Solvent-Induced Syntheses, Crystal Structures, Magnetic Properties, and Single-Crystal-to-Single-Crystal Transformation of Azido-Cu(II) Coordination Polymers with 2-Naphthoic Acid as Co-ligand

Based on the solvent-induced effect, three new azido-copper coordination polymers-[Cu(2-na)(N-3)] (1), [Cu(2-na)(N-3)] (2), and [Cu(2-na)(N-3)(C2H5OH)] (3) (where 2-na = 2-naphthoic acid)-have been successfully prepared. Structure analysis shows that the Cu(II) cations in compounds 1-3 present tetra-, penta-, and hexa-coordination geometries, respectively. Compound 1 is a well-isolated one-dimensional (ID) chain with the EO-azido group, while 2 is an isomer of 1 and exhibits a two-dimensional (2D) layer involving the EE-azido group. Thermodynamically, density functional theory (DFT) calculation reveals that 2 occupies the stable state and I locates in the metastable state. Compound 3 consists of a ID chain with triple bridging mode, which is derived from 1, and undergoes a single-crystal-to-single-crystal transformation by soaking in ethanol solvent; the powdery product of 1, namely 1b, could be yielded after the dealcoholization of compound 3. Magnetic measurements indicate that compounds 1-3 perform strong intrachain ferromagnetic interactions, experiencing long-range magnetic ordering and slow magnetic relaxation. Compound 1 features the metamagnetic behavior with a transition temperature of 15 K, while 2 and 3 display spin glass behavior with the phase transition temperatures of 15 and 12 K, respectively. Magneto-structure relationships are investigated as well.