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Two lanthanide single-molecule magnets (SMMs) [Dy3(μ3-OH)(HL-1)3(H2O)3](NO3)2·3H3O (1, H3L-1 = (E)-3-(((8-hydroxyquinolin-2-yl)methylene)amino)propane-1,2-diol) and [Dy6(μ3-OH)4(H2L-2)4(HL-2)2(L-2)2] (2, H3L-2 = (E)-2-hydroxy-N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide) were synthesized and characterized structurally and magnetically. Complex 1 contains a triangular Dy3 core in which the three Dy3+ ions share a μ3-OH− anion and the deprotonated ligands of (HL-1)2− serve both capping and bridging functions, while 2 displays a centrosymmetric hexanuclear DyIII structure with two similar Dy3 triangular cores ligated by two fully deprotonated (L-2)3− ligands, each of which shares two μ3-OH− anions. All the DyIII ions are eight-coordinated with quasi D2d or C2v symmetry. Magnetic studies reveal that 1 exhibited two-step magnetic relaxation under an applied dc field of 800 Oe, with effective energy barriers of 40.1 and 31.0 K for the slow relaxation (SR) and fast relaxation regimes (FR), respectively. Meanwhile, 2 only showed a tail of slow magnetic relaxation at above 2 K. Ab initio calculations have been carried out to show the nature of their different magnetic properties. [ABSTRACT FROM AUTHOR]

Manipulating the transition temperature (T1/2) of spin-crossover (SCO) complexes capable of fulfilling practical criteria through different synthetic strategies is one of the main focuses in the field of molecular magnetism. The reaction of the tricyanometallate precursor [(Tp*)FeIII(CN)3]− and Fe(II) salt with the "facially" tridentate ligand tris(2-pyridyl)phosphine oxide (TPPO) and NCE− anions afforded three isostructural {Fe III2 Fe II2 } square complexes {[(Tp*)FeIII(CN)3]2[FeII(TPPO)]2[NCE]2}·Sol (E = S, Sol = 2CH3OH·6H2O, 1; E = Se, Sol = 2MeCN·2CH2Cl2·2H2O, 2; E = BH3, Sol = 4CH3OH·2MeCN, 3). Detailed structural analysis, variable-temperature IR analysis, magnetic susceptibility measurements and DFT calculations revealed that all compounds exhibit complete and one-step SCO behaviour between the {Fe III,LS2 Fe II,HS2 } and {Fe III,LS2 Fe II,LS2 } electronic states. As the ligand field increases from NCS− to NCSe− to NCBH3−, T1/2 shifts dramatically from 214 to 250 to 288 K for 1, 2 and 3, respectively, demonstrating another effective way to tune the SCO properties of the [FeIII–CN–FeII] systems through the introduction of NCE− co-ligands. [ABSTRACT FROM AUTHOR]

The supramolecular self-assembly synthetic strategy provides a valid tool to obtain polynuclear Fe(II) complexes having effective communication between the metal centres and distinct spin crossover behaviour. Despite the great success in constructing various magnetic molecules, progress has not been made in SCO complexes based on azido bridges. In this article, the coordination-driven supramolecular assembly based on 3,6-substituted pyridazine and azide is presented to afford two Fe(II) grid-like complexes: [(L)4Fe II4 (N3)4][BPh4]4·sol (1, L = 3,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine and 2, L = 3,6-di(pyridin-2-yl)pyridazine). The substitution of pyridinyl groups in 2 instead of pyrazolyl ones in 1 led to the only example exhibiting spin-crossover behaviour (T1/2 = 230 K) among the azido-bridged complexes. In addition, a temperature-dependent photoluminescence study of 2 demonstrates a visible synergetic effect between the SCO event and the luminescence. [ABSTRACT FROM AUTHOR]

The self-assembly of Co(II) salts, pyridazine derivatives and azides afforded two azido-bridged [2×2] grid-type complexes {[(L)4Co II4 (N3)4][BPh4]4}·sol (1, L = 3,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (pzdz) and sol = 4CH3CN·3CHCl3·2CH3OH and 2, L = 3,6-di(pyridin-2-yl)pyridazine (pydz) and sol = 4CH3CN). Upon comparison with other related grid-like complexes, the incorporation of end-on azido-bridges resulted in overall intramolecular ferromagnetic couplings, and thus endowed complexes 1 and 2 single molecule magnet behaviour with field-induced slow magnetic relaxation. [ABSTRACT FROM AUTHOR]

A linear trinuclear ferrous complex [FeII3(pymp)4(MeOH)2][BPh4]2·2MeOH (1) (Hpymp = 2-[(pyridine-2-ylimine)-methyl]phenol) was isolated and characterized both structurally and magnetically. A magnetic study revealed the ferromagnetic coupling (J = +3.54 cm−1) within the [FeII3] units and uniaxial magnetic anisotropy (D = −1.21 cm−1) of the molecule. Slow relaxation of the magnetization at below 5 K and an effective energy barrier of 26.0(2) cm−1 under a 1200 Oe applied dc field were evidenced. Moreover, clear magnetic hysteresis loops were observed at below 2.5 K, which further corroborated the single-molecule magnet behavior of 1. [ABSTRACT FROM AUTHOR]

The introduction of NaBPh4 into a methanolic solution of CoCl2·6H2O and 2-[(pyridine-2-ylimine)-methyl]phenol (Hpymp) afforded {[CoII3(pymp)4(MeOH)2][BPh4]2}·2MeOH (1) with a centro-symmetrically linear trinuclear structure. Magnetic analysis of 1 exhibited significant intracluster ferromagnetic exchange (2.4 cm−1) and slow relaxation of magnetization in both zero and non-zero static fields below 5 K, giving the first [CoII3] single molecule magnet with an effective energy barrier of 17.2(3) cm−1 under a 500 Oe dc field. [ABSTRACT FROM AUTHOR]

The self-assembly of organic TCNQF- radicals (2-fluoro-7,7,8,8-tetracyano-p-quinodimethane) and the anisotropic [Tb(valpn)Cu]3+ dinuclear cations produced a singlechain magnet (SCM) involving stacking interactions of TCNQF- radicals (H2valpn is the Schiff base from the condensation of o-vanillin with 1,3-diaminopropane). Static and dynamic magnetic characterizations reveal that the effective energy barrier for the reversal of the magnetization in this hetero-tri-spin SCM is significantly larger than the barrier of the isolated single-molecule magnet based on the {TbCu} dinuclear core. [ABSTRACT FROM AUTHOR]

Abstract: Treatment of [NEt4][(Tp∗Me)FeIII(CN)3]·H2O with nickel(II) trifluoromethanesulfonate affords {[(Tp∗Me)FeIII(CN)3]2[NiII(DMF)4]2[OTf]2}·2DMF (1) while {[(Tp∗Me)FeIII(CN)3]2[NiII(bpy)2]2[ClO4]2}·3MeCN·2H2O·MeOH (2) is obtained from Ni(ClO4)2·6H2O and 2,2′-bipyridine mixtures. In the frame of an isotropic Heisenberg model, the experimental χT versus T data were modeled well with the following best set of parameters: J/k B =+9.0(4) and +8.5(4)K and g av =2.4(1) and 2.5(1) for 1 and 2, respectively; the first excited state (S = 2) for 1 and 2 are ca. 18 and 16.