Construction of Bis-pyrazole Based Co(II) Metal-Organic Frameworks and Exploration of Their Chirality and Magnetic Properties Sudeshna Bhattacharya, † Arijit Goswami, † Bappaditya Gole, ‡ Sumi Ganguly, † Sukhen Bala, † Satirtha Sengupta, † Sumit Khanra, § and Raju Mondal* ,† † Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Raja S. C. Mullick Road, Kolkata 700032, West Bengal, India ‡ Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India § Department of Chemical Sciences, Indian Institute of Science Education and Research, Kolkata, Mohanpur, West Bengal 741252, India * S Supporting Information ABSTRACT: In continuation of our interest in pyrazole based multifunctional metal- organic frameworks (MOFs), we report herein the construction of a series of Co(II) MOFs using a bis-pyrazole ligand and various benzene polycarboxylic acids. Employment of different acids has resulted in different architectures ranging from a two-dimensional grid network, porous nanochannels with interesting double helical features such as supramolecular chicken wire, to three-dimensional diamondoid networks. One of the distinguishing features of the network is their larger dimensions which can be directly linked to a relatively larger size of the ligand molecule. Conformational flexibility of the ligand also plays a decisive role in determining both the dimensionality and topology of the final structure. Furthermore, chirality associated with helical networks and magnetic properties of two MOFs have also been investigated. ■ INTRODUCTION The last two decades have witnessed a tremendous growth in the field of metal-organic frameworks (MOFs) owing to their diverse potential applications, ranging from gas sorption and storage, magnetism, catalysis to biomedical utilities. 1 Such potential bulk properties of MOFs are often found to be intimately related to the network topology and dimension- alities. 2 One such topology related property would be chirality of the framework. It has been observed that, even in absence of any chiral ligand, chirality in a network can be induced via spontaneous resolution. 20 The resultant chiral MOFs can be of great importance in the fields of chiral heterogeneous catalysis and chiral separation. The structural modularity, on the other hand, depends heavily on the appropriate combination of metal centers, coordinating functional groups, and the geometry of the predesigned ligands. 3 Accordingly, ligand molecules with various functional groups, with different conformations and spacers between the coordinating sites, have been extensively used. 4 However, one can hardly overlook the overwhelming usage of pyridyl and carboxylate as coordinating functional groups, despite their serious shortcomings toward functional materials. 5 For example, MOFs made of neutral pyridyl-based linkers frequently end up with a structure where non- coordinated anions occupy the channels of the frameworks, reducing the porosity in the framework. 6 This is exactly where relatively less explored azole based ligands are really handy. It has been observed that polyazole bridging ligands with strong metal-nitrogen bonds provide remarkably strong chemical and thermal stability and lead to a slow but steady shift in favor of azole based MOFs synthesis. 7 Notwithstanding of their strong presence in traditional coordination complex synthesis, 1H-pyrazole based ligands especially containing a flexible backbone are seldom reported in the literature. 8 This is particularly true for magnetic polymeric networks, one of the most studied branch of MOFs. 9 In particular, the relationship between the structural aspects of MOFs and magnetic properties has attracted extensive attention in recent times with the aim of understanding the fundamental factors governing magnetic properties. Despite a plethora of recent literature sources on magnetic MOFs, such networks based on 1H-pyrazole based ligands still remain one of the most intriguing yet elusive varieties. 10 Notwithstanding, pyrazole based ligands offer a broad scope of study of magnetic MOFs. Flexibility of the ligands is another interesting and key issue, yet often overlooked during MOF synthesis. 11 A rigid ligand almost invariably leads to an inflexible framework. On the Received: January 31, 2014 Revised: May 5, 2014 Article pubs.acs.org/crystal © XXXX American Chemical Society A dx.doi.org/10.1021/cg500174g | Cryst. Growth Des. XXXX, XXX, XXX-XXX