The compound (phthalocyaninato)nickel(II) bromide, Ni(pc)Br, has been synthesized by the oxidation of Ni(pc) with Br2. Comparison of this compound with its isostructural partner Ni(pc)I provides a first glimpse of the effects of change of oxidant on the properties of crystalline porphyrinic molecular metals. Ni(pc)Br, C32H16BrN8Ni, crystallizes with two formula units in space group Dih-P4/mcc of the tetragonal system in a cell of dimensions a = 13.793 (7) Å and c = 6.431 (4) Å (167 K). The structure is identical with that of Ni(pc)I and consists of stacks of Ni(pc) molecules segregated from chains of halogen in the form of Br3 -ions; both stacks and chains run parallel to the c axis of the crystal. Each Ni(pc) molecule is centered on a site of 4 /m symmetry and is constrained to be planar and perpendicular to the stacking axis. Successive rings in the unit cell are staggered by 39.1 (6)°. Although there is room for about 13% more Br3 -than I3 -in such channels, the halogen to Ni(pc) ratio of 1:1 and the degree of oxidation, 1/3electron/Ni(pc) ring, is the same for both Ni(pc)Br and Ni(pc)I. Despite these structural similarities the electrical conductivity and magnetic properties of Ni(pc)Br (a ≈ 100 IT1 cm1at room temperature) differ significantly from those of Ni(pc)I (a ≈ 600 Ω- 1 cm-1at room temperature), both in value and in temperature variation. Analysis of the EPR measurements suggests that the trihalide chain plays a lesser role in charge transport in Ni(pc)Br and that the Ni(pc) stacks become further decoupled as the temperature is lowered below ca. 75 K. The present results give the first clear evidence that it is inappropriate to ignore anion effects and concentrate on the metal-organic framework in discussions of M(L)X systems.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry