Spirocyclic phosphonium salts of the type [(CH2)(4)P(CH2)(4)](+) X- with X = I-3 (1a), I (1b), picrate (1c), benzoate (1d), and Cl (1e) were prepared from 1,4-diiodobutane and elemental phosphorus followed by metathesis reactions. The crystal structures of 1b and 1c and of 1d(H2O) have been determined by X-ray diffraction methods, In the cations of these salts the phosphorus atoms are shared by two five-membered rings in envelop conformations. In the picrate 1 c the cations show an unsymmetrical ring folding pattern (point group C-1), while the geometry of the cations of the iodide 1b and the benzoate hydrate [1d(H2O)] approaches the symmetry of point group C-2. These structures can be taken as models for the as yet unknown molecular geometries of the corresponding hydrocarbon (CH2)(4)C(CH2)(4) and silane (CH2)(4)-Si(CH2)(4). Treatment of 1e with organolithlum reagents RLi affords spirocyclic pentaorganophosphoranes RP[(CH2)(4)](2) with R = Me, Et, n-Bu, VI, and Ph (2a-e) in good (R = Me, Et, n-Bu) to low yields (R = VI, Ph). The products are isolated as colorless liquids, of which only 2a, 2b, and 2d can be distilled without decomposition. Single crystals of 2a were obtained by low-temperature in situ crystal growth. The molecule has a trigonal bipyramidal configuration with the methyl group in an equatorial position and the two five-membered rings spanning axial/equatorial positions of the polyhedron. Deviations from the standard trigonal bipyramidal geometry are small. The compounds 2a-e are fluctional in solution as demonstrated by NMR spectroscopy.