CONDUCTIVITY STUDIES OF ION-PAIRING IN TRANSITION-METAL ORGANICS
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The dependence of equivalent conductances on the concentration of THF solutions of (5-C5H5)Fe(CO)3+BPh4-, (5- C5H5)Fe(CO)2PMe2Ph+BPh4-, (Ph3P)2N+HFe(CO)4-. Et4N+(-H)[Cr(CO)5]2-, and Li+Mo(CO)5C(O)Ph- and of CH3CN solutions of (5-C5H5)Fe(CO)2PMe2Ph+BPh4-, (6-C6H6)Mn(CO)3+BPh4-, and (6-C6H6)Mn(CO)3+ClO4- were analyzed according to the Fuoss and Fuoss-Hsia equations. Ion-pair dissociation constants, KD, of 10-5 were found for the cyclopentadienylmetal carbonyl salts in THF; the large cations Et4N+ and (Ph3P)2N+ were found to be as associated to metal carbonyl anions as were the alkali metal solvates, Li(THF)x+ or Na(THF)y+. A stronger ion pair was observed for the lithium acylate as indicated by a KD on the order of 10-7. Dissociation constants of approximately 10-3 determined for the cyclopentadienyl- and arenemetal carbonyls are among the smallest ever reported for salts in acetonitrile. Exact sites of ion interaction were not discernible in this study; however ion center-to-center distance parameters indicated that all of the salts studied in THF existed as contact ion pairs. 1976, American Chemical Society. All rights reserved.