DETERMINATION OF THE INCOMMENSURATELY MODULATED STRUCTURE OF (PERYLENE)CO(MNT)(2)-(CH2CL2)(0.5) BY DIRECT-METHODS
LAM EJW, BEURSKENS PT, SMITS JMM, VAN SMAALEN S, DE BOER JL, FAN HF
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE
51: 779-789 Part 5 OCT 1 1995


Abstract:
For the organic conductor (perylene)Co(mnt)(2)-(CH2Cl2)(0.5), where mnt is maleonitriledithiolate, the incommensurate displacive modulation is determined using X-ray diffraction data for main reflections and first- and second-order satellites, collected at a temperature of 283 K. The lattice parameters of the unit cell of the average structure are: a = 6.5441 (13), b = 11.7173 (15), c = 16.4251 (17) Angstrom, alpha = 92.092 (11), beta = 95.343 (16), gamma = 94.67 (2)degrees, with V = 1248.6(3)Angstrom(3) and Z = 2. The components of the modulation wavevector are given by: q(1) = 0.211 (13), q(2) = -0.1374(5), q(3) = -0.368(2). The symmetry of the modulated structure is given by the (3+1)-dimensional superspace group P ($) over bar 1 (q(1), q(2), q(3)). Direct methods were used to obtain a starting model for the modulation. The subsequent refinement converged to R = 0.126 for 2835 observed (I/sigma > 2.5) reflections. Partial R factors are 0.111 for 1450 main reflections, 0.143 for 1188 first-order satellites and 0.263 for 197 second-order satellites. The modulation is described by sawtooth-shaped functions for the Co and S atoms and by rigid-body modulations, up to third-order harmonics, for the perylene units and parts of the mnt fragments. The largest amplitudes were found for the Co (0.77 Angstrom) and S atoms (0.48-0.63 Angstrom) and were mainly directed along the a axis. The four equatorial Co-S distances are only slightly affected by the modulation, but the two apical Co-S distances show large variations with distances ranging from 2.05 to 3.86 Angstrom. These variations are out of phase. This causes the coordination of the Co atom to vary from a distorted octahedral coordination by six S atoms to a region with fivefold coordination and vice versa. The valence of the Co atom, as calculated by the bond-valence method, varies between 2.92 and 3.57. The stacking of the Co(mnt)(2) units can be described by oligomeric packages of four or five dimerized Co(mnt)(2) units.