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The tetranuclear iron(III) compounds [Fe4(μ3-O)2(μ-LZ)4] (1–3) were obtained by reaction of FeCl3 with the shortened salen-type N2O2 tetradentate Schiff bases N,N'-bis(salicylidene)-o-Z-phenylmethanediamine H2LZ (Z = NO2, Cl and OMe, respectively), where the one-carbon bridge between the two iminic nitrogen donor atoms guide preferentially to the formation of oligonuclear species, and the ortho position of the substituent Z on the central phenyl ring selectively drives towards Fe4 bis-oxido clusters. All compounds show a flat almost-symmetric butterfly-like conformation of the {Fe4(μ3-O)2} core, surrounded by the four Schiff base ligands, as depicted by both the X-ray molecular structures of 1 and 2 and the optimized geometries of all derivatives as obtained by UM06/6-311G(d) DFT calculations. The strength of the antiferromagnetic exchange coupling constants between the iron(III) ions varies among the three derivatives, despite their magnetic cores remain structurally almost unvaried, as well as the coordination of the metal ions, with a distorted octahedral environment for the two-body iron ions, Feb, and a pentacoordination with trigonal bipyramidal geometry for the two-wing iron ions, Few. The different magnetic behavior within the series of examined compounds may be ascribed to the influence of the electronic features of Z on the electron density distribution (EDD) of the central {Fe4(μ3-O)2} core, substantiated by a Quantum Theory of Atoms In Molecules (QTAIM) topological analysis of the EDD, as obtained by UM06 calculations 1–3. [ABSTRACT FROM AUTHOR]

In continuation of our work on supramolecular architectures of single-molecule magnets (SMMs) as a promising strategy in developing their magnetic performance, in this paper we report the synthesis and single crystal X-ray structure of the centered triangular tetrairon(III) SMM, [Fe4(PhpPy)2(dpm)6], Fe4 (Hdpm = dipivaloylmethane, H3PhpPy = 2-(hydroxymethyl)- 2-(4-(pyridine-4-yl)phenyl)propane-1,3-diol), and its assembly in the coordination polymer {[Fe4(PhpPy)2(dpm)6Ag](ClO4)}n, Fe4Ag, upon reaction with silver(I) perchlorate. Thanks to the presence of the pyridyl rings on the two tripodal ligands, Fe4 behaves as divergent ditopic linker, and due to the Fe4:AgClO4 1:1 ratio, Fe4Ag probably possesses a linear arrangement in which silver(I) ions are linearly coordinated by two nitrogen atoms, forming 1D chains whose positive charge is balanced by the perchlorate anions. The stabilization of such a polymeric structure can be ascribed to the long distance between the two donor nitrogen atoms (23.4 Å) and their donor power. Fe4Ag shows slow relaxation of the magnetization which follows a thermally activated process with Ueff/kB = 11.17(18) K, τ0 = 2.24(17) 10-7 s in zero field, and Ueff/kB = 14.49(5) K, t0 = 3.88(8) 10-7 s in 1-kOe applied field, in line with what reported for tetrairon(III) SMMs acting as building blocks in polymeric structures. [ABSTRACT FROM AUTHOR]

The trinuclear copper(II) compounds [Cu 3 (μ 3 -OH)( G L1) 3 ](ClO 4 ) 2 ( 1 – 4 ) and [Cu 3 (μ 3 -OH)( G L2) 3 ](ClO 4 ) 2 ( 5 – 8 ) with tridentate NNO Schiff base ligands G L1 − and G L2 − derived from 5-G-substituted salicylaldehydes (G = NO 2 , Br, H, Me) and the diamines 1,2-ethanediamine and 1,3-propanediamine, respectively, were investigated aiming at shedding light on possible magneto-structural correlation in this class of complexes. All derivatives contain [Cu 3 (μ 3 -OH)(L) 3 ] 2+ cations with partial cubane Cu 3 O 4 cores, and the metal ions are linked together in a pyramidal fashion by a triple-bridging hydroxido group, giving rise to propellers with three [Cu(L)] + blades. In these spin-frustrated magnetic systems, the three copper(II) ions within a cluster communicate anti-ferromagnetically (−2 J Ŝ i · Ŝ j convention) through the bridging OH group with coupling constants J ranging from −4.5(1) for 4 (G = Me) to −10.1(1) cm −1 for 1 (G = NO 2 ), and stabilization of the doublet S  = 1/2 ground state. The structural features of the complexes reveal very minimal deviations upon variation of G or the diamine flexibility along the whole series of compounds, preserving almost constant magnetic cores. Similar conclusions are also drawn by DFT gas-phase geometry optimizations of the [Cu 3 (μ 3 -OH)(L) 3 ] 2+ cations. Therefore, confident of excluding structural influences on the magnetic super-exchange path, the modulating factor of J in our derivatives can be sought after the different electronic demand of G. Atomic NBO charges support this point, revealing small but systematic variations in the electron density flow along the blades and the positive charge on copper(II) ions with the electronic nature of G, with the most remarkable effect given by the nitro group. Topological analysis of electron density according to the Quantum Theory of Atoms In Molecules further support the distinguishing role of this group with respect to the other substituents taken into consideration, besides providing indirect information about the super-exchange path. [ABSTRACT FROM AUTHOR]

