Synthesis, structural investigation, and solid-state properties of iodine-doped zirconium diphthalocyanine, [ZrPc2]I3.I2.
Crystals of iodine-doped zirconium(IV) diphthalocyanine, [ZrPc(2)]I(3).I(2) (where Pc = C(32)H(16)N(8)), were grown directly in the reaction of pure zirconium powder with phthalonitrile under a stream of iodine at 260 degrees C. [ZrPc(2)]I(3).I(2) crystallizes in the space group P2(1)/m (No. 11) of the monoclinic system with lattice parameters of a = 6.735(1), b = 25.023(5), and c = 17.440(3) A, beta = 99.43(3) degrees, and Z = 2. The crystals of [ZrPc(2)]I(3).I(2) are built up from two pseudo-monodimensional aggregates: one-electron-oxidized [ZrPc(2)](+) units; weak interacting triiodide I(3)(-) ions with neutral diiodine molecules. The I(3)(-) ions and neutral I(2) molecules in the crystal of [ZrPc(2)]I(3).I(2) have been also detected by Raman spectroscopy. The [ZrPc(2)](+) units form stacks along the a axis, while the polymeric...I(3)(-)...I(2)...I(3)(-)...I(2)(-)... 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 [ZrPc(2)](I(3))(2/3) in which both monodimensional aggregates, i.e., the stacks of partially oxidized [ZrPc(2)](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 ZrPc(2) complex by iodine is ligand centered and homogeneously affecting both phthalocyaninato rings of ZrPc(2); thus, the formal oxidation state of both Pc rings in [ZrPc(2)]I(3).I(2) is nonintegral (-1.5). The UV-vis spectrum of [ZrPc(2)] I(3).I(2) is very similar to the spectrum of unoxidized ZrPc(2) complex in the B Soret and Q spectral region. However, in the spectrum of [ZrPc(2)] I(3).I(2) one additional band at approximately 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 (d sigma/dT > 0). The charge transport mainly proceeds along the pseudo-monodimensional stacks of [ZrPc(2)](+) units. The relatively high conductivity along the stacks of one-electron-oxidized [ZrPc(2)](+) units results from the staggering orientation of Pc rings (rotation angle 45.0(2) degrees ) that leads to the short inter-ring C(alpha)(pyrrole)[bond]C(alpha)(pyrrole) contacts (2.839(3)-3.024(3) A). These C(alpha)-pyrrole atoms make appreciable contribution to the partially occupied pi-molecular orbital of Pc macrocycle and the greatest overlap of the HOMO orbitals that form the conduction band of partially oxidized molecular crystals.
Janczak
Jan
J
Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, Okólna 2 str., 50-950 Wrocław, Poland. janczak@int.pan.wroc.pl