Experimental and Theoretical Studies on the Magnetic Properties of Manganese(II) Compounds with Mixed Isocyanate and Carboxylate Bridges

Two manganese(II) isocyanate complexes with different flexible zwitterionic dicarboxylate ligands, [Mn 2 (bcpp)(NCO) 4 ] n ( 1 ; bcpp=1,3‐bis( N ‐carboxylatomethyl‐4‐pyridinio)propane) and [Mn 2 (bcp)(NCO) 4 ] n ( 2 ; bcp=bis( N ‐carboxylatomethyl)‐4,4′‐bipyridinium, have been synthesized and characterized by X‐ray crystallography and magnetic measurements. Both compounds consist of two‐dimensional coordination layers in which uniform anionic chains with mixed (NCO) 2 (COO) triple bridges are cross‐linked by flexible cationic 4,4′‐trimethylenedipyridinium spacers. Magnetic studies revealed antiferromagnetic interactions through the triple bridges ( J =−8.0 cm −1 ( 1 ) and J =−8.6 cm −1 ( 2 )), which are stronger than those in the isoelectronic analogue (N 3 ) 2 (COO). To complement the experimental data, periodic and finite‐cluster DFT and CASPT2 calculations were performed on the dimeric units of the (NCO) 2 (COO) and (N 3 ) 2 (COO) mixed‐bridged systems to support the Heisenberg picture and stress the relative efficiency of the magnetic couplers. It was found that the isocyanate ligand plays a greater role in the conveyance of antiferromagnetic behavior than the azide counterpart, and that both pseudohalide bridges function cooperatively with the carboxylate group.