Amino acids are bidentate ligands, forming transition metal amino acid complexes. Complexes with multiple bidentate ligands have geometric isomers. Xanthates bind to transition metal cations as bidentate ligands. Hyponitrite can act as a bridging or chelating bidentate ligand. The tartrate tetraanions serve as bidentate alkoxide ligands. Dimethoxyethane forms chelate complexes with cations and acts as a bidentate ligand. Chiral phosphine ligands can be generally classified as mono- or bidentate. In the bidentate ligand ethylene diamine forms a chelate complex with the copper ion. It binds strongly to metal cations as both a bidentate and tridentate chelating agent. The bond is either an ester, chelating, or bidentate bridging linkage. Glycine functions as a bidentate ligand for many metal ions. It can also act as a bidentate ligand through its two carboxylate groups. Importantly, oxalate is often encountered as a bidentate, chelating ligand, such as in potassium ferrioxalate. The complex has D symmetry, with four bidentate nitrate ligands. The two bidentate nitrate ligands are in trans configuration.