Systematic investigations on magneto-structural correlations of copper(ii) coordination polymers based on organic ligands with mixed carboxylic and nitrogen-based moieties

Abstract

Reaction of copper(II) tetrazolate-5-carboxylate with different neutral N-donor spacer ligands under hydrothermal conditions leads to the formation of five new coordination polymers, [Cu(tzc)(pyz)_0.5(H₂O)₂]_n·H₂O (1), [Cu(tzc)(pyz)]_n (2), [Cu(tzc)(pym)(H₂O)]_n (3), [Cu(tzc)(dpe)_0.5(H₂O)]_n (4) and [Cu(tzc)(azpy)_0.5(H₂O)]_n (5) (tzc = tetrazolate-5-carboxylate, pyz = pyrazine, pym = pyrimidine, dpe = 1,2-di(4-pyridyl)ethylene and azpy = 4,4′-azopyridine). All five structures were characterized by X-ray single-crystal measurements and bulk material can be prepared phase pure in high yields. The crystal structures of the hydrates 1, 3, 4 and 5 show dimeric [Cu₂(N_tzc–N_tzc)₂] building units formed by μ₂-N1,O1:N2 bridging tzc ligands as the characteristic structural motif. These six-membered entities in 1, 4 and 5 are connected by μ₂-N,N′ bridging N-donor ligands into 1D chains and in 3 into 2D layers. In the crystal structure of compound 2 adjacent Cu(II) cations are connected by μ₂-N1,O1:N4,O2 bridging tzc ligands into chains, which are further connected by μ₂-N,N′ bridging pyz ligands forming 2D layers. Extensive hydrogen bonds in all compounds play an important role in the construction of their supramolecular networks. Investigations of their thermal properties reveal water release upon heating according to the formation of anhydrates before starting decomposing above 220 °C. Furthermore, the magnetic properties have been studied leading to consistent global antiferromagnetic exchange interactions with coupling constants of J = 3 ± 1 cm⁻¹ and long-range antiferromagnetic ordering states at lower temperatures.