Co-crystal and crystal: Supramolecular arrangement obtained from 4-aminosalicylic acid, bpa ligand and cobalt ion Humberto C. Garcia, Ronaldo T. Cunha, Renata Diniz, Luiz Fernando C. de Oliveira ⇑ Núcleo de Espectroscopia e Estrutura Molecular, Departamento de Química, Universidade Federal de Juiz de Fora, Juiz de Fora, MG 36036-900, Brazil article info Article history: Received 3 November 2011 Received in revised form 23 November 2011 Accepted 23 November 2011 Available online 1 December 2011 Keywords: Crystal and co-crystal Raman spectroscopy Supramolecular chemistry Crystal structure Molecular spectroscopy abstract In this study, the synthesis, spectroscopic properties (infrared and Raman) and crystal structures of two new compounds co-crystal and crystal named HASbpa (1) and [Co(bpa)(H 2 O) 4 ]AS 2 4H 2 O (2) have been reported, where bpa is trans-1,2-bis(4-pyridyl)ethane, HAS is 4-aminosalicylic acid and AS  is aminosa- licylate anion. The crystalline arrangement of the compound 1 exhibits a triclinic system with space group P  1. The formation of a structure known as co-crystal, composed by building blocks in their neutral form; being the first work of this type involving the HAS and nitrogen ligand as bpa. For compound 2,a monoclinic system was observed with P2 1 /c space group. The crystalline arrangement of the structure consisted of a covalent one-dimensional cationic [Co(bpa)(H 2 O) 4 ] 2+ chain, which interacts by hydrogen bonding, p-stacking and electrostatic interactions with aminosalicylate anions and water molecules that were trapped in the crystal. These interactions form supramolecular cavities denominated as pseudo honeycombs. For compound 1, the infrared spectrum revealed the presence of bands at 1643 and 1601 cm 1 assigned to the stretching mode of CO [m(CO)] and CC/CN groups [m(CC/CN)]. For the Raman spectrum, these same modes appear around 1644 and 1602 cm 1 related to HAS and bpa blocks, respec- tively. For compound 2, the largest displacement of the bands compared to free ligand suggested the for- mation of covalent bonds between bpa ligand and metallic site and loss of the proton in HAS molecule. In the infrared spectrum we can observe the presence of bands around 1635 and 1618 cm 1 attributed to the stretching m(COO  ) and m(CC/CN), for the Raman spectrum these same modes appear around 1631 and 1619 cm 1 related to AS  and bpa ligand respectively. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The synthesis and design of molecules capable of spontaneously association into large and well defined systems by noncovalent intermolecular interactions remain one of the foremost challenges in supramolecular chemistry. Nature offers countless examples of self-assembling processes which inspire the work of the synthetic chemist, the creation of analogues from natural complex systems [1]. Recent studies in the literature show that specificity and energetic nature are key determinants of many biochemical phe- nomena, including substrate selection by enzymes and gene regu- lation of metabolic activity [2]. In recent years the study of supramolecular chemistry started to have great prominence in scientific research in both physical and biological aspects, in order to try understanding the phenomena of self-assembly and self-organization. Feature frequently present in chemical systems that show noncovalent interactions as hydro- gen bonding, electrostatic, CAHp, p-stacking and hydrophobic interactions, which may arise mainly from the type of building block used for formation of supramolecular arrangements [3,4] and new structures known scientifically by the name of co-crystals [5–7]. In this context, the organic ligand 4-aminosalicylic acid (HAS) has appeared as a hopeful building block, due to its different coordi- nation sites, as well as its pharmacological properties [8], being used since 1940 as an antibiotic to treat tuberculosis and has also been shown to be safe and effective in the treatment of inflammatory bowel diseases (IBDs), namely distal ulcerative colitis and Crohn’s disease, for over 70 years [9]. However, works involving the coordi- nation chemistry of HAS associated with transition metal ions and nitrogen ligands have been rarely discussed in the literature, and have becoming a focus of great interest to our research group [10]. The other ligand employed in this investigation is trans-1,2- bis(4-pyridyl)ethane or simply bpa, which is an versatile bifunc- tional building block used in the design and construction of molecular complexes due to its aliphatic chain [A(CH 2 ) 2 A] between two pyridyl rings [11,12]. It cannot only act as bidentate bridging li- gand, but can also serve as a terminal ligand or an uncoordinated guest molecule, which may be further involved in hydrogen bonding and/or p-stacking interactions, due to the presence of aromatic ring. Furthermore, magnetic properties, host–guest, gas storage and 0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.11.039 ⇑ Corresponding author. Tel./fax: +55 32 3229 3310. E-mail address: luiz.oliveira@ufjf.edu.br (L.F.C. de Oliveira). Journal of Molecular Structure 1010 (2012) 104–110 Contents lists available at SciVerse ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc