The mesomorphism of a series of complexes of Pd(II), Pt(II) and Ag(I) is discussed and systematic structural variations are highlighted which lead to an appreciation of important factors determining the liquid-crystalline polymorphism of these complexes. Models are proposed for cubic phase formation and the occurrence of an unusual lamellar phase in-between a SmC and a columnar phase is discussed.{Basis of a presentation given at Materials Discussion No. 4,[11][12][13][14]

The methanol-catalyzed elimination of Cl- from the “activated” anionic species [PPN][Ru3(μ-Cl)(μ-PhCCPh)(CO)9] (1) in the presence of bis(diphenylphosphino)methane (dppm) constitutes a rational high-yield route (>90%) to either the unique unsaturated 46-e (alkyne)triruthenium cluster, Ru3(μ-PhCCPh)(CO)7(dppm) (2), or its 48-e CO adduct, Ru3(μ-PhCCPh)(CO)8(dppm) (3). Whereas the CO-induced conversion of 2 into 3 is complete within few seconds at 25 °C under 1 atm of CO, the reverse transformation takes 1 h at 80 °C. The X-ray structure analysis of 2 is reported, revealing a perpendicular conformation of the alkyne relative to the metal triangle. The high reactivity of 2 is substantiated by a high chemical reactivity toward 2-e donors. Its reaction with 1 equiv of dppm (25 °C, 3 h) leads to the bis-dppm-substituted complex, Ru3(μ-PhCCPh)(CO)6(dppm)2 (4) (53% yield). Reaction of 2 with hydrogen gas (1 atm, 25 °C, 10 min) yields the dihydrido species, Ru3(μ-H)2(μ-PhCCPh)(CO)7(dppm) (5) (89% yield) existing as a mixture of two isomers differing in the orientation of the alkyne relative to the edge-bridging dppm ligand. Complex 2 reacts with a terminal alkyne like phenylacetylene under mild conditions to afford a mixture of the “fly-over” type compound Ru3{μ-HCC(Ph)C(O)(Ph)CCPh}(dppm)(CO)6 (6) (57% yield) and the diruthenacyclopentadiene derivative Ru2{μ-HCC(Ph)(Ph)CCPh}(μ-dppm)(CO)4 (7) (20% yield). The structure of 6 reveals the occurrence of a disymmetric edge-bridging dialkenyl ketone ligand HCC(Ph)C(O)(Ph)CCPh, resulting from regioselective coupling between the two alkynes and a carbonyl group. The formal unsaturation of 6 is masked by a weak interaction between the terminal C−Ph bond of the organic chain and one of the metal centers. Facile loss of this interaction is induced by mild thermolysis of 6. As a consequence, free rotation of the organic moiety around the metal−metal edge brings the opposite end of the organic chain (i.e., the C−H bond) close to the opposite face, thereby favoring CH activation to convert the alkenyl end into a vinylidene. This leads to quantitative formation of the vinylidene alkenyl ketone derivative, Ru3(μ-H){μ-CC(Ph)C(O)(Ph)CCPh}(dppm)(CO)6 (8) (94% yield). The X-ray structure of 8 is reported. Unsuccessful attempts to release the organic moiety from the cluster core are described. The reaction of a THF solution of 6 with CO in a reactor [P(CO) = 10 atm, T = 80 °C] leads to the new binuclear “fly-over” species Ru2{μ-HCC(Ph)C(O)(Ph)CCPh}(CO)6 (9a), thereby indicating that elimination of the edge-bridging dppm and cluster fragmentation are more favorable than elimination of a free ketone from the intact cluster. The X-ray structure of Ru2{μ-HCC(C3H7)C(O)(Ph)CCPh}(CO)6 (9b) (resulting from the coupling between diphenylacetylene and 1-pentyne) is reported.

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In the liquid crystal phase behavior of surfactants, cubic phases are common and can, in principle, be found between any pair of adjacent phases. 1 In a binary water/surfactant phase diagram, the formation of phases as a function of water content depends on interactions between the polar headgroups and the water solvent, and also on the size of the polar headgroup versus the volume occupied by the hydrophobic chains. In an organized assembly of these surfactant molecules, one can imagine that a surface between the two incompatible parts, that is the hydrophilic and hydrophobic parts, is generated and that this interface possesses a variable curvature, with the degree of curvature depending on the above parameters. Thus, the formation of a particular phase depends strongly on the idea of interfacial curvature, that is the curvature at the hydrophilic/hydrophobic interface.In thermotropic liquid crystals, there exists a family of mesogens where interfacial curvature is also crucial in determining the phase behavior. 2 These are the polycatenar mesogens 3 which are composed of an extended, rigid core and three or more terminal chains and here the interface in question is that between the aromatic core and the terminal alkyl chains. Of these mesogens, perhaps the most interesting are those with four terminal chains with two found at each end in the 3,4-positions of phenyls rings. Here, at short chain lengths, nematic and smectic C phases are formed, while at longer chains lengths, columnar phases are observed. The lamellar (S C ) phase forms because in order to accommodate the greater cross-section of the chains relative to the core, the core tilts. However, as the chains grow longer, they occupy a much greater volume compared to the core which induces curvature in the lamellar phase, causing the lamellae to break down and forming a columnar phase composed of aggregates of molecules. 4 In certain cases, cubic phases are observed at intermediate chain length 5 and hence at intermediate curvature; the building block here is also clearly related to aggregate formation.The mesomorphism of calamitic (rodlike) mesogens is typically characterized by the formation of nematic and a whole family of smectic phases and interfacial curvature does not normally play a role in explanations of the observed behavior as the interface is planar. For example, smectic phase formation can be accounted for by the microphase separation between the central, more rigid part of the molecules and the flexible terminal chains. Cubic phases are seen here, too, and the first examples were reported by Gray in the late 1950s. 6 Although much more common than they were, cubic phases still remain rather rare and the driving force for their formation is not well understood in the case of calamitic mesogens. 7 Some time ago, we reported on the observation of cubic phases in some formally ionic, calamitic complexes of silver(I) ( Figure 1). 8 The phase behavior of these materials is noteworthy because they show nematic, 9 S A and S C phases in addition t...