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New coordination compounds of iron(II) sulfate, hexafluorosilicate, and perrhenate with 2,6-bis(benzimidazole-2-yl)pyridine (L), namely, [FeL2]SO4 ∙ H2O (I), [FeL2]SiF6 ∙ H2O (II), and [FeL2](ReO4)2 ∙ 1.5H2O (III) have been synthesized. The complexes have been studied by static magnetic susceptibility, electronic (diffuse reflectance), IR, and Mossbauer spectroscopy, and X-ray diffraction. The μeff(T) study of dehydrated complexes I–III (1–3) within the range 80–520 K has shown the spin transition 1А1 ⇔ 5Т2. A two-stage transition is observed in complex 1, whereas one-stage transitions occur in complexes 2 and 3. The forward spin transition temperatures (Тс↑) of complexes 1–3 are 423 and 503, 476, 362 K, respectively. Complex 3 sustains an abrupt spin transition with a hysteresis in the μeff(T) curve (ΔT = 21 K).

Rhenium(VII) and molybdenum(VI) extraction with kerosene solutions of α-branched tertiary carboxylic Versatic acids derivatives containing hydrazide C(O)NHNH2 and C(O)NHNCH3)2 fragments instead of carboxyl group has been studied. Optimal extraction conditions have been determined depending on H2SO4, HCl, and extractant concentrations and composition of extracted complexes has been established. The mechanism of extraction and back extraction of perrhenate ion with ammonia solutions has been suggested.

The crystal structure was determined and the physicochemical properties were studied for tetrapropylammonium pertechnetate and perrhenate. Pr4NMO4 (M = Tc, Re) are isostructural and crystallize as colorless prismatic crystals in the orthorhombic system, space group Pna21, Z = 4. For M = Tc at 25°C, a = 13.22(4) A, b = 12.35(3) A, c = 10.13(4) A; for M = Re at −120°C, a = 13.169(2) A, b = 12.311(2) A, c = 10.107(1) A. The Re-O distances are 1.677(12), 1.704(5), 1.719(4), and 1.739(11) A. Each anion in this structure has four neighboring cations with Re…N distances of 5.06–5.34 A. The solubility product of Pr4NTCO4 is (6.19 ± 0.50) × 10−5 mol2/L2. The Gibbs energy of dissolution of [(C3H7)4N]TcO4 in dilute aqueous solutions is 24.0 ± 0.5 kJ/mol. The association constant K1 for (Pr4N+)…(TcO4−) in water and aqueous solutions is 10.8 ± 0.7 L/mol. The solubility of Pr4NTcO4 increases with the solution acidity, similarly to the solubility of Bu4NTcO4. Upon precipitation of Pr4NTcO4 from model solutions containing (2.0–7.5) × 10−2 mol/L Tc in 3–4 M HNO3, (2.0–7.5) × 10−8 mol/L 239PuO2(NO3)2, and 5.7 mCi/L 106Ru(NO)(NO3)3, the technetium decontamination factors from 239Pu and 106Ru were (0.5–1.5) × 102 and (6.0–7.5) × 102, respectively.

The silver complex with phenazine [Ag(Phz)2(H2O)]ReO4 (Phz is C12H8N2) has been synthesized, and its crystal structure has been determined. The crystals are triclinic: space group \(P\bar 1\), a = 9.587(1) A, b = 10.875(1) A, c = 11.668(1) A, α = 104.98(1)°, β = 103.87(1)°, γ = 92.94(1)°, V = 1132.6(2) A3, Z = 2, ρcalc = 2.160 g/cm3. The structure is composed of the [Ag(Phz)2(H2O)]+ silver cationic complexes and ReO4− anions. The Ag+ ion is coordinated by two nitrogen atoms of independent phenazine molecules and the water oxygen atoms and has a T-shaped coordination (Ag-Nav 2.223 A, Ag-Ow 2.498(8) A). Phenazine, being an electron-donor ligand, forms columns due to π-π stacking interaction between the aromatic groups. The water molecules form hydrogen bonds with the oxygen atoms of water molecules of neighboring complexes and with oxygen atoms of the ReO4− anions.

