Structure of hexa-2,4-diyne-1,6-diyl bis(4-methylbenzoate)

Abstract

C22H1806, Mr---3784, monoclinic, C2/c, a =23-084(4), b=4.269(11), c = 19.071 ( 3 ) A , / 3 = 97.82 (1) °, V = 1861.9 ,~3, Z = 4, Dx = 1.35 Mg m 3,A(Mo Ka) = 0.71073 A, /z = 0.092 mm-l , F(000) = 792, room temperature, R = 0.030 and wR = 0.032 for 981 diffractometer reflections with Fo > 6o(Fo). Only one crystal form was obtained from a variety of solvents. The crystal surfaces become red on exposure to X-rays, but the bulk crystal does not undergo polymerization even after prolonged exposure to heat or Xor y-radiation. The monomer molecules form a regular inclined stack along the crystal y direction.The distance between reactive 1...4' acetylenic C atoms in adjacent molecules is 4.00/~, the angle between the diacetylene chain and the stacking direction is 59.4 ° . Experimental. The title compound was prepared at room temperature by the dropwise addition of 4methoxybenzoyl chloride in tetrahydrofuran to a stirred mixture of hexa-2,4-diyne-l,6-diol and triethylamine in tetrahydrofuran. Recrystallization from ethanol gave pale-yellow crystals; yield 77%, m.p. 387-388 K, found C=69.8 , H = 4 . 8 % ; C22H1806 requires C = 69-8, H = 4.8%. Further recrystallization by room-temperature evaporation of acetone, methanol, chloroform, diethyl ether or dichloromethane solutions gave colourless needles. These were examined optically but all specimens appeared to have the same crystal form. Differential scanning calorimetry (Mettler TA 3000) over the range 303-453 K in a nitrogen atmosphere showed no reaction exotherm before or after the melting 0108-2701/89/091461-03503.00 point; samples started to decompose at 453 K. There was no obvious polymerization when samples were subjected to pressure in a KBr disc press. When crystals were exposed to X-rays they developed red surfaces suggesting some polymerization or other surface reaction, but there were no detectable changes to the diffraction angles or intensities of X-ray reflections. A sample of single crystals was also exposed to y-radiation (50 Mrads over 7 d) at the Scottish Universities Reactor, East Kilbride. The surfaces of these crystals became black but again oscillation and Weissenberg X-ray photography showed no change to the space group, nor any detectable changes to cell parameters or relative intensities of reflections. Two crystals grown from acetone solution (and not previously subjected to Xor y-radiation) were used for X-ray measurements. Crystal (1) had dimensions 0-48 x 0-40 x 0.08 mm and was mounted along the b axis. Crystal (2) had dimensions 0.40 x 0-38 x 0.10 mm and was mounted along the [110] face diagonal. The space group and approximate cell parameters were calculated from oscillation and Weissenberg photographs (Cu Ka radiation). Accurate cell parameters and intensity data were measured using a Stoe Stadi-2 diffractometer with graphitemonochromated Mo Kte radiation. Cell parameters determined from to and 20 angles of 20 hOl reflections (21 < 20 < 29 °) from crystal (1) and 14 nnl reflections (19 < 20< 35 °) from crystal (2). Intensity data were measured for the layers h, 0---, 5, l from crystal (1), and m + n, n, l for m = 0,2,4,6 from crystal (2). (Diagonal layers with m = odd are systematically © 1989 International Union of Crystallography 1462 HEXA-2,4-DIYNE1,6-DIYL BIS(4-METHOXYBENZOATE) Table 1. Atomic fractional coordinates and equivalent isotropic thermal parameters (Ueq) with e.s.d.'s in parentheses U~q=(U, U2U3) '/3 where U~ are the diagonal elements of the diagonalized orthogonalized U 0. tensor.