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Magneto-Structural Correlations: Synthesis of a Family of End-On Azido-Bridged Manganese(II) Dinuclear Compounds with S = 5 Spin Ground State
文摘
The preparation of a series of multidentate pyridyl-imine ligands, L1-L3, and their reactivity with the Mn II/N B>3-system is described (L1 = [N,N-bis(pyridine-2-yl)benzylidene]ethane-1,2-diamine; L2 = [N,N-bis(pyridine-2-yl)benzylidene]propane-1,3-diamine, and L3 = [N,N-bis(pyridine-2-yl)benzylidene]butane-1,4-diamine). Complexescomprising dinuclear end-on bis( -azido)-bridged manganese(II) units of formulas [Mn2(L1)2(N3)4][Mn2(L1)2(N3)2(CH3OH)2](ClO4)2 (two cocrystallized dinuclear units, 1·2), [Mn2(L2)2(N3)2](ClO4)2 (3), and [Mn2(L3)2(N3)2](ClO4)2 (4) havebeen synthesized. The crystal structures of complexes 1-4 as well as their magnetic properties are presented.Each manganese atom of cocrystallized complexes in compound 1·2 is heptacoordinated, displaying Mn-N-Mnangles,  , of 102.53(12) and 101.70(12) and Mn···Mn distances of 3.5091(7) and 3.4680(7) Å. On the otherhand, each manganese center in compounds 3 and 4 is located within an octahedral coordination environment, thecomplexes displaying angles of 104.29(11) and 103.60(18), respectively, and Mn···Mn vectors of 3.5371(7)and 3.5338(10) Å, respectively. Magnetic susceptibility studies revealed the presence of intramolecular ferromagneticsuperexchange, yielding an S = 5 spin ground state in all complexes. Fitting of the experimental data led tocoupling constants, intermolecular exchange values, and g factors (in the J/zJ'/g format) of 0.77 cm-1/0.01 cm-1/2.20 (1·2), 2.04 cm-1/0.01 cm-1/1.99 (3), and 1.75 cm-1/-0.05 cm-1/2.04 (4), respectively (using H = -2JS1S2as the convention for the Heisenberg spin-Hamiltonian). These results are consistent with predictions from recentDFT calculations performed on end-on bis(-N3-)-bridged MnII dinuclear complexes. A plot of experimental J vs ,including data from the only preexisting compound of this kind, reveals a linear relationship, which could be thefirst evidence of a possible magneto-structural correlation between these two parameters. | |
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