New multifunctional phosphonic acid for metal phosphonate synthesis Piotr Garczarek a,⇑ , Jan Janczak b , Jerzy Zon ´ a,⇑ a Department of Medicinal Chemistry and Microbiology, Faculty of Chemistry, Wrocław University of Technology, Wybrze _ ze Wyspian ´skiego 27, 50-370 Wrocław, Poland b Institute of Low Temperatures and Structure Research, Polish Academy of Sciences, 2 Okólna St., P.O.Box 1410, 50-950 Wrocław, Poland highlights " A new multifunctional phosphonic acid, 3-amino-5-(dihydroxyphosphoryl)benzoic acid, has been synthesized and characterized. " It crystallizes in P1 space group and forms a three dimensional supramolecular structure using seven hydrogen bonds. " Molecular structure makes it potentially interesting for synthesis of open framework metal phosphonates. article info Article history: Received 8 November 2012 Received in revised form 29 November 2012 Accepted 29 November 2012 Available online 11 December 2012 Keywords: Phosphonic acid Metal phosphonate Metal–organic framework Supramolecular chemistry abstract A new heterotopic phosphonic acid, 3-amino-5-(dihydroxyphosphoryl)benzoic acid (1) has been synthe- sized and obtained in the crystalline form. Second multifunctional phosphonic acid – namely 3-(dihydr- oxyphosphoryl)-5-nitrobenzoic acid (2) has also been obtained, following a different synthetic route than previously reported. Compound 1 crystallizes in a centrosymmetric space group of the triclinic system as monohydrate, AC 6 H 3 (NH 2 )(COOH)PO 3 H 2 H 2 O– 1a. The molecule in the crystal exists in a zwitterionic form, in which one of the proton of the phosphonic group is transferred to the amine group. The zwitter- ionic molecules interact to each other and with water molecules via NAH ... O and OAH ... O hydrogen bonds forming a three-dimensional network. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Metal organic frameworks (MOFs) have received much atten- tion from many research groups around the world in the last ten years [1,2]. This fact is not surprising as MOF materials form a new class of hybrid compounds – often porous – that posses numerous potential industrial and social applications. Gas storage [3] and separation [4], catalysis [5], drug delivery [6] and non-lin- ear optics [7] are just some of them. The most promising feature of MOF materials is the potential ability to fine-tune the size and shape of its pores as well as their functionality. The most popular O-donor organic species used in metal–or- ganic framework synthesis are carboxylic acids. There are several known carboxylic ligands and some of them like 1,4-benzenedi- carboxylic acids are already considered substrates for industrial- scale MOF synthesis [8]. Along with them, there is another impor- tant group of O-donor, which are phosphonic acids [9]. These compounds, although not so popular in MOF synthesis as carbox- ylic acids and having some drawbacks, still pose an interesting research field. First phosphonate based hybrid materials were syn- thesized by Alberti et al. [10]. Most of already used phosphonic acids formed layered-pillared networks when reacting with metal ion species. It is a matter of concern for researchers to obtain metal phosphonate porous mate- rials, that do not have the layer-pillared architecture. Layer- pillared metal phosphonates are already well studied by Clearfield and co-workers [11,12]. Although materials of such topology can posses some porosity they also have some disadvantages. As poros- ity is mostly achieved by using a phosphate or small monophosph- onate as a co-ligand – so called spacers – pores tend to have wide size distribution owning to the random distribution of spacers. On the other hand non-layered metal-phosphonates tend to form open frameworks. Synthesis of MP’s that not posses such topology can be achieved by using two different approaches [2]. The first one is to use organic ligands that are not linear. Change of angle be- tween binding phosphonate groups interacting with metal moie- ties can usually let one to acquire metal organic phosphonate framework of non-layered topology. One example of such ligand is methylenediphosphonic acid [13]. The second approach con- cerns using ligands with additional functional groups that have the ability to chelate metal ions thus braking the tendency to form layered structure. Such groups are: carboxylic [14], hydroxyl, and 0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2012.11.069 ⇑ Corresponding authors. Fax: +48 71 3284064. E-mail addresses: piotr.garczarek@pwr.wroc.pl (P. Garczarek), jerzy.zon@pwr. wroc.pl (J. Zon ´ ). Journal of Molecular Structure 1036 (2013) 505–509 Contents lists available at SciVerse ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc