Zinc and lithium hydrogen-beta-glutamate: large-pore network layer structures

The symmetrical anion [beta-GluH](-) of beta-glutamic acid [beta-GluH(2)] has been introduced into crystal engineering of metal complexes for the first time. Neutralization of aqueous solutions of beta-glutamic acid with zinc oxide or lithium hydroxide affords crystalline samples of zinc bis(hydrogen-beta-glutamate) trihydrate and lithium hydrogen-beta-glutamate hydrate, respectively. [Zn(beta-GluH)(2)(H2O)(3)] has a layer structure with corrugated sheets featuring a square-grid pattern of the tetra-coordinated zinc dications and bridging [O2C-CH2CH(NH3)CH2-CO2](-) anions (in their gauche-conformation). The uniform meshes of the network are based on puckered 32-membered rings. Neighbouring undulated layers are mutually shifted into a space-filling indentation which also generates a network of hydrogen bonds involving the ammonio and carboxylate groups and the intercalated water molecules. [Li(beta-GluH)(H2O)] has a less corrugated layer structure based on a parallelogram-grid of lithium cations which are connected by three bridging [beta-GluH](-) anions (in their anti-conformation). The water molecule is part of the tetrahedral coordination sphere of the metal atom. The layers represent a mixed-mesh network with pores based on 8- and 32-membered rings. Neighbouring layers are mutually shifted to allow for extensive hydrogen bonding.