Fluorinated tetrairon(III) Single-Molecule Magnets (SMMs) [Fe 4 (L 1 ) 2 (dpmF 6 ) 6 ] ( 1dpmF 6 ), [Fe 4 (L 2 ) 2 (dpmF 6 ) 6 ] ( 2dpmF 6 ), and [Fe 4 (L 2 ) 2 (pta) 6 ] ( 2pta ) were assembled combining the tripodal ligands H 3 L 1 = 2-hydroxymethyl-2-phenylpropane-1,3-diol and H 3 L 2 = S -5-hydroxy-4,4-bis(hydroxymethyl)pentyl ethanethioate with fluorinated β -diketones analogues of dipivaloylmethane (Hdpm), namely 1,1,1-trifluoro-2,6,6-trimethyl-2-(trifluoromethyl)heptane-3,5-dione (HdpmF 6 ) and pivaloyltrifluoroacetone (Hpta). The new compounds, along with [Fe 4 (L 1 ) 2 (dpm) 6 ] ( 1dpm ) and [Fe 4 (L 1 ) 2 (pta) 6 ] ( 1pta ), were designed in order to investigate the effect of fluorination degree on processability by thermal sublimation. The two different functional groups on the tripodal ligands, i.e. C 6 H 5 in H 3 L 1 and (CH 2 ) 3 SAc in H 3 L 2 , are suitable for promoting physisorption and chemisorption on surfaces, respectively. Direct current magnetic data are typical for the metal-centred triangular topology of Fe 4 complexes, with antiferromagnetic nearest-neighbour coupling constants in the range 16–18 cm −1 and an S = 5 ground spin state. Alternating current susceptibility measurements showed that slow magnetic relaxation persists in fluorinated compounds. When heated in high vacuum (10 −7 mbar), 2dpmF 6 and 2pta undergo thermal decomposition before subliming, while 1dpmF 6 was found to sublimate at 497 ± 5 K in the same conditions, being the third sublimable SMM of this family after 1pta (440 ± 5 K) and 1dpm (500 ± 10 K). [ABSTRACT FROM AUTHOR]

A 3D metal-organic framework (MOF) having single-molecule magnet (SMM) linkers was prepared in crystalline form by using a tetrairon(III) complex functionalised with two divergent pyridyl groups, namely [Fe4(pPy)2(dpm)6] ( 1; H3pPy=2-(hydroxymethyl)-2-(pyridin-4-yl)propane-1,3-diol, Hdpm=dipivaloylmethane). Reaction of 1 with silver(I) perchlorate afforded {[Fe4(pPy)2(dpm)6]2Ag}ClO4 ( 2), which crystallises in a cubic face-centred lattice and exhibits two interlocked diamondoid networks. In 2, the SMMs act as linear ditopic synthons, and silver(I) ions as tetrahedral nodes coordinated by four pyridyl nitrogen atoms. The magnetic properties of 1 ( S=5 and D≈−0.4 cm−1 in the ground spin state) are largely preserved in 2, which shows slow magnetic relaxation with an anisotropy barrier of Ueff/ kB=11.46(10) K in zero field and 14.25(8) K in an applied field of 1 kOe. However, crystal symmetry triggers highly noncollinear magnetic anisotropy contributions oriented at 109.47° from each other along the threefold axes of AgN4 tetrahedra, a unique scenario fully confirmed by a single-crystal cantilever torque magnetometry investigation. Magnetisation curves down to 0.03 K demonstrated the occurrence of a wide hysteresis loop when the magnetic field was swept along one of the four Ag−N bonds. By symmetry, the crystalline compound can then be persistently magnetised parallel or antiparallel to the four main diagonals of the unit cell, although the crystals have no overall second-order anisotropy. [ABSTRACT FROM AUTHOR]

Tetrairon(III) single-molecule magnets [Fe4(pPy)2(dpm)6] ( 1) (H3pPy=2-(hydroxymethyl)-2-(pyridin-4-yl)propane-1,3-diol, Hdpm=dipivaloylmethane) have been deliberately organized into supramolecular chains by reaction with RuIIRuII or RuIIRuIII paddlewheel complexes. The products [Fe4(pPy)2(dpm)6][Ru2(OAc)4](BF4)x with x=0 ( 2 a) or x=1 ( 2 b) differ in the electron count on the paramagnetic diruthenium bridges and display hysteresis loops of substantially different shape. Owing to their large easy-plane anisotropy, the s=1 diruthenium(II,II) units in 2 a act as effective seff=0 spins and lead to negligible intrachain communication. By contrast, the mixed-valent bridges ( s=3/2, seff=1/2) in 2 b introduce a significant exchange bias, with concomitant enhancement of the remnant magnetization. Our results suggest the possibility to use electron transfer to tune intermolecular communication in redox-responsive arrays of SMMs. [ABSTRACT FROM AUTHOR]

