EPR AND STRUCTURAL INVESTIGATIONS ON SINGLE-CRYSTALS OF K2NBO2F5.H2O

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) angstrom, b = 8.926 (3) angstrom, c = 9.266 (2) angstrom, beta = 99.93 (1)-degrees, 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 gamma-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: g(xx) = 2.039 (1), g(yy) = 2.013 (1), g(zz) = 2.054 (1); A(xx)(93Nb) = 0.62 (2), A(yy)(93Nb) = 0.79 (2), A(zz)(93Nb) = 0.93 (2) mT; Q(xx)(93Nb) = Q(yy)(93Nb) = 0.065, Q(zz)(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.