Syntheses, Structures, and Magnetic Properties of Three One-Dimensional End-to-End Azide/Cyanate-Bridged Copper(II) Compounds Exhibiting Ferromagnetic Interaction: New Type of Solid State Isomerism

The work in this paper presents the syntheses, structures, and magnetic properties of three end-to-end (EE) azide/cyanate-bridged copper(II) compounds [CuIIL1(μ1,3-NCO)]n·2nH2O (1), [CuIIL1(μ1,3-N3)]n·2nH2O (2), and [CuIIL2(μ1,3-N3)]n (3), where the ligands used to achieve these species, HL1 and HL2, are the tridentate Schiff base ligands obtained from [1 + 1] condensations of salicylaldehyde with 4-(2-aminoethyl)-morpholine and 3-methoxy salicylaldehyde with 1-(2-aminoethyl)-piperidine, respectively. Compounds 1 and 2 crystallize in the monoclinic P21/c space group, while compound 3 crystallizes in the orthorhombic Pbca space group. The metal center in 1–3 is in all cases pentacoordinated. Three coordination positions of the metal center in 1, 2, or 3 are satisfied by the phenoxo oxygen atom, imine nitrogen atom, and morpholine (for 1 and 2) or piperidine (for 3) nitrogen atom of one deprotonated ligand, [L1]− or [L2]−. The remaining two coordination positions are satisfied by two nitrogen atoms of two end-to-end bridging azide ligands for 2 and 3 and one nitrogen atom and one oxygen atom of two end-to-end bridging cyanate ligands for 1. The coordination geometry of the metal ion is distorted square pyramidal in which one EE azide/cyanate occupies the apical position. Variable-temperature (2–300 K) magnetic susceptibilities of 1–3 have been measured under magnetic fields of 0.05 (from 2 to 30 K) and 1.0 T (from 30 to 300 K). The simulation reveals a ferromagnetic interaction in all three compounds with J values of +0.19 ± 0.01, +0.79 ± 0.01, and +1.25 ± 0.007 cm–1 for 1, 2, and 3, respectively. Compound 1 is the sole example of a ferromagnetically coupled EE cyanate-bridged 1-D copper(II) system. In addition, a rare example of supramolecular isomerism and a nice example of magnetic isomerism have been observed and most interestingly a new type of solid state isomerism has emerged as a result of the comparison of the structure and magnetic properties of 2 with a previously published compound (2A) having the same composition and even the same crystal system and space group (New J. Chem. 2001, 25, 1203–1207).