Rectangular and hexagonal columnar mesophases in dinuclear rhodium(II) (alkyloxy)benzoate complexes

Abstract

The complexes [Rh2(μ-O2CC6H4-4-OC nH2n+1)4] (n = 8-14), [Rh2(μ-O2CC6H3-3,4-(OC 10H21)2)4], and [Rh2(μ-O2CC6H2-3,4,5-(OC 10H21)3)4] were prepared by the reaction of [Rh2(μ-O2CCH3)4] with the corresponding (alkyloxy)benzoic acids. The adducts [Rh2(μ-O2CC6H4-4-OC 10H21)4(CO)2] and [Rh2(μ-O2CC6H4-4-OC 8H17)4(N2C4H 4)n] were obtained by treatment with CO and pyrazine, respectively. Cyclic voltammograms of [Rh2(μ-O2CC6H4-4-OC nH2n+1)4] complexes show reversible one-electron oxidation processes. The thermal behavior of the complexes was investigated by optical microscopy and DSC, and the structures of the mesophases and solid phases obtained were determined by X-ray diffraction. The complexes [Rh2(μ-O2CC6H4-4-OC nH2n+1)4] (n = 10-14) display two orthorhombic crystal phases at room temperature (space groups Pmmm and Pbmn) and a columnar mesophase of rectangular (orthorhombic) symmetry (space group Cmmm). For the n = 10 homologue the cell parameters are as follows: a = 23.50 Å, b = 13.19 Å, c = 4.82 Å, (Z = 1), in the Pmmm phase; a = 49.30 Å, b = 12.96 Å, c = 4.86 Å (Z = 2), in the Pbmn phase; a = 55.05 Å, b = 13.06 Å, c = 4.86 Å (Z = 2), in the Cmmm mesophase. The eight-chained complex shows two columnar phases, one rectangular at room temperature (likely Cmmm; a = 45.7 Å, b = 30.01 Å) and a hexagonal one above 138°C (P6/mmm; a = 29.1 Å). The twelve-chained derivative exhibits a 3D monoclinic phase at room temperature (space group P2/m; cell parameters a = 33.28 Å, b = 20.38 Å, c = 10.10 Å, γ = 113.3°, Z = 1) and a hexagonal columnar mesophase at higher temperatures (P6/mmm; a = 26.6 Å). © 1992 American Chemical Society.