Unusual ligand coordination for cesium

When complexed by tetrabenzo-24-crown-8, the cesium ion can accommodate unp recedented ligation, The structures of the following complexes are presente d. [Cs(tetrabenzo-24-crown-8)(eta(1)-NCMe)(2)(eta(2)-NCME)][NO3] (1): tricl inic P (1) over bar, a = 12.0119(14) Angstrom, b = 13.3680(15) Angstrom, c = 13.7859(12) Angstrom, alpha = 89.124(8)degrees, beta = 66.928(9)degrees, gamma = 71.536(10)degrees V= 1916.7(4) Angstrom(3), Z = 2: [CS(tetrabenzo-2 4-crown-8)(eta(1)-NCMe)(2)(eta(2)-CH2Cl2)[NO3] (2): triclinic, P (1) over b ar, a = 12.295(3) Angstrom, b = 13.295(3) Angstrom, c = 13.782(3) Angstrom, alpha = 89.105(17)degrees, beta = 66.096(18)degrees, gamma = 71.980(19)deg rees, V = 1929.5(8) Angstrom(3), Z = 2, These structures are the first repo rted examples of linear eta(2)-acetonitrile coordination to any metal ion a nd the first structures illustrating eta(2)-acetonitrile and dichloromethan e ligation to an alkali metal ion. possible steric and electronic origins o f these unusual metal-ligand interactions are discussed.