Stoichiometry, Mössbauer spectrum, and magnetic susceptibility of the one‐dimensional conductor iridium carbonyl chloride Available to Purchase

Carbon and chlorine analyses of the linear chain compound Ir(CO)₃Cl confirm the report by Krogmann et al. that it is partially oxidized. The results are consistent with the formulation Ir(CO)_3−xCl_1+x(x = 0.08 ± 0.02) or Ir(CO)₃Cl_1+x(x = 0.10 ± 0.03). The latter formulation is preferred because recoilless absorption measurements of the 73 keV ¹⁹³Ir γ‐ray show no indication of a line attributable to a species other than partially oxidized Ir(CO)₃Cl units. Presumably the ``extra'' chloride occurs in disordered interchain positions. The Mössbauer absorption is a temperature independent (1.8 – 35 °K) doublet with isomer shift − 0.03 ± 0.01 mm/sec relative to iridium metal and quadrupole splitting 2.11 ± 0.02 mm/sec. For 4.3 ≤ T < 25 °K, the molar magnetic susceptibility corrected for ligand and metal core diamagnetism, $χM′$⁠, follows the Curie law $χM′ = 38 × 10−6 + (6.79 × 10−4)/T;$ for 25 < T ≤ 280 °K, the susceptibility is given by $χM′ = 25 × 10−6 + (1.03 × 10−3)/T$⁠. The susceptibility and Mössbauer results indicate that in the range 1.8–280 °K the charges arising from partial oxidation of Ir(CO)<sub>3</sub>Cl chains are not localized on individual atoms. The results are therefore inconsistent with a model requiring transition from a metallic state to a smallbandgap magnetic Mott insulator, but can be accounted for in terms of the interrupted metal strand model or the one‐dimensional disorder model. For the latter, the Curie contribution to the susceptibility leads to an estimate that the disorder ``localized'' states are spread over ∼ 25 Ir atoms. If the Curie component of the susceptibility is assigned to paramagnetic structure defects, the results are also consistent with the model in which a high‐temperature metallic state undergoes a continuous transition to a low temperature Peierls band insulator. The origin of the discontinuity at T ≈ 25 °K in the slope of the T⁻¹ dependence of $χM′$ is at present unknown.