Structural and magnetic investigation of CoII/MnII-based MIL-53 analogues with mixed ligands of neutral N-oxides and organic carboxylates

Abstract

Two Co^II-based MIL-53 analogues Co(PNO)(BDC) (1) and Co(MPNO)(BDC) (2) were synthesized by hydrothermal methods with neutral μ₂-oxo bridging ligands: pyridyl N-oxide (PNO) and 4-methylpyridine N-oxide (MPNO), and 1,4-benzenedicarboxylic acid (H₂BDC). Variable temperature magnetic susceptibility measurements indicate that 1 and 2 show weak ferromagnetism with the critical Néel temperature about 3 K for both 1 and 2, due to spin canting. As isoreticular structures, Co₂(BPNO)(BDC)₂·2DMF (3), Mn(PNO)(BDC) (4) and Mn₂(BPNO)(BDC)₂·2DMF (5) (BPNO = 4,4′-bipyridyl N,N′-dioxide) which were previously reported by us, were also subjected to variable temperature magnetic susceptibility measurements. Their magnetic properties are presented herein, and the magneto-structural correlations are discussed in detail. The systemic magnetic investigation of this series of Co^II/Mn^II-based MIL-53 analogues showed that the existence of solely higher symmetric trans-CoO^B₄O^N₂ is the main factor for 1 and 2 showing spin canting behavior.