Selective Growth of Polymorphs: An Investigation of the Organic Nonlinear Optical Crystal 5-Nitro-2-thiophenecarboxaldehyde-4-methylphenylhydrazone

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• 作者：Feng Pan ; Christian Bosshard ; Man Shing Wong ; Christophe Serbutoviez ; Kurt Schenk ; Volker Gramlich ; and P. Gü ; nter
• 刊名：Chemistry of Materials
• 出版年：1997
• 出版时间：June 1997
• 年：1997
• 卷：9
• 期：6
• 页码：1328 - 1334
• 全文大小：464K
• 年卷期：v.9,no.6(June 1997)
• ISSN：1520-5002

文摘

An organic nonlinear optical crystal,5-nitro-2-thiophenecarboxaldehyde-4-methylphenylhydrazone (NTMPH), has been prepared and investigated with regard topolymorphism,growth, and characterization of the structural and physical properties.Recrystallization ofNTMPH in various solvents under different conditions showed theexistence of threecrystalline phases, red greenish plates (NTMPH-I) in space groupP2₁/n, red orange prisms(NTMPH-II) in space group Pna2₁, and blackneedle (NTMPH-III) in space groupP2₁/n.The crystal structures of NTMPH showed that three differentintermolecular forces dominatethe stabilization of one- or two-dimensional structures (calledsecondary structures in thiswork) of the three phases of the NTMPH crystals, namely the hydrogenbonding, dipole-dipole interactions, and the van der Waals forces for NTMPH-I, -II,and -III crystals,respectively. The thermal analysis showed that within thetrimorphs the NTMPH-I crystalhas the lowest thermodynamic stability with the lowest melting pointand enthalpy, butNTMPH-II and -III crystals possess a higher thermodynamic stabilityand are calledthermodynamic phases. The NTMPH-I crystal is easily crystallizedin most conditions andis called a kinetic phase, whereas NTMPH-II and -III arecrystallized with a highersupercooling (equal to a higher chemical potential), which also meansthat higher energybarriers for the nucleation of NTMPH-II and -III must be overcome.Since crystalstructures cannot be designed precisely based on the molecularproperties, especially forflexible molecules, the finding and selective growth of interestingpolymorphic crystals isan essential step for the development of highly active nonlinearoptical materials.