Janusz Szklarzewicz

Molecule-based magnetic materials based on dinuclear ruthenium carboxylate and octacyanotungstate

Two structurally different polymeric complexes consisting of ruthenium(II,III) pivalate ([Ru2(piv)]4+) (Hpiv = pivalic acid) and octacyanotungstate(V) ([W(CN)8]3−) ions, [{Ru2(piv)4}3W(CN)8(H2O)] (1) and (PPh4)2[Ru2(piv)4W(CN)8]·0.5H2O (2), were synthesized. The infrared spectra as well as diffused reflectance spectra confirmed the existence of the ruthenium(II,III) pivalate dimer in 1 and 2. The X-ray crystal structure analysis of 2 showed an alternating arrangement of [Ru2(piv)]4+ and [W(CN)8]3− ions in a one-dimensional chain. The temperature-dependent magnetic susceptibility of 2 showed a ferrimagnetic-like behavior. However, the field dependent magnetization curve at 2 K indicates that this complex has an S = 0 ground state. The X-ray crystal structure analysis of 1 showed a two-dimensional layered structure made up of windmill-shaped 28 membered-rings of alternating arrangement of [Ru2(piv)]4+ and [W(CN)8]3−. The magnetic susceptibility and zero-field-cooled and field-cooled magnetization data of 1 showed that this complex is ferrimagnetic with Tc = 44 K. The field dependence of magnetization exhibited a hysteresis with a coercive field of 5600 Oe at 5 K.

Spacer-dependent structural and physicochemical diversity in copper(II) complexes with salicyloyl hydrazones: a monomer and soluble polymers.

Complexation of copper(II) with a series of heterodonor chelating Schiff bases (LL) of salicylic acid hydrazide and aliphatic or cycloaliphatic ketones affords soluble one-dimensional (1D) metallopolymers containing Schiff bases as bridging ligands. Single-crystal X-ray diffraction results reveal nanometer-sized metallopolymeric wires [Cu(μ-LL)(2)](n) with off-axis linkers and a zigzag geometry. Octahedrally coordinated copper centers, exhibiting a Jahn-Teller distortion, are doubly bridged by two Schiff-base molecules in the μ(2)-η(1),η(2) coordination mode. The use of dibutylketone with long alkyl chains as a component for Schiff base formation leads to a distorted square planar monomeric copper(II) complex [Cu(LL)(2)], as evidenced by its X-ray crystal structure. The compounds are characterized by elemental analyses and IR and UV-vis spectroscopy, as well as magnetic susceptibility and cyclic voltammetry measurements. Electrochemical studies on the complexes reveal an existence of polymeric and monomeric forms in solution and the dependence of Cu(II)/Cu(I) reduction potentials on alkyl groups of salicyloyl hydrazone ligands. Polymeric complexes form conducting films on Pt electrodes upon multicycle potential sweeps.

Preparation and characterisation of [M(CN)4O(pz)]2− complexes (M=Mo or W) and their reactivity towards molecular oxygen

Abstract The synthesis and characterisation of (PPh4)2[M(CN)4O(pz)]·3H2O (M=Mo or W; pz=pyrazine) are presented. The salts are reactive towards molecular oxygen, both in solution and in the solid state, with formation of (PPh4)2[M(CN)4O(O2)]. The X-ray crystal structure of the molybdenum compound confirmed the presence of a peroxo ligand cis to the MO bond; the OO bond distance is 1.41 A. The IR spectra exhibit two absorption bands in the 950–850 cm−1 region assigned to the terminal MO group [917 (Mo) and 933 (W) cm−1] and the peroxo group [893 (Mo) and 871 (W) cm−1]. The possible mechanism of molecular oxygen uptake by pyrazine complexes is discussed.

Crystal structures of mixed-ligand oxocyano complexes of molybdenum(IV) and tungsten(IV) and their reactivity towards molecular oxygen studied by IR spectroscopy

The series of compounds, (PPh4)2[M(CN)4O(L)]·xH2O [M = Mo, W; L = pyrazine (pz), pyridine (py); Ph = phenyl group; x = 0, 2, 3], (PPh4)3[Mo(CN)5O]·7H2O and K(PPh4)2[Mo(CN)5O]·5H2O, which are able to bind molecular oxygen giving peroxo complexes (PPh4)2[M(CN)4O(O2)], have been synthesised. The substrates were characterised by thermogravimetric analysis, vibrational and UV-VIS spectroscopy and the crystal structure determination of (PPh4)2[M(CN)4O(pz)]·3H2O. The latter salts are isomorphous and consist of anions of approximately octahedral geometry, forming a three-dimensional hydrogen-bonded network with channels that enable the penetration of dioxygen. The solid state reactions of all the salts with O2 have been studied by measuring their infrared spectra. The integrated intensities of the O–O, pz or py, MO and CN bands change with time according to pseudo-first-order kinetics. The rate constants kobs range from 0.37 × 10−4 to 1.04 × 10−4 s−1 at 323 K. A detailed study of the function of temperature has been undertaken for (PPh4)2[W(CN)4O(pz)]·3H2O. The activation parameters, ΔH# = 68 ± 13 kJ mol−1 and ΔS# = −117 ± 39 J K−1 mol−1, were determined and an associative mechanism of dioxygen uptake was assumed.

