COMMUNICATION www.rsc.org/dalton | Dalton Transactions Spin canting in an unprecedented three-dimensional pyrophosphate- and 2,2¢-bipyrimidine-bridged cobalt(II) framework† Nadia Marino, a Teresa F. Mastropietro, a Donatella Armentano, a Giovanni De Munno,* a Robert P. Doyle, b Francesc Lloret c and Miguel Julve* c Received 29th July 2008, Accepted 5th August 2008 First published as an Advance Article on the web 30th August 2008 DOI: 10.1039/b813097n The three-dimensional cobalt(II) compound of formula {[Co 2 (P 2 O 7 )(bpym) 2 ]·12H 2 O} n , where the pyrophosphate and 2,2¢-bipyrimidine act as bridging ligands, is a new example of a spin-canted antiferromagnet with T c = 19 K. The design and synthesis of porous metal–organic frameworks (MOFs) has attracted great attention in recent years. 1 The interest in such systems arises from the intriguing and versatile character of their architecture and their useful and promising properties for the construction of functional materials. 2 One of the most efficient synthetic routes to prepare novel porous MOFs with unique structures and properties consists of exploiting the self-assembling properties of appropriate metal ions with multifunctional bridging ligands. In recent studies, some of us have focused on the pyrophos- phate anion (P 2 O 7 4- ) as a ligand with the aim of investigating its ability to mediate electronic interactions between the magnetic centers when acting as a bridge. In spite of the biological relevance of pyrophosphate 3 and the large number of thorough studies concerning phosphate metabolism by the metal ions, 3c,4 crystal structures of pyrophosphate-containing coordination compounds are still rare. 5 This paucity of structural data on pyrophosphate- bridged complexes is due to several factors, the main ones being the easy hydrolysis it undergoes 6 and its high negative charge. These features make the current investigation of its coordination chem- istry more appealing. A recent search (August 2008) in the Cam- bridge Crystallographic Database shows that the structural reports on pyrophosphate-containing complexes deal only with low- dimensional compounds. Among these, a mononuclear copper(II) species, 5c homodinuclear copper(II), 5d cobalt(II), 5a manganese(II) and nickel(II) 5b compounds and tetranuclear vanadium(IV) and zinc(II) 5c complexes, where the metal ions are partially blocked with chelating ligands, have been recently described. Aiming at enriching this family with higher dimensionality species with interesting magnetic properties, we used the neutral 2,2¢-bipyrimidine molecule (bpym) as coligand thinking of its well-known ability to behave as a bridging ligand and to mediate magnetic interactions between the paramagnetic centers it links. 7 a Dipartimento di Chimica, Universit` a della Calabria, via P. Bucci 14/c, 87036, Rende, Cosenza, Italy. E-mail: demunno@unical.it b Department of Chemistry, Syracuse University, Syracuse, New York, 13244- 4100, USA c Departament de Qu´ ımica Inorg` anica/Instituto de Ciencia Molecular (IC- Mol), Universitat de Val` encia, Pol´ ıgono La Coma s/n, 46980, Paterna, Val` encia, Spain. E-mail: miguel.julve@uv.es †Electronic supplementary information (ESI) available: Details of the crystallography for 1, Fig. S1–S3 and Table S1. CCDC reference number 689770. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b813097n Herein we report the synthesis,‡ X-ray analysis at low temperature§ and preliminary magnetic study¶ of the first ex- ample of a covalently-bonded, three-dimensional pyrophosphate- bridged complex of formula {[Co 2 (P 2 O 7 )(bpym) 2 ]·12H 2 O} n (1), which behaves as a spin-canted antiferromagnet with T c = 19 K. Compound 1 is made of a neutral three-dimensional pyrophosphate- and bpym-bridged cobalt(II) network (Fig. 1) and crystallization water molecules. Its structure shows a mo- tif analogous to that found in the anionic oxo- or hydroxo- and oxalate-bridged iron(III) [Fe 2 (m-ox) 2 Cl 2 (m-O)] n 2n- or [Fe 2 (m- ox) 2 Cl 2 (m-OH)] n n- open frameworks, 8 where the bpym group plays the role of the bridging oxalate and the pyrophosphate replaces both the oxo/hydroxo bridge and the terminal chlorine atom. Fig. 1 A view of a fragment of the 3D network of compound 1 along the diagonal of the crystallographic a and b axes. The hydrogen atoms on the bpym ligand and the crystallization water molecules have been omitted for clarity. Each cobalt atom exhibits a distorted octahedral environment, being bonded to four nitrogen atoms of two cis crystallographic non-equivalent bpym groups and two oxygen atoms of the pyrophosphate anion (Fig. 2). One of the two bpym molecules is disordered. A reasonable model for this disorder was found by identifying two ligand positions (see ESI†). Consequently, the metal centers occupy symmetrically equivalent positions but their chemical environments somewhat vary (Table S1†) in a statistical way. The values of the Co–N [ranging from 2.115(6) to 2.194(4) A ˚ ] and Co–O [mean value 2.048(2) A ˚ ] bond lengths and those of the metal–metal separation through the pyrophosphate bridge [5.335(2) A ˚ ] and the bis-bidentate bpym [average value 5.777(2) A ˚ ] in 1 are in agreement with those reported in the literature for other bpym- 7b–e and pyrophosphate-bridged 5a cobalt(II) complexes. 5152 | Dalton Trans., 2008, 5152–5154 This journal is © The Royal Society of Chemistry 2008 Published on 30 August 2008. Downloaded by CNR on 26/01/2015 12:11:02. View Article Online / Journal Homepage / Table of Contents for this issue