Interactions between metal ions and carbohydrates. The coordination behavior of neutral erythritol to lanthanum and erbium ions

Lanthanide ions and erythritol form metal–alditol complexes with various structures. Lanthanum nitrate and erbium chloride coordinate to erythritol to give new coordination structures. The lanthanum nitrate–erythritol complex (LaEN), 2La(NO3)3·C4H10O4·8H2O, La3+ exhibits the coordination number of 11 (namely 11 polar atoms bound to one lanthanum) and is 11-coordinated to two hydroxyl groups from one erythritol molecule, six oxygen atoms from three nitrate ions and three water molecules. One erythritol molecule is coordinated to two La3+ ions and links the two metal ions together. The ratio of M:L is 2:1. The erbium chloride–erythritol complex (ErE), ErCl2·C4H9O4·2C2H5OH was obtained from ErCl3 and erythritol in aqueous ethanol solution and the structure shows that deprotonation reaction occurs in the reaction process. The Er3+ cation is 8-coordinated with three hydroxyl groups of one erythritol molecule, two hydroxyl groups from another erythritol molecule, two ethanol molecules, and one chloride ion. Erythritol provides its three hydroxyl groups to one erbium cation and two hydroxyl groups to another erbium cation, that is, one hydroxyl group is coordinated to two metal ions and therefore loses its hydrogen atom and becomes a oxygen bridge. Another chloride ion is hydrogen bonded in the structure. The results indicate the complexity of metal–sugar coordination.

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