Structural determination and characterization of copper and zinc bis-glycinates with X-ray crystallography and mass spectrometry

X-ray crystallography, inductively coupled plasma spectroscopy, electrospray mass spectroscopy, and combustion elemental analysis were used to determine the content and structure of copper and zinc bis-glycinate crystals. Crystals were grown from copper sulfate-glycine and zinc hydroxide-glycine solutions. The crystal structures were then resolved by X-ray crystallography, and data from electrospray mass spectroscopy along with elemental analyses are used to support the crystal structure. The copper compound consists of Cu chelated by two glycinate units in a cis configuration. A water molecule bonds to Cu forming a distorted square pyramid. These units are bonded through the free carboxylate oxygens into polymeric chains that are in turn connected through hydrogen bonds. In contrast, the zinc compound, while also chelated by two glycine units, has a trans configuration. These units are bonded together into tetra-zinc glycinate clusters by bonding to carboxylate oxygens creating distorted metal square pyramid coordination polyhedra. The mass spectra confirm the polymeric nature of the metal glycinates.