State selected ion-molecule reactions by a TESICO technique. VI. Vibronic-state dependence of the cross sections in the reactions O+ 2(X 2Π g , v; a 4Π u , v)+H2→ O2H++H, H+ 2+O2 J. Chem. Phys. 77, 4441 (1982) The causes of the previously reported temperature dependence of the g values of the CU(H20)~ + ions in Cu 2 + doped Zn(H 2 0)6(GeF 6 ) and the Tutton's salts M 2 Zn(H 2 0)6(S04)2' where M = K+, Rb+, NH 4 +, and Cs+, supplemented by new experimental measurements on the K + salt, have been investigated. The ground state dynamics of the complexes have been modeled on the cubic E X E J ahn-Teller Hamiltonian perturbed by an orthorhombic lattice strain. For each compound, the vibronic energy levels and associated wave functions were calculated numerically, the overall g values at any temperature being given by a thermal average of the g values of the individual vibronic energy levels, because of rapid exchange between the levels. For the Tutton's salts it was found that the low temperature g values are strongly influenced by the tetragonal component of the lattice strain, with this corresponding to an axial compression of the ligand field. The temperature dependence of the g tensors, on the other hand, was found to depend largely on the orthorhombic component of the lattice strain. For the K + and NH4+ salts, where structural data are available, the strain parameters derived using the model are in good agreement with the geometries reported for the Zn (H 2 0) ~ + host complexes. For Cu2+ doped Zn(H 2 0)6(GeF 6 ) the model implies a lattice strain of tetragonal symmetry corresponding to a slight elongation of the axial metal-ligand bonds. The results are compared with those reported previously by Silver and Getz, and other workers, who used a simple model involving temperature dependent equilibria between energy levels corresponding to different orientations of the Cu (H 2 0) ~ + ions in the host lattices to interpret the temperature dependence of the g tensors.

The crystal structure of the deuterated Tutton salt (ND 4 ) 2 [Cu(D 2 O) 6 ](SO 4 ) 2 determined by X-ray diffraction at several temperatures between 100 and 321 K is reported. The intermediate and longest Cu-O bond lengths of the Jahn-Teller distorted octahedral Cu(D 2 O) 6 2+ ion progressively converge as the temperature is raised above ∼200 K, and this is accompanied by a partial rotation of the ammonium and sulfate groups. The g-values derived from the EPR spectrum of the compound exhibit similar behavior, as do those of ∼1% Cu 2+ doped into the isomorphous zinc(II) compound. The temperature dependence of the g-values of Cu 2+ -doped (ND 4 ) 2 [Zn(D 2 O) 6 ](SO 4 ) 2 may be interpreted satisfactorily by a model which assumes a Boltzmann thermal distribution between two energy states which differ solely in the orientation of the Cu(D 2 O) 6 2+ ion in the lattice. However, such a model does not satisfactorily explain the behavior of pure (ND 4 ) 2 [Cu(D 2 O) 6 ](SO 4 ) 2 , and it is suggested that this is due to cooperative interactions. A new model, in which the probable energy state of each complex is estimated after taking into account the likely orientations of its neighbors in the lattice, is described. Application of this model suggests that the thermal behavior is dominated by the cooperative interactions between complexes, these being transmitted via the hydrogen-bonding network. Comparisons are drawn with the cooperative interactions observed in more strongly coupled Jahn-Teller systems and in compounds for which the structural changes are associated with equilibria between two spin states.

The first example of a pressure-induced Jahn-Teller distortion switch has been observed in a single-crystal time-of-flight neutron diffraction study of the Tutton salt ( N D~)~[ C U ( D Z O )~] ( S~~)~ at T = 15 K, P = 1 bar (h) and T = 15 K, P = 1.5 kbar (h). Also studied was the hydrogenous salt ( N H~)~[ C U ( H~O )~] ( S O~)~ at T = 14 K, P = 1.4 kbar (HH). The unit cell parameters are as follows: h, a = 9.451(2) (2), Z = 2, V = 674.5(2) A3, space group = P21/a. Application of 1.5 kbar of pressure to the deuterated crystal produces a decrease in the lengths of the a and b axes by 0.315(2) and 0.451(4) A, respectively, whereas the c axis increases by 0.275( 1) A. Comparison of the 4. and L~H structures shows that the long axis of the Jahn-Teller distortion has switched by 90°, Le., Cu(l)-0(7) = 2.022(2) and Cu(1)-O(8) = 2.310(2) A for 4. vs Cu(1)-0(7) = 2.290(2) and Cu(1)-O(8) = 2.014(2) A for h, so that the DH and HH structures are similar. For HH Cu(1)-0(7) = 2.272(2) and Cu(1)-O(8) = 2.005(2) A. The switching of the long axis of the Jahn-Teller distortion appears to be associated with the rotation of the ND4+ ion with a concomitant change in the hydrogen bonding of the coordinated water molecules with the S042-ions. The resulting adiabatic potential energy surfaces are calculated using tetragonal and orthorhombic strain parameters estimated from the

High-frequency and high-field electron paramagnetic resonance (HFEPR) spectroscopy (using frequencies of approximately 90-550 GHz and fields up to approximately 15 T) has been used to probe the non-Kramers, S = 1, Ni(2+) ion in a series of pseudotetrahedral complexes of general formula NiL(2)X(2), where L = PPh(3) (Ph = phenyl) and X = Cl, Br, and I. Analysis based on full-matrix solutions to the spin Hamiltonian for an S = 1 system gave zero-field splitting parameters: D = +13.20(5) cm(-1), /E/ = 1.85(5) cm(-1), g(x) = g(y) = g(z) = 2.20(5) for Ni(PPh(3))(2)Cl(2). These values are in good agreement with those obtained by powder magnetic susceptibility and field-dependent magnetization measurements and with earlier, single-crystal magnetic susceptibility measurements. For Ni(PPh(3))(2)Br(2), HFEPR suggested /D/ = 4.5(5) cm(-1), /E/ = 1.5(5) cm(-1), g(x) = g(y) = 2.2(1), and g(z) = 2.0(1), which are in agreement with concurrent magnetic measurements, but do not agree with previous single-crystal work. The previous studies were performed on a minor crystal form, while the present study was performed on the major form, and apparently the electronic parameters differ greatly between the two. HFEPR of Ni(PPh(3))(2)I(2) was unsuccessful; however, magnetic susceptibility measurements indicated /D/ = 27.9(1) cm(-1), /E/ = 4.7(1), g(x) = 1.95(5), g(y) = 2.00(5), and g(z) = 2.11(5). This magnitude of the zero-field splitting ( approximately 840 GHz) is too large for successful detection of resonances, even for current HFEPR spectrometers. The electronic structure of these complexes is discussed in terms of their molecular structure and previous electronic absorption spectroscopic studies. This analysis, which involved fitting of experimental data to ligand-field parameters, shows that the halo ligands act as strong pi-donors, while the triphenylphosphane ligands are pi-acceptors.

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