The preparation, spectroscopic characterisation and crystal structures of [FcP(mu-Se)Se]2, [FcP(mu-Se2)Se]2 and [PhP(mu-Se2)Se]2 are reported. Crystallographic data reveal planar four-membered PSePSe and skewed six-membered P2Se4 rings, respectively, in all cases with trans arrangement of organic substituents and exo selenium atoms. Whilst stable at room temperature in solid state, NMR data suggest the six-membered rings of both the ferrocenyl and phenyl compounds decompose in the solution with loss of red selenium, forming PSe2PSe five-membered rings.

The ligand 4,5-bis(diphenylphosphino)-sym-octahydroacridine N,P,P′-trioxide (10) was obtained from a multistep synthesis and characterized by spectroscopic methods, and two crystal forms were examined by single-crystal X-ray diffraction techniques. The coordination behavior of the trifunctional ligand toward La(NO 3 ) 3 and Nd-(NO 3 ) 3 was examined, and the molecular structures of the complexes La(10)(NO 3 ) 3 ‚MeOH and Nd(10)(NO 3 ) 3 ‚ MeOH were determined by single-crystal X-ray diffraction methods. The molecules form chains along the z axis in which the ligand bonds in a bidentate mode to one La(NO 3 ) 3 or Nd(NO 3 ) 3 by using the N-O and one of the PdO donor centers. The second PdO donor group in the ligand bridge bonds to a second La(10)(NO 3 ) 3 or Nd-(10)(NO 3 ) 3 unit. The coordination behavior of 10 contrasts with that of the related but structurally more flexible trifunctional ligand 2,6-bis[(diphenylphosphino)methyl]pyridine N,P,P′-trioxide, which acts as a tridentate ligand toward f-element ions.

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Reaction of naphthalene-1.8-bis(dichlorophosphine) with sodium selenide and selenium gives naphthalene-1,8-diyl)-1,3,2,4-diselenoxodiphosphetane 2,4-diselenide (27), a molecule with its four-membered PSePSe ring spanned by a naphthalene-1,8-diyl backbone. 27 was fully characterised, including by X-ray diffraction. Unusually, the reaction yielded not only 27, but also a polymeric or oligomeric material that was selenium deficient, containing significant amount of species with phosphorus atoms not fully oxidised to P(V). Reactions of the selenium deficient material with simple alcohols afforded two 1,2-diphosphaacenaphthenes, which were structurally characterised.