Jadwiga Szydłowska

Nematic phase formed by banana-shaped molecules

Most mesogens formed by banana-shaped molecules exhibit liquid-like smectic phases. Here we present the synthesis and properties of homologous series of derivatives of resorcinol and 2,6-disubstituted pyridine. One of these classes of bent-core molecules displays the nematic phase.

Liquid crystal phases formed by asymmetric bent-shaped molecules

A few series of asymmetric bent-core compounds with different branches were obtained. Depending on the flexibility and the parity of the unit that joins the central ring with the branches the typical rod-like or banana phases are observed. It is shown that asymmetric materials usually have a broader mesophase range than their symmetric analogues. The rich variety of lamellar and broken-layer columnar phases were found for asymmetric compounds, some of the phases being ferroelectric. Biaxial and uniaxial ferroelectric phases were observed. It has also been proven that some mesophases showing optical bistability under electric fields are unambiguously antiferroelectric.

Fluorinated metallomesogens – lamellar versus columnar phase formation

Two series of tetradental cis-enaminoketone Ni(II) and Cu(II) complexes with their mesogenic core substituted by different combination of hydrocarbon or fluorocarbon chains have been synthesized. Depending on the type and position of the substituted groups, compounds reveal either calamitic or columnar mesophases. Replacing the alkyl chains by perfluorinated chains stabilizes the columnar phase. A unique phase sequence of isotropic–columnar hexagonal–re-entrant isotropic–smectic (I–Colh–Ire–SmA) has been observed on cooling for some of the obtained compounds.

Bent-shaped mesogens without an azomethine joint

A new series of banana-shaped mesogens with ethylene links in the branches and laterally substituted are presented. They form B1, B2, B6 and B7-like phases. The B7-like and B2 phases are not miscible although identical crystallographic structures are deduced from X-ray studies. The switching in the B7-like phase is without a threshold and occurs only in a small number of domains. Dielectric measurements do not confirm ferroelectric properties for the B7-like phase, and only a weak non-collective relaxation process was observed. In the B2 phase a collective and weak dielectric mode was detected. The B1 phase exhibits a columnar structure with a large rectangular cell 111.6 × 51 A2.

KAgF3, K2AgF4 and K3Ag2F7: important steps towards a layered antiferromagnetic fluoroargentate(II),

Crystal structure and magnetic properties of K2AgF4, related to recently studied Cs2AgF4, have been scrutinized. It crystallizes orthorhombic (Cmca No.64) with a = 6.182(3) A, b = 12.632(5) A, c = 6.436(3) A (Z = 4, V = 502.6(7) A3). K2AgF4 exhibits slightly puckered [AgF2] sheets and a compressed octahedral coordination of Ag(II) and it is not isostructural to related Cs2AgF4. Violet–coloured K2AgF4 orders ferromagnetically below 26 K. The DFT calculations reproduce semiconducting properties and ferromagnetism of K2AgF4 at the LSDA + U level but only if substantial values of Mott–Hubbard on-site electron–electron repulsion energies for Ag and F are used in calculations. We have also succeeded to solve the crystal structure of a brown KAgF3 (1D antiferromagnet below 64 K; GdFeO3–type, PnmaNo. 62, a = 6.2689(2) A, b = 8.3015(2) A, c = 6.1844(2) A, Z = 4, V = 321.84(2) A3) and to prepare K3Ag2F7, a novel KAgF3/K2AgF4 intergrowth phase and a member of the Ruddlsden–Popper KnAgFn+2 series (n = 1.5). Dark brown K3Ag2F7 crystallizes orthorhombic (K3Cu2Cl7-type, CccaNo. 68, setting 2) with a = 20.8119(14) A, b = 6.3402(4) A, c = 6.2134(4) A (Z = 4, V = 819.87(9) A3).

