A single phase sample of La 0.85 Ca 0.15 MnO 3 with uniform cation distribution and complete oxygen stoichiometry was synthesized by freeze-drying technique and studied by a variety of methods. The sample is ferromagnetic below T C ϭ170 K with Mn ϭ2.9(1) B at 10 K. Precise examination of the crystal structure by a combination of electron diffraction, high-resolution electron microscopy, and neutron powder diffraction revealed a monoclinic distortion of the GdFeO 3-type structure ͓S.G. P2 1 /c, aϭ7.74476(6) Å, b ϭ5.50398(4) Å, cϭ5.47351(4) Å, ␤ϭ90.091(2) 0 ͔ with nonequivalent MnO 2 layers alternating along the a axis. The crystal structure is characterized by a specific pattern of Mn-O distances implying an unconventional orbital ordering type. A possible relation to charge ordering is described within the bond valence sum framework.

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Orthometalated aryl oxime complexes cis-(C,S)-[PtII(C6H3-2-CMeNOH-5-R)Cl(Me2SO)] (1, R = H (a), MeO, Me, F, and Cl) undergo deoxygenation of dimethyl sulfoxide (DMSO) in methanol in the presence of HCl to afford the Pt(IV) dimethyl sulfide complexes fac-[PtIV(C6H3-2-CMeNOH-5-R)Cl3(Me2S)] (2), the composition of which was confirmed by an X-ray structural study of 2a. The mechanism of the deoxygenation coupled with the oxidation of Pt(II) to Pt(IV) was investigated using cyclic voltammetry, UV−vis, and 1H NMR spectrometry techniques at 40−60 °C in the presence of HCl, LiCl, and NaClO4. The conversion of 1 into 2 does not occur intramolecularly and involves two time-resolved phases which were studied independently. The first is the substitution of chloride for DMSO to afford the anionic reactive complexes cis-[Pt(C6H3-2-CMeNOH-5-R)Cl2]- (1 Cl), which are involved in the acid-promoted interaction with free DMSO in the second phase. The formation of 1 Cl follows the usual two-term rate law k obs1 = k s + k Cl[LiCl], the k Cl-driven pathway being negligible for the electron-rich complex with R = MeO. Thus-generated complexes 1 Cl, in contrast to their precursors 1, are more susceptible to oxidation, and the irreversible peak for 1 Cl, E(p1), is observed ca. 300 mV more cathodically compared to that of 1. The second phase is acid-catalyzed and at low LiCl concentrations follows the rate expression k obs2[H+]-1 = k 10‘ + k 10[LiCl]. The complexes with the electron-withdrawing substituents R react faster, and there is a linear correlation between log k 10 and E(p1). The first-order in the acid is discussed in terms of two kinetically indistinguishable mechanisms involving the rate-limiting either electron transfer from 1 Cl to protonated DMSO (mechanism 1) or insertion of the SO bond of free DMSO into the platinum−hydride bond of the reactive hydride complex of Pt(IV), cis-[Pt(C6H3-2-CMeNOH)(H)Cl2], to afford a {Pt−SMe2−OH} fragment. Its protonation by HCl and dissociation of water gives the final product 2 (mechanism 2). 1H NMR evidence is presented for the formation of the hydride species on protonation of a Pt(II) complex, whereas a density functional study of the two mechanisms indicates that mechanism 2 is less energy demanding. The system studied is viewed as a functioning mimetic of the Mo-dependent enzyme DMSO reductase because of several common features observed in catalysis.