Unit cell determination of 2,3,9,10,16,17,23,24-octapentoxyphthalocyanine and its nickel derivative using electron and X-ray powder diffraction

2,3,9,10,16,17,23,24-Octapentoxyphthalocyanine and its nickel derivative ha ve been studied by means of electron and X-ray powder diffraction. The resu lts reveal that the metal-free compound forms monoclinic crystals (space gr oup C2/c) with unit cell constants a = 4.202 nm, b = 0.4977 nm, c = 3.345 n m, beta = 98.9 degrees and Z = 4 molecules per unit cell. 2,3,9,10,16,17,23 ,24-Octapentoxyphthalocyaninatonickel(II) is likely to be isomorphous to it s metal-free analogue, but occurs in a second phase which is also stable at room temperature. This is identified to be a crystalline primitive hexagon al phase with cell constants a = b = 2.50 nm and c = 0.33 nm. It is assumed that the molecules form a columnar structure along the c-axis, whereas the hexagonal cross-section in the ab-plane goes back to the molecular disc sh ape. Imaging of monoclinic crystals of 2,3,9,10,16,17,23,24-octapentoxyphth alocyanine in an energy-filtering transmission electron microscope (EFTEM) can be performed to resolve 2 nm structures only, owing to specimen damage. According to the diffraction pattern, the micrograph provides a view along [001] and shows directly that the structure can be described in terms of p arallel columnar stacks of molecules along the b-axis, the distance between neighbouring stacks being 1/2a. The results show that the structures of bo th the metal-free compound and its nickel analogue are dominated by pi-pi i nteractions between the macrocycles, which is a marked difference from the structures of 1,4,8,11,15,18,22,25-octasubstituted phthalocyanines. Copyrig ht (C) 2000 John Wiley & Sons, Ltd.