Abstract:The magnetic moment of copper in copper(I1) acetate is known to decrease as the temperature is lowered (1, 2). This anonlalous effect has been explained by assuming that the copper ions are arranged in isolated pairs which interact strongly through exchange forces (3). X-Ray studies, supporting this explanation, have shown that copper(I1) acetate monohydrate exists as a binuclear molecule Cu2(CH3C02) 4.2H20 in which the copper ions are situated close together (4). By analogy, a similar structure has been sugge… Show more
“…EXAFS studies revealed that the metal basal plane remained virtually unchanged both in the lamellar crystal and mesomorphic phase [169]. However, variable temperature infrared analyses showed an increase in the stretching frequencies of the CH 2 group as a result of disordering of the alkyl chains in the mesophase [167] in agreement with dilatometric and 1 H-NMR studies [170]. These results confirmed that the mesophase was composed of partially disordered alkyl chains anchored to unperturbed metal basal plane aggregates.…”
Investigations on the phase behaviors and structural properties of mono-, di-and poly-valent metal carboxylates are reviewed with reference to developments in experimental and theoretical concepts surrounding their liquid crystalline properties. The main methods of structural investigation such as X-ray diffraction, infrared and 13 C-NMR spectroscopies are examined in detail on the basis of common synthetic routes leading to the isolation of pure compounds. A detailed review of the thermal behaviors of several metal carboxylates is presented along with proposed theories and molecular models for odd-even alternation, chain length effects, phase structures and mesophase formation. Theories explaining the effects of metal ion radii and chain unsaturation are also discussed. Proposed degradation mechanisms resulting in the formation of various products and kinetic studies are also considered. Though this review highlights a number of investigations on the structural and phase properties of the mostly widely studied carboxylates, the results presented here strongly indicate that there is room for further studies on some of these systems.
“…EXAFS studies revealed that the metal basal plane remained virtually unchanged both in the lamellar crystal and mesomorphic phase [169]. However, variable temperature infrared analyses showed an increase in the stretching frequencies of the CH 2 group as a result of disordering of the alkyl chains in the mesophase [167] in agreement with dilatometric and 1 H-NMR studies [170]. These results confirmed that the mesophase was composed of partially disordered alkyl chains anchored to unperturbed metal basal plane aggregates.…”
Investigations on the phase behaviors and structural properties of mono-, di-and poly-valent metal carboxylates are reviewed with reference to developments in experimental and theoretical concepts surrounding their liquid crystalline properties. The main methods of structural investigation such as X-ray diffraction, infrared and 13 C-NMR spectroscopies are examined in detail on the basis of common synthetic routes leading to the isolation of pure compounds. A detailed review of the thermal behaviors of several metal carboxylates is presented along with proposed theories and molecular models for odd-even alternation, chain length effects, phase structures and mesophase formation. Theories explaining the effects of metal ion radii and chain unsaturation are also discussed. Proposed degradation mechanisms resulting in the formation of various products and kinetic studies are also considered. Though this review highlights a number of investigations on the structural and phase properties of the mostly widely studied carboxylates, the results presented here strongly indicate that there is room for further studies on some of these systems.
“…Examples for the structures of binuclear complexes are given in Scheme . 1 Examples for Binuclear Complexes a a Left to right: dinuclear azopalladium(II) complex, alkoxy-substituted bis(1,5-diphenyl-1,3,5-pentanetrionato)dicopper(II) complex, and dinuclear tetraalkanoate−copper(II) complex 2 Synthetic Route to Ring- and N-Substituted Salicylaldimine Complexes 3 …”
Section: Introductionmentioning
confidence: 99%
“… a Left to right: dinuclear azopalladium(II) complex, alkoxy-substituted bis(1,5-diphenyl-1,3,5-pentanetrionato)dicopper(II) complex, and dinuclear tetraalkanoate−copper(II) complex …”
The synthesis and mesomorphic (liquid crystal) properties of new binuclear dihalocopper(II) complexes derived from N- and ring-substituted salicylaldimine Schiff bases are reported, together with the mesomorphic properties of their monomeric precursor complexes. With just N-substituents both the dichlorodicopper(II) binuclear complexes and their mononuclear analogues are waxy solids with melting points that increase with their N-chain length. However, with both N- and ring-substituents in the 4-positions, the mononuclear and binuclear complexes are each liquid crystalline or mesogenic, except in case of the mononuclear complexes where the N-substituent is straight chain alkyl. The other mononuclear complexes exhibit a variety of liquid crystal phases: smectic A, C, and E (SA, SC, and SE, respectively). The liquid crystal phase SA is observed in the binuclears with shorter chain N-substituents p-R-O-C6H4- and shorter chain ring-substituents. The chain lengths were increased until the phase behavior expanded to a further form SC in the case of an N-substituent p-C14H29O-C6H4- and a -OC12H25 ring substituent. This points the way toward achieving multiphase behavior with these binuclear systems. The Cu-Br analogues of the binuclear complexes behave similarly but with significant qualitative differences, specifically lower mesophase stability and higher melting temperatures. The structures of the nonmesogenic binuclears ([Cu(N-dodecylSal)X]2, X=Cl, Br) were determined with the aid of X-ray crystallography. These are prototypes for the structures of the binuclear complexes and especially for the shape of the central Cu2O2 X2 core in the binuclears: distorted planar coordination about the copper with distortion toward tetrahedral measured by a characteristic twist angle tau (0 degrees planar; 90 degrees tetrahedral). The binuclear complexes also show magnetic coupling which can be used to estimate the geometry. For [Cu(N-dodecylSal)X]2 tau>36 degrees, which corresponds to weaker coupling than observed in the mesogenic binuclears where a stronger magnetic coupling indicates a geometry closer to planar (tau=25 degrees). The mesophases were characterized by differential scanning calorimetry (DSC) analysis and optical polarized microscopy.
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