PREPARATION AND X-RAY CRYSTAL-STRUCTURE DETERMINATION OF A HOLMIUM(III) COMPOUND WITH AN AROMATIC DIPEPTIDE - HO(GLY-L-TYR)CL3.6H2O

The holmium(III) dipeptide complex [Ho(C11H14N2O4)(H2O)5]Cl3.H2O was characterized by single crystal X-ray diffraction. The orthorhombic unit cell with the space group P2(1)2(1)2(1) has the dimensions: a = 5.938(2), b = 19.037(4), c = 19.612(4) angstrom and contains four formula units. The Ho3+ ions are eight-coordinate; three of the ligand oxygens are provided by the peptides and the remaining five by water molecules. Both the carbonyl and the carboxyl groups are involved in bonding to the metal ions. The carboxyl groups bridge the neighbouring holmium atoms creating linear polymers, with the chains lying along the y-axis. The structure of the title compound differs significantly from that of the neodymium diglycine complex reported earlier. The X-ray data are discussed in relation to the other known calcium structures with peptides and lanthanide compounds with amino acids.