Synthesis, X-Ray Crystal Structure and Reactivity of Dichloro(phthalocyaninato)niobium(IV) (New Polymorph) and Trichloro(phthalocyaninato)niobium(V)

Abstract

Dichloro(phthalocyaninato)niobium(IV), PcNbCl 2, has been isolated as a new polymorph and its X-ray crystal structure solved. Crystals are triclinic: formula C 32 H 16 Cl 2 N 8 Nb , space group P1, cell parameters a = 8.707(2) Å, b = 12.288(3) Å, c = 12.801(3) Å, α = 80.72(2) °, β = 85.43(2) °, γ = 76.62(2) °, V = 1313.7(6) Å3, Z = 2. The molecular structure closely resembles that already found for the monoclinic polymorph. Thus, Nb ( IV ) is six-coordinated in a cis arrangement, being displaced out of the inner N 4 square planar system of the phthalocyanine ring by 0.898(1) Å, towards the two chlorine atoms (average Nb - N ( Pc ) bond distance: 2.130(15) Å; Nb-Cl bond distances: 2.408(1) and 2.396(1) Å; angle Cl1-Nb-Cl2: 80.7 °). The main difference between the two polymorphs is the different stacking of the molecules in the crystal lattice. PcNbCl 3 is also triclinic: formula C 32 H 16 Cl 3 N 8 Nb , space group P1, cell parameters a = 12.086(2) Å, b = 13.710(2) Å, c = 8.345(1) Å, α = 93.49(2) °, β = 100.95(2) °, γ = 79.79(2) °, V = 1335.6(4)Å3, Z = 2. In the molecular structure the Pc chromophore and the three chlorine atoms are at opposite sites with respect to the Nb atom, which is seven coordinate (average Nb-N ( Pc ) bond distance: 2.178(5) Å; Nb-Cl bond distances: 2.482(1), 2.426(1) and 2.380(1) Å; angles Cl-Nb-Cl : 85.3(0), 80.3(0), and 76.5(0) °). The stability of PcNbCl 2 and PcNbCl 3 towards water has been examined. The reactivity of PcNbCl 2 with pyrocathecol, oxalic acid, H 2 SO 4 and iodine has also been examined and has led to the isolation and characterization of the following Nb ( IV ) and Nb ( V ) species: PcNb IV (cat), PcNb IV (oxal), PcNb IV SO 4, PcNb V Cl 2 I , PcNb V (cat)I.