A tetranuclear complex from the employment of pyridine-2,6-dimethanol in copper(II) nitrate chemistry: Synthetic, structural and magnetic studies

The use of pyridine-2,6-dimethanol (pdmH2) in copper(II) nitrate chemistry is reported. The reaction of Cu(NO3)2·3H2O with one equivalent of pdmH2 in MeCN affords the known mononuclear complex [Cu(pdmH2)2](NO3)2 (1) in high-yield. The reaction of 1 and NaOMe in an 1:1 ratio, as well as the reaction between Cu(NO3)2·3H2O, pdmH2 and NaOMe in an 1:1:1 ratio, in MeOH gives the tetranuclear complex [Cu4(NO3)2(pdmH)4(H2O)(MeOH)](NO3)2 (2) in moderate yields. The cation of 2 possesses a slightly distorted tetrahedral Cu4 topology with a [Cu4(μ2-OR)4]4+ core. The pdmH− ions behave as η1:η1:η2:μ2 ligands. Strong intramolecular hydrogen bonds and π–π stacking interactions provide thermodynamic stability on compound 2. Variable-temperature, solid-state dc magnetic studies were carried out on complex 2 in the 2.0–300 K range. The data indicate predominant antiferromagnetic exchange interactions and a resulting S = 0 ground state, which is expected for a solely, μ2-alkoxide-bridged system with obtuse Cu–O–Cu bond angles that magnetically behaves as a Cu4 ring. A simplified 1 − J model was found to be adequate to describe the variable-temperature dc susceptibility data. The data were fitted to the appropriate equation derived from the Hamiltonian H = −J1(S1 · S2 + S2 · S4 + S3 · S4 + S1 · S3), giving the parameters J1 = −99.5 cm−1 and g = 2.11(4). The combined work demonstrates the ligating flexibility of the pdmH2 chelate and its usefulness in the synthesis of oligo- and polynuclear CuIIx clusters with interesting structural and magnetic properties, without requiring the co-presence of carboxylate ligands.

The copper(II) nitrate/pyridine-2,6-dimethanol reaction system has provided access to a mononuclear CuII complex and an antiferromagnetically-coupled (S = 0) tetranuclear cluster containing the [CuII4(μ2-OR)4]4+ core.Figure optionsDownload as PowerPoint slide