Structural diversity in heavier alkali metal salts of a heteroleptic magnesium triamide anion

The synthesis of alkali metal magnesiates M[Mg(NONTCHP)(HMDS)] (M = K, Rb or Cs; HMDS = bis(trimethylsilyl)amide; NONTCHP = 4,5-bis(2,4,6-tricyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene) via coordination of [Mg(NONTCHP)] with M(HMDS) is reported. Each complex is characterised using single crystal X-ray diffraction measurements and NMR spectroscopic methods. In the solid-state, each system exists as a 1D-polymer that assembles via bridging M‧‧‧π(arene) interactions to two [Mg(NONTCHP)(HMDS)]– units. For K[Mg(NONTCHP)(HMDS)], polymerization occurs via coordination of each K-center to TCHP and xanthene arene rings. In contrast, for the heavier group 1 magnesiates, Rb[Mg(NONTCHP)(HMDS)] and Cs[Mg(NONTCHP)(HMDS)], the alkali metals exhibit alternating xanthene, xanthene- and TCHP, TCHP-coordination along the polymer chain. This work highlights the influence that group 1 metal cations can have on the long-range structure of bis(anilido)xanthene magnesiate complexes.