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 ⁷⁹$Br$ and ⁸¹$Br$ 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 ⁷⁹$Br$ are $A=1272.110(1),$ $B=516.1125(2),$ $C=441.3775(2),$ $eQqaa=267.16(3),$ $eQqab=−409.81(4),$ and $eQqbb=21.49(4),$ and those for ⁸¹$Br$ are $A=1271.045(4),$ $B=510.0079(2),$ $C=436.7687(2),$ $eQqaa=225.40(6),$ $eQqab=−341.62(4),$ and $eQqbb=15.65(4).$ 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.