BRITT COTTINGHAM RESUME

Paper Preparation and crystal structure of the oxalato-bridged Cr III –Ag I two-dimensional compound {Ag 3 (H 2 O)[Cr(dpa)(ox) 2 ] 3 } n ? 2nH 2 O (dpa ~ 2,2’-dipyridylamine) Consuelo Yuste Vivas, a Fernando S. Delgado, b Catalina Ruiz-Pe ´rez b and Miguel Julve* a a Departament de Quı ´mica Inorga `nica/Institut de Cie `ncia Molecular, Facultat de Quı ´mica, Universitat de Vale `ncia, 46100 Burjassot, Vale `ncia, Spain. E-mail: [email protected]; Fax: 134 963544322 b Laboratorio de Rayos X y Materiales Moleculares, Departamento de Fı ´sica Fundamental II, Universidad de La Laguna, Avda. Astrofı ´sico Francisco Sa ńchez s/n, 38206 La Laguna, Tenerife, Spain Received 13th November 2003, Accepted 24th December 2003 First published as an Advance Article on the web 13th January 2004 The reaction of the mononuclear complex [Cr(dpa)(ox) 2 ] 2 (dpa ~ 2,2-dipyridylamine) with Ag 1 in aqueous solution affords the two-dimensional compound {Ag 3 (H 2 O)[Cr(dpa)(ox) 2 ] 3 } n ?2nH 2 O(1) whose structure has been determined by single-crystal X-ray diffraction. Six crystallographically independent metal atoms (three chromium and three silver atoms) occur in 1. The three [Cr(dpa)(ox) 2 ] 2 units in 1 act as ligands towards the silver atoms through the two oxalate groups. Each oxalate group acts as bridging ligand adopting five coordination modes: bis-bidentate, bis-bidentate/monodentate (outer), bis-bidentate/monodentate (inner), bidentate/bis-monodentate (outer) and bidentate/monodentate (outer). The use of the [Cr(AA)(ox) 2 ] 2 (AA ~ bidentate nitrogen donor) building block in the design of heterometallic species of different dimensionalities is discussed in the light of the available structural results. Introduction The tris-chelated species [Cr(ox) 3 ] 32 (ox ~ oxalate dianion) is one of the best examples of illustrating the richness of the synthetic strategy of heterometallic species which is based on the use of complexes as ligands (the so-called building block approach). Taking advantage of its stability and inertness together with its high negative charge and the presence of six oxalate–oxygen donors, oxalate-bridged heterometallic two- 1–11 and three-dimensional 12–15 (nD) anionic networks were obtained by several research groups in the last decade. Curiously, their dimensionality is dependent on the nature of the countercation which is indeed the templating agent of the overall structure. So, honeycomb 2D structures of formula Cat[M II M III (ox) 3 ] result when Cat 1 is either an organic countercation of the type XR 4 1 (X ~ N, P; R ~ aryl, alkyl) 1b,2,3a,4,5,7b,8,11a or an organometallic decamethylmetallo- cenium unit [A(Cp*) 2 ] 1 (A ~ Fe, Co; Cp* ~ pentamethylcy- clopentadienyl), 7a–c,11b whereas the tris-chelated [B(bpy) 3 ] 21 complex (bpy ~ 2,2’-bipyridine) affords chiral anionic 3D networks of formulae [M II 2 (ox) 3 ] 2 , [M I M III (ox) 3 ] 2 and [M II - M III (ox) 3 ] 2 . 11a,12–14,15a These nD systems are examples of polyfunctional molecular-based materials which in addition to their interesting magnetic properties, 1–3,5–15 can exhibit elec- trical conductivity, 7d predesigned chirality 11,15 and non-linear optical activity. 9 In an attempt to design lower dimensionality oxalato- bridged heterometallic complexes, the [Cr(ox) 3 ] 32 precursor was transformed into the [Cr(AA)(ox) 2 ] 2 species (AA ~ bidentate nitrogen donor) which is still anionic but having only two terminally bound oxalate ligands. Its reaction with fully solvated metal ions or preformed complexes which are coordinatively unsaturated, has provided quite a large family of new oxalato-bridged heterometallic species. 16–19 The bimetallic layered compound of formula {Ag 3 (H 2 O)[Cr(dpa)(ox) 2 ] 3 } n ? 2nH 2 O(1) is one of them and its preparation, and spectroscopic and structural characterization are presented here. A thorough discussion of the different new topologies of the reported heterometallic assemblies obtained using the [Cr(AA)(ox) 2 ] 2 precursor [AA ~ 2,2’-bipyridine (bpy), 2,2’-bipyrimidine (bpym), 1,10-phenanthroline (phen) and 2,2’-dipyridylamine (dpa)] 16–19 as a ligand is carried out. Experimental Materials and methods Lithium and silver perchlorates were purchased from commer- cial sources and used as received. PPh 4 [Cr(dpa)(ox) 2 ]?H 2 O was prepared as reported elsewhere. 19 Elemental analyses (C, H, N) were carried out using an EA 1108 CHNS-O elemental analyzer. IR spectrum of 1 (4000–400 cm 21 ) was recorded on a Nicolet Avatar 360 FT-IR spectrometer with the sample prepared as a KBr pellet. Synthesis {Ag 3 (H 2 O)[Cr(dpa)(ox) 2 ] 3 } n ?2nH 2 O(1). LiClO 4 (1 mmol) was added to an aqueous suspension (20 cm 3 ) of stoichiometric amounts of PPh 4 [Cr(dpa)(ox) 2 ]?H 2 O (0.25 mmol) and AgClO 4 (0.25 mmol). After two hours under continuous stirring at room temperature, the white solid of PPh 4 ClO 4 formed was filtered off and discarded. Slow evaporation of the remaining purple solution in the darkness yielded single crystals of 1 as deep red cubes. Anal. Calcd. for C 42 H 33 N 9 O 27 Cr 3 Ag 3 : C, 32.02; H, 2.11; N, 8.00. Found: C, 31.90; H, 1.85; N, 7.92. Selected IR data (KBr/cm 21 ): 3250 m (N–H stretching), 1710 s, DOI: 10.1039/b314686c CrystEngComm, 2004, 6(4), 11–18 11 This journal is # The Royal Society of Chemistry 2004

BRITT COTTINGHAM RESUME

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