Synthesis, crystal structure and charge transport properties of one-electron oxidized zirconium diphthalocyanine, [ZrPc2]IBr2.

Abstract

Crystals of the new one-electron oxidized zirconium diphthalocyanine, [ZrPc2]IBr2 (Pc = C32H16N8) were grown directly from phthalonitrile and pure zirconium powder under the oxidation conditions of IBr at 220 _C. [ZrPc2]IBr2 crystallises in the space group P21/m of the monoclinic system, with lattice parameters of: a = 6.697(1), b = 25.483(5), c = 16.918(3)A ˚ , b = 100.03(3)_ and Z = 2. The crystals of [ZrPc2]IBr2 are built up from one-electron oxidized [ZrPc2]+ units that form stacks parallel to a axis of the crystal and mixed electron-rich trihalide ions of IBr2 _. The iodine atom of the IBr2 ions is located at the inversion center, so the IBr2 _ ions are linear and symmetrical. The mutual arrangement of [ZrPc2]+ and IBr2 _ ions is different to that found in the one-electron oxidized [ZrPc2]I3 Æ I2 complex as well as to that found in the tetragonal crystals of partially oxidized [ZrPc2](I3)2/3. EPR experiment shows that the oxidation of the diamagnetic ZrPc2 complex by IBr is ligand centered. The UV–Vis spectrum of [ZrPc2]IBr2 shows, besides the bands observed in the spectrum of ZrPc2, one additional band at _496 nm, which indicates the existence of the one-electron oxidized phthalocyaninato(1_)p-radical ligand and it is assigned to the electronic transition from a deeper level to the half-occupied HOMO level. The single-crystal electrical conductivity data shows anisotropy and non-metallic character in conductivity (dr/dT > 0). The charge transport mainly proceeds along the stacks of one-electron oxidized [ZrPc2]+ units. The relatively high conductivity along the [ZrPc2]+ stack results from the staggered configuration of the Pc-rings (rotation angle 45.0(3)_) that makes short inter-ring Ca(pyrrole)–Ca(pyrrole) contacts (2.858(2)–3.017(3)A ˚ ) and greatest overlap of the HOMO orbitals that form the conduction band of the molecular materials.