Synthesis and Mesogenic Properties of Binuclear Copper(II) Complexes Derived from Salicylaldimine Schiff Bases

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• 作者：Reinhard Paschke ; Stefan Liebsch ; Carsten Tschierske ; Michael A. Oakley ; and Ekkehard Sinn
• 刊名：Inorganic Chemistry
• 出版年：2003
• 出版时间：December 15, 2003
• 年：2003
• 卷：42
• 期：25
• 页码：8230 - 8240
• 全文大小：1353K
• 年卷期：v.42,no.25(December 15, 2003)
• ISSN：1520-510X

文摘

The synthesis and mesomorphic (liquid crystal) properties of new binuclear dihalocopper(II) complexes derivedfrom N- and ring-substituted salicylaldimine Schiff bases are reported, together with the mesomorphic properties oftheir monomeric precursor complexes. With just N-substituents both the dichlorodicopper(II) binuclear complexesand 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 liquidcrystalline or mesogenic, except in case of the mononuclear complexes where the N-substituent is straight chainalkyl. The other mononuclear complexes exhibit a variety of liquid crystal phases: smectic A, C, and E (S_A, S_C,and S_E, respectively). The liquid crystal phase S_A is observed in the binuclears with shorter chain N-substituentsp-R-O-C₆H₄- and shorter chain ring-substituents. The chain lengths were increased until the phase behaviorexpanded to a further form S_C 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-Branalogues of the binuclear complexes behave similarly but with significant qualitative differences, specificallylower 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 forthe structures of the binuclear complexes and especially for the shape of the central Cu₂O₂ X₂ core in thebinuclears: distorted planar coordination about the copper with distortion toward tetrahedral measured by acharacteristic twist angle mages/gifchars/tau.gif" BORDER=0 > (0mages/entities/deg.gif"> planar; 90mages/entities/deg.gif"> tetrahedral). The binuclear complexes also show magnetic couplingwhich can be used to estimate the geometry. For [Cu(N-dodecylSal)X]₂ mages/gifchars/tau.gif" BORDER=0 > > 36mages/entities/deg.gif">, which corresponds to weakercoupling than observed in the mesogenic binuclears where a stronger magnetic coupling indicates a geometrycloser to planar (mages/gifchars/tau.gif" BORDER=0 > = 25mages/entities/deg.gif">). The mesophases were characterized by differential scanning calorimetry (DSC) analysisand optical polarized microscopy.