Cu 2+ -Induced formation of cage-like compounds containing pyrazole macrocycles Francisco Escartí, a Carlos Miranda, b Laurent Lamarque, b Julio Latorre, a Enrique García-España,* a M. Kumar, b Vicente J. Arán b and Pilar Navarro* b a Departamento de Quimica Inorganica, Universidad de Valencia, c/ Dr. Moliner, 50, 46100-Burjassot Valencia, Spain. E-mail: enrique.garcia-es@uv.es b Instituto de Química Médica, Centro de Química Orgánica Manuel Lora Tamayo, CSIC, Juan de la Cierva 3, 28006 Madrid, Spain. E-mail: iqmnt38@iqm.csic.es Received (in Cambridge, UK) 14th November 2001, Accepted 14th March 2002 First published as an Advance Article on the web 28th March 2002 The crystal structure of the complex [Cu 4 (H 22 L) 2 (H 2 O) 2 - (ClO 4 ) 2 ](ClO 4 ) 2 ·2H 2 O where L is a new pyrazole ligand containing 1,5-diaminopentane spacers represents a new form of obtaining metal ion-induced inorganic–organic cages. The build-up of compounds defining closed cavities plays a crucial role in supramolecular chemistry. 1 Classical approaches for the preparation of cage-type receptors very often involve long and multistep synthetic routes; the preparation of the first cryptands being a paradigm of this point. More recently several other approaches for the obtention of this kind of receptors have been put forward. Of particular relevance are those strategies in which the coordination of a specific substrate either of organic or inorganic nature induce the recognition site of a receptor in a determined shape. Within this approach, the work of Fujita’s group on the Pd 2+ induced-fit of pyridine based molecular host of different architectures and that of the groups of Mingos and Ramón-Vilar on the formation of nickel cages with thiourea type ligands under anion control are of particular relevance to this communication. 2,3 Herewith we communicate on a novel way of organising a cage-like compound taking advantage of the particular charac- teristics of pyrazole as a ligand and the geometrical coordina- tion preferences of Cu 2+ . Recently we have reported on the Cu 2+ complex formation of the 1H-pyrazole polyamine coronand L 1 and of the cage ligand L 2 . 4–6 The first of these receptors L 1 takes up, both in solution and in the solid state, two Cu 2+ metal ions. Its X-ray structure revealed a strongly distorted square pyramidal coordination geometry around each copper centre. The base of the pyramid is comprised of two nitrogen atoms of the two deprotonated pyrazolate moieties and by the two secondary nitrogen atoms closest to them in the chain (see Scheme 1). A central secondary nitrogen atom of the chain occupies the apical position. The binuclear Cu 2+ complex of the cryptand type ligand L 2 displayed similar coordination features. 5 Therefore, with the initial purpose of facilitating the coordinative interactions with axial ligands we proceeded to substitute the diethylenetriamine bridges in L 1 by 1,5-diamino- pentane bridges to obtain receptor L. 7 Interestingly, addition of Cu 2+ to an aqueous solution of L in molar ratio Cu 2+ +L of 2+1 originated a red coloured solution. Room-temperature evaporation of this solution yielded red crystals suitable for X-ray analysis. The crystal structure reveals the Cu 2+ -induced formation of the centrosymmetric cage [Cu 4 (H 22 L) 2 ](H 2 O) 2 (ClO 4 ) 2 ](ClO 4 ) 2 ·2H 2 O. In contrast with L 1 which formed discrete binuclear [Cu 2 (H 22 L 1 )] 2+ species, the molecular features of L favour an arrangement in which two molecules of L are connected together by four Cu 2+ metal ions. Each one of the four metal centres is bound by two secondary nitrogen and two pyrazole nitrogen atoms belonging to different macrocyclic subunits (Scheme 1) forming the base of a strongly distorted square pyramid. All the pyrazole fragments are deprotonated and behave as exobidentate ligands. The Cu–N distances involving the sp 2 pyrazolate nitrogen atoms are slightly shorter (Cu(1)– N(1) 1.91(1) Å, Cu(1)–N(2) 1.898(8) Å and Cu(2)–N(5) 1.925(9) Å, Cu(2)–N(8) 1.876(15) Å) than those involving the nitrogen atoms of the aliphatic bridge (Cu(1)–N(3) 2.07(2) Å, Cu(1)–N4) 2.064(8) Å and Cu(2)–N(6) 2.08(2) Å, Cu(2)–N(7) 2.07(1) Å). The severely distorted axial positions are occupied by an oxygen of a perchlorate anion (Cu(1)–O (4) 2.526(9) Å and by one water molecule (Cu(2)–O(10) 2.51(1) Å). (Fig. 1) The other perchlorate anions in the structure that are acting as counter ions display strong disorder. The Cu(1)–Cu(2) distance of 3.967 Å falls within the range found for related complexes.† 4–6,8 Scheme 1 This journal is © The Royal Society of Chemistry 2002 936 CHEM. COMMUN. , 2002, 936–937 DOI: 10.1039/b110409h