Two-Dimensional Networks Based on Mn₄ Complex Linked by Dicyanamide Anion:  From Single-Molecule Magnet to Classical Magnet Behavior

Abstract

Three two-dimensional (2D) network compounds based on Mn(III)/Mn(II) tetranuclear single-molecule magnets (SMMs) connected by dicyanamide (dcn-) linkers have been synthesized: [Mn4(hmp)4(Hpdm)2(dcn)2](ClO4)2 x 2 H2O x 2 MeCN (2), [Mn4(hmp)4Br2(OMe)2(dcn)2] x 0.5 H2O x 2 THF (3), [Mn4(hmp)6(dcn)2](ClO4)2 (4), where Hhmp and H2pdm are 2-hydroxymethylpyridine and pyridine-2,6-dimethanol, respectively. The [Mn4]/dcn- system appears very versatile, but enables its chemistry to be rationalized by a fine-tune of the synthetic conditions. The double cuboidal [Mn4] unit is preserved in the whole family of compounds, despite strong modifications of its Mn(II) coordination sphere. The chemical control of the coordination number of dcn- on the Mn(II) sites has been the key to obtain the following series of compounds: a discrete cluster, [Mn4(hmp)6(NO3)2(dcn)2] x 2 MeCN (1), 2D networks (2, 3, and 4), and the previously reported 3D compound, [Mn4(hmp)4(mu3-OH)2][Mn(II)(dcn)6] x 2 MeCN x THF. Direct current magnetic measurements show that both Mn2+-Mn3+ and Mn3+-Mn3+ intra-[Mn4] magnetic interactions are ferromagnetic leading to an S(T) = 9 ground state for the [Mn4] unit. Despite the very similar 2D lattices in 2-4, the two kinds of orientation of the [Mn4] unit (i.e., angle variations between the two easy axes) lead to different magnetic properties ranging from SMM behavior for 2 and 1 to a long-range canted antiferromagnetic order for 4. Compound 3 is more complicated as the magnetic measurements strongly suggest the presence of a canted antiferromagnetic order below 2.1 K, although the magnetization slow relaxation is simultaneously observed. Heat capacity measurements confirm the long-range magnetic order in 4, while in 3, the critical behavior is frozen by the slow relaxation of the anisotropic [Mn4] units.

Two New Three-Dimensional Pillared-Layer Co(II) and Cu(II) Frameworks Involving a [M2(EO-N3)2] Motif from a Semi-Flexible N-Donor Ligand, 5,5′-Bipyrimidin: Syntheses, Structures and Magnetic Properties

“…Moreover, the distortion of the octahedral Co(II) site might display considerable anisotropy, which also contributes to the spin canting in 1. Some similar results have been reported for other Co(II) compounds [29][30][31][32]. indicative of the spontaneous, ferromagnetic-like magnetization, due to spin canting.…”

“…Moreover, the distortion of the octahedral Co(II) site might display considerable anisotropy, which also contributes to the spin canting in 1. Some similar results have been reported for other Co(II) compounds [29][30][31][32]. To investigate low-temperature magnetic behavior, zero-field-cooled (ZFC) and field-cooled (FC) magnetizations were performed for 1 at 10 Oe in the range of 2.0-40 K ( Figure S5).…”

Magnetic Cluster Excitations

“…At this point a further link between molecular nanomagnets and quantum spin systems emerges, as not only small clusters may be incorporated into the network but also large clusters or molecular nanomagnets, which should be expected to result in an interesting interplay between the complex quantum states realized within a cluster and the complex phases generated in extended lattices. Indeed, the synthesis of extended exchange-coupled networks of, e.g., Cu 3 molecular units or single-molecule magnets have already been reported (Ivanov et al, 2010;Miyasaka et al, 2006;Morimoto et al, 2009). All in all, the competition between the quantum states in a magnetic cluster and the cooperativity introduced through an extended network of inter -cluster interactions should continue to be an attractive playground for research.…”

Synthesis, Crystal Structures, and Magnetic Properties of Ternary M(II)-Dicyanamide-hydroxypyridine Complexes

“…In contrary, under base condition, 2-hydroxypyridinetype ligands, such as hmpH, hepH, and 2,6-pyridinedimethanol, have been found to act as bridging ligands to generate some fascinating polynuclear metal-clusters [79][80][81][82] and the extended 1D or 2D metal cluster-based coordination polymers with dca as bridges in recent years [83][84][85].…”