Synthesis, structure and magnetism of new single molecule magnets composed of MnII2MnIII2 alkoxo-carboxylate bridged clusters capped by triethanolamine ligandsElectronic supplementary information (ESI) available: Detailed magnetisation discussion, Mn bond valence sums (Table S1), H-bonding details (Table S2). See http://www.rsc.org/suppdata/dt/b3/b312672b/

Abstract

A family of tetranuclear mixed-valent Mn(II)(2)/Mn(III)(2) complexes of type [Mn(4)(LH(2))(2)(LH)(2)(H(2)O)(x)(RCO(2))(2)](Y)2.nS has been synthesised and structurally characterised, where LH(3) = triethanolamine (N(CH(2)CH(2)OH)(3)), (R=CH(3), x=2, Y = CH(3)CO(2)-, n=2, S = H(2)O; 1), (R=C(6)H(5), x=0, Y=C(6)H(5)CO(2)-, n=1, S = CH(3)CN; 2), (R=C(2)H(5), x=0, Y=ClO(4)(-), n=0; 3). A common structural core was deduced from X-ray crystallography and consists of a rhomboidal (planar-diamond) array with two 7-coordinate Mn(II) "wingtip (w)" centres and two 6-coordinate Mn(III) "body (b)" centres. The Mn(III) ions are bridged to the Mn(II) ions by mu3-oxygen atoms from a deprotonated alcohol "arm" of each tridentate LH(2-) ligand and by mu2-oxygen atoms from each tetradentate LH(2)(-) ligand. The four nitrogen atoms from LH(2-) and LH(2)(-) groups, together with bridging and terminal carboxylates oxygens complete the outer coordination sites around the Mn atoms. A feature of these clusters is that they are linked together in the crystal lattice by hydrogen-bonding interactions involving a non-coordinated hydroxyl arm on each LH(2-) group. Detailed DC and AC magnetic susceptibility measurements and magnetisation isotherms have been made on the three complexes and show that intra-cluster ferromagnetic coupling is occurring between the S = 2 Mn(III) and S = 5/2 Mn(II) ions to yield S = 9 ground states. The g, J(bb) and J(wb) parameters have been deduced. Inter-cluster antiferromagnetic coupling was noted in and this influences the magnetisation versus field behaviour and the temperature and magnitude of the out-of-phase AC chi"M maxima in comparison to those observed for and. An Arrhenius plot of the reciprocal temperature of the maxima in chi"M obtained at different frequencies (10 to 1500 Hz), in the range 1.75 K to 4 K, against the natural logarithm of the magnetization relaxation rate (1/tau) yielded values of the activation energies and pre-exponential factors for two of these new tetranuclear single-molecule magnets (SMMs), and. The activation energies were compared with the potential energy barrier height, U, for magnetisation direction reversal (U = DS(2)) using the axial zero-field splitting parameter, D, deduced from the DC M/H isotherm analysis for these S = 9 species. The very small separation of S = 9 and 8 levels for these clusters highlights the limitations in the determination of D values from M/H data at low temperatures.

Cyanide Single-Molecule Magnets Exhibiting Solvent Dependent Reversible “On” and “Off” Exchange Bias Behavior

“…Mixed-metal cyanide compounds constitute an excellent platform for studying magnetic bistability in molecules commonly referred to as single-molecule magnets (SMMs), a term that was coined in the mid-1990s to describe molecules that exhibit slow relaxation of their magnetization. − Since the discovery of slow paramagnetic dynamics in [Mn 12 O 12 (O 2 CCH 3 ) 16 (H 2 O) 4 ] (Mn12–Ac), − considerable effort has been directed toward the goal of increasing the intrinsic barrier height for magnetization reversal, U , which is equal to S 2 | D | for integer S values and ( S 2 – 1/4)| D | for half-integer S with D being the axial component of the magnetic anisotropy (considering the following Hamiltonian of anisotropy: H = DS z 2 ). Much of the research in this area has focused on increasing the barrier by preparing molecules with large spin ground states ( S ) but this approach has not led to an appreciable increase in the barrier height of SMMs. − …”

A Large [Mn10Na]4 Loop of Four Linked Mn10 Loops

“…The main reason for this interest is the fact that such molecules can function as magnets below a critical temperature, providing a new “bottom-up” approach to nanoscale magnetic materials . Although there are now many species displaying single-molecule magnet (SMM) behavior, most of them from manganese carboxylate chemistry, 1c− there is a continuing need for new structural types. One of the most successful synthetic approaches to new polynuclear clusters involves the use of chelates containing alcohol groups because alkoxides are good bridging groups and thus favor the formation of polynuclear products. 1b,− Recently, we have been investigating the use of 1,3-propanediol (pdH 2 ) in manganese carboxylate chemistry .…”

“…Although there are now many species displaying single-molecule magnet (SMM) behavior, most of them from manganese carboxylate chemistry, 1c− there is a continuing need for new structural types. One of the most successful synthetic approaches to new polynuclear clusters involves the use of chelates containing alcohol groups because alkoxides are good bridging groups and thus favor the formation of polynuclear products. 1b,− Recently, we have been investigating the use of 1,3-propanediol (pdH 2 ) in manganese carboxylate chemistry . We herein report the synthesis, crystal structure, and magnetic properties of a molecular aggregate that consists of four repeating units of the new [Mn 10 Na(μ 3 -O) 2 (O 2 CMe) 13 (pd) 6 (py) 2 ] ( 1 ) loop linked through the Na + ions.…”

“…This aggregate is not planar but instead folds to give a saddlelike conformation, as shown in Figure b. Note that although there are a few examples of discrete and polymeric aggregates of 3d metal clusters linked through alkali- or alkaline-earth-metal ions with an overall nuclearity >6, none of them has a nuclearity >20. 5a,, It is also interesting that [ 1 ] 4 represents the first example of a loop constructed from smaller loops. The shortest Mn···Mn separation between different Mn 10 units of [ 1 ] 4 is relatively large at 6.382 Å.…”

Synthesis, Crystal Structures, and Magnetic Properties of Mixed-Valent Tetranuclear Complexes with Y-Shaped MnII2MnIII2 Core

“…Specifically, tetranuclear manganese complexes have received considerable interest because the unique tetranuclear manganese cluster structure with calcium ion was found in the PS-II in green plants [9][10][11][12]. Many kinds of tetranuclear Mn II 2 Mn III 2 complexes have appeared in the literature, and butterfly-shaped tetranuclear Mn II 2 Mn III 2 complexes have remarkable magnetic properties with ferromagnetic couplings and SMM behavior [13][14][15]. Based on this background, we have focused on the synthesis of manganese complexes with multidentate organic ligands [16][17][18][19][20][21][22][23][24][25][26][27][28].…”