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

Abstract

Two-dimensional layered compounds with different counteranions, [{Mn(salen)}4C6](BF4)2·2(CH3OH) (1) and [{Mn(salen)}4C6](PF6)2·2(CH3OH) (2) (salen2- = N,N'-bis(salicylideneiminato), C62- = C6H12(COO)22-), were synthesized by assembling [Mn(salen)(H2O)]X (X- = BF4- and PF6-) and C6H12(CO2-)2 (C62-) in a methanol/2-propanol medium. The compounds have similar structures, which are composed of Mn(salen) out-of-plane dimers bridged by μ4-type C62- ions, forming a brick-wall-type network of [-{Mn2}-OCO-] chains alternately connected via C6H12 linkers of C62- moieties. The counteranions for 1 and 2, i.e., BF4- and PF6-, respectively, are located between layers. Since the size of BF4- is smaller than that of PF6-, intra-layer inter-chain and inter-plane nearest-neighbor MnMn distances are shorter in 1 than in 2. The zigzag chain moiety of [-{Mn2}-OCO-] leads to a canted S = 2 spin arrangement with ferromagnetic coupling in the MnIII out-of-plane dimer moiety and antiferromagnetic coupling through -OCO- bridges. Due to strong uniaxial anisotropy of the MnIII ion, the [-{Mn2}-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 TN = 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.