The first 3D coordination polymer containing a nucleobase as a bridging ligand, [[Cu2(mu-ade)4(H2O)2][Cu(ox)(H2O)]2 x approximately 14H2O]n (1), has been synthesized by reaction of adenine (Hade) with a basic solution of K2[Cu(ox)2] x 2H2O (ox = oxalato dianion). Compound 1 crystallizes in the trigonal space group R3 with a = b = 31.350(1) angstroms, c = 14.285(1) angstroms, V = 12158.7(10) angstroms3, and Z = 9. X-ray analysis shows a covalent 3D network in which the copper(II) centers are bridged by tridentate mu-N3,N7,N9 adeninate ligands. The compound has relatively large, nanometer-sized tubes associated with the self-assembly process directed solely by metal-ligand interactions. The covalent 3D framework remains intact upon removal of the guest water molecules trapped in the nanotubes. Magnetic measurements indicate an overall antiferromagnetic behavior of the compound.

The reaction of nucleobases (adenine or purine) with a metallic salt in the presence of potassium oxalate in an aqueous solution yields one-dimensional complexes of formulas [M(mu-ox)(H(2)O)(pur)](n) (pur = purine, ox = oxalato ligand (2-); M = Cu(II) [1], Co(II) [2], and Zn(II) [3]), [Co(mu-ox)(H(2)O)(pur)(0.76)(ade)(0.24)](n)(4) and ([M(mu-ox)(H(2)O)(ade)].2(ade).(H(2)O))(n) (ade = adenine; M = Co(II) [5] and Zn(II) [6]). Their X-ray single-crystal structures, variable-temperature magnetic measurements, thermal behavior, and FT-IR spectroscopy are reported. The complexes 1-4 crystallize in the monoclinic space group P2(1)/a (No. 14) with similar crystallographic parameters. The compounds 5 and 6 are also isomorphous but crystallize in the triclinic space group P (No. 2). All compounds contain one-dimensional chains in which cis-[M(H(2)O)(L)](2+) units are bridged by bis-bidentate oxalato ligands with M(.)M intrachain distances in the range 5.23-5.57 A. In all cases, the metal atoms are six-coordinated by four oxalato oxygen atoms, one water molecule, and one nitrogen atom from a terminal nucleobase, building distorted octahedral MO(4)O(w)N surroundings. The purine ligand is bound to the metal atom through the most basic imidazole N9 atom in 1-4, whereas in 5 and 6 the minor groove site N3 of the adenine nucleobase is the donor atom. The crystal packing of compounds 5 and 6 shows the presence of uncoordinated adenine and water crystallization molecules. The cohesiveness of the supramolecular 3D structure of the compounds is achieved by means of an extensive network of noncovalent interactions (hydrogen bonds and pi-pi stacking interactions). Variable-temperature magnetic susceptibility measurements of the Cu(II) and Co(II) complexes in the range 2-300 K show the occurrence of antiferromagnetic intrachain interactions.

The synthesis, crystal structure and variable-temperature magnetic measurements of the compounds [Mn(mu-ox)(H2O)(7H-pur-kappaN9)]n (1), {[Mn(mu-ox)(H2O)2].(7H-ade).(H2O)}n (2) and {[Cu(mu-ox)(H2O)(7H-ade-kappaN9)][Cu(mu-ox)(mu-H2O)(7H-ade-kappaN9)]. approximately 10/3H2O}n (3), (where ox: oxalato dianion, pur: purine, and ade: adenine) are reported. Compounds 1and 2 contain one-dimensional chains in which manganese(II) atoms are bridged by bis-bidentate oxalato ligands. The distorted octahedral geometry around each metal centre is completed in compound 1 by one water molecule and the imidazole N9 donor site of the purine ligand, which is a rare example of direct binding between the Mn(II) ion and the N donor site of an isolated nucleobase. Unlike 1, the adenine moiety in compound 2 is not bonded to manganese atoms and the metal coordination polyhedron is filled by two water molecules in a cis-arrangement. Its crystal building is constructed from pi-stacked layers of Watson-Crick hydrogen-bonded adenine...(H2O2)...adenine aggregates and zig-zag Mn(II)-oxalato chains held together by means of a strong network of hydrogen bonding interactions. The nucleobase exists in the lattice as the 7H-adenine tautomer which represents an unprecedented solid-state characterization of this minor tautomer as free molecule (without metal coordination) stabilized through non-covalent interactions. Compound consists of two slightly different [Cu(ox)(H2O)(7H-ade-kappaN9)] units in which the nucleobase coordinates through the imidazole N9 atom. The planar complex entities are parallel stacked and joined by means of long Cu-O bonds involving oxygen atoms from the oxalato and the aqua ligands, giving one-dimensional chains with a [4 + 1] square-planar pyramidal and a [4 + 2] octahedral coordination around the metal centre, respectively. Self-assembled process of compound 3 is further driven by an in-plane network of hydrogen bonding interactions to generate a porous 3D structure containing parallel channels filled by guest water molecules. Variable-temperature magnetic susceptibility measurements of all the complexes show the occurrence of antiferromagnetic interactions between the paramagnetic centres. DFT calculations have been performed to check the influence of packing in the stability of the 7H-amino tautomer of 2 and in the complex geometry of 3.

The compound [Mn(mu-ox)(4atr)2]n (1) (ox = oxalato and 4atr = 4-amine-1,2,4-triazole) has been synthesized and characterized by FT-IR spectroscopy, thermal analysis, variable-temperature magnetic measurements, and X-ray single-crystal diffraction methods. The crystal structure of compound 1 consists of one-dimensional linear chains in which trans-[Mn(4atr)2]2+ units are sequentially bridged by centrosymmetric bis-bidentate oxalato ligands. Cryomagnetic measurements show an overall antiferromagnetic behavior of the compound. Isolated chains of this polymer have been obtained by sonication of 1 in ethanol or treatment of the polymer with NaOH and morphologically characterized on highly oriented pyrolitic graphite and mica surfaces by atomic force microscopy and scanning tunneling microscopy. The procedures employed to obtain single chains of this coordination polymer open a route for future nanotechnological applications of these types of materials.