Crystal structure of ammonium/potassium trans-bis(N-methyliminodiacetato-kappa O-3,N,O ')chromate(III) from synchrotron data

The structure of the title compound, [(NH4)(0.8)K-0.2][Cr(C5H7NO4)(2)](C5H7NO4 is methyliminodiacetate; mida), has been determined from synchrotron data. The Cr-III atom is located on a centre of symmetry and is coordinated by two N atoms and four O atoms of two facially arranged tridentate mida ligands, displaying a slightly distorted octahedral coordination environment. The Cr-N and mean Cr-O bond lengths are 2.0792 (14) and 1.958 (14) angstrom, respectively. The cation site is located on a twofold rotation axis and shows occupational disorder, being occupied by ammonium and potassium cations in a 0.8:0.2 ratio. In the crystal, intermolecular hydrogen bonds involving the N-H groups of the ammonium cation as donor and the two non-coordinating O atoms of the carboxylate group as acceptor groups consolidate the three-dimensional packing.