INFLUENCE OF BF4(-) POSITION ON THE N=N DISTANCE OF TRIALKYLDIAZENIUMCATION SALTS

The crystal structures of two bis(trialkyldiazenium) bis(tetrafluorobo rate) salts, 1 and 2, are reported. The structure of 2 provides eight chemically identical but crystallographically different 2-tert-butyl-2 -azonia-3-azabicyclo[2.2.2]oct-2-ene units for examing the effects of the neighboring BF4- groups on the N=N geometry. Each bis(cation) has one N=N group with two neigboring BF4- and a second N=N group with onl y one nearby BF4- group. The twelve BF4- groups nearest to the N=N gro ups of 2 (B,N distances < 4.14 Angstrom) are oriented above or below t he R(2)N=NR planes having BN degrees N+Cbr, torsion angles \92.9\ to \ 108.6\degrees. The N=N distances cluster into two groups with six valu es ranging from 1.241(4) to 1.251(4) Angstrom and two values of 1.257( 4) and 1.261(4) Angstrom, The N=N bonds in 1 are 1.244(4) and 1.245(4) Angstrom. The 0.020 Angstrom difference in the N=N distances in 2 cor responds to a Pauling N=N bond order decrease from 2.0 for the shorter d(N=N) units to 1.9 for the longer ones. It appears unlikely that F,N degrees bonding is involved in causing the bond length change.