Synthesis, Structural Investigation, and Solid-State Properties of Iodine-Doped Zirconium Diphthalocyanine, [ZrPc₂]I₃·I₂

Crystals of iodine-doped zirconium(IV) diphthalocyanine, [ZrPc2]I3·I2 (where Pc = C32H16N8), were grown directly in the reaction of pure zirconium powder with phthalonitrile under a stream of iodine at 260 °C. [ZrPc2]I3·I2 crystallizes in the space group P21/m (No. 11) of the monoclinic system with lattice parameters of a = 6.735(1), b = 25.023(5), and c = 17.440(3) Å, β = 99.43(3)°, and Z = 2. The crystals of [ZrPc2]I3·I2 are built up from two pseudo-monodimensional aggregates: one-electron-oxidized [ZrPc2]+ units; weak interacting triiodide I3- ions with neutral diiodine molecules. The I3- ions and neutral I2 molecules in the crystal of [ZrPc2]I3·I2 have been also detected by Raman spectroscopy. The [ZrPc2]+ units form stacks along the a axis, while the polymeric ···I3-···I2···I3-···I2-··· zigzag chains are located in the crystal along the b axis, so both pseudo-monodimensional aggregates are perpendicular to each other. This arrangement is different from that found in the tetragonal crystals of [ZrPc2](I3)2/3 in which both monodimensional aggregates, i.e., the stacks of partially oxidized [ZrPc2]2/3+ units and chains of symmetric triiodide ions, are parallel. EPR experiment together with the X-ray single-crystal analysis clearly shown that oxidation of the diamagnetic ZrPc2 complex by iodine is ligand centered and homogeneously affecting both phthalocyaninato rings of ZrPc2; thus, the formal oxidation state of both Pc rings in [ZrPc2]I3·I2 is nonintegral (−1.5). The UV−vis spectrum of [ZrPc2] I3·I2 is very similar to the spectrum of unoxidized ZrPc2 complex in the B Soret and Q spectral region. However, in the spectrum of [ZrPc2] I3·I2 one additional band at ∼502 nm is observed, which indicates the existence of the one-electron-oxidized phthalocyaninato(−) radical ligand and is assigned to the electronic transition from a deeper level to the half-occupied HOMO level. The single-crystal electrical conductivity data show anisotropy and nonmetallic character in conductivity (dσ/dT > 0). The charge transport mainly proceeds along the pseudo-monodimensional stacks of [ZrPc2]+ units. The relatively high conductivity along the stacks of one-electron-oxidized [ZrPc2]+ units results from the staggering orientation of Pc rings (rotation angle 45.0(2)°) that leads to the short inter-ring Cα(pyrrole)−Cα(pyrrole) contacts (2.839(3)−3.024(3) Å). These Cα-pyrrole atoms make appreciable contribution to the partially occupied π-molecular orbital of Pc macrocycle and the greatest overlap of the HOMO orbitals that form the conduction band of partially oxidized molecular crystals.