X-ray crystallographic studies of tricarbonylchromium complexes of calix[4]arene conformers: On an unusual conformation which appears in cone conformers

The structures of three arene-tricarbonylchromium complexes prepared from cone and 1,3-alternate-25, 26,27,28-tetrapropoxycalix[4]arene(1) and Cr(CO)₆ were determined by single crystal X-ray studies. Crystal data for 1,3-alternate-1·Cr(CO)₃ are space group P2₁/a, a=19.496(3)Å, b=11.118(2)Å, c=19.121(2)Å, β=109.95°(1) and V=3895ų. The structure was refined to Rw=0.068. Crystal data for cone-1·Cr(CO)₃ are space group P2₁/a, a=21.457(4)Å, b=12.184(1)Å, c=14.816(2)Å, β=91.61°(1) and V=3872ų. The structure was refined to Rw=0.077. Crystal data for cone-1·2Cr(CO)₃ are space group P2₁/a, a=18.019(3)Å, b=41.347(4)Å, c=11.743(2)Å, β=97.39°(1) and V=8676ų. The single crystal included two similar but slightly different structures but the data were successfully refined to Rw=0.092. The structure of 1,3-alternate-1·Cr(CO)₃ differs only slightly from that of the regular 1,3-alternate calix[4]arene. In contrast, cone-1·Cr(CO)₃ and cone-1·2Cr(CO)₃ show an unusual conformation with a pair of faced gablelike roofs, which is considerbly distorted from the regular cone calix[4]arene. The origin of this distortion is discussed in combination with the spectral studies.