Formation of racemate and mesocate complexes from an achiral tripodal ligand containing three benzimidazole groups

Two complexes of the achiral tripodal ligand tris(1-benzimidazolylethyl)amine (nteb), viz., [Mn(nteb)(2)(H2O)(2)](ClO4)(2).CH3-OH, 1, and [Ag-2(nteb)(2))(CF3CO2)](2).2H(2)O, 2, have been synthesized and characterized by IR, H-1 NMR, and EPR spectroscopy (1), electrospray mass spectrometry, thermogravimetric analysis, and X-ray crystallography. Compound 1 contains chiral complex cations due to the same handedness of two nteb ligands (deltadelta or lambdalambda) but crystallizes as a racemate, while 2 contains a dinuclear mesocate because of the opposite handedness (deltalambda) of two nteb ligands. Crystal data for 1: space group P (1) over bar with a = 9.471(4) Angstrom, b 16.884(7) Angstrom, c = 19.906(8) Angstrom, alpha = 77.930(7)degrees, = 88.063(7)degrees, gamma = 89.706(7)degrees, V = 3111(2) Angstrom(3), and Z = 2. Crystal data for 2: space group P (1) over bar with a = 9.3390(12) Angstrom, b = 10.2168(13) Angstrom, c = 16.382(2) Angstrom, alpha = 75.721(3)degrees, beta = 87.857(3)degrees, gamma = 71.738(3)degrees, V = 1437.2(3) Angstrom(3), and Z = 1. In 1, water serves as an auxiliary ligand, connected to one imidazole N atom of each nteb ligand through a H-bridge; the cationic complexes are associated intermolecularly via pi...pi interactions. In contrast to 1, the coordination to the Ag+ ions in 2 occurs in a heterochiral manner and produces a dinuclear mesocate.