Discotic liquid crystals of transition metal complexes 45: parity effect of the number of d-electrons on stacking distances in the columnar mesophases of octakis-(m-alkoxyphenoxy)phthalocyaninato metal(II) complexes

Abstract

We have synthesized 34 novel homologous discotic liquid crystals, octakis(m-alkoxyphenoxy)phthalocyaninato metal(II) {abbreviated as (m- CnOPhO)8PcM (M = Co(1), Ni(2), Cu(3), Zn(4) and H2 (5); n = 8(a), 10(b), 12(c), 14(d), 16(e), 18(f) and 20(g))}, and investigated parity effect of the number of d-electrons on the stacking distances in their columnar mesophases. It was revealed from temperature-dependent wide angle X-ray diffraction studies that each of the cobalt(II) (d7) complexes (1a–1g) and the copper(II) (d9) complexes (3b–3g) showed a single hexagonal ordered columnar (Colho) mesophase with a very short stacking distance at 3.3 Å, and that the nickel(II) (d8) complexes (2a–2g) and the metal-free (d0) derivatives (5a–5g) showed a single pseudo-hexagonal ordered columnar (Colrho) mesophase with a little bit longer stacking distances at 3.4 Å. Very interestingly, the nickel complex (2a) and metal-free derivatives (5a–5c) gave an extremely big (001) reflection peak with the second (002) reflection peak. Furthermore, the zinc(II) (d10) complexes (4a–4g) showed two different rectangular ordered columnar mesophases, Colro(P2/m) and Colro(P21/a), with a little bit longer stacking distance at 3.4 Å. Thus, the shorter stacking distance, 3.3 Å, appeared for the odd number of d-electrons, whereas the longer stacking distance, 3.4 Å, appeared for the even number of d-electrons. Hence, the stacking distances depend on parity of the number of d-electrons in the central metal(II). To our best knowledge, it is the first example of parity effect on the stacking distances in columnar mesophases.