Syntheses, crystal structures and magnetic properties of three bis(end-on azide) bridged dicopper(II) complexes derived from half-condensed ligands: Observation of the smallest Cu–azide–Cu bridge angle in dinuclear systems

The work in this paper presents the syntheses, characterization, crystal structures and magnetic properties of bis(end-on azide) bridged dicopper(II) complexes [CuIIL1(μ1,1-N3)] (1), [CuIIL2(μ1,1-N3)] (2) and [CuIIL3(μ1,1-N3)]·MeOH (3), where HL1, HL2 and HL3 are half-condensed ligands produced from, respectively, 3-ethoxysalicylaldehyde and ethylenediamine, salicylaldehyde and trans-1,2-diaminocyclohexane, and 3-methoxysalicylaldehyde and trans-1,2-diaminocyclohexane. While compound 1 crystallizes in the monoclinic crystal system and P21/c space group, the crystal system and space group for 2 and 3 are triclinic and P1¯. There are two independent units, Unit-I and Unit-II, in 3. Each metal center in 1–3 is pentacoordinated and adopts a distorted square pyramidal coordination geometry. Each of the two bridging azide nitrogen atoms occupies an equatorial position of one copper(II) center, but the axial position of the second metal center. The Cu–N3–Cu bridge angle in 1, 2 and Unit-II of 3 lie in the range 87.8–90.8°, while Unit-I in 3 displays a Cu–N3–Cu angle of 84.3°, which is the smallest bridge angle observed so far in end-on azide bridged dicopper(II) systems. Variable-temperature (2–300 K) magnetic studies reveal weak antiferromagnetic interactions in 1–3 with J values (H = −JS1S2) of −10.16, −4.18 and −1.43 cm–1, respectively.

Graphical abstractThree bis(μ1,1-) dicopper(II) complexes derived from [1+1] condensed ligands containing salicylaldehyde/3-methoxysalicylaldehyde/3-ethoxysalicylaldehyde and ethylenediamine/trans-1,2-diaminocyclohexane are described. In one case, interestingly, the Cu–azide–Cu bridge angle is 84.3°, the smallest observed so far in dinuclear systems.Figure optionsDownload full-size imageDownload as PowerPoint slide