Chalcogen arsenide clusters of iron with a functional carboxyl group: Synthesis, structures, and thermolysis

The carbonyl clusters [Fe₃(??₃-Q)(??₃-AsR)(CO)₉] (Q = Se and Te; R = meta- and para-HOOCC₆H₄) were obtained from the salts K₂[Fe₃(??₃-Q)(CO)₉] and organoarsenic diiodides RAsI₂ prepared by reducing iodination of arsonic acids RAsO(OH)₂ according to a novel method. The structures of the clusters were identified by X-ray diffraction. The crystal packing motifs of the dimers of the cluster molecules and their relationship with the solubility of the clusters are discussed. The sequential steps of the thermolysis (decarbonylation, decarboxylation, and decomposition of the organic fragment) of the clusters were studied. The presence and location of the carboxyl group does not influence the decarbonylation temperature.     

Synthesis and molecular structures of cyclopentadienyl sulfide complexes of chromium with cymantrenyl-thiolate bridging ligands

Interaction of [Cp₂Cr₂(CO)₄[μ-SC₅H₄Mn(CO)₃]₂ with sulphur gave binuclear complex Cp₂Cr₂[μ-SC₅H₄Mn(CO)₃]₂(μ-S) (I) (Cp = π-C₅H₅) and triangular cluster Cp₃Cr₃[μ-SC₅H₄Mn(CO)₃](μ-S)₂(μ₃-S) (II). I was also synthesized from Cp₂Cr₂(μ-SCMe₃)₂(μ-S) and (CO)₃Mn(C₅H₄SH). Interaction between I and Co₂(CO)₈ resulted in triangular mixed-metal cluster Cp₂Cr₂[μ-SC₅H₄Mn(CO)₃](μ³-S)₂Co(CO)₂ (III). The molecular structures of I–III were determined by means of single-crystal X-ray diffraction analysis.     

Heterometallic derivatives of dicarbonylcyclopentadienylrhenium disulfide containing chromium pentacarbonyl and bis(triphenylphosphine)platinum

The reaction of Cp′Re(CO)₂THF (Cp′ = C₅H₄Me), THF is tetrahydrofuran) with sulfur affords Cp′Re(CO)₂S₂(I) and [Cp′Re(CO)₂]₂S (II). The synthesized compounds are isolated chromatographically and characterized by X-ray diffraction analysis. The adduct Cp′Re(CO)₂S₂Cr(CO)₅ (III) is synthesized by the reaction of compound I with Cr(CO)₅(THF). The adduct CpRe(CO)₂S₂Cr(CO)₅ (IV) is obtained similarly from known CpRe(CO)₂S₂ and Cr(CO)₅(THF). The reaction of compound I with (PPh₃)₂Pt(C₂Ph₂) results in the removal of Ph₂C₂ and one sulfur atom to form Cp′Re(CO)₂SPt(PPh₃)₂ (V). The structures of compounds I–V are determined by X-ray diffraction analysis (CIF files CCDC nos. 984554 (I), 984555 (II), 984556 (III), 984557 (IV), and 984558 (V)). Compound I contains the three-membered cycle ReS₂ with the ordinary S-S bond (2.044(4) Å) and shortened Re-S bonds (average 2.434(3) Å). The three-membered cycle Re₂S containing the ordinary Re-Re bond (2.932(1) Å) and shortened Re-S bonds (2.371(1) Å) is observed in compound II. In compounds III and IV, the formation of the ordinary S-Cr(CO)₅ bond (2.406(1) Å) with one of the sulfur atoms almost does not change the geometry of the ReS₂ fragment. The thermal decomposition of compound III proceeds with the elimination of six CO ligands in the range 110–160°C and then with the loss of CO and Cp′ in the range 160–430°C and the formation of the inorganic residue ReCrS₂. Compound V contains the triangular framework ReSPt with the ordinary Pt-Re bond (2.7882(3) Å) and substantially shortened bonds Re-S (2.3984(9) Å) and Pt-S (2.2724(8) Å). It is assumed that compounds II and V can be presented as products of the π-coordination of the double bonds in Cp′(CO)₂Re=S with the Cp′Re(CO)₂ or Pt(PPh₃)₂ groups, respectively.     

Synthesis and molecular structures of the cobalt complexes (η4-C4Me4)Co(CO)2SnCl3, (η4-C4Me4)Co(CO)2(TeI2Ph), and (η4-C4Me4)Co(CO)2 (TeBrIPh) with the shortened Co-Sn and Co-Te bonds

The complex (η⁴-C₄Me₄)Co(CO)₂I (I) reacted with excess SnCl₂ in boiling THF to give, through replacement of the iodide ligand by the fragment SnCl₃, the mononuclear complex (η⁴-C₄Me₄)Co(CO)₂SnCl₃ (II) containing the Co-Sn bond (2.459(1) ?). In a reaction of complex I with phenyltellurenyl halides PhTeI and PhTeBr, an analogous insertion into the cobalt-iodine bond yielded (η⁻C₄Me₄)Co(CO)₂(TeI₂Ph) (III) and (η⁴-C₄Me₄)Co(CO)₂(TeBrIPh) (IV), respectively. This type of coordination of the aryltellurenyl halide fragment to the transition metal atom was observed for the first time. X-ray diffraction analysis revealed a substantial shortening of the formally single Co-Sn and Co-Te bonds in complexes II–IV compared to the sum of the covalent radii of the corresponding atoms. Original Russian Text ? Yu.V. Torubaev, A.A. Pasynskii, A.R. Galustyan, p. Mathur, 2009, published in Koordinatsionnaya Khimiya, 2009, vol. 35, No. 1, pp. 3–7.     

Temperature hysteretic effect and its influence on colossal magnetoresistance of La0.33Nd0.33Ca0.33MnO3

Electrical resistance (R) measurements of a bulk La_0.33Nd_0.33Ca_0.33MnO₃ perovskite in magnetic fields up to 40 kOe have revealed anomalous temperature hysteretic effects both in 0 Oe and 20 kOe magnetic fields. The sharp peak observed in the R vs. T plot indicates the occurrence of metal-to-insulator (M-I) transition at a temperature of T _MI=110 K and 140 K, for cooling and warming paths, respectively. An applied magnetic field of 20 kOe reduces the resistance and shifts T _MI to 160 K and 185 K for cooling and warming, respectively. We have observed a much higher resistance in the cooling path than in the warming path leading to the hysteretic resistance ratio (R _cool/R _warm) of 200 at 110 K and 1.8 at 160 K for 0 Oe and 20 kOe, respectively. Record values of colossal magnetoresistance (CMR) have been achieved. The CMR value reaches nearly 99% in the temperature ranges of 90 K to 140 K and 90 K to 170 K for 20 kOe and 40 kOe magnetic fields in the cooling mode, respectively. The observed unusual behavior is attributed to the co-existence of La-rich and Nd-rich domains assumed to be distributed randomly in the compound.