Magneto-structural versatility of copper(ii)-3-phenylpropionate coordination polymers with N-donor coligands

Abstract

A novel series of copper(II) coordination polymers [Cu₂(O₂CC₈H₉)₄(pyz)]_n (1), [Cu₂(O₂CC₈H₉)₄(dps)]_n (2), {[Cu(O₂CC₈H₉)₂(dps)(H₂O)]·H₂O}_n (3), {[NaCu(O₂CC₈H₉)₂(bpm)(NO₃)]·H₂O}_n (4), and [Cu₄(O₂CC₈H₉)₆(OH)₂(bpp)₂]_n (5) [O₂CC₈H₉⁻ = 3-phenylpropionate anion, pyz = pyrazine, dps = di(4-pyridyl)sulfide, bpm = 2,2′-bipyrimidine, and bpp = 1,3-bis(4-pyridyl)propane] have been synthesized and magneto-structurally investigated. Compounds 1 and 2 belong to a large group of copper(II) carboxylates where bis-monodentate pyz (1) and dps (2) ligands connect the paddle-wheel [Cu^II₂(μ-O₂CC₈H₉)₄] units leading to alternating copper(II) chains. The structure of 3 consists of uniform chains of trans-[Cu^II(O₂CC₈H₉)₂] units linked by the bis-monodentate dps ligand. Compound 4 consists of heterobimetallic chains where [Na^I₂Cu^II₂(μ-O₂CC₈H₉)₄(NO₃)₂] units are doubly bridged by bis-bidentate bpm ligands. Compound 5 is also a chain compound whose structure is made up by tetranuclear [Cu^II₄(μ₃-OH)₂(μ-O₂CC₈H₉)₄(O₂CC₈H₉)₂] units which are doubly bridged by bis-monodentate bpp ligands. The magnetic properties were investigated in the temperature range 1.8–300 K. Strong antiferromagnetic interactions across the quadruple syn–syn carboxylate are observed in 1 and 2 [J = −378 (1) and −348 cm⁻¹ (2)] whereas a weak ferromagnetic coupling through the double out-of-plane oxo(carboxylate) bridge occurs in 4 [J = +2.66 cm⁻¹], the spin Hamiltonian being defined as H = −JS₁·S₂ with S₁ = S₂ = S_Cu = 1/2. A quasi Curie law is observed for 3 (θ = −0.36 cm⁻¹), the bis-monodentate dps ligand being a very poor mediator of magnetic interactions. The analysis of the magnetic properties of 5 is quite complex because of the presence of two crystallographically independent tetracopper(II) units with single-μ-hydroxo, di-μ-hydroxo, μ₃-hydroxo and single-μ-hydroxo plus double syn,syn carboxylate bridges in each one. The nature and values of the magnetic couplings for 5 obtained by fitting (intermediate, strong and weak antiferromagnetic interactions for the three former exchange pathways respectively, and intermediate ferromagnetic interactions for the latter one) were substantiated by DFT type calculations.