EPR and Structural Investigations on Single Crystals of K<inf>2</inf>NbO2F<inf>5</inf>•H<inf>2</inf>O

The single-crystal structural investigation of dipotassium pentafluoroperoxoniobate hydrate, K2NbO2F5•H2O (DPPN), is reported. The crystals are monoclinic with space group C2, and the unit cell dimensions are a = 8.927 (4) Å, b = 8.926 (3) Å, c = 9.266 (2) Å, β = 99.93 (1)°, and Z = 4. The least-squares refinement of positional and anisotropic thermal parameters for all non-hydrogen atoms led to an R factor of 0.057. The EPR spectra of a γ-irradiated single crystal of DPPN suggest a Nb hole species stable at room temperature. The anomalous behavior in spacing, number, and intensity of Nb hyperfine lines has been successfully explained by including a quadrupolar term in the Hamiltonian. The spin-Hamiltonian parameters for this hole species are as follows: gxx = 2.039 (1), gyy = 2.013 (1), gzz = 2.054 (1); Axx(93Nb) = 0.62 (2), Ayy(93Nb) = 0.79 (2), Azz(93Nb) = 0.93 (2) mT; Qxx(93Nb) = Qyy(93Nb) = 0.065, Qzz(93Nb) = −0.130 mT. The EPR results further indicate that the unpaired electron in the [NbO2F5]− radical occupies the nonbonding orbital of the peroxo oxygen atoms; this is further supported by EHMO calculations done on the precursor. © 1991, American Chemical Society. All rights reserved.