The effect of a dansyl group on the co-ordinative ability of N-protected amino acids. Part 2. Binary copper(II) complexes and their pyridine and 2,2′-bipyridine adducts. Crystal and molecular structure of the complexes aquabis(N-dansylglycinato-O)bis(pyridine)copper(II) and (2,2′-bipyridine)(N-dansylglycinato-NO)(methanol)copper(II), and neutral N-dansylglycine

Abstract

Some binary copper(II) complexes with N-dansylglycine (5-dimethylaminonaphthalene-1-sulphonylglycine) and their amine adducts with pyridine (py) and 2,2′-bipyridine (bipy) have been synthesized. Compounds of formula Cu(dnsglyO)₂·2CH₃OH, Cu(dnsglyO)₂·4H₂O, [Cu(dnsglyO)₂(py)₂(H₂O)], and [Cu(dnsglyNO)(bipy)(CH₃OH)][dnsglyO =N-dansylglycinate(1 –), dnsglyNO =N-dansylglycinate(2 –)] were separated in the solid state and characterized by means of thermogravimetric, spectroscopic and magnetic measurements. For the free ligand and the amine adducts the crystal structure was also determined by the heavy-atom method and refined by least-squares calculations. The [Cu(dnsglyO)₂(py)₂(H₂O)] complex is monoclinic, space group P2/c, with unit-cell dimensions a= 21.274(5), b= 5.71 9(5), c= 19.154(5)Å, β= 116.9(1)°, Z= 2; R= 0.061 for 1 845 observed reflections. The Cu^II ion, lying on the two-fold axis, is co-ordinated by two carboxylic oxygens of two symmetrically related amino-acid molecules and by two pyridine nitrogens in the basal plane of a tetragonal pyramid; the apical position is occupied by a water molecule, placed on the same two-fold axis at a very short distance from the Cu^II ion [Cu–O(5) 2.196(9)Å]. The [Cu(dnsglyNO)(bipy)(CH₃OH)] complex is monoclinic, space group P2₁, with unit-cell dimensions a= 13.980(4), b= 11.087(3), c= 8.31 5(3)Å, β= 102.5(1)°, Z= 2; R= 0.085 for 1 160 observed reflections. The Cu^II ion displays tetrahedrally distorted square-pyramidal geometry arising from ligation of a dnsglyNO^2– ion and a bipy molecule in the basal plane and of a methanolic oxygen in the apical position. N-Dansylglycine is monoclinic, space group P2₁/n, with unit-cell dimensions a= 21.653(5), b= 10.982(3), c= 5.935(2)Å, β= 93.51(8)°, Z= 4; R= 0.061 for 2 295 observed reflections. The ligand molecule is found to undergo conformational changes only upon amide deprotonation and the comparison with the structural results obtained for similar complexes of N-tosylglycine shows that the size of the aromatic group may have some influence on the co-ordination polyhedra.