hydrated compounds show non-classical spin-crossover behaviour associated with the removal of lattice water molecules, which initially stabilize the low-spin state. However for two of them, the perchlorate and the iodide compounds, the transition temperature is shifted to higher temperatures by dehydration. For the corresponding dehydrated compounds, the transition temperature T1/2 increases with decreasing anion radii. [Fe(hyetrz)3]I2 represents one of the few Fe(II) spin-crossover materials showing a spin transition in the close vicinity of room temperature (291 K) accompanied by a thermal hysteresis (12 K).

X-ray and electrochemical characterization of high-spin cobalt(II) triazene-1-oxide complexes. Molecular structure of bis[3-(2-methoxyphenyl)-1-ethyltriazen-1-olato]cobalt(II)

Abstract The X-ray crystal structure of the title compound was determined. The complex displays strongly distorted octahedral geometry with weak bonds between the methoxy group oxygens and the central ion. The related complex with ortho-chlorine substituted ligands was shown to undergo conversion to the low-spin, square-planar isomer upon doping to the lattice of its nickel(II) analogue. Cyclic voltammery measurements showed that the oxidation potentials of the high-spin, pseudo-octahedral cobalt(II) complexes of triazene-l-oxides are ca 0.1–0.2 V higher than those found for low-spin, square-planar cobalt(II) bis-chelates thereof.

X-Ray structure of an oxomolybdenum(V) dimer containing a novel bridging system: pyridinium di-µ-oxo-µ-acetato-bis[oxodi(isothiocyanato)molybdate(V)]

X-Ray diffraction has established the structure of [Mo2O4(MeCO2)(NCS)4]3– ions as containing molyb-denum atoms linked by a double oxygen bridge and an acetate anion.

Crystal and molecular structure of palladium(II), copper(II) and zinc(II) complexes of 1-methyl-3-(4-methyl)phenyltriazen-1-oxide

AbstractThe structures of palladium(II), copper(II) and zinc(II) bis(chelates) of 1-methyl-3-(4-methyl)phenyltriazen-1-oxide have been determined by single-crystal X-ray methods. The crystals of [Pd(OMeN3C6H4Me-4)2] (I) are triclinic witha=7.410(3),b=7.806(3),c=8.371(2) Å, α=65.80(2), β=88.73(3), γ=81.04(3)°,Z=1, space group

cis–trans isomerism and rotational isomerism in triazene-1-oxide bis-chelates of palladium(II)

P\bar 1