Development of a set of crystallographic programs; Crystal structures of two aromatic di-n-oxide CuCl2 complexes and xanthotoxin

Abstract

Part I. A set of crystallographic programs is described for use on an IB 1800 computer system. The computer system includes a 32K core, 2 magnetic tapes, 1 disk, printer, card reader and X-Y plotter. The program set includes data reduction for PAILRED data, absorption correction, Rogers' N(z) Test, Wilson Statistics, Fourier summation using both fixed and floating point arithmetic, full-matrix least squares refinement, variable size block-matrix least squares refinement, bond distance calculations, calculation of E. symbolic addition, tangent refinement, Sayre's sign relations, contour drawing, standard deviations, structure drawing and an analysis of errors program. The card input formats are included in an appendix with complete IBM 1800 FORTRAN source programs available at the crystallography laboratory at Texas Christian University. The complex tris(azobispyridine di-N-oxide) dicopper(II) chloride, (ONC5H4N = NC5H4NO)3)(CuCl2)2 crystallizes in space group P1 with a = 11.185Å, b = 10.410Å, c = 7.86Å, alpha = 97.8°, beta = 81.6°, gamma=103.7°, z=1. The two equivalent Cu atoms are oxygen bridged. One ligand connects [diagram] units forming a polymeric chain. The other ligand is bonded weakly to Cu, 2.27Å, at one oxygen and remains free at the other oxygen. The Cu coordination is square pyramidal with the oxygen of the weakly bonded ligand at the apex. The Cu atom is displaced 0.28 Å out of the basal plane toward the apex. The structure was solved by 3-D Patterson synthesis and refined to an R factor of 7.1% using 1090 non-zero reflections. The complex bis(2-methylpyrazine di-N-oxide) copper (II) chloride crystallizes in space group Pbca with a = 10.284 Å, b= 11.839 Å, c=11.744 Å, Z=4. The Cu atoms lie on centers of symmetry and exhibit a tetragonally distorted octahedral coordination. The methyl group is ortho to the tightly bonded oxygen, Cu-O = 1.975 Å. The second oxygen occupies the apex site of an equivalent Cu at a Cu-O distance of 2.735 Å. The structure was solved by Patterson techniques and refined to an R factor of 11.1% (wgtd. R = 6.2%) using 706 non-zero reflections. Two crystalline forms of Xanthotoxin (8-methoxy-3'.2':6.7-furocoumarin) are known. Xanthotoxin I crystallizes in space group Pna2_1 with a = 12.94 Å, b= 15.86 Å, c=4.87 Å, z=4. The molecule is planar except for the methyl group which is forced out of the plane due to steric hindrance at the 1 and 1' ring oxygen positions. The structure was solved by applying symbolic addition and tangent refinement techniques and refined to an R of 4.6% using 648 observed reflections.