Alkali metal-templated assembly of cyanometalate "boxes" (NEt4)3{M[Cp*Rh(CN)3]4[Mo(CO)3]4} (M = K, Cs).: Selective binding of Cs+

The box-like cages {M[Cp*Rh(CN)(3)](4)[Mo(CO)(3)](4)}(3-) form as the sole metal-containing products of the reaction of [Cp*Rh(CN)(3)](-) and (eta(6)-C6H3Me3)Mo(CO)(3) in the presence of K+ and Cs+. Well-defined species could not be identified in solutions of Cp*Rh(CN)(3)(-) and (eta(6)-C6H3Me3)Mo(CO)(3) in the absence of alkali metal cations. The new cages were isolated as their Et4N+ salts, M = K+ (1), Cs+ (2). Crystallographic characterization of 1 and 2 reveals box-like M-8(mu-CN)(12) cages containing alkali metal cations. The cages feature 12 external CO and 4 external C5Me5 ligands. In 1, the K+ is disordered over two off-center positions, whereas in the case of 2, the Cs+ is centered in the cage with a formal coordination number of 24. Otherwise, the structures of the two compounds are virtually indistinguishable. The persistence of the solid-state structures in solution was established through C-13 NMR spectroscopy and electrospray mass spectrometric measurements. Cs-133 NMR spectroscopy, which readily distinguishes free from included Csf, shows that the boxes preferentially bind Cs+ relative to K+.