pubs.acs.org/crystal Published on Web 12/04/2009 r 2009 American Chemical Society DOI: 10.1021/cg900943x 2010, Vol. 10 357–364 Stepwise Topotactic Transformations (1D to 3D) in Copper Carboxyphosphonate Materials: Structural Correlations Konstantinos D. Demadis,* ,# Maria Papadaki, # Miguel A. G. Aranda,* ,‡ Aurelio Cabeza, ‡ Pascual Olivera-Pastor, ‡ and Yiannis Sanakis § # Crystal Engineering, Growth and Design Laboratory, Department of Chemistry, University of Crete, Voutes Campus, Crete, GR-71003, Greece, ‡ Departamento de Quı´mica Inorg  anica, Universidad de M alaga, Campus Teatinos S/N 29071-M alaga, Spain, and § Institute of Materials Science, NCSR “Demokritos”, 15310 Ag. Paraskevi Attikis, Greece Received August 10, 2009; Revised Manuscript Received October 20, 2009 ABSTRACT: In this report, we demonstrate a topotactic transformation of a [Cu(HPAA)(H 2 O) 2 ] 3 H 2 O one-dimensional (1D) hybrid (HPAA = HO 3 PCH(OH)CO 2 , hydroxyphosphonoacetate dianion) to an anhydrous Cu(HPAA) three-dimensional (3D) framework, via the 1D intermediate Cu(HPAA)(H 2 O) 2 . Removal of lattice water from 1D [Cu(HPAA)(H 2 O) 2 ] 3 H 2 O yields 1D Cu(HPAA)(H 2 O) 2 and results in alterations in hydrogen bonding interactions (chain 333 H 2 O 333 chain), and, in turn, compaction of the chains as well as “slipping”. These changes are accompanied by creation of a new hydrogen bonding scheme (chain 333 chain) involving the phosphonate groups and the hydroxyl/carboxy moieties. The initial zigzag 1D chain is retained throughout the dehydration process. In 3D Cu(HPAA) the resulting vacant sites on Cu (generated by removal of both Cu- bound waters) are occupied by phosphonate oxygens from neighboring chains. All three materials have been characterized by X- ray diffraction and a variety of other techniques and their structures have been determined. Introduction Research in supramolecular chemistry and crystal engineer- ing has been advanced thanks to the availability of a plethora of suitable multifunctional ligands. 1 Predominant among these are carboxylate-, 2 (imid- or pyr-)azole-, 3 polypyridyl-, 4 and organoborate 5 based ligands. In particular, materials that contain polyphosphonate building blocks have been investi- gated intensely for some time now. 6 Part of these investigations concern bifunctional carboxyphosphonate ligands, in which phosphonate and carboxylate moieties are present in the same ligand backbone. 7 Examples of such “mixed” phosphonate/ carboxylate ligands are shown schematically in Scheme 1. Topotactic transformations among crystalline inorganic- organic coordination polymers and other complexes have been demonstrated for a number of systems. 8 For example, two compounds, CoCl 2 (1,4-dioxane)(H 2 O) 2 and CoCl 2 (1,4-diox- ane), undergo a crystal-to-crystal transformation from one- dimensional (1D) chains in the former into a three-dimensional (3D) diamondoid network in the latter accompanied by a drastic change in magnetic properties. 8a Reversible crystal-to- crystal cross-linking of a ribbon of Co-citrate cubanes to form a two-dimensional (2D) net were reported. 8b Reversible crystal- to-crystal dehydration accompanied by channel formation was reported for calixarene-based architectures. 8c Another reversi- ble crystal-to-crystal transformation from achiral hexanuclear clusters [{Fe III (Tp)(CN) 3 } 4 {Fe II (MeCN)(H 2 O) 2 } 2 ] 3 10H 2 O 3 2MeCN (1) (Tp = hydrotris(pyrazoly)borate) to a chiral 1D double zigzag chain via generation/cleavage of coordination bonds was reported and involves the reversible change in magnetization between antiferromagnetic in a zero-dimen- sional (0D) cluster and ferrimagnetic in a 1D chain. 8d Framework interconversions and topotactic transforma- tions are much less known in metal phosphonate chemistry. 9 Some notable examples follow. Depending on the acidity of the reaction medium, Ba(HOOCC 6 H 4 PO 3 H) 2 can be con- verted to Ba 3 (OOCC 6 H 4 PO 3 ) 2 3 2H 2 O and vice versa. As an intermediate in these reactions, BaH(OOCC 6 H 4 PO 3 ) is for- med. 9a Similar interconversion chemistry was reported for the Sr 2þ analogue. 9b Our research groups have recently reported a reversible dehydration/hydration process and ammonia up- take in a calcium tetraphosphonate 2D layered hybrid. 10 Metal phosphonate materials that contain either metal- bound or interstitial water molecules are ideal candidates for dehydration-induced framework transformations. A prere- quisite, however, is that after the dehydration step no frame- work collapse ensues. Thermogravimetry is a useful technique in assaying the stability of the framework after the loss of volatile molecules. Hence, in this report we demonstrate a dehydration-induced topotactic transformation of a hydrated [Cu(HPAA)(H 2 O) 2 ] 3 H 2 O 1D hybrid (HPAA = HO 3 PCH- (OH)CO 2 , hydroxyphosphonoacetate dianion) to an anhy- drous Cu(HPAA) 3D framework, via the 1D intermediate Cu(HPAA)(H 2 O) 2 . All these materials have been character- ized by X-ray diffraction and a variety of other techniques and their structures have been determined. Experimental Section The designation Cu-L-x-y-nD is followed throughout the manu- script, where L is the ligand dianion HPAA 2- , x is the number of copper-bound water molecules, y is the number of lattice water molecules, and n is the dimensionality of the framework. Thus, for the three compounds discussed herein, the following designation is used: CuðHPAAÞðH 2 OÞ 2  3 H 2 O Cu-L-2-1-1D ½CuðHPAAÞðH 2 OÞ 2  Cu-L-2-0-1D ½CuðHPAAÞ Cu-L-0-0-3D Synthetic Details. Compound Cu-L-2-1-1D was prepared accord- ing to a recently published procedure. 11 Compound Cu-L-2-0-1D *Corresponding authors. E-mail: demadis@chemisry.uoc.gr (K.D.D.); g_aranda@uma.es (M.A.G.A.).