Synthesis, X-ray characterization and density functional theory studies of N<SUP>6</SUP>-benzyl-N<SUP>6</SUP>-methyladenine-M(II) complexes (M=Zn, Cd): The prominent role of -, C-H••• and anion- interactions

We report the synthesis and X-ray characterization of the N-6-benzyl-N-6-methyladenine ligand (L) and three metal complexes, namely [Zn(HL)Cl-3]H2O (1), [Cd(HL)(2)Cl-4] (2) and [H2L](2)[Cd-3(-L)(2)(-Cl)(4)Cl-6]3H(2)O (3). Complex 1 consists of the 7H-adenine tautomer protonated at N3 and coordinated to a tetrahedral Zn(II) metal centre through N9. The octahedral Cd(II) in complex 2 is N-9-coordinated to two N-6-benzyl-N-6-methyladeninium ligands (7H-tautomer protonated at N3) that occupy apical positions and four chlorido ligands form the basal plane. Compound 3 corresponds to a trinuclear Cd(II) complex, where the central Cd atom is six-coordinated to two bridging -L and four bridging -Cl ligands. The other two Cd atoms are six-coordinated to three terminal chlorido ligands, to two bridging -Cl ligands and to the bridging -L through N3. Essentially, the coordination patterns, degree of protonation and tautomeric forms of the nucleobase dominate the solid-state architectures of 1-3. Additionally, the hydrogen-bonding interactions produced by the endocyclic N atoms and NH groups stabilize high-dimensional-order supramolecular assemblies. Moreover, energetically strong anion- and lone pair (lp)- interactions are important in constructing the final solid-state architectures in 1-3. We have studied the non-covalent interactions energetically using density functional theory calculations and rationalized the interactions using molecular electrostatic potential surfaces and Bader's theory of atoms in molecules. We have particularly analysed cooperative lp- and anion- interactions in 1 and (+)-(+) interactions in 3.