The tungsten complex W(CO)4(phen)(phen=1,10-phenanthroline) reacted in toluene refluxing for 24 hours with unpurified dibutyl maleate, which was commercially purchased, to give a dark brown solution. The solution was separated by column chromatography on silica gel and two main chromatographic bainds were collected. The orange block crystals (1) and the red orange platelet crystals (2) were obtained by slow diffusion of petroleum ether into the toluene solutions of the two bands respectively.The crystal structures are W(CO)2(phen) (DBF)2(1) and W(CO)2(phen)(DBF)(DBM) (2) (DBF=dibutyl fumarate, DMB=dibutyl maleate), determined by the X-ray diffraction method. In the molecules of both crystals tungsten atom coordination is distorted octahedral with the two CO groups and phen in the equatorial plane and the metal binds in an η^2 fashion to C-C bonds of DBM or DBF. Grystal data for complex 1: space group R-3, a=3.026 4 (4) nm , b=3.026 4(4) nm,c=2.135 2 (4) nm, α=90°, β=90°, γ=120°. V=16.936(4) nm^3, Dc=1.547 g/cm^3, Z=18, R=0.49 1 for 6 624 independent reflections. Crystal data for complex 2: space group P2 (1)/n, a=1.038 2(2) nm, b=1.428 1 (3) nm, c=2.530 3(5) nm, α＝90°,β =92.74(3)°, γ＝90°, V=3.747 (0) nm^3, Dc=1.554g/cm^3, Z=4, R=0.039 3 for 8 562 independent reflections. The analysis of the contents for DBM and DBF in the unpurified dibutyl maleate and the quantitative calculation for the total content of DBF in the two products indicate that in the coordination reaction the ligand DBM was probably partly isomerized into DBF which is more stable.

Key words: ISOMER, LIGANDS, PHENANTHROLINE, METHYLBENZENE, X- RAY DIFFRACTION ANALYSIS, TUNGSTEN COMPLEX