Crystal engineering with a purine rare tautomer: structures and luminescence properties

Abstract

Cadmium, a metal known to be toxic to living systems through unfavorable interactions with biomolecules, interacts with purine nucleobases through N7 imino nitrogen and induces modifications by altering amino–imino tautomeric equilibrium. Herein, we report unique crystallographic signatures of cadmium complexes of N9-benzyl-N⁶-methoxyadenine, a rare imino tautomer of adenine. These complexes exhibit a variety of coordination numbers and spatial geometries, highlighting the ability of nucleobases to form diverse supramolecular architectures, enabling better understanding of metal–DNA interactions. The Cd²⁺ ion in complex 1 has a coordination number of four with a distorted tetrahedral geometry, while 2 and 3 are hexa-coordinated, where 2 displays a discrete distorted octahedron geometry and 3 appears as a dinuclear complex. On the other hand, complex 4 exhibits a less common hepta-coordination mode with a distorted pentagonal bipyramidal geometry. The luminescence properties of these cadmium complexes are also reported.