Dimeric Ir-II phthalocyaninates with an Ir-Ir bond; Crystal structure of di(pyridinephthalocyaninato(2)-iridium(II))

Blue, diamagnetic di(iridiumphthalocyaninate(2-)), [(Irpc(2-))(2)] is prepared by controlled thermal decomposition of di(acido)phthalocyaninatoiridates in an inert, high-boiling solvent like 1-chloronaphthalene or under reduced pressure (T < 350 degrees C). It is soluble in pyridine (py) yielding the blue violet, diamagnetic py adduct [{Ir(py)pc(2-)}(2)]. This crystallizes in the orthorhombic space group P2(1)2(1)2(1) (no. 19) With Z = 4. The short Ir-Ir distance (2.707(1) Angstrom) indicates a strong Ir-Ir single bond. Due to the axial coordination of the py ligands the Ir atoms are virtually bond in the centre (Ct) of the pc ligands (d(Ir-Ct) = 0.06(1) Angstrom). The pc ligands are staggered (alpha(N-Ir-Ir'-N') = 43(1)degrees). In spite of the short interplanar distance (d(Ct-Ct)=2.827(7) Angstrom) the pc ligands are only slightly distorted (one wagging, one doming). One py ligand is disordered. Ir-N-py distances are 2.35(2) and 2.291(1) Angstrom. Due the labilizing trans influence of the Ir-Ir bond these distances are rather long. The (N(py-)lr1-Ir2-N-py') skeleton is almost linear (177.2(4)degrees). The Ir-N-iso distance is 1.99(2)Angstrom. Four quasi-reversible one electron transfer processes at -1.34, -0.82, 0.55 and 0.82 V are observed in the differential pulse voltammogram of [{Ir(py)pc(2-)}(2)]. The process at 0.55 V is assigned to the redox couple [{Ir(py)pc(2-)}(2)]/[{(py)pc(-)Ir-Irpc(2-)(py)}](+), according to the VIS spectrum of the product obtained by oxidation with iodine. In the UV-VIS-NIR spectrum of the dimer dissolved in pyridine the B region is split into two bands at 14970 (B-) and 17300 cm(-1) (B+) of equal intensity due to strong excitonic coupling. The excitonic coupling/structure relationship of different mono- and dinuclear diphthalocyaninates is discussed. The Ir-Ir stretching vibration at 135 cm(-1) is selectively enhanced in the FT-Raman spectrum.