CRYSTAL-STRUCTURES AND ELECTRON-PARAMAGNETIC-RESONANCE SPECTRA OF [CU(P(C5H4N)(3))(2)]BR-2-CENTER-DOT-8H(2)O AND CU2-DOPED [ZN(P(C5H4N)(3))(2)]BR-2-CENTER-DOT-8H(2)O, EXAMPLES OF A DYNAMIC JAHN-TELLER EFFECT IN 2 DIMENSIONS()

Crystals of [Cu{P(C5H4N)(3)}(2)]Br-2 . 8H(2)O, studied at 173 K are tr iclinic, space group P $(1) over bar$$, with unit-cell dimensions a = 9.082(4), b = 11.340(1), c = 9.084(2) Angstrom, alpha = 98.40(4), beta = 94.78(3), gamma = 98.27(7)degrees and Z = 1; those of [Zn{P(C5H4N)( 3)}(2)]Br-2 . 8H(2)O studied at 293 K are monoclinic, space group C2/m with a = 12.506(6), b = 13.588(7), c = 11.593(7) Angstrom, beta = 101 .62(4)degrees and Z = 2. The structures were refined to final R = 0.05 0 for 3192 reflections with I greater than or equal to 3.0 sigma(I) an d R = 0.033 for 1737 reflections with I greater than or equal to 3.0 s igma(I), respectively. The centrosymmetric copper complex has two Cu-N bonds [2.002(4) Angstrom] considerably shorter than the other four [2 .189(5) x 2, 2.191(5) Angstrom x 2]. However, the temperature dependen ce of the EPR spectrum suggests that in fact the complex has a tetrago nally elongated octahedral geometry with two possible orientations in the crystal lattice, these differing by interchange of the directions of the long and intermediate Cu-N bond directions. These forms are in dynamic equilibrium, with an activation energy of approximate to 600 c m(-1) for the interchange. Analysis of the relative intensities of the EPR signals observed at approximate to 10 K suggests an energy differ ence between the structural isomers of approximate to 4 cm(-1). The zi nc complex has crystallographic 2/m symmetry with two independent Zn-N distances [2.150(3) x 2; 2.187(3) Angstrom x 4]. The temperature depe ndence of the EPR spectrum of this compound doped with approximate to 1% Cu2+ is similar to that of the pure copper(II) compound, but with a lower activation energy for interchange of the structural isomers. Th e dynamic behaviour of the copper(II) complex in the two compounds is discussed in terms of a potential surface obtained by considering the effects of Jahn-Teller coupling and lattice strain interactions. Bondi ng parameters derived from the electronic spectrum are consistent with the tetragonally elongated octahedral co-ordination geometry proposed .