Slow Magnetic Relaxation, Antiferromagnetic Ordering, and Metamagnetism in Mn (H dapsc)-Fe (CN) Chain Complex with Highly Anisotropic Fe-CN-Mn Spin Coupling.

Reactions of [Mn(H dapsc)Cl ]⋅H O (dapsc=2,6- diacetylpyridine bis(semicarbazone)) with K [Fe(CN) ] and (PPh ) [Fe(CN) ] lead to the formation of the chain polymeric complex {[Mn(H dapsc)][Fe(CN) ][K(H O) ]} ⋅1.5n H O (1) and the discrete pentanuclear complex {[Mn(H dapsc)] [Fe(CN) ] (H O) }⋅4 CH OH⋅3.4 H O (2), respectively. In the crystal structure of 1 the high-spin [Mn (H dapsc)] cations and low-spin hexacyanoferrate(III) anions are assembled into alternating heterometallic cyano-bridged chains. The K ions are located between the chains and are coordinated by oxygen atoms of the H dapsc ligand and water molecules. The magnetic structure of 1 is built from ferrimagnetic chains, which are antiferromagnetically coupled. The complex exhibits metamagnetism and frequency-dependent ac magnetic susceptibility, indicating single-chain magnetic behavior with a Mydosh-parameter φ=0.12 and an effective energy barrier (U /k ) of 36.0 K with τ =2.34×10  s for the spin relaxation. Detailed theoretical analysis showed highly anisotropic intra-chain spin coupling between [Fe (CN) ] and [Mn (H dapsc)] units resulting from orbital degeneracy and unquenched orbital momentum of [Fe (CN) ] complexes. The origin of the metamagnetic transition is discussed in terms of strong magnetic anisotropy and weak AF interchain spin coupling.