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.     

Solvent Effects on the piezochromism of molybdenum(IV) and tungsten(IV) anions [M(CN)3O(diimine)]−

Solvatochromism of the [Mo(CN)₃O(phen)]⁻ ion has been studied. Solvent effects on pressure dependence (up to 1.25 kbar) of wavelengths of maximum absorption for charge-transfer bands of several molybdenum(IV) and tungsten(IV) complexes, [M(CN)₃O(diimine)]⁻ (M = Mo or W), are described. The effects of applied pressure are larger for less polar unstructured solvents than for highly polar hydrogen-bonded solvents. This revised version was published online in June 2006 with corrections to the Cover Date.     

Reaction of trans-tetracyanodioxomolybdate(IV) with salicylaldehyde as an important stage in the Schiff base ligand formation. Kinetics and mechanism

The kinetics of the reaction between the protonated species of trans-[Mo(CN)4O2]4– and salicylaldehyde (Hsal) was studied in the 7.8–12.0 pH range in H2O-MeOH mixtures. Spectroscopic characterization of the product indicates that the aqua and cyano ligands are substituted by sal– with formation of the [Mo(CN)3O (sal- 2O,O)]2– ion. The formation quotient, Kf for the overall reaction=31 (±1) at 25°C. In the presence ofan excess of ligand, the rate law is of the formd[Mo(CN)3O(sal- 2O,O)2–]/dt =kobs[Mo(CN)4O (H2O)2–]. The kobs value is equal to 2.9 (±8)×10–3 at 25°C. The activation parameters H (kobs) and S (kobs) are 103 (±9)kJmol–1 and 45 (±8)JK–1mol–1, respectively. The amount of the product formed decreases with increasing pH but the rate of the product formation increases. The reaction mechanism and the possible formation of Schiff base ligands in the presence of amines are discussed.     

Novel vanadyl complexes with 2-hydroxy-3-methyl-2-cyclopenten-1-one

Two examples of novel vanadyl complexes of 2-hydroxy-3-methyl-2-cyclopenten-1-one, Hmcp, with 1:2 stoichiometry have been characterised by elemental analysis, i.r. and optical spectral studies. [VOCl₂(H₂O)(Hmcp)₂] (1) contains neutral Hmcp coordinated to vanadium through a carbonyl oxygen and both molecules are trans to each other. [VO(mcp)₂H₂O] (2) contains the mono-anionic form of Hmcp. Both complexes have distorted octahedral geometry.     

A novel cyano complex of tungsten(IV) with 2, 2′-bipyridyl

Summary (bpyH)₃(H₃O)[W(CN)₈]·H₂O reacts at high temperature to give the ionic species [W(bpy)(CN)₆]^2–. Tetraphenylphosphonium and tetraphenylarsonium salts were isolated as solids whereas the acid and its alkali metal salts were investigated in solution. The new complexes were characterized by u.v. and visible, i.r. and e.s.r. spectrometry, t.g. and d.t. analysis. The intensively coloured salts exhibit solvent—dependent absorption bands at low energy assigned to Wbpy transitions.     

Electron-transfer kinetics and mechanism of the reduction of octacyanometallates(IV) (M = Mo,W) by hydroxide ion in aqueous solution

Summary The kinetics of the reduction of octacyanometallates(IV) in alkaline aqueous medium have been studied spectrophotometrically. The experimental results are in agreement with following rate law:-d[M(CN) _inf8 ^sup3– ]/dt = k _obs[M(CN) _inf8 ^sup3– ]²[OH^–][Na⁺] where k _obs = 4.1 × 10^–2M^–3s^–1 (Mo) and 4.0 × 10^–4 M^–3 s^–1 (W). The rate data were used to calculate the thermodynamic activation parameters H and S . A mechanism of the reaction is discussed.On leave from Faculty of Chemistry, Forest Engineering Institute, Archangelsk, Russia.     

Motion of cations and phase situation in solid tetrabutylammonium octacyanomolybdate(V)

Summary Studies of the i.r. spectra, lattice parameters and the proton second moment in [n-Bu₄N]₃[Mo(CN)₈] over the 77K to 383 K region are reported.¹Hn.m.r. data provide evidence for different rotational processes which are discussed in some detail. Atca. 260 K and 295 K the compound exibits anomalous changes in i.r. spectra and lattice parameters. The results reveal the existence of polymorphism in solid tetrabutylammonium octacyanomolybdate(V).     

Kinetic study of the reaction between protonatedtrans-dioxotetracyanomolybdate(IV) and 2,2′-bipyridyl

Summary The kinetics of the reaction between the protonated forms of [MoO₂(CN)₄]^4– and 2,2-bipyridyl (bpy) have been studied in the 8.5–11.7 pH range. This study showed that the diprotonated form, [MoO(OH₂)(CN)₄]^2– is the only reactive species. The rate-limiting step is the substitution of the aqua ligand. This is followed by fast closure of the chelate ring, accompanied by the substitution of a cyanide ligand. With excess bpy the relatively slow formation of an adduct occurs. The nature of this adduct is discussed.     

Solvent effects on piezochromism of transition metal complexes

We report solvent effects on the piezochromic behaviour of wavelengths of maximum absorption for metal-to-ligand charge-transfer (m.l.c.t.) bands of several molybdenum–diimine–carbonyl and titanium or vanadium–cyclopentadienyl or ethylmaltolate–thiocyanate complexes. These and previously published data are collated in an attempt to establish a pattern for solvent effects on piezochromism of m.l.c.t. bands. Strategies for the design of compounds and complexes for use in establishing a clear pattern for such effects are outlined.     

Novel features in the stereochemistry of octacyanides: Phase transition in tetra-n-butylammonium octacyanotungstate(V)

Tetra-n-butylammonium octacyanotungstate(V) has been found to exist in three phases at the temperature range 90–353 K. The IR and ¹H-NMR spectra as well as thermogravimetric and powder diffraction studies support these structural changes. The phase transitions were found in the temperature range 273–283 K (T₁) and 333–343 K (T₂).