Copper(ii) assembling with bis(2-pyridylcarbonyl)amidate and N,N′-2,2-phenylenebis(oxamate)

Abstract

We herein present the synthesis and X-ray structures of five copper(II) complexes of formulae [Cu(bpca)(CF₃SO₃)(H₂O)]·H₂O (1), [Cu(bpca)(Phpr)(H₂O)]·3/2H₂O (2), {[Cu(bpca)]₂[Cu(opba)(H₂O)]}·H₂O (3), {[Cu(bpca)]₂(H₂opba)}₂·6H₂O (4) and [Cu(bpca)(EtH₂opba)]_n (5), where bpca = bis(2-pyridylcarbonyl)amidate, Phpr = 3-phenylpropionate, CF₃SO₃⁻ = triflate (anion of the trifluoromethanesulphonic acid), H₄opba = N,N′-1,2-phenylenebis(oxamic acid), and EtH₃opba = monoethyl ester derivative of the H₄opba. 1 and 2 are mononuclear copper(II) complexes where the copper atom is five-coordinate in distorted square pyramidal surroundings with a tridentate bpca and a water molecule (1)/carboxylate oxygen (2) building the basal plane and a triflate oxygen (1)/water molecule (2) filling the apical position. 3 is a neutral tricopper(II) complex where the [Cu(opba)(H₂O)]²⁻ unit acts as a bis-bidentate ligand toward two peripheral [Cu(bpca)]⁺ fragments. The three crystallographically independent copper(II) ions in 3 are five-coordinate with two nitrogen and two oxygen atoms (inner copper atom)/three bpca-nitrogen and an oxamate oxygen (outer copper atom) building the basal plane plus a water molecule (inner copper)/an oxamate oxygen (outer copper) in the apical position (inner copper atom) of somewhat distorted square pyramidal surroundings. 4 is a centrosymmetric tetracopper(II) compound where four [Cu(bpca)]⁺ fragments are assembled by two H₂opba²⁻ groups adopting an unusual bidentate/bis-monodentate bridging mode. The two crystallographically independent copper(II) ions in 4 are also five-coordinate having the three bpca-nitrogens in basal positions, the other two sites of the distorted square pyramid being filled by two oxygens of either a bidentate oxamate (at one copper centre) or two bis-monodentate oxamates (at the other copper atom). 5 is a zigzag chain of [Cu(bpca)(H₂O)]⁺ units which are connected through the EtH₂opba⁻ ligand adopting a bidentate/monodentate bridging mode across the monodeprotonated oxamate group. Each copper(II) ion in 5 is six-coordinate in an elongated octahedral CuN₃O₃ chromophore. The magnetic properties of 3–5 were investigated in the temperature range 1.9–300 K. 3 exhibits an intermediate intramolecular antiferromagnetic interaction [J = −65.8(2) cm⁻¹ with the Hamiltonian H = −J(S_Cu1·S_Cu2 + S_Cu2·S_Cu3)] which leads to a low-lying spin doublet at low temperatures. A weak antiferromagnetic coupling between the inner copper(II) ions occurs in 4 [J = −2.36(2) cm⁻¹, H = −JS₁·S₂)] and a very small intrachain antiferromagnetic interaction is observed in 5 [J = −0.17(1) cm⁻¹ with H = −J∑_iS_i·S_i+1]. These values are analyzed by means of simple orbital symmetry considerations and compared with those previously reported for parent systems.