Syntheses, Structures Tuned by 4,4′-Bipyridine and Magnetic Properties of a Series of Transition Metal Compounds Containing o-Carboxylphenoxyacetate Acid

Abstract

Nine compounds based on o-carboxylphenoxyacetate acid (H2OCPA) ligand: [Cu(OCPA)(4,4′-bipy)0.5]n (1), {[Cu2(OCPA)2(4,4′-bipy)2(H2O)]·H2O}n (2), [Co2(OCPA)2(4,4′-bipy)(H2O)4] (3), {[Co(OCPA)(4,4′-bipy)0.5(H2O)]·H2O}n (4), {[Co(OCPA)(4,4′-bipy)1.5]·0.5H2O}n (5), [Ni2(OCPA)2(4,4′-bipy)(H2O)4] (6), {[Ni(OCPA)(4,4′-bipy)1.5]·2H2O}n (7), {[Zn(OCPA)(4,4′-bipy)0.5(H2O)]·H2O}n (8), and [Mn(OCPA)(H2O)]n (9) (4,4′-bipy = 4,4′-bipyridine) were synthesized by hydrothermal methods. The results of structural analyses reveal that the giant structural divergence of the compounds with same metal ions mainly originated from the different amounts of 4,4′-bipy used in syntheses. For Cu-containing compounds, the structural divergences are from one-dimensional (1D) chain 1 to two-dimensional (2D) network 2; for Co, through binuclear 3 to 1D ladder-like 4, and to another different 1D ladder-like chain 5; for Ni, from binuclear 6 to 1D chain 7. But for Zn and Mn, 1D chain 8 and 2D network 9 are obtained with the presence of excess 4,4′-bipy. Compound 9 crystallizes in chiral space group P21 with a second harmonic generation (SHG) efficiency of 0.8 times that of urea. The magnetic studies show that compounds 1 and 9 have antiferromagnetic coupling between the adjacent metallic ions. Compound 4 is a weak ferromagnet based on antiferromagnetic interaction and spin canting. Both the bifurcation temperature of the field-cooled (FC) and zero-field-cooled (ZFC) and the peaks of the real χM′ and the imaginary χM″ parts of alternating current (AC) magnetic susceptibilities are observed at 2.2 K, indicated that the critical temperature Tc is 2.2 K. A very little hysteresis loop is observed with a small coercive field of 20 Oe.