V. M. Novotortsev

Antiferromagnetic complexes involving metalmetal bonds : I. Synthesis and molecular structure of an antiferromagnetic dimer with a CrCr bond

The binuclear complex (C5H5)2Cr2(S)(SCMe3)2 was prepared by refluxing a solution of chromocene and t-butylmercaptane in heptane. The structure of the product was determined by single crystal X-ray diffraction. The chronium atoms are linked by a sulphide bridge (SCr 2.24 A;, <CrSCr 74.1° and two SCMe3 bridges (CrS 2.38 A;, <CrSCr 68.3–69.3°). The two cyclopentadienyl ligands (CC 1.41 A;, CrC 2.23 A;) are in apical positions, their ring planes being parallel to each other. The complex is an antiferromagnet (−2J cm−1) despite the small CrSCr angles and short chromiumchromium distance (2.689 A;) indicative of strong CrCr bonding.

Antiferromagnetic complexes with metal-metal bonds: IX. Synthesis and molecular structures of methylcyclopentadienylchromium(III) sulfide diamagnetic tetramer and the antiferromagnetic copper(II) bromide adduct of the tetranuclear cluster (MeC5H4)4Cr4(μ3-O)(μ3-S)3

Abstract Reaction of (MeC5H4)2Cr with HSCMe3 gave (MeC5H4)2Cr2S(SCMe3)2 (I) in the form of violet antiferromagnetic crystals ( − 2J = 478 cm−1). Pyrolysis of I in xylene and its reaction with a CuBr2 solution in THF/Et3N (1/1) leads to readily-soluble black diamagnetic crystals of (MeC5H4)4Cr4S4(II). An oxygen-containing antiferromagnetic analog of complex II, (MeC5H4)4Cr4O4(III) was isolated on oxidation of (MeC5H4)2Cr with traces of oxygen in the presence of Ar. The reaction of I with CuBr2 in the absence of Et3N yielded black-green needle-like crystals of the antiferromagnetic adduct (MeC5H4)4Cr4S3O · CuBr2(IV) (μeff at room temperature is 3.91 BM). The structures of II and IV were established by X-ray crystallography. The molecule of II contains a metallotetrahedral Cr4 skeleton (CrCr 2.822(2) A) with faces centered at the μ3-bridged S atoms (CrS 2.248(2) A). Each Cr atom is bonded to a η5-MeC5H4 (CrCaver. 2.241(9) A). In IV the tetrahedral Cr4 skeleton is distorted owing to the μ3-O bridging ligand (CrCr 2.70(1)–2.78(1) A, CrSaver. 2.25(2) A, CrO 2.07(2)–2.12(2) A) and to CuBr2 coordination to a sulfur atom (CuBr 2.23(2) A, BrCuBr 163.9(8)°, Cu···S 320 A).

Heterometallic Coordination Polymers Assembled from Trigonal Trinuclear Fe2Ni-Pivalate Blocks and Polypyridine Spacers: Topological Diversity, Sorption, and Catalytic Properties.

Linkage of the trigonal complex [Fe2NiO(Piv)6] (where Piv(-) = pivalate) by a series of polypyridine ligands, namely, tris(4-pyridyl)triazine (L(2)), 2,6-bis(3-pyridyl)-4-(4-pyridyl)pyridine (L(3)), N-(bis-2,2-(4-pyridyloxymethyl)-3-(4-pyridyloxy)propyl))pyridone-4 (L(4)), and 4-(N,N-diethylamino)phenyl-bis-2,6-(4-pyridyl)pyridine (L(5)) resulted in the formation of novel coordination polymers [Fe2NiO(Piv)6(L(2))]n (2), [Fe2NiO(Piv)6(L(3))]n (3), [Fe2NiO(Piv)6(L(4))]n·nHPiv (4), and [{Fe2NiO(Piv)6}4{L(5)}6]n·3nDEF (5, where DEF is N,N-diethylformamide), which were crystallographically characterized. The topological analysis of 3, 4, and 5 disclosed the 3,3,4,4-connected 2D (3, 4) or 3,4,4-connected 1D (5) underlying networks which, upon further simplification, gave rise to the uninodal 3-connected nets with the respective fes (3, 4) or SP 1-periodic net (4,4)(0,2) (5) topologies, driven by the cluster [Fe2Ni(μ3-O)(μ-Piv)6] nodes and the polypyridine μ3-L(3,4) or μ2-L(5) blocks. The obtained topologies were compared with those identified in other closely related derivatives [Fe2NiO(Piv)6(L(1))]n (1) and {Fe2NiO(Piv)6}8{L(6)}12 (6), where L(1) and L(6) are tris(4-pyridyl)pyridine and 4-(N,N-dimethylamino)phenyl-bis-2,6-(4-pyridyl)pyridine, respectively. It was shown that a key structure-driven role in defining the dimensionality and topology of the resulting coordination network is played by the type of polypyridine spacer. Compounds 2 and 3 possess a porous structure, as confirmed by the N2 and H2 sorption data at 78 K. Methanol and ethanol sorption by 2 was also studied indicating that the pores filled by these substrates did not induce any structural rearrangement of this sorbent. Additionally, porous coordination polymer 2 was also applied as a heterogeneous catalyst for the condensation of salicylaldehyde or 9-anthracenecarbaldehyde with malononitrile. The best activity of 2 was observed in the case of salicylaldehyde substrate, resulting in up to 88% conversion into 2-imino-2H-chromen-3-carbonitrile.

