Strong and Anisotropic Superexchange in the Single-Molecule Magnet (SMM) [(Mn6OsIII)-Os-III](3+): Promoting SMM Behavior through 3d-5d Transition Metal Substitution

Höke V, Stammler A, Bögge H, Schnack J, Glaser T. Strong and Anisotropic Superexchange in the Single-Molecule Magnet (SMM) [(Mn6OsIII)-Os-III](3+): Promoting SMM Behavior through 3d-5d Transition Metal Substitution. Inorganic Chemistry. 2014;53(1):257-268.The reaction of the in situ generated trinuclear triplesalen complex [(talen(t-Bu2))Mn-3(III)(solv)(n)](3+) with (Ph4P)(3)[Os-III(CN)(6)] and NaClO4 center dot H2O affords [(Mn6OsIII)-Os-III] (ClO4)(3) (= [{(talen(t-Bu2))Mn-3(III)}(2){Os-III(CN)(6)}](ClO4)(3)) in the presence of the oxidizing agent [(tacn)(2)Ni-III] (ClO4)(3) (tacn =1,4,7-triazacyclononane), while the reaction of [(talen(t-Bu2))-Mn-3(III)(solv)(n)](3+) with K-4[Os-II(CN)(6)] and NaClO4 center dot H2O yields [(Mn6OsII)-Os-III](ClO4)(2) under an argon atmosphere. The molecular structure of [(Mn6OsIII)-Os-III](3+) as determined by single-crystal X-ray diffraction is closely related to the already published [(Mn6Mc)-M-III](3+) complexes (M-c = Cr-III, Fe-III, Co-III, Mn-III). The half-wave potential of the Os-III/Os-II couple is E-1/2 = 0.07 V vs Fc(+)/Fc. The FT-IR and electronic absorption spectra of [(Mn6OsII)-Os-III](2+) and [(Mn6OsIII)-Os-III](3+) exhibit distinct features of dicationic and tricationic [(Mn6Mc)-M-III](n+) complexes, respectively. The dc magnetic data (mu(eff) vs T, M vs B, and VTVH) of [(Mn6OsII)-Os-III](2+) are successfully simulated by a full-matrix diagonalization of a spin-Hamiltonian including isotropic exchange, zero-field splitting with full consideration of the relative orientation of the D-tensors, and Zeeman interaction, indicating antiferromagnetic Mn-III-Mn-III interactions within the trinuclear triplesalen subunits (J(Mn-Mn)((1)) = -(0.53 +/- 0.01) cm(-1), (H) over cap (ex) = -2 Sigma(i(i)center dot(S) over cap (j)) as well as across the central Os-II ion (J(Mn-Mn)((2,cis)) = -(0.06 +/- 0.01) cm(-1), (J(Mn-Mn)((2,trans)) = -(0.15 +/- 0.01) cm(-1)), while D-Mn = -(3.9 +/- 0.1) cm(-1). The mu(eff) vs T data of [(Mn6OsIII)-Os-III](3+) are excellently reproduced assuming an anisotropic Ising-like Os-III-Mn-III superexchange with a nonzero component J(Os-Mn)((aniso)) = -(11.0 +/- 1.0) cm(-1) along the Os-Mn direction, while J(Mn-Mn) = -(0.9 +/- 0.1) cm(-1) and D-Mn = -(3.0 +/- 1.0) cm(-1). Alternating current measurements indicate a slower relaxation of the magnetization in the SMM [(Mn6OsIII)-Os-III](3+) compared to the 3d analogue [(Mn6FeIII)-Fe-III](3+) due to the stronger and anisotropic M-c-Mn-III exchange interaction

Cyanido-Bridged Fe(III)–Mn(III) Heterobimetallic Materials Built From Mn(III) Schiff Base Complexes and Di- or Tri-Cyanido Fe(III) Precursors

International audienceThe reaction of [Fe(III)L(CN)(3)](-) (L being bpca = bis(2-pyridylcarbonyl)amidate, pcq = 8-(pyridine-2-carboxamido)quinoline) or [Fe(III)(bpb)(CN)(2)](-) (bpb = 1,2-bis(pyridine-2-carboxamido)benzenate) ferric complexes with Mn(III) salen type complexes afforded seven new bimetallic cyanido-bridged Mn(III)-Fe(III) systems: [Fe(pcq)(CN)(3)Mn(saltmen)(CH(3)OH)]*CH(3)OH (1), [Fe(bpca)(CN)(3)Mn(3-MeO-salen)(OH(2))]*CH(3)OH*H(2)O (2), [Fe(bpca)(CN)(3)Mn(salpen)] (3), [Fe(bpca)(CN)(3)Mn(saltmen)] (4), [Fe(bpca)(CN)(3)Mn(5-Me-saltmen)]*2CHCl(3) (5), [Fe(pcq)(CN)(3)Mn(5-Me-saltmen)]*2CH(3)OH*0.75H(2)O (6), and [Fe(bpb)(CN)(2)Mn(saltmen)]*2CH(3)OH (7) (with saltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene)bis(salicylideneiminato) dianion, salpen(2-) = N,N'-propylenebis(salicylideneiminato) dianion, salen(2-) = N,N'-ethylenebis(salicylideneiminato) dianion). Single crystal X-ray diffraction studies were carried out for all these compounds indicating that compounds 1 and 2 are discrete dinuclear [Fe(III)-CN-Mn(III)] complexes while systems 3-7 are heterometallic chains with {-NC-Fe(III)-CN-Mn(III)} repeating units. These chains are connected through π-π and short contact interactions to form extended supramolecular networks. Investigation of the magnetic properties revealed the occurrence of antiferromagnetic Mn(III)***Fe(III) interactions in 1-4 while ferromagnetic Mn(III)***Fe(III) interactions were detected in 5-7. The nature of these Mn(III)***Fe(III) magnetic interactions mediated by a CN bridge appeared to be dependent on the Schiff base substituent. The packing is also strongly affected by the nature of the substituent and the presence of solvent molecules, resulting in additional antiferromagnetic interdinuclear/interchain interactions. Thus the crystal packing and the supramolecular interactions induce different magnetic properties for these systems. The dinuclear complexes 1 and 2, which possess a paramagnetic S(T) = 3/2 ground state, interact antiferromagnetically in their crystal packing. At high temperature, the complexes 3-7 exhibit a one-dimensional magnetic behavior, but at low temperature their magnetic properties are modulated by the supramolecular arrangement: a three-dimensional antiferromagnetic order with a metamagnetic behavior is observed for 3, 4, and 7, and Single-Chain Magnet properties are detected for 5 and 6