CALAMITIC OR COLUMNAR MESOMORPHISM DETERMINED BY NUMBER AND POSITION OF SUBSTITUENTS IN ENAMINOKETONE CU(II), NI(II) AND CO(II) COMPLEXES

New enaminoketone metalomesogens with an almost equilateral triangular shape of the mesogenic core have been synthesized. They form either calamitic or columnar mesophases depending on the number and position of the substituted chains. The stability of the columnar as well as of the calamitic phases depends substantially on the central metallic ion.

Formation of mesophases by fluorinated enaminoketone Ni(II), Cu(II) and VO(II) complexes

Mesogenic tetradentate cis‐enaminoketone Ni(II), Cu(II) and VO(II) complexes with rod‐like and disc‐like molecular shapes were synthesized. In these compounds some of the alkyl chains were perfluorinated. Replacing the alkyl chains by fluorinated chains stabilizes the columnar hexagonal Colh phase whereas lamellar phases are destroyed.

Silver(II) triflate with one-dimensional [Ag(II)(SO3CF3)4/2]∞ chains hosting antiferromagnetism

Silver(II) triflate, previously reported by Leung et al. in 1979 (Can. J. Chem., 1979, 57, 326–329), crystallizes in a triclinic P cell with a = 4.9117(11) A, b = 5.1136(10) A, c = 11.033(3) A, α = 79.955(14)°, β = 75.771(16)°, γ = 61.571(17)° and V = 235.68(10) A3 and is isomorphous to Cu(SO3CF3)2. The compound has a layered structure with an interlayer separation of 10.67 A; the van der Waals gaps open between the CF3 groups from neighbouring sheets. Ag(II) is coordinated by six O atoms in the form of an elongated octahedron; the adjacent Ag2+ cations are linked via –OSO– bridges; direct –O– bridges are absent. The [Ag(II)(SO3CF3)2]∞ layers consist of one-dimensional chains which interact weakly with each other via longer Ag⋯OSO–Ag contacts. This results in a 1D rather than 2D antiferromagnetic ordering, which can be described via the Bonner–Fisher model with a superexchange constant, Jintra-chain, of 104 K (9.0 meV) per pair of interacting Ag2+ cations. The magnetic ordering persists even at room temperature leading to a broad ESR signal with g = 2.199. DFT calculations confirm the 1D character of electronic structure and antiferromagnetism residing within the [Ag(II)(SO3CF3)4/2]∞ chains with a |Jinter-chain|/|Jintra-chain| ratio of ∼10−3 to 10−2. The calculated indirect bandgap at the Fermi level of ∼1 eV opens between rather flat valence and conduction bands, which are predominated by contributions from Ag and O atoms. Ag(SO3CF3)2 is extremely sensitive to moisture and decomposes instantly when exposed to atmosphere. When dry, it rapidly decomposes thermally above 120 °C, but its slow exothermic decay to AgSO3CF3 takes place even at room temperature. Silver(II) triflate is also photosensitive and irradiating it with a 632.8 nm laser radiation at a power greater than 0.17 mW leads to its decomposition to Ag(I) triflate and Ag(I)2S2O7.

Modulated and intercalated smectic phases formed by dimeric molecules

A series of molecules having a hydroxyl group attached to the end of one terminal chain were found to form a sequence of smectic antiphases, SmA, Sm, Sm and Cr, with a growing degree of in-plane molecular ordering. The bilayer structure of the modulated phases is due to the formation, through hydrogen bonding, of molecular dimers that are linear in shape. Moving the hydroxy group to a position closer to the molecular core resulted in a similar sequence of non-modulated, monolayer smectic phases. The related dimeric compounds in which the same mesogenic cores were covalently linked by an alkyl chain formed intercalated smectic phases.

Synthesis and properties of a new series of mesogenic compounds with pyridine, oxidopyridinium, thienyl and furyl moieties

This paper presents the synthesis and mesophase properties of several homologous series of structurally related compounds in which the aromatic ring attached to 4′-alkyloxybiphenyl-4-ol was systematically changed. The homologues with achiral and chiral terminal groups were studied. New compounds forming both antiferroelectric and ferroelectric phases were obtained for pyridyl and phenyl derivatives.