New family of Ln9Mn4 (Ln = Gd, Tb, Dy) and Y9Mn4 clusters from the use of methyl-2-pyridyl-ketone oxime in heterometallic Mn chemistry

Abstract

A new family of [Ln9Mn4O8(OH)4(O2CPh)17(mpko)4] (LnIII = Gd (2), Tb (3), Dy (4); 2MnIII, 2MnIV) clusters and their diamagnetic YIII analog (1) have been obtained from the reaction of Mn(O2CPh)2, LnCl3 or YCl3, methyl-2-pyridyl-ketone oxime (mpkoH), and NMe4OH in a 2:2:2:4 M ratio in MeCN/CH2Cl2 (22:3 mL). The crystal structure of 4·CH2Cl2·8MeCN reveals a very low-symmetry core comprising a [Dy2Mn2O4] cubane sandwiched between a {Dy7MnO4(OH)4} unit and an external Mn atom; alternatively, it can be described as a zig-zag 1-D {MnIVOMnIVO2MnIIIOMnIII}6+ unit sandwiched between Dy5 and Dy4 units. Fitting of the variable-temperature, solid-state dc and ac magnetic susceptibility data on the Mn4 unit of 1 revealed dominant antiferromagnetic (AF) Mn⋯Mn interactions: J1 = −22.5(9) cm−1, J2 = −7.6(5) cm−1, and J3 = +0.30(3) cm−1, with a constant g = 1.97, where J1, J2, and J3 are the J(MnIVMnIV), J(MnIVMnIII), and J(MnIIIMnIII) exchange parameters, respectively. These parameters indicate an S = 4 ground state with ST = 3 and ST = 2 excited states at 2.4 and 4.2 cm−1, respectively, above it. The many non-equivalent Mn∙∙∙Gd interactions in Gd9Mn4 complex 2 were deduced to include both F and AF interactions leading to an S = 18 or 19 ground state. Complexes 3 and 4 exhibited frequency-dependent ac out-of-phase (χ“M) signals below 4 K indicating them to be weak SMMs.