Slow relaxation of the magnetization observed in an antiferromagnetically ordered phase for SCM-based two-dimensional layered compounds.

Two-dimensional layered compounds with different counteranions, [{Mn(salen)} ₄ C6](BF ₄ ) ₂ ·2(CH ₃ OH) (1) and [{Mn(salen)} ₄ C6](PF ₆ ) ₂ ·2(CH ₃ OH) (2) (salen ^2- = N,N'-bis(salicylideneiminato), C6 ^2- = C ₆ H ₁₂ (COO) ₂ ^2- ), were synthesized by assembling [Mn(salen)(H ₂ O)]X (X ^- = BF ₄ ^- and PF ₆ ^- ) and C ₆ H ₁₂ (CO ₂ ^- ) ₂ (C6 ^2- ) in a methanol/2-propanol medium. The compounds have similar structures, which are composed of Mn(salen) out-of-plane dimers bridged by μ ⁴ -type C6 ^2- ions, forming a brick-wall-type network of [-{Mn ₂ }-OCO-] chains alternately connected via C ₆ H ₁₂ linkers of C6 ^2- moieties. The counteranions for 1 and 2, i.e., BF ₄ ^- and PF ₆ ^- , respectively, are located between layers. Since the size of BF ₄ ^- is smaller than that of PF ₆ ^- , intra-layer inter-chain and inter-plane nearest-neighbor MnMn distances are shorter in 1 than in 2. The zigzag chain moiety of [-{Mn ₂ }-OCO-] leads to a canted S = 2 spin arrangement with ferromagnetic coupling in the Mn ^III out-of-plane dimer moiety and antiferromagnetic coupling through -OCO- bridges. Due to strong uniaxial anisotropy of the Mn ^III ion, the [-{Mn ₂ }-OCO-] chains could behave as a single-chain magnet (SCM), which exhibits slow relaxation of magnetization at low temperatures. Nevertheless, these compounds fall into an antiferromagnetic ground state at higher temperatures of T _N = 4.6 and 3.8 K for 1 and 2, respectively, than active temperatures for SCM behavior. The spin flip field at 1.8 K is 2.7 and 1.8 kOe for 1 and 2, respectively, which is attributed to the inter-chain interactions tuned by the size of the counteranions. The relaxation times of magnetization become longer at the boundary between the antiferromagnetic phase and the paramagnetic phase.