Abstract: The formation and the magnetic properties of the copper(II) compounds [Cu(L1)(py)](ClO4) (1a) and [Cu(L2)(py)](ClO4) (2a), bearing the NNO tridentate Schiff base ligand L1− =(E)-2-((3-aminoethylimino)methyl)phenolate or L2− =(E)-2-((3-aminopropylimino)methyl)phenolate (obtained by monocondensation of salicylaldehyde, salH, and ethylenediamine, en, or 1,3-propylenediamine, tn, respectively) and pyridine (py) are presented. These complexes are converted into new mono-, di- and trinuclear derivatives, whose nature depends on the length of the diamine used and hence on the size of the corresponding metallacycle. Pyridine can be substituted by a molecule of N,N-dimethylformamide (DMF) in compound 2a, leading to the mononuclear [Cu(L2)(dmf)](ClO4) (2b), while 1a undergoes only decomposition under similar conditions. Pyrazine does not act as bridging ligand between two copper centres by substitution of py, but its reaction with 2a yields either the dinuclear compound [Cu2(L2)2(ClO4)2] (2c), with exclusion of pyridine, or the trinuclear [Cu3(L2)3(μ3-OH)](ClO4)2 (2d), where pyrazine acts as base generating OH−, and it does not appear in the product. Reaction of 1a with pyrazine yields only the trinuclear [Cu3(L1)3(μ3-OH)](ClO4)2 (1d). Also with 2,2′-bipyridine (2,2′-bpy) dinuclear complexes are not formed, but bpy acts as bidentate ligand to copper yielding the pentacoordinated mononuclear compounds [Cu(L1)(2,2′-bpy)](ClO4) (1e) and [Cu(L2)(2,2′-bpy)](ClO4) (2e). The crystal structures of compounds 2b, 2c and 1e have been solved and are reported. The magnetic susceptibilities χ M(T) of 1a and 2a have been studied, showing the absence of any measurable Cu–Cu interaction for 1a (en, five-membered ring), while a weak but interesting intermolecular Cu–Cu ferromagnetic coupling (J =+0.96(3)cm−1) through the short dimeric Cu···O contacts is detected for 2a (tn, six-membered ring). The X-band EPR spectrum of 2a in a frozen methanol solution at 70K shows the hyperfine coupling of mononuclear copper with the three coordinated 14N atoms, yielding seven narrow lines. [Copyright &y& Elsevier]

The reactivity of the shortened salen-type ligands H3salmp, H2salmen and H2sal(p-X)ben with variable para-substituent on the central aromatic ring (X = tBu, Me, H, F, Cl, CF3, NO2) towards the trivalent metal ions manganese(III) and iron(III) is presented. The selective formation of the dinuclear complexes [M2(μ-salmp)2], M = Mn (1a), Fe (2a), [M2(μ-salmen)2(μ-OR)2)], R = Et, Me, H and M = Mn (3a–c) or Fe (4a–c), and (M2(μ-sal[p-X]ben)2(μ-OMe)2), X = tBu, Me, H, F, Cl, CF3, NO2 and M = Mn (5a–g) or Fe (6a–g), could be identified by reaction of the Schiff bases with metal salts and the base NEt3, and their characterization through elemental analysis, infrared spectroscopy, mass spectrometry and single-crystal X-ray diffraction of 2a·2AcOEt, 2a·2CH3CN and 3c·2DMF was performed. In the case of iron(III) and H3salmp, when using NaOH as a base instead of NEt3, the dinuclear complexes [Fe2(μ-salmp)(μ-OR)(salim)2], R = Me, H (2b,c) could be isolated and spectroscopically characterized, including the crystal structure of 2b·1.5H2O, which showed that rupture of one salmp3− to two coordinated salim− ligands and release of one salH molecule occurred. The same hydrolytic tendency could be identified with sal(p-X)ben ligands in the case of iron(III) also by using NEt3 or upon standing in solution, while manganese(III) did not promote such a C–N bond breakage. Cyclic voltammetry studies were performed for 3b, 4b, 5a and 6a, revealing that the iron(III) complexes can be irreversibly reduced to the mixed-valence FeIIFeIII and FeII2 dinuclear species, while the manganese(III) derivatives can be reversibly oxidized to either the mixed-valence MnIIIMnIV or to the MnIV2 dinuclear species. The super-exchange interaction between the metal centers, mediated by the bridging ligands, resulted in being antiferromagnetic (AFM) for the selected dinuclear compounds 3b, 4b, 5a, 5e,5f, 6a and 6e. The coupling constants J (–2JŜ1·Ŝ2 formalism) had values around −13 cm−1 for manganese(III) compounds, among the largest AFM coupling constants reported so far for dinuclear MnIII2 derivatives, while values between −3 and −10 cm−1 were obtained for iron(III) compounds. [ABSTRACT FROM AUTHOR]