Non-Isotype Crystals of 2,6-Diaminopurinium(1+) Salts with Bis(pyridine-2,6-dicarboxylate)metal(II) anions (M = Co or Cu) M.P. Brandi-Blanco1, D. Choquesillo-Lazarte2, A. Castiñeiras3, J.M. González-Pérez4 and J. Niclós-Gutiérrez4 1
Present address: Technische Universität Dortmund, Fakultät Chemie, Lehrstuhl für Bioanorganische Chemie, Otto-Hahn-Strasse 6, D-44227 Dortmund, Germany.
[email protected] 2 IACT-CSIC, Laboratorio de Estudios Cristalográficos, Edif. Inst. Lopez-Neyra, PTCS. Avda. del Conocimiento, s/n. E-18100 Armilla (Granada), Spain.
[email protected] 3 Department of Inorganic Chemistry, Faculty of Pharmacy, University of Santiago de Compostela, E-15782 Santiago de Compostela, Spain.
[email protected] 4 Department of Inorganic Chemistry, Faculty of Pharmacy, University of Granada, E-18071 Granada, Spain.
[email protected],
[email protected]
Summary Adeninium(1+) ions generate isostructural series of compounds (H2ade)2[MII(pdc)2]·3H2O (M = Mn, Co, Ni, Cu or Zn). Hade+ exists as nearly coplanar pairs of tautomers A:B = H2(N1,N9)ade+: H2(N3,N7)ade+. These base pairs are H-bonded in a ladder (A:B) n . In the crystal of (H2dap)2[CuII(pdc)2]·4H2O the 2,6-diaminopurinium(1+) ions only exist as the tautomer H 2(N3,N7)dap+, but forming two non-equivalent homo-pairs, {H2dap(1)+}2 and {H2dap(2)+}2, both using N1 as acceptor but an N6-H or N2-H bond as H-donor. These homo-pairs alternate in the laddered chains. The crystal of (H2dap)2 [CoII(pdc)2]·6H2O has also the tautomer H2(N3,N7)dap+ forming two non-equivalent homo-pairs, but with or without the mediation of water: {H2dap(1)+}2 and {H2dap(2)+·H2O}2, respectively.
Introduction Salts of metal complexes with cationic forms of organic ligands are a source of structural information of the ‘out-sphere’ interligand interactions. In ©2008 by MEDIMOND S.r.l.
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the salt (H2(N1,N9)ade)[Cu(HEDTA)(H2O)] 2H2O}2 [1, EGOWIG in CSD], derived from ethylenediaminotetraacetic acid (H4EDTA), the H2ade+ and [Cu(HEDTA)(H2O)]- ions recognise each other by two rather linear H-bonding interactions with two O atoms from the same coordinated HEDTA-carboxylate group. Furthermore, in the crystal, pairs ions recognise each other by means of a strong π,π-stacking interaction between H2ade+ cations. These cations also generate isostructural series of salts (H2ade)2[MII(pdc)2]·3H2O (M = Mn, Co, Ni, Cu or Zn) with nearly coplanar pairs of tautomers A:B = H2(N1,N9)ade+:H2(N3,N7)ade+. Moreover, these base pairs build laddered Hbonded chains (A:B)n [2,3]. Increasing the number of exo-cyclic groups, the aim of this work is to extend this research to 2,6-diaminopurinium(1+) salts of [MII(pdc)2]2- (H2pdc = pyridine-2,6-dicarboxylic acid; see Fig. 1).
Materials, methods and supplementary structural information H2pdc, Hdap and M2(CO3)(OH)2 (M = Co, Cu) are commercially available (Aldrich) and were used as received. The novel compounds were prepared by addition of stoichiometric amounts of Hdap (1 mmol) to an aqueous solution of the acid bis-chelates, MII(H2pdc)(pdc), obtained in aqueous solutions by reactions of the basic MII carbonate and H2pdc, respectively. By controlled evaporation of the salts, suitable single crystals of 1 and 2 appeared. X-ray diffraction data were collected with a Bruker X8 Kappa APEXII diffractometer. The structures were solved by direct methods (SHELXS-97) and refined by full-matrix least-squares techniques (SHELXL-97). Both compounds crystallize in triclinic system, space group P-1, final R1 0.061 and 0.049 for 1 and 2, respectively.
Results and discussion The salt (H2dap)2[CuII(pdc)2]·4H2O (1, Fig. 2-A) consists of the anion [Cu(pdc)2]2-, two independent cations H2dap+ and non coordinated water. In
Figure 1. Hdap (with conventional N-numbering notation) and H2pdc.
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Figure 2. A) The asymmetric unit of (H2dap)2[CuII(pdc)2]·4H2O (1). Coordination bond lengths (Å) and trans-angles (º): Cu1-N1 1.919(3), Cu1-N13 1.985(3), Cu1-O4 2.064(3), Cu1-O11 2.088(3), Cu1-O16 2.312(3), Cu1-O23 2.297(3), N1-Cu1-N13 174.9(1), O4-Cu1-O11 157.8(1), O23-Cu1-O16 151.8(1). B) The two independent homo-pairs of cations H2(N3,N7)dap+ nearly perpendicular H-bonded in a fragment of the laddered chain.
the anion the CuII exhibits a 2+2+2 distorted octahedral coordination and the ligand pdc-1 and pdc-2 are not equivalents. The shortest distances are Cu1N1 and Cu1-N13, close to 1.95 Å, but pdc-1 gives Cu-O(carboxyl) distances (~ 2.07 Å) shorter than those of pdc-2 (~2.30 Å). There are many H-bonding interactions. For symmetry reasons, the independent cations build planar homo pairs {H2(N3,N7dap(1)+}2 and {H2(N3,N7)dap(2)+}2. Both pairs use N1 as acceptor but one N6-H or N2-H bond as H-donor. In addition, cations of pairs-1 use the N7-H bonds from each other side to bind N9 atoms of cations of pairs-2, in such a way that both types of homo-pairs are alternated nearly in perpendicular within laddered chains (Fig. 2-B). The planes of two adjacent pair define a dihedral angle of 80.8º (89.4º in the related adeninium(1+) salt [2,3]. In this crystal, there are not relevant π,π-stacking interactions between aromatic rings. The electronic spectrum of 1 shows two bands, at 12440 and 7365 cm-1, the latter more intense. In addition its axial ESR spectrum is of the ‘reverse type’, with g⊥ 2.23 >> g// 2.03 > 2.02. These spectra are related to the above referred distortion in the CuII coordination [2,3]. Data of 1 and 2 have been deposited at the CCDC with CCDC Nos. 696883 and 696884, respectively. The salt (H2dap)2[CoII(pdc)2]·6H2O (2, Fig. 3-A) belong to the same spacial group that 1, but they are not isotype crystals. The CoII atom has a distorted 2+1+2+1 octahedral coordination. In both compounds the cations appertain to the same tautomer H(N3,N7)dap+, which form two different homo-pairs. But in the CoII derivative there is a deeper structural difference (Fig. 3-B and 3C). The centro-symmetric pair {H2(N3,N7dap(1)+}2 (Fig. 3-B) has two sym-
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Figure 3. A) The asymmetric unit of (H2dap)2[CoII(pdc)2]·6H2O (2). Coordination bond lengths (Å) and trans-angles (º): Co1-N1 2.014(2), Co1-N13 2.027(2), Co1-O4 2.164(2), Co1-O11 2.103(2), Co1-O16 2.223(2), Co1-O23 2.162(2), N1-Co1-N13 164.8(1), O11-Co1-O4 149.1(1), O23-Co1-O16 151.(1). B) Homo-pair {H2dap-1}2. C) Homo-pair {(H2O)(H2dap-1}2.
metry related H-bonds, of the type N2-H···N1, whereas the pair {(H2O)·(H2(N3,N7dap(2)+)}2 consist of an H-bonded motif with two H2dap+cations and two water molecules, as is showed in the figure 3-C). The bridging water molecules acts as H-donor and H-acceptor in O-H···N9 and N3-H···O interactions, respectively.
Concluding remark The novel salts (H2dap)2[MII(pdc)2]·nH2O (M= Co, Cu) differ from the isotypical series (H2ade)2[MII(pdc)2]·3H2O in the absence of two distinct tautomers for the cation H2dap+ and in lack of iso-structuralism.
References [1] D. CHOQUESILLO-LAZARTE, M.P. BRANDI-BLANCO, I. GARCÍA-SANTOS, J. M. GONZÁLEZ PÉREZ, A. CASTIÑEIRAS, J. NICLÓS-GUTIÉRREZ, Interligand interactions involved in the molecular recognition between copper(II) complexes and adenine or related purines, Coord. Chem. Rev., 252, 1241-1256, 2008, and references therein. [2] M.P. BRANDI-BLANCO, DOCTORAL THESIS, University of Granada, Department of Inorganic Chemistry (Faculty of Pharmacy), Granada, Spain, 2007.
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Acknowledgements Financial support: Project CTQ2006-15329-C02/BQU (ERDF-EC, MECSpain). MPBB thanks to the ‘Ramón Areces Foundation’ for a postdoctoral grant. DChL thanks CSIC-EU for an I3P postdoctoral research contract. The “Factoría de Cristalización, CONSOLIDER INGENIO-2010” provided X-ray diffraction facilities.
