Synthesis of ferrocenylacetylide derivatives of gold-ruthenium and gold-osmium clusters. Crystal structures of M3(AuPPh3)(C≡CFc)(CO)9 (M=Ru or Os; Fc is ferrocenyl)

The synthesis and crystal structures of the clusters M₃(AuPPh₃)(C≡CFc)(CO)₉ (M=Ru,3a; or M=Os,3b) are described. Compound3a was synthesized by deprotonation of Ru₃H(C≡CFc)(CO)₉ under the action of KOH/EtOH followed by treatment of the anionic complex [Ru₃(C≡CFc)(CO)₉]⁻ with chloro(triphenylphosphine)gold. Compound3b was prepared by the reaction of Os₃(CO)₁₀(NCMe)₂ with FcC≡CAuPPh₃, which was synthesized by the reaction of FcC≡CNa with ClAuPPh₃. The pentanuclear cluster Ru₄(AuPPh₃)(C≡CFc)(CO)₁₂ (4a), which was prepared by the reaction of3a with Ru₃(CO)₁₂, was characterized by spectral methods. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1295–1299, July, 2000.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

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.