Hexagonal Co6 and zigzag Co4 cluster based magnetic MOFs with a pcu net for selective catalysis

Abstract

Two hydrophobic 3D cobalt-cluster based magnetic MOFs, [Co₃(pimdc)₂(H₂O)₆]·5H₂O (1) and Co₂(Hpimdc)₂ (2) (H₃pimdc = 2-propyl-imidazole-4,5-dicarboxylic acid), have been hydrothermally synthesized and magnetically characterized. Both of them exhibit a regular pcu net with hexagonal Co₆ and zigzag Co₄ clusters as 6-connected nodes, respectively. The magnetic studies indicate that 1 displays predominant antiferromagnetic interactions within the Co₃(pimdc) triangle, while 2 shows spin-canting antiferromagnetic behaviour with larger canting angles. Furthermore, after heating under vacuum conditions, activated 1 exhibits an excellent catalytic selectivity in the allylic oxidation reaction of cyclohexene to form an α,β-unsaturated ketone, which indicates that the opened Co(II) sites play a significant role in the heterogeneous catalytic process.