Tetra(methylamine)platinum(II) chloroplatinate(II) and tetra(ethylamine)platinum(II) bromoplatinate(II) are confirmed as being isostructural with Magnus' green salt, Pt(NH3)4PtC14. The dimensions of the tetragonal cells are a=10.32, c=6.58, and a=12.27, c=6"71 A respectively; the space group is P4/mnc. Tetra(ethylamine)platinum(II) chloroplatinate(II) forms triclinic crystals, space group PI, with a=7.56, b=9"78, c=7.24 A, a=98"3 °, fl= 113"1 °, ~,= 103.4°; it has a similar structure in that cation and anion alternate in chains, but the cation is non-planar and orbital overlap between adjacent platinum atoms is inhibited. The differing optical properties of this compound are thus explained. The variation in structure is ascribed to packing effects.The crystal structure of Magnus' green salt, Pt(NH3)4PtCI4 and hereafter MGS, comprises chains of square-planar cations and anions.Sacked directly over one another, with a Pt-Pt sep~.ration of 3.26A (Atoji, Richardson & Rundle, 1957). Both the green colour and the dichroism exhibited by these crystals are distinct from those characteristic of the constituent ions (Yamada, 1951), and have been attributed to weak metal-metal bonding. The compound Pt(NH2CH3)4PtC14 is also green and similar in dichroism to MGS, but the analogues with higher amines are pink, and show only the dichroism of the chloroplatinate(II) ion. The methylamine compound is similar in powder diffraction pattern to MGS, whereas the ethylamine compound is not (Miller, 1961), and it has been assumed that steric effects inhibit the chain structure and thus prevent the metal-metal bond interaction• Subsequently it has been shown (Yamada, 1962(Yamada, , 1965) that crystals of Pt(amine)aPtBr4 and Pt(amine)aPtI4 are all abnormally coloured and dichroic, whether amine be ammonia, methylamine, ethylamine or various higher amines. This clearly indicated that the difference in structure of the higher amine chloroplatinates(II) is not caused by intra-chain steric interference, and Yamada (1965) suggested that it may be due to a weakening influence of the chlorine ligand on the metal-metal bond. This view is not supported * Present address" Chemistry Department, University of Auckland, Private Bag, Auckland, New Zealand.by reflectance spectra studies (Miller, 1965): nor indeed by Yamada's own single-crystal spectra, from which it is apparent that the band shifts are less and not greater in bromoplatinates(II) vis-d-vis chloroplatinates-(II). Further, the compounds Pt(NH3)4PtC14, Pt(NH3)4PdC14, Pd(NH3)4PtC14 and Pd(NH3)4PdC14 show varying spectral shifts, yet all have the MGS structure, with the same metal-metal separation (Miller, 1961(Miller, , 1965). It appears that chemical variations affect the optical phenomena far more than the crystal structure, and the difference in behaviour of tetra(ethylamine)platinum(II) chloroplatinate(II) remains anomalous. We have examined crystals of several of these compounds in an attempt to elucidate this problem.In each case, compounds were prepared by mixing solutions containing...

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The crystal structure of the title compound has been elucidated by the symbolic addition procedure and the eleven-membered carbocyclic ring of the sesquiterpene shown to have the conformation previously reported for the humulene molecule in the humulene-silver nitrate adduct, the mean deviation between corresponding torsion angles in the two molecules being 8' . Crystallographic data for the diepoxide are a = 15-265(10), b = 5.794(3), c = 16.055(8) A, p = 103' 24(4)', Z = 4, space group P2,/c. Diffractometer (Mo-K, radiation) and photographic (Cu-K, radiation) intensity data were merged to give 11 27 lFol values, and least-squares adjustment of the atomic co-ordinates and thermal parameters converged a t R 7.5%. THE sesquiterpene humulene2(1) has an elevenmembered triene ring which undergoes interesting transannular reactions, e.g. the tricyclic compounds cc-caryoyhyllene alcohol (2) and humulene bromohydrin (3) are produced by treatment of the hydrocarbon with sulphuric acid and N-bromosuccinimide,* respectively, Humulene forms a bis(si1ver nitrate) adduct,5 and X-ray analyses of this adduct established the trans-stereochemistry of all three double bonds in the hydrocarbon.6~~ The complexed hydrocarbon in the adduct has the conformation (4), and transannular cyclisations of this conformation rationalize the stereochemistries of products t No reprints available.

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