The crystal structure of
normalAgO
has been determined by means of neutron diffraction. The nuclear scattering of Ag and O atoms has made it possible to determine the positions of the oxygen atoms and to modify the space group which was reported for this compound from x‐ray data. No magnetic diffractions were observed even at liquid helium temperature; the absence of magnetic scattering confirms the diamagnetism of the compound. The lattice was found to be monoclinic, space group
P21/normalc
, with four formula weights of
normalAgO
in the unit cell. The silver atoms are not equivalent, and in the structure there are two Ag‐O distances of 2.18Aå and 2.03Aå; the first one corresponds to colinear Ag(I)‐O bonds, the second distance corresponds to square planar Ag(III)‐O bonds.
The antiferromagnetie structures of KCrF S, KMnF 3, ELFeFs, KCoF S, KNiFs, and KCuF~, have been obtained by neutron diffraction. The Mn, Fe, Co, and Ni double fluorides exhibit an ordering in which the divalent 3d ion is coupled antiferromagnetically to its six nearest neighbors. In the chromium double fluoride, the magnetic structure consists of ferromagnetic (001) sheets, coupled antiferromagnetically along the [001] direction. No magnetic scattering is observed in the neutron diffraction pattern of the copper double fluoride.The magnetic structures and the observed crystallographic distortions are discussed in terms of an indirect exchange mechanism and in terms of the crystal field theory, respectively.
PREPARATION and behaviour of zerovalent platinum, palladium, and nickel compounds have been described.1 They show remarkable properties such as a co-ordination number which can be abnormally as low as two or three and basicity, especially as proton acceptors, according to a variety of reaction patterns which have been reported recently.2JOf particular interest is the compound tris-triphenylphosphino)platinum, [Pt (PPh,) ,] , owing to its co-ordination number and its spectroscopy behaviour. The infrared spectrum of this conipound in Nujol shows a strong absorption band,4 with some asymmetry, due to Pt-P stretching a t 422 & 2 cm.-l indicating a distorted Dsh or CSv
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