Complexes [(4-MeC6H4)4Sb]2+[Hg2I6]2− (I), [(4-MeC6H4)4Sb]2+[HgI4]2− (II), [(4-MeC6H4)4Sb]3+[Sb3I12]2− (III), were synthesized by reactions of tetra-p-tolylantimony iodide with mercury iodide and antimony iodide, respectively. Tetra-p-tolylantimony perrhenate [(4-MeC6H4)4Sb]+[ReO4]− (IV) was prepared from tetra-p-tolylantimony chloride and sodium perrhenate in acetone. Crystal structures of complexes I, II, and IV were determined by X-ray crystallography. Mercury and rhenium atoms have tetrahedral coordinations in these complexes. The Hg-I and Re-O distances in the structures of I, II, and IV vary within 2.7719(13)–2.7908(12)A, 2.7028(3)–2.9163(3) A, and 1.693(3)–1.744(3) A, respectively. Antimony atoms in two crystallographically independent trinuclear centrosymmetric [Sb3I12]2− anions of complex III have an octahedral environment. Each terminal SbI3 fragment (Sb-It, 2.8265(9)–2.8333(10)A) is bound to the central atom through tree bridging iodine atoms (Sb(2)-Ibr, 3.2275(9)–3.3620(10)A). The distances between the central Sb atom and bridging iodine atoms are much shorter (Sb(1)-Ibr, 3.0153(6)–3.0316(6) A; Sb(3)-Ibr, 2.9926(6)–3.0074(6) A).

Rhenium(VII) extraction with 2-ethylhexanoic acid N′,N′-dialkylhydrazides in kerosene from acidic media was studied. Optimal extraction conditions were established depending on H2SO4, HCl and extractant concentrations and the composition of extracted complexes. A mechanism of perrhenate ion extraction and back-extraction with ammonium solutions was proposed.

We studied equilibrium and kinetic characteristics of rhenium sorption by Busofit-based fibrous carbon materials (FCMs) treated electrochemically with recovery potentials varying from −900 to +600 mV from aqueous solutions in the presence of natural biopolymer chitosan. Materials obtained in the anodic potential region and at the open-circuit potential have the best capacity characteristics. The highest rhenium capacity is observed for the material prepared at the recovery potential +600 mV. The relevant sorption isotherm is described by the Langmuir equation with the constant 73.0 ± 8.1 mL/mg; the half-conversion time is 3 min.

The reaction of tetraphenylantimony chloride with sodium perrhenate or potassium chlorate yields tetraphenylantimony perrhenate (I) and tetraphenylantimony chlorate (II), respectively. Complex I was also synthesized from pentaphenylantimony and triphenylantimony diperrhenate in toluene. According to X-ray diffraction, crystals I and II consist of almost regular tetrahedral tetraphenylstibonium cations (CSbC, 109.4(2)°–109.5(7)° in I and 109.1(1)°–109.6(1)° in II) and [ReO4]− (OreO, 107.6(3)°–113.3(5)°) and [ClO3]− (OClO, 96.3(9)°, 116.4(5)°) anions, respectively. The average Sb-C bond lengths (2.094(3) A in I, 2.097(2) A in II) are close to the sum of the covalent radii of the Sb and C atoms. The average distances Re-O in complex I (1.672(4) A) and Cl-O in complex II (1.315 A) correspond to multiple bonds.

Bimetal alkoxo complexes of rhenium, niobium, and tantalum with the general formula M4O2(OR)14(ReO4)2, where M = Nb or Ta and R = Me or Et, were prepared in ∼80% yield by reacting niobium or tantalum alkoxide M(OR)5 (R = Me or Et) with rhenium heptoxide Re2O7 in toluene. Comparative analysis of the molecular structures of the complexes was carried out by means of single-crystal X-ray diffraction and IR spectroscopy. The effect of the organic ligand and crystallization temperature on the geometry of the perrhenate group was studied. The solubility of the aforementioned alkoxo complexes in organic solvents increases with increasing hydrocarbon chain length of the ligand.

Coordination compounds of iron(II) perrhenate with 4-propyl-1,2,4-triazole (L), [Fe3L6(ReO4)4(H2O)2](ReO4)2(I), [Fe3L6(H2O)6](ReO4)6·H2O(II), and FeL3(ReO4)2(III), were synthesized. Compounds I and III were studied by static magnetic susceptibility measurements and by IR and electronic spectroscopy. These complexes exhibit a reversible 1 A 1 ⇄ 5 T 2 spin transition and thermochromism. Compound I exhibits a spin transition without hysteresis at 185 K. The temperatures of forward and reverse transition for III are 250 and 244 K, respectively. Complex II isolated by crystallization from an acidified aqueous solution of compound I has a linear trinuclear structure of the cation (X-ray diffraction data). The structure of complex I was assumed to be similar, while compound III has a polymeric structure.