Zn(II) and Cd(II) complexes with 3-furoic acid. Exploring the role ofC–H⋅⋅⋅O interactions

Abstract

Hydrogen bond interactions implying C–H groups and O atoms either from carboxylate, carbonyl, or ether functionalities have been demonstrated to play a pivotal role in the packing of crystal structures. To analyze and compare their significance in metal carboxylate complexes with pyridine derivatives (dPy), we have synthesized four Zn(II) and Cd(II) compounds containing 3-furoic acid (3-FA) and two different pyridine ligands (isonicotinamide, isn; and 4-acetylpyridine, 4-acpy) affording two isostructural dimeric complexes [Zn(μ-3-FA)(3-FA)(isn)2]2 (<strong>1</strong>) and [Cd(μ-3-FA)(3-FA)(isn)2]2 (<strong>2</strong>), one dimeric paddle-wheel [Zn(μ-3-FA)2(4-acpy)]2 (<strong>3</strong>), and one monomer [Cd(3-FA)2(4-acpy)2(OH2)] (<strong>4</strong>). Their crystal structures have been elucidated and studied in detail, showing variable coordination modes of the 3-FA ligand and different coordination numbers. The C–H⋅⋅⋅O interactions analysis of the four complexes in combination with their previously reported analogs with 2-furoic (2-FA) and piperonylic (HPip) acids, highlights the importance of such associations in the final crystal arrangement benefitting from cooperative effects. Finally, the photophysical properties in MeOH solution of <strong>1–4</strong> have been analyzed and their quantum yields calculated and compared.