Syntheses and X-ray crystal structure of (dq) 2 [M (CN) 8 ] ·5H 2 O (M = Mo, W; dq = diquat)

Abstract Reaction between diquat (dq=6,7-dihydrodipyrido- [1,2-a:2′,1′-c] pyrazinediium) and [M (CN) 8] 4− (M=Mo or W) led to the isolation of (dq) 2 [M (CN) 8] ·5H2O salts. Both salts were found to be isomorphic. The [M (CN) 8] 4− anion has an approximately dodecahedral D2d configuration. The structure consists of a three dimensional hydrogen bonded network. The intensely coloured solids (hydrated and anhydrous) show ion-pair charge-transfer (IPCT) interaction which is discussed in terms of their structure.

New cyano complex of W(V), (AsPh4)[W(bpy)(CN)6]: reversible redox system W(bpy)(CN)6−/W(bpy)(CN)62−

The preparation and spectroscopic characterization of the new cyano complex of W(V), (AsPh4)[W(bpy)(CN)6], is reported. While the light yellow crystalline salt is thermally stable in the solid state and in aqueous solution, in light it undergoes photoreduction to the W(IV) analogue with the initial quantum yield φ0365=0.17 in H2O. The electronic absorption spectrum in the visible part shows ligand-to-metal charge-transfer (LMCT) bands which are solvent dependent. Linear correlations between vmax versus Reichardt ET parameter were found. The ESR spectrum at 77 K shows characteristic g tensors with g1=1.9352, g2=1.9523 and g3=1.9726 (gav=1.9486 at 293 K). Cyclic voltammetry measurements indicate a reversible one-electron, reduction leading to W(bpy)(CN)62− with formal redox potential E0=0.845 V (in 0.1 M aqueous KCl, dependent on the nature of the solvent. A new synthetic route to (AsPh4)2[W(bpy)(CN),]·5H2O is also presented.

Oxo-tricyano complexes of molybdenum(IV) with salicylaldehydehydrazone

Abstract[Mo(CN)4O(H2O)]2− reacts with hydrazine and salicylaldehyde in aqueous solution to give [Mo(CN)3O(salhy)]2− (Hsalhy = salicylaldehydehydrazone), isolated as green (Ph4P)2[Mo(CN)3O(salhy)] · 6H2O. In CHCl3, the product converts within seconds into (Ph4P)2[Mo(CN)3O(salhy)] · H2O · 2CHCl3 yielding microcrystals having a metallic golden sheen. The complexes were characterised by elemental analysis, t.g. and d.t.a., u.v.–vis. absorption, i.r., 1H-n.m.r. spectroscopy and by magnetic susceptibility measurements. The visible spectra in various solvents are dominated by the metal-to-ligand charge-transfer bands with absorption maxima linearly dependent on the Reichardt ET parameter. In halogenated alkanes, the unusual hipsochromic band shift is interpreted in terms of possibile solvent bonding to the metal centre. Cyclic voltammetry indicates that the salt undergoes reversible one electron oxidation with E1/2 = −0.473 V in DMSO versus ferrocene.

Oxo-tricyano complexes of molybdenum(IV) and tungsten(IV) with bidentate Schiff bases

SummaryThe reaction of [M(CN)4O(OH2)]2− (M = Mo or W) with 2-acetylpyridine and methyl-or butyl-amine in a water-MeOH mixture gave [M(CN)3O(L-L)]- (L-L= Schiff base ligand), isolated as [AsPh4]+ salts. The complexes have been characterized by elemental analysis, and electronic, i.r. and1H-n.m.r. spectroscopy. The Schiff base ligands complex in a bidentate manner through the two nitrogen atoms giving mixed-ligand compounds similarly to 2,2′-bipyridyl or 1,10-phenanthroline.

Preparation and characterization of octacyanomolybdates(IV and V) and octacyanotungstates(IV and V) with 2,2′-bipyridylium cation

Abstract Reaction of protonated 2,2′-bipyridine (bpy) with octacyanometalates(IV and V), [M(CN)8]n− (M = Mo or W, n = 3 or 4), gave the following complexes: {(bpyH)3[M(CN)8]·4H2O}, {(bpyH)3(H3O)[M(CN)8]·H2O}, {(bpyH2)2[W(CN)8]·3H2O} and {(bpyH2)K2[W(CN)8]·2H2SO4·7H2O}. These salts were characterized by electron absorption and reflectance spectrometry, IR, Raman and ESR spectrometry, thermo gravimetry and differential thermal analysis, cyclic voltammetry and potentiometry. The solubility of the salts in water and some polar organic solvents has been measured. The intensively coloured salts of molybdenum(IV) and tungsten(IV) have been discussed in terms of the bpyH+-[M(CN)8]4− ion pairs, which exhibit an outer-sphere electron transfer between adjacent redox sites.

Structure and properties of the ion pair charge-transfer complex of octacyanotungstate(IV) with the 2,2′-bipyridinium dication

The X-ray crystal structure of (bpyH2)2[W(CN)8]·4H2 O (bpyH2=2,2′-bipyridinium) is described. The [W(CN)8]4− anion has an approximately square antiprismatic (D4d) conformation, seemingly imposed by strong anion–water–cation hydrogen-bonding interactions. Bond distances in the anion are: WC 2.150(5), 2.163(5); CN 1.128(6), 1.145(6)Å and the angles WCN are 177.6(5), 178.3(5)°. The dihydrate and the anhydrous salt are both intensely black solids, exhibiting ion-pair charge-transfer interaction between cation and anion. E.s.r. spectra indicate that 30% of the tungsten is present as WV in the solid state, but that in solution only the WIV complex is present. The electron withdrawing effect of the cation is discussed and compared with that in a series of salts with different bipyridinium cations.