N-heterocyclic amine-directed structures and properties of two Cu(ii) diphosphonates

Abstract

By introducing the second organic N-heterocyclic ligands 4′-(4-pyridyl)-4,2′:6′,4′′-terpyridine (pyterpy) and 4,4′-bipyridyl (4,4′-bipy), two examples of Cu(II)-diphosphonates, [Cu₃(HL)₂(Hpyterpy)₂]·2H₂O 1 and [Cu₄(HL)₂(4,4′-bipy)(H₂O)₅] 2 based on 1-hydroxyethylidenediphosphonic acid (H₅L = CH₃C(OH)(PO₃H₂)₂), have been hydrothermally obtained and characterized by powder X-ray diffraction, elemental analysis, IR, TG-DSC. The single-crystal X-ray diffractions reveal that compound 1 has a one-dimensional fishbone-like chain constructed by anions [Cu₃(HL)₂²⁻]_n while simultaneously organic cations [Hpyterpy⁺]_n suspending both sides, and compound 2 exhibits two-dimensional inorganic-organic alternate arrangement layer built from 1-D ladder-like inorganic chain with tetranuclear cluster [Cu₄O₁₀] via4,4′-bipy linkage. The results of electrochemical measurements indicate half-wave potential of 1 (E_1/2¹ = 1.01 V) is less than that of 2 (E_1/2² = 1.20 V), indicating a good D-A system in ICT for 1. Moreover fluorescent measurements reveal that emission intensity of 1 centered at 422 nm is larger than that of 2 emitted at 420 nm, caused by intraligand π*–π emission state of organic N-heterocyclic amine (λ_ex = 233 nm). Magnetism data indicate that compound 1 exhibits ferrimagnetic interactions between metal centers, while compound 2 has antiferromagnetic property.