Measurements of structural and quadrupole coupling parameters for bromoferrocene using microwave spectroscopy

Rotational spectra for two isotopomers of bromoferrocene were measured using pulsed-beam Fourier transform microwave spectroscopy. Transitions were observed for the ⁷⁹Br and ⁸¹Br isotopomers in the 5-9 GHz range. Rotational constants and the quadrupole coupling tensors were obtained from the data. The rotational constants and quadrupole coupling parameters for ⁷⁹Br are A=1272.110(1), B=516.1125(2), C=441.3775(2), eQq_aa=267.16(3), eQq_ab=-409.81(4), and eQq_bb=21.49(4), and those for ⁸¹Br are A=1271.045(4), B=510.0079(2), C =436.7687(2), eQq _aa=225.40(6), eQq_ab=-341.62(4), and eQq_bb=15.65(4). The measured rotational constants were used to determine the following structural parameters of bromoferrocene: r(Fe-(C5H5))=1.63(2), r(Fe-(C5H4Br))=1.67(3), r(C-Br)=1.875( 11), and r (C-C) =1.433(1) Å. The values of the quadrupole coupling parameters in the principal quadrupole axis systems and the C-Br bond axis systems are compared with similarly derived parameters for chloroferrocene, chlorobenzene, and bromobenzene. Previous data for chloroferrocene has been reanalyzed to obtain refined quadrupole parameters.