Octadentate flexible ligands as a platform for a variety of homo and heterometallic complexes containing diphenoxido and phenoxido/azido bridging groups: synthesis, structure and magnetic properties

We have synthesised a family of N5O3 octadentate ligands, H3L1, H3L2 and H3L3, which only differ in the substituent of the salicylaldehyde moiety (H for H3L1; 5-OMe for H3L2 and 5-NO2 for H3L3). These ligands react with CuII, NiII and MnII to produce non-symmetrical dinuclear Cu2, Ni2 and Mn2 species, in which metal ions are connected by a double phenoxide bridging group. Sequential reaction of H3L1 with NiII and azide afforded a heterobridged tetranuclear compound [Ni4(L1)2(μ-N3)(H2O)2]ClO4·3H2O, in which two diphenoxido bridged dinuclear Ni2 units are linked by an end-to-end azido bridging group. The reaction of H3L2 with NiII and subsequently with CuII and azide afforded a heteropentametallic (Ni4Cu) compound in which two diphenoxido bridged dinuclear Ni2 units are linked to the central CuII atom through phenoxido/1,1-azido double bridges. Characterisation was done by spectroscopic, ESI-MS+, analytical techniques including single crystal X-ray structure analyses, and magnetic measurements. The six dinuclear complexes exhibit weak antiferromagnetic (AF) interactions through the double phenoxido bridging group. The Ni4 complex shows weak AF interactions inside the Ni2 dinuclear units and medium to strong AF interactions between these Ni2 units transmitted by the 1,3- azido bridging group. However, the pentanuclear heterometallic complex (Ni4Cu) shows ferromagnetic interactions through all the magnetic pathways.