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Thermal and Light-Induced Spin Transitions in 3D Hofmann-type Frameworks Built on Nonlinear 3-Substituted Pyridine
Alejandro Orellana-Silla1, Rubén Turo-Cortés1, Manuel Meneses-Sánchez1
1Instituto de Ciencia Molecular/Departamento de Química Inorganica, Universidad de Valencia, Catedratico Beltrán Martínez 2, Paterna, València E-46980, Spain.
Abstract:
Integration of spin crossover (SCO) properties in 3D frameworks made up of cyano-bimetallic layers connected through pillaring organic ligands, the so-called Hofmann-type coordination polymers (HCPs)- represents an important source of multifunctional advanced materials. Typically, these 3D structures are constituted by 4-substituted pyridine-based linear pillars which afford HCPs with regular pcu topology. Here, we have investigated the suitability of the 3-substituted pyridine and pyrimidine bis-monodentate ligands 2,5-di(pyridin-3-yl)aniline (3-dpyan) and 2,5-di(pyrimidin-5-yl)aniline (bpmdan) as alternative building blocks to explore new structural topologies and functionalities. In this context, we have prepared the compounds Fe(3-dpyan)[Ag(CN)2]2·2MeOH (1·2MeOH), Fe(3-dpyan)[Ag(CN)2]2···0.35NO2Bz·MeOH (1·0.35NOBz·MeOH), Fe(3-dpyan)[Au(CN)2]2·NO2Bz (1·NOBz), and Fe(bpmdan)[Ag(CN)2]2·CH3Bz (2·CHBz) (MeOH = methanol, NO2Bz = nitrobenzene, CH3Bz = toluene). Our structural studies have revealed that 1·2MeOH and 1·0.35NOBz·MeOH exhibit isomorphous doubly interpenetrated 3D structures strongly differing from the unusual noninterpenetrated ones exhibited by 1·NOBz and 2·CHBz. Temperature-dependent magnetic susceptibility measurements have shown that all the reported compounds exhibit thermal-induced SCO properties, and moreover, three of them display Light Induced Excited Spin State Trapping at low temperatures (LIESST effect). The studied compounds show a wide diversity of SCO behaviors, ranging from abrupt complete one-step SCO centered at 253 K (1·NOBz) to gradual and incomplete multistepped SCO centered at 120 K (1·0.35NOBz·MeOH). This assorted SCO properties are discussed and correlated to the acquired chemical and structural information.
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