Antiferromagnetic mixed-valence Cu(I)–Cu(II) two-dimensional coordination polymers constructed by double oximato bridged Cu(II) dimers and Cu^ISCN based one-dimensional anionic chains

Abstract

One dinuclear Cu(II) complex [Cu₂L²₂(EtOH)_0.5(ClO₄)](ClO₄) (1) has been synthesized by reacting an oxime-based tridentate Schiff base ligand, 3-[2-(diethylamino)ethylimino]butan-2-one oxime (HL²), with Cu^II(ClO₄)₂, whereas the reaction of another similar ligand, 3-[2-(dimethylamino)ethylimino]butan-2-one oxime (HL¹) and this ligand (HL²) with Cu^II(ClO₄)₂ in the presence of NaSCN yielded two rare mixed-valence Cu(I)–Cu(II) two-dimensional (2D) coordination polymers, ²∞[{(Cu^II₂L¹₂)}{Cu^I₄(μ_1,3-SCN)₂(μ_1,1,3-SCN)₄}]_n (2) and ²∞[{(Cu^II₂L²₂)}{Cu^I₂(μ_1,3-SCN)₂(μ_1,1,3-SCN)₂}]_n (3), respectively. The presence of SCN– during the synthesis of the complexes induces reduction of a part of the Cu(II) to Cu(I) giving rise to these two novel mixed-valence 2D coordination polymers 2 and 3. All three complexes have been structurally and magnetically characterized. In complex 1, the square pyramidal Cu(II) atoms are joined by the double oximato bridges. On the other hand, the railroad track-like 2D sheet of 2 and stair-like arrangement of the 2D layer of 3 have been constructed by the connection of one-dimensional (1D) anionic chains ([Cu^I₂(SCN)₃]_n^n– in 2 and [Cu^I(SCN)₂]_n^n– in 3) through the cationic oximato bridged dinuclear units ([Cu^II₂L¹₂]²⁺ in 2 and [Cu^II₂L²₂]²⁺ in 3) via the sulfur atom of the thiocyanato ligand. In both complexes, Cu(I) and thiocyanato ligand form 1D infinite chains, but their different stoichiometry and coordination environments around the copper centers result in different structures. Variable-temperature (2–300 K) magnetic susceptibility measurements show that complexes 1–3 exhibit a strong antiferromagnetic interaction between two Cu(II) ions via N,O oximato bridges with J values −549.6, −578.7 and −663.8 cm^–1, respectively.