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SummaryThe crystal and molecular structure of cyclopentadienyltin(I1) chloride has been determined from three-dimensional X-ray data. The crystals are orthorhombic, space group Pc~~Tz. The unit cell, of dimensions a = 5.711(5), b = 6.225(5), c = 17.24(2) a, contains four molecules. The structure has been refined by full matrix least squares techniques to a final R value of 0.083 for 717 independent reflections. In the crystal unsymmetrical tin-chlorine bridges are present between the units of &H,SnCl.It is suggested that in cyclopentadienyltin(I1) compounds the cyclopentadienyl group occupies more than one coordination site as a result of the donation of x electron density from the cyclopentadienyl ring into an empty acceptor orbital of the tin atom having 7r symmetry.

SUMMARYA computerized conductometric procedure for the determination of stability constants of the complexes of crown ethers (16-crown-5, benzo-l&crown-S and 12-crown-4) with alkali metal salts in polar solvents is described, based on a microcomputer-controlled titration system. For the control of the experiments from software, a modular computer program was written in FORTH computer language. The procedure is especially suitable for the study of 1:2 metal ion/ligand complexes, which occur frequently with the compounds used. For the study of the interaction between crown ethers and neutral molecules, an indirect procedure is outlined.Crown ethers and related compounds are capable of forming complexes with many metal salts, with organic salts (such as organic ammonium, arenediazonium and guanidinium salts) and with many (neutral) organic molecules. For the determination of the (thermodynamic) stability of these complexes, a large variety of methods and procedures has been reported; these have been reviewed [l] . In this laboratory, a polarographic procedure has been developed for the computerized determination of stability constants of CEcomplexes with (alkali) metal salts and neutral compounds in polar solvents P,31* The conductance of an electrolyte solution depends on the number and nature of the ionic species present in the solution. In view of the fact that crown ethers form complexes with a variety of cations, and with the assumption that the mobility of the free cations is different from their complexes, conductometry is a technique that can be applied to the study of amplexation of cations by crown ethers. For neutral species, the technique cannot be applied as such. An indirect procedure, however, is a possible alternative for the study of the interaction between crown ethers and these species.

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