Synthesis, crystal structures and magnetic properties of M(II)Cu(II) chains (M = Mn and Co) with sterically hindered alkyl-substituted phenyloxamate bridging ligands.
A series of neutral oxamato-bridged heterobimetallic chains of general formula [MCu(L(x)2 (S)2] · p S · q H2O [p = 0-1, q = 0-2.5; L1 = N-2,6-dimethylphenyloxamate, S = DMF with M = Mn (1a) and Co (1b); L2 = N-2,6-diethylphenyloxamate, S = DMF with M = Mn (2a) and Co (2b) or S = DMSO with M = Mn (2c) and Co (2 d); L3 = N-2,6-diisopropylphenyloxamate, S = DMF with M = Mn (3a) and Co (3b) or S = DMSO with M = Mn (3c) and Co (3d)] were prepared by treating the corresponding anionic oxamatocopper(II) complexes [Cu(L(x))(2)]2- (x = 1-3) with M(2+) cations (M = Mn and Co) in DMF or DMSO as the solvent. The single-crystal X-ray structures of 2a and 3a reveal the occurrence of well-isolated, zigzag, oxamato-bridged manganese(II)-copper(II) chains. The intrachain Cu···Mn distances across the oxamato bridge are 5.3761(7) and 5.4002(17) Å for 2a and 3a, respectively, whereas the shortest interchain Mn···Mn distances are 9.4475(16) and 8.1649(14) Å for 2a and 3 a, respectively. All of these M(II) Cu(II) chains (M = Mn and Co) exhibit 1D ferrimagnetic behaviour with moderately strong intrachain antiferromagnetic coupling between the square-planar Cu(II) and octahedral high-spin M(II) ions across the oxamato bridge [-J=31.4-35.2 and 33.4-44.8 cm(-1) , respectively; H = ∑(i)-JS(M,i) (S(Cu,i) +S(Cu,i-1))]. Only the Co(II) Cu(II) chains show slow magnetic relaxation effects characteristic of single-chain magnets (SCMs). Analysis of the magnetic relaxation dynamics of 3d shows a thermally activated mechanism (Arrhenius law dependence) with values of the pre-exponential factor (τ(0) = 2.6 × 10(-9) s) and activation energy (E(a) =7.7 cm(-1) ) that are typical of SCMs. In contrast, two relaxation regimes are observed for 2d in different temperature regions (τ(0) = 3.2 × 10(-10) s and E(a) = 24.7 cm(-1) for T < 4.5K and τ(0) = 3.2 × 10(-14) s and E(a) = 37.5 cm(-1) for T>4.5K).
Departament de Química Inorgànica/Instituto de Ciencia Molecular (ICMol), Universitat de València, Paterna, Valencia, 46980 (Spain), Fax: (+34) 963544322.
Jesús
J
Ferrando-Soria
Emilio
E
Pardo
Rafael
R
Ruiz-García
Joan
J
Cano
Francisco
F
Lloret
Miguel
M
Julve
Yves
Y
Journaux
Jorge
J
Pasán
Catalina
C
Ruiz-Pérez