Peroxide induced tin oxide coating of graphene oxide at room temperature and its application for lithium ion batteries

We describe a new, simple and low-temperature method for ultra-thin coating of graphene oxide (GO) by peroxostannate, tin oxide or a mixture of tin and tin oxide crystallites by different treatments. The technique is environmentally friendly and does not require complicated infrastructure, an autoclave or a microwave. The supported peroxostannate phase is partially converted after drying to crystalline tin oxide with average, 2.5 nm cassiterite crystals. Mild heat treatment yielded full coverage of the reduced graphene oxide by crystalline tin oxide. Extensive heat treatment in vacuum at >500 °C yielded a mixture of elemental tin and cassiterite tin oxide nanoparticles supported on reduced graphene oxide (rGO). The usefulness of the new approach was demonstrated by the preparation of two types of lithium ion anodes: tin oxide-rGO and a mixture of tin oxide and tin coated rGO composites (SnO(2)-Sn-rGO). The electrodes exhibited stable charge/discharge cyclability and high charging capacity due to the intimate contact between the conductive graphene and the very small tin oxide crystallites. The charging/discharging capacity of the anodes exceeded the theoretical capacity predicted based on tin lithiation. The tin oxide coated rGO exhibited higher charging capacity but somewhat lower stability upon extended charge/discharge cycling compared to SnO(2)-Sn-rGO.

Antiferromagnetic complexes involving metal—metal bonds: V &. Synthesis, molecular structures and magnetic properties of an adduct, (CpCrSCMe3)2S·Mn2(CO)9, and a cluster, (CpCr)2(μ2-SCMe3)(μ3-S)2Co(CO)2, containing the CrCrCo metallocycle*

Summary The photochemical reaction of the antiferromagnetic binuclear complex (CpCrSCMe 3 ) 2 S (I, Cp=cyclopentadienyl) with Mn 2 (CO) 10 in THF yields the adduct (CpCrSCMe 3 ) 2 S·Mn 2 (CO) 9 (IV). According to X-ray diffraction data, the fragments in IV are linked through an Mn−S bond (2.448(2) A), and the geometry of I changes only insignificantly upon the addition of Mn 2 (CO) 9 : the Cr−Cr bond distance changes from 2.689(8) A in I to 2.740(8) A in IV, the Cr−S( sulphide ) bond length increases from 2.24(1) A (I) to 2.31(1) A (IV), whereas the Cr−S (thiolate) bond and CrSCr angles (72.7(3) and 71.4(3)°) remain almost unaffected. Accordingly, formation of the adduct has little affect on the magnetic properties of I (the exchange parameter, −2 J , value is equal to 440 cm −1 for IV and 430 cm −1 for I). Compound I reacts with Co 2 (CO) 8 in THF at 20°C without UV irradiation to give the trinuclear cluster, (Cp 2 Cr 2 SCMe 3 )-(μ 3 -S) 2 Co(CO) 2 (V). Compound V is antiferromagnetic (−2 J 530 cm −1 , the Co atom is diamagnetic) and, according to the X-ray structural data, contains the CrCrCo metallacycle (the bond lengths are: Cr−Cr, 2.617(1); Cr−Co, 2.579(1) and 2.592(1) A) and sulphide bridges above and below the metallacycle plane. The effect of the coordination number of M on the transformations of the adducts of the type (CpCrSCMe 3 ) 2 S·M 2 (CO) n is discussed.

Structure and magnetic properties of iron(II) chloride tetrahydrofuranate (2FeCl2·3THF)2

Abstract On interacting FeCl3 with Cp2ReH in THF at room temperature while single crystals of the complex (2FeCl2·3THF)2 (I) were obtained. The structure of (I) was established by total X-ray analysis. Crystals of the complex are (space group P 1 ) with the unit cell parameters: a = 10.027(4), b = 10.983(6), c = 10.589(6) A; α = 116.86(4)°, β = 98.23(4)°, γ = 68.09(4)°, Z = 1, V = 964.7 A3. Four Fe(II) atoms in the molecule are bonded through the μ3-bridging Cl atoms (Fe-Clav = 2.46 A), with the coordination sphere of each metal atom being supplemented by the bonding with two or one THF molecule (FeOav = 2.12 A). All the Fe⋯Fe distances in the molecule were non-bonding. The unique magnetic properties of (I) are shown to be specified by the co-existence of ferro- and antiferromagnetic exchange interactions.

Formation of antiferromagnetic heteronuclear thiolate and sulfide bridged complexes: II. Synthesis, magnetic properties, and molecular structures of the clusters Cp2Cr2(μ-SCMe3)2(μ4-S)W2(μ-I)2(CO)4(NO)2 and Cp2Cr2(μ3-S)2(μ-SCMe3)2W(SCMe3)(NO)

The reaction between the antiferromagnetic complex Cp2Cr2(μ-SCMe3)2(μ-S) (1) and WI(CO)4(NO) (2) was studied. At 40–50°C the predominant product was the antiferromagnetic adduct Cp2Cr2(μ-SCMe3)2(μ4-S)W2(μ-I)2(CO)4 (NO)2 (3) (CrCr 2.764(4) A, W ⋯ W 3.559(1) A, −2J = 338 cm−1), in which a sulfur atom bridges all four metal atoms. Further heating of 3 in the presence of an excess of 1 afforded the trinuclear antiferromagnetic cluster Cp2Cr2(μ3-S)2 (μ-SCMe3)2W(SCMe3)(NO) (7) (WCr 3.090(1) A, CrCr 3.027(1) A, −2J = 246 cm−1) which can also be prepared by direct reaction between 1 and 2 (ratio 3:2) at 80°C in toluene. It is suggested that this process via the formation of an unstable intermediate CpCr(μ-SCMe3)2(μ-S)W(CO)2(NO). In an attempt to use the trinuclear cluster Fe3S2(CO)9 as a metal containing ligand for 2, the known iron clusters Fe2S2(CO)6 and (ON)4Fe4S4 were isolated. All products, including the two iron clusters, were characterized by X-ray diffraction studies at −60°C.

Antiferromagnetic complexes involving metalmetal bonds. II. The conditions for observation and means of intented variation of antiferromagnetic properties of binuclear complexes involving CrCr and VV bonds

Abstract The complex (CpCrSCMe 3 ) 2 S (I), contains a CrCr bond (2.689 A) and at the same time shows antiferromagnetic properties (−2J = 430 cm −1 ). It reacts with PhEH (E is S, Se) or MeI to give binuclear complexes (CpCrEPh) 2 S or [(CpCrSCMe 3 ) 2 SMe] + I − characterized by exchange parameter, −2J, values of 496, 398, and 350 cm −1 , respectively. Reaction between Cp 2 Cr and PhEH yields the antiferromagnetic trimer [CpCr(SPh) 2 ] 3 (−2J = 194 cm −1 ) and dimer [CpCr(SePh) 2 ] 2 (−2J = 208 cm −1 ). CpV(CO) 4 reacts with PhEH to give dimeric complexes [CpV(EPh) 2 ] 2 one of which shows antiferromagnetic behaviour (E = Se, −2J = 700 cm −1 ) and the other one is a diamagnetic substance (E = S, −2J>> 1000 cm −1 ). The magnetic properties of the complexes are treated in terms of the exchange channel model. It is shown that antiferromagnetic behaviour (magnetic moment decreases with temperature) of binuclear complexes involving direct metalmetal bonds may be expected when the paramagnetic ions are in high-spin states (S ⩾ 1). In such complexes, variations in metalmetal bond strength caused by ligand substitution may be studied by the methods of magnetochemistry.

Manufacture of magnetic granular structures in semiconductor-ferromagnet systems

The requirements are formulated to be fulfilled by magnetic granular structures that have the giant magnetoresistance (GMR) in semiconductor-ferromagnet systems. AIIBIVC2V-Mn(CV), AIIICV-Mn(CV), and A3IIC2V-Mn(CV) semiconductor-ferromagnet systems are shown to be eutectic systems and to be promising for the preparation of granular structures with high magnetoresistance values. Magnetic granular structures have been prepared in Zn(Cd)GeAs2-MnP(As), Zn(Cd)3P(As)2-MnP(As), and (Al,Ga,In)Sb-MnSb systems and the origin of magnetoresistance in these systems is shown to be due to the structure of Mn(CV) ferromagnet clusters.

Ferromagnetism of manganese-doped InSb alloys

InSb samples containing 0.22–1.42 wt % manganese were synthesized and identified. The unit cell parameter decreased as the manganese concentration increased. The samples contained microinclusions of manganese antimonides. Electrical and magnetic measurements showed two ferromagnetic phases (In1−xMnxSb solid solution with Tc ∼ 7 K and MnSb with Tc ∼ 580 K) and a ferrimagnetic phase (Mn2Sb). The samples had p-type conductivity with a charge carrier concentration of about 1020cm−3. The semiconductor conductivity was observed at low temperatures and changed to the metal conductivity with temperature elevation.