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 (η 6 -C 6 H 3 Me 3 )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 (η 6 -C 6 H 3 Me 3 )Mo(CO) 3 in the absence of alkali metal cations. The new cages were isolated as their Et 4 N + salts, M = K + ( 1 ), Cs + ( 2 ). Crystallographic characterization of 1 and 2 reveals box-like M 8 (μ-CN) 12 cages containing alkali metal cations. The cages feature 12 external CO and 4 external C 5 Me 5 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 13 C NMR spectroscopy and electrospray mass spectrometric measurements. 133 Cs NMR spectroscopy, which readily distinguishes free from included Cs +, shows that the boxes preferentially bind Cs + relative to K + .