Dalton Transactions PAPER Cite this: Dalton Trans., 2013, 42, 10964 Received 29th April 2013, Accepted 23rd May 2013 DOI: 10.1039/c3dt51123e www.rsc.org/dalton Zn(II) coordination polymer of an in situ generated 4-pyridyl ( 4 Py) attached bis(amido)phosphate ligand, [PO 2 (NH 4 Py) 2 ] - showing preferential water uptake over aliphatic alcohols† Arvind K. Gupta, Sanjog S. Nagarkar and Ramamoorthy Boomishankar* Two polymorphic 2D-coordination polymers of composition [ZnL(HCO 2 )] ∞ were synthesized from an in situ generated ligand [PO 2 (NH 4 Py) 2 ] − (L − ). The ligand L − was generated by a facile metal-assisted P–N bond hydrolysis reaction from the corresponding phosphonium salt 1, [P(NH 4 Py) 4 ]Cl, or from the neutral phosphoric triamide 2, [PO(NH 4 Py) 3 ]. The de-solvated sample of the polymer [ZnL(HCO 2 )] ∞ features polar micropores and shows a type I isotherm for CO 2 sorption whereas a type II behaviour was observed for N 2 . The vapour sorption isotherm of the de-solvated sample of [ZnL(HCO 2 )] ∞ shows preferential adsorp- tion of water vapour over aliphatic alcohols. Introduction Separation of water from alcohols such as methanol or ethanol is an important industrial process especially in the purifi- cation of bioethanol, a sustainable energy source. In bioetha- nol, water forms an azeotropic mixture with ethanol and hence cannot be removed completely by usual distillation pro- cedures. 1 One of the active areas of research is the use of metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) for the selective separation of water and alco- hols. 2 Although traditional rigid porous MOFs and zeolites have been shown to act as prominent chemical storage and separation media, 3 the use of flexible/soft PCPs that are sensi- tive to guest molecules exhibiting guest dependant structural and functional transformations have gained recent interest for size or shape selective separation. 4 Normally, these dynamic framework materials are obtained either by the use of metal ions that can adapt to more than one coordination geometry or by using a flexible ligand system. 5 While the former method is restricted only to certain kinds of ligand systems the latter one is suited to most of the metal ions. Hence, the synthesis and use of newer ligand motifs that aid in the generation of dynamic framework materials have attracted a great deal of research interest. 6 In this effort, phosphorus centred ligand motifs, viz. phosphonate monoesters, carboxylated phos- phines, phosphine oxides and phosphonium salts, have received recent attention, as they can provide a flexible peri- pheral ligand platform around the central phosphorus. 7,8 Further, the framework based on the ligand [PO(C 6 H 4 - pCO 2 H) 3 ] and the Zn 2+ ion has been shown to selectively uptake lightweight gases in its pores in a reversible manner. 7a In another report, the MOF based on Ba 2+ ions and the phos- phonate monoester ligand tetraethyl 1,3,6,8-pyrenetetrapho- sphonate has been shown to exhibit very high hydrophobicity and stability towards water. 8b Our group has been focused on the chemistry of amino-functionalized P(V) derivatives 9 and has recently shown the reactivity of certain flexible multi-site ligands such as the pyridylamino functionalized phospho- nium cation, [P(NH 2 Py) 4 ] + and the phosphoric triamide, [PO(NH 2 Py) 3 ]( 2 Py = 2-pyridyl) leading to novel examples of Ag(I) clusters. 10 Further, Hong and co-workers have shown that the analogous 3-pyridyl ligand [PO(NH 3 Py) 3 ] is also flexible along the N–P–N bond and can exist in syn or anti-conformation in the self-assembled [M 6 L 8 ] 12+ complex cages depending on the metal ions. 11 In view of the current interest in the synthesis of flexible/dynamic coordination polymers we set out to employ the amino–P(V) ligands containing 4-pyridyl substituents, as we presumed that the presence of multiple 4-pyridyl substitu- ents on the tetrahedral P(V) backbone would facilitate the for- mation of infinite polymeric structures. Herein, we report on the synthesis of two polymorphic two-dimensional PCPs, † Electronic supplementary information (ESI) available: For experimental pro- cedure, structural description for 1 and 2, crystallographic data tables, TGA and PXRD data for 4 and additional figures. CCDC 906702–906707 for 1, 2, 3, 4 and 3a. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt51123e Department of Chemistry, Mendeleev Block, Indian Institute of Science Education and Research (IISER), Pune, Dr Homi Bhabha Road, Pune – 411008, India. E-mail: boomi@iiserpune.ac.in; Fax: +912025908186 10964 | Dalton Trans., 2013, 42, 10964–10970 This journal is © The Royal Society of Chemistry 2013 Published on 23 May 2013. Downloaded by National Dong Hwa University Library on 24/11/2014 04:40:37. View Article Online View Journal | View Issue