Two-dimensional networks based on Mn4 complex linked by dicyanamide anion:: From single-molecule magnet to classical magnet behavior

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: [Mn-4(hmp)(4)(Hpdm)(2)-(dcn)(2)](ClO4)(2)(.)2H(2)O(.)2MeCN (2), [Mn-4(hmp)(4)Br-2(OMe)(2)(dcn)(2)](.)0.5H(2)O(.)2THF (3), [Mn-4(hmp)(6)(dcn)(2)](ClO4)(2) (4), where Hhmp and H(2)pdm are 2-hydroxymethylpyridine and pyridine-2,6-dimethanol, respectively. The [Mn-4]/dcn(-) system appears very versatile, but enables its chemistry to be rationalized by a fine-tune of the synthetic conditions. The double cuboidal [Mn-4] 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, [Mn-4(hmp)(6)(NO3)(2)(dcn)(2)](.)2MeCN (1), 2D networks (2, 3, and 4), and the previously reported 3D compound, [Mn-4(hmp)(4)(mu(3)-OH)(2)][Mn-II(dcn)(6)](.)2MeCN(.)THF. Direct current magnetic measurements show that both Mn2+ Mn3+ and Mn3+-Mn3+ intra-[Mn-4] 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 [Mn-4] 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.