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Chemistry ; 25(64): 14583-14597, 2019 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-31361924


Reactions of [Mn(H2 dapsc)Cl2 ]⋅H2 O (dapsc=2,6- diacetylpyridine bis(semicarbazone)) with K3 [Fe(CN)6 ] and (PPh4 )3 [Fe(CN)6 ] lead to the formation of the chain polymeric complex {[Mn(H2 dapsc)][Fe(CN)6 ][K(H2 O)3.5 ]}n ⋅1.5n H2 O (1) and the discrete pentanuclear complex {[Mn(H2 dapsc)]3 [Fe(CN)6 ]2 (H2 O)2 }⋅4 CH3 OH⋅3.4 H2 O (2), respectively. In the crystal structure of 1 the high-spin [MnII (H2 dapsc)]2+ 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 H2 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 (Ueff /kB ) of 36.0 K with τ0 =2.34×10-11  s for the spin relaxation. Detailed theoretical analysis showed highly anisotropic intra-chain spin coupling between [FeIII (CN)6 ]3- and [MnII (H2 dapsc)]2+ units resulting from orbital degeneracy and unquenched orbital momentum of [FeIII (CN)6 ]3- complexes. The origin of the metamagnetic transition is discussed in terms of strong magnetic anisotropy and weak AF interchain spin coupling.

Inorg Chem ; 56(15): 8926-8943, 2017 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-28686422


Two one-dimensional cyano-bridged coordination polymers, namely, {[MnII(dapsc)][MnIII(CN)6][K(H2O)2.75(MeOH)0.5]}n·0.5n(H2O) (I) and {[MnII(dapsc)][MnIII(CN)6][K(H2O)2(MeOH)2]}n (II), based on alternating high-spin MnII(dapsc) (dapsc = 2,6-diacetylpyridine bis(semicarbazone)) complexes and low-spin orbitally degenerate hexacyanomanganate(III) complexes were synthesized and characterized structurally and magnetically. Static and dynamic magnetic measurements reveal a single-chain magnet (SCM) behavior of I with an energy barrier of Ueff ≈ 40 K. Magnetic properties of I are analyzed in detail in terms of a microscopic theory. It is shown that compound I refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the MnIII-CN-MnII spin coupling resulting from a nonmagnetic singlet ground state of orbitally degenerate complexes [MnIII(CN)6]3-. The prospects of [MnIII(CN)6]3- complex as magnetically anisotropic molecular building block for engineering molecular magnets are critically analyzed.