A Unique Discrete Tetranuclear Cu′–Cu(N-N)2Cu–Cu′ Copper(II) Complex, Built from a μ3‑1,2,4-Triazolato-μ-carboxylato Ligand, as an Effective DNA Cleavage Agent

The title compound, characterized by means of an X-ray structure analysis, represents an easy example of a noncatena “1 + 2 + 1” tetranuclear copper­(II) μ3-triazolate compound. [Cu4(atc)2(dien)4(ClO4)2]­(ClO4)2·2H2O (1), where H2atc = 5-amino-l,2,4-triazole-3-carboxylic acid and dien = diethylenetriamine = 1,4,7-triazaheptane, contains two copper atoms linked by a double diazinic bridge, each of which is further connected to a third and fourth copper atom (Cu′) through the triply bridging triazolato ring and the bidentate carboxylato group of the atc2– ligands. The copper–copper distances within the tetranuclear unit are Cu–Cu = 4.059 Å, Cu–Cu′ = 5.686 and 6.370 Å, and Cu′–Cu′ = 11.373 Å. The compound self-assembles into a tridimensional hydrogen-bonded network to generate a MOF. 1 exhibits antiferromagnetic behavior with g = 2.10(1), J = −34.1(2) cm–1 and j = −5.50(3) cm–1, where J is the coupling constant of the central Cu–Cu pair and j the coupling constant of the two Cu–Cu′ (Cucentral–Cupheripheral) pairs, as defined by H = −J S2S2a – j (S1S2 + S2aS1a). Complex 1 has been tested as nuclease mimic. It shows good binding propensity to calf thymus DNA, with a binding constant value of 6.20 × 106 M–1 (Kapp) and ΔTm = 18.3 °C. Moreover, the compound displays efficient oxidative cleavage of pUC18 DNA, even at low concentration, in the presence of a mild reducing agent (ascorbate), with a rate constant for the conversion of supercoiled to nicked DNA (kobs) of ∼0.126 min–1. The good reactivity of 1 toward DNA is explained from the electrostatic interactions of the cationic species produced in solution.