Magnetothermal Studies of a Series of Coordination Clusters Built from Ferromagnetically Coupled {Mn^II₄Mn^III₆} Supertetrahedral Units

Abstract

Three high-nuclearity mixed valence manganese(II/III) coordination clusters, have been synthesised, that is, [Mn(III) (6)Mn(II) (4)(μ(3)-O)(4)(HL(1))(6)(μ(3)-N(3))(3)(μ(3)-Br)(Br)](N(3))(0.7)/(Br)(0.3)⋅3 MeCN⋅2 MeOH (1) (H(3)L(1)=3-methylpentan-1,3,5-triol), [Mn(III) (11)Mn(II) (6)(μ(4)-O)(8)(μ(3)-Cl)(4)(μ,μ(3)-O(2)CMe)(2)(μ,μ-L(2))(10)Cl(2.34)(O(2)CMe)(0.66)(py)(3)(MeCN)(2)]⋅7 MeCN (2) (H(2)L(2)=2,2-dimethyl-1,3-propanediol and py is pyridine), and [Mn(III) (12)Mn(II) (7)(μ(4)-O)(8)(μ(3)-η(1)N(3))(8)(HL(3))(12)(MeCN)(6)]Cl(2)⋅10 MeOH ⋅MeCN (3) (H(3)L(3)=2,6-bis(hydroxymethyl)-4-methylphenol) with high ground-spin states, S=22, 28±1, and 83/2, respectively; their magnetothermal properties have been studied. The three compounds are based on a common supertetrahedral building block as seen in the Mn(10) cluster. This fundamental magnetic unit is made up of a tetrahedron of Mn(II) ions with six Mn(III) ions placed midway along each edge giving an inscribed octahedron. Thus, the fundamental building unit as represented by compound 1 can be described as a Mn(10) supertetrahedron. Compounds 2 and 3 correspond to two such units joined by a common edge or vertex, respectively, resulting in Mn(17) and Mn(19) coordination clusters. Magnetothermal studies reveal that all three compounds show interesting long-range magnetic ordering at low temperature, originating from negligible magnetic anisotropy of the compounds; compound 2 shows the largest magnetocaloric effect among the three compounds. This is as expected and can be attributed to the presence of a small magnetic anisotropy, and low-lying excited states in compound 2.

Magnetic “Molecular Oligomers” Based on Decametallic Supertetrahedra: A Giant Mn49 Cuboctahedron and its Mn25Na4 Fragment

“…[7,[22][23][24]29] Complex 1 was also found to behave as aS MM and thus it is the second largest Mn cluster and homometallic SMM reported. [1] It should be pointed out that although compounds containing the [Mn III 6 Mn II 4 (m 4 -O) 4 ] 18+ supertetrahedral core are often found to display entirely ferromagnetic exchange interactions and the maximum possible spin ground states, [19][20][21][22]24] this is not the case for 1 and 2,i nw hich the corresponding maximum values would be,b yf ar, record values of S = 209/2 and 105/2, respectively.O bviously in the case of these two compounds,a part from the exchange interactions within the decametallic supertetrahedral core which are expected to be ferromagnetic,t here are also additional couplings between the neighboring M 10 repeating units,s ome of which are antiferromagnetic.F or this reason, although predominant ferromagnetic behavior was realized for both complexes,t he spin ground states observed are significantly lower than the maximum possible values.H owever,t hese magnetic systems have the potential to display larger S values if some of the antiferromagnetic interactions are switched to ferromagnetic ones by synthesizing analogues of 1 and 2 with slightly different structural parameters,such as bond lengths and angles and peripheral ligation, as was accomplished in the past for other magnetic systems. [29] These compounds are also the first molecular species containing more than two repeating decametallic supertetrahedra and their cores are related to each other and also to that of the Mn 17 "dimeric" analogues consisting of two edge-sharing decametallic supertetrahedra.…”

“…One ideal structural type to act as abuilding block in high nuclearity clusters is the [Mn III 6 Mn II 4 (m 4 -O) 4 ] 18+ supertetrahedral core which combines ab eautiful, high symmetry (T d ) metal topology and interesting magnetic properties. [19] In addition, it has been stabilized in discrete form with several ligands [19][20][21] and under various reaction conditions,a nd has appeared as the repeating unit in zero-dimensional Mn 17 [22,23] and Mn 19 [24] clusters and in the giant Mn 36 Ni 4 "loop-of-loops and supertetrahedra" aggregate, [12] , with that of 1 describing an "A rchimedean solid" called ac uboctahedron. Additionally,t he compounds are structurally related, with the core of 2 being almost identical to afragment of that of 1.Magnetism studies revealed the existence of dominant ferromagnetic exchange interactions in both 1 and 2 leading to ground-state spin values of 61/2 and 51/2, respectively.I na ddition, the magnetocaloric effect for both complexes is seen to develop over as ignificantly wide temperature range.F inally,c ompound 1 displays single-molecule magnet (SMM) behavior and is the second largest homometallic 3d SMM reported to date.…”

“…Thea symmetric unit of 1 [25] consists of two independent quarters of the Mn 49 cation (Figure 1a 4 ] 18+ supertetrahedral core, [19][20][21][22][23][24] whereas the m 3 -MeO À ligands bridge three Mn 3+ ions.T he peripheral ligation is completed by 24 fully deprotonated hp 2À ligands connecting two Mn 2+ and one Mn 3+ ions in a h 2 :h 2 -m 3 mode,s ix severely disordered HCO 2 À ligands bridging exclusively Mn 3+ ions, and 12 terminal DMF molecules bound to the 12 outer Mn 2+ ions.…”

Recent Progress in the Realm of Homonuclear Ln6 Single molecule magnets: Structural Overview and Synthetic Approaches

“…Typically, the first category is represented by symmetric arrangement of the six metal centers to construct a metallic wheel/ring, while the other category is typified by the relatively more familiar combinations of interconnected triangles. Rather than distinguishing these SMM materials based on the symmetry-aspect, it seems more judicious to divide the entire regime of the reported hexanuclear SMMs into two more general broad classifications: First class being the homonuclear Ln 6 series where the metal centers are solely 4f-elements, whereas the second class comprises of the heteronuclear entities composed of both 3d-and 4f-metal centers (Randell et al, 2013;Boskovic et al, 2002;Brechin et al, 2002;King et al, 2004;Zheng et al, 2007;Manoli et al, 2007;Feng et al, 2010;Stamatatos et al, 2011;Nayak et al, 2010;Kotzabasaki et al, 2011;Yang et al, 2011;Costa et al, 2012;Charalambous et al, 2012;Chakraborty et al, 2012;Mukherjee et al, 2014). Hereafter, our discussion will revolve around the first class only.…”

Two cyanide-bridged compounds composed of Schiff base–manganese(III) building block with dicyanamido and hexacyanocobaltate(III) as ligands: Crystal structure, thermostability and magnetic property

“…Up to now, remarkable progress has been achieved on this field, serving as the typical example of lots of relevant one-dimensional (1D) transition-metal compounds with fascinating molecular structures and magnetisms [16][17][18][19]. The magnetic properties of chain-like compounds largely depend on intrachain interaction which is effectively effected by short bridged ligands such as cyano, azido, hydroxyl, carboxyl and thiocyanate because of these ligands provide unique feature for transmitting magnetic coupling between adjacent spin centers [20,21].…”