The photochemical substitution of benzene in [Cb*Co(C 6 H 6 )] + (Cb* ) C 4 Me 4 ) with benzo-15-crown-5 (1) gives the corresponding π-complexArene exchange is reversible, and both 1 and 3 can be regenerated by irradiation of 2 and 4 with excess benzene. The reaction of [Cb*Co(C 6 H 6 )] + with 0.5 equiv of 3 gives dinuclear complex [trans-Cb*Co(µ-η 6 ,η 6 -C 6 H 4 (OCH 2 CH 2 OCH 2 CH 2 O) 2 C 6 H 4 )CoCb*] 2+ (5). The structures of cations 4 and 5 were confirmed by X-ray diffraction. The electrochemical behavior of complexes prepared was studied. The sodium-binding ability of cobalt complexes 2, 4, and 5 (determined by NMR titration; K a ) 2500, 800, and 50, respectively) was found to be much smaller than that of the free crown ethers 1 and 3 (K a ) 200 000 and 5 000 000). DFT calculations suggest that this decrease is mainly due to electrostatic repulsion of Co + and Na + centers.