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, [Mn2(bcpp)(NCO)4]n (1; bcpp=1,3-bis(N-carboxylatomethyl-4-pyridinio)propane) and [Mn2(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 (N3)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 (N3)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.