CrystEngComm COMMUNICATION Cite this: DOI: 10.1039/c5ce01581b Received 6th August 2015, Accepted 3rd December 2015 DOI: 10.1039/c5ce01581b www.rsc.org/crystengcomm From pink to blue and back to pink again: changing the CoIJII) ligation in a two-dimensional coordination network upon desolvation† Diana Chisca, a Lilia Croitor, a Eduard B. Coropceanu, b Oleg Petuhov, b Svetlana G. Baca, a Karl Krämer, c Shi-Xia Liu, c Silvio Decurtins, c Hector J. Rivera- Jacquez, d Artëm E. Masunov de and Marina S. Fonari* a Heating of a pink two-dimensional CoIJII) coordination network {[Co 2 IJμ 2 -OH 2 )IJbdc) 2 IJS-nia) 2 IJH 2 O)IJdmf)]·2IJdmf)·(H 2 O)} n (1) built from 1,4-benzenedicarboxylic acid (H 2 bdc) residues and thio- nicotinamide (S-nia) ligands initiates a single-crystal-to-single- crystal transition accompanied by removal of both coordinated and co-crystallized solvents. In the dry blue form, [CoIJbdc)IJS-nia)] n (dry_1), the CoIJII) centers changed from an octahedral to a square pyramidal configuration. Porous coordination polymers (PCPs) 1 including metal organic–frameworks (MOFs) 2 has become a rapidly growing area of chemistry in the past decades. 3 This is mainly due to the intriguing topological architectures and potential applications of MOFs in fields such as gas storage, catalysis, separation, ion exchange, and molecular magnetism. 4 These solids not only possess regular porosity with high pore volume, but contain tunable organic groups within the molecular framework. This allows an easy modulation of the pore size. MOFs that show a structural response to external stimuli such as guest sorption, temperature, or mechanical pressure are of particular interest. 5 In addition to the rigid three-dimensional (3D) polymeric coordination networks, the flexible two-dimensional (2D) structures are attracting considerable attention. 6 Many fasci- nating examples have been documented since Zaworotko's seminal work. 7 This work highlighted the superstructural di- versity in the laminated solids, the possibilities of the ratio- nal design of both hydrophilic and hydrophobic surfaces, and their common inherent ability to mimic clays by interca- lation of a wide range of organic guest molecules. The breath- ing behaviour, the ability of the metal sites in the regular grids to work as catalytically active centers, the preference in CO 2 gas capture and gas stepwise adsorption were reported. 8 Coordination layers were proposed as a source of crystalline sheets with nanometer thickness for molecular sieving. Their ability to achieve high proton conductivity and high water sorption under low humidity conditions has been demon- strated. A novel strategy to design and synthesize homochiral PCPs 9 and non-linear optical (NLO) materials from layered PCPs was disclosed. 10 The unusual properties of 2D coordination networks prompted us to introduce pyridine-n-aldoxime/dioxime li- gands as pillars or chelating agents. These bulky metallo- chelate corner fragments in carboxylic networks can afford potentially porous structures that are able to accommodate small molecules in the crystal lattices. 11 Here we combine 1,4-benzenedicarboxylic acid (H 2 bdc) with thionicotinamide (S-nia), resulting in a CoIJII)-based 2D coordination network that undergoes a single-crystal-to- single-crystal (SC–SC) transition in the solid state upon desolvation. Our choice is based on the following: 1) struc- tural similarity of S-nia to the pyridine-n-aldoximes, previously explored by us; 10,11 2) all reported data are restricted to organic solids; 12 3) this molecule is one of the commercially available analogs of nicotinamide, and 4) it presents opportu- nities for the generation of hydrogen-bonded networks for 2D stacked layers. The latter would support Kitagawa's idea of inventing “metallo-amino acid” ensembles. 13 CrystEngComm This journal is © The Royal Society of Chemistry 2015 a Institute of Applied Physics Academy of Sciences of R. Moldova, Academy str., 5, MD2028, Chisinau, Moldova. E-mail: fonari.xray@phys.asm.md; Fax: +373 22 725887; Tel: +373 22 738154 b Institute of Chemistry Academy of Sciences of R. Moldova, Academy str., 3, MD2028, Chisinau, Moldova c Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012-Bern, Switzerland d NanoScience Technology Center, Department of Chemistry, Department of Physics, and Florida Solar Energy Center, University of Central Florida, 12424 Research Parkway, Ste. 400, Orlando, Florida 32826, USA e Department of Condensed Matter Physics, National Research Nuclear University MEPhI, Kashirskoye shosse 31, Moscow, 115409, Russia † Electronic supplementary information (ESI) available: General information, synthetic procedures, IR spectra, XRPD, TGA, DSC, figures of crystal packing, de- tails of periodical optimizations and spectral predictions. CCDC 1416671, 1416672 and 1430303. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5ce01581b Published on 17 December 2015. Downloaded by Gazi Universitesi on 18/12/2015 08:03:57. View Article Online View Journal