New copper(II) compound having protonated forms of ethylenediaminetetraacetate(4−) ion (EDTA) and adenine (AdeH): synthesis, crystal structure, molecular recognition and physical properties of (AdeH2)[Cu(HEDTA)(H2O)]·2H2O

The stoichiometric reaction of Cu2CO3(OH)2, ethylenediaminetetraacetic acid (H4EDTA=C2H4(N(CH2CO2H)2)2) and adenine (AdeH) in water yields crystalline samples of adeninium aqua-(ethylenediamine-N,N,N′-triacetato-N′-acetic)copper(II) dihydrate. The compound (AdeH2)[Cu(HEDTA)(H2O)]·2H2O was studied by TG analysis (with FT-IR study of the evolved gasses), IR, electronic and ESR spectra, magnetic susceptibility data, and single crystal X-ray diffraction methods (monoclinic system, space group P21/c (a=7.053(1), b=42.540(5), c=7.798(1) Å, β=104.24(1)°, Z=4, and final R1=0.042 for 5113 independent reflections). The asymmetric unit consists of a salt of adeninium(1+) and the aqua-copper(II) complex of HEDTA3− as chelating agent, and two crystallisation water molecules. The Cu(II) atom exhibits an elongated octahedral coordination (type 4+1+1). The pentadentate HEDTA3− ligand has a typical E,G/R configuration and a free N-carboxymethyl arm. The uncoordinated AdeH2 + ion recognises the anion [Cu(HEDTA)(H2O)]− through two rather linear NH⋯O hydrogen bonds involving the protonated N1 heterocyclic atom and one H atom of the exocyclic-N6 amino group with two O atoms of the same HEDTA3− carboxylate group (173(3) or 175(3)°, and 2.64(1) or 2.80(1) Å, respectively). This ion pair recognises itself by a π,π-stacking between the six-membered aromatic rings of adjacent AdeH2+ ions which lay out slightly slipped (β=γ=10.1°) and anti-parallel at 3.34 Å, thus forming aggregates {(AdeH2)[Cu(HEDTA)(H2O)]}2. The remaining OH (carboxy or water) and NH (heterocyclic or exocyclic) polar bonds interact with O carboxylate or water atoms or N3 and N7 adeninium atoms building the crystal in an extensive 3D-hydrogen bonded network.