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 ( 1 a ) and Co ( 1 b ); L²=N‐2,6‐diethylphenyloxamate, S=DMF with M=Mn ( 2 a ) and Co ( 2 b ) or S=DMSO with M=Mn ( 2 c ) and Co ( 2 d ); L³=N‐2,6‐diisopropylphenyloxamate, S=DMF with M=Mn ( 3 a ) and Co ( 3 b ) or S=DMSO with M=Mn ( 3 c ) and Co ( 3 d )] were prepared by treating the corresponding anionic oxamatocopper(II) complexes [Cu(L^x)₂]^2? (x=1–3) with M²⁺ cations (M=Mn and Co) in DMF or DMSO as the solvent. The single‐crystal X‐ray structures of 2 a and 3 a 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 2 a and 3 a , respectively, whereas the shortest interchain Mn ??? Mn distances are 9.4475(16) and 8.1649(14) Å for 2 a and 3 a , respectively. All of these M^IICu^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?J S _M,i( S _Cu,i+ S _Cu,i?1)]. Only the Co^IICu^II chains show slow magnetic relaxation effects characteristic of single‐chain magnets (SCMs). Analysis of the magnetic relaxation dynamics of 3 d shows a thermally activated mechanism (Arrhenius law dependence) with values of the pre‐exponential factor (τ₀=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 2 d in different temperature regions (τ₀=3.2×10^?10 s and E_a=24.7 cm^?1 for T<4.5 K and τ₀=3.2×10^?14 s and E_a=37.5 cm^?1 for T>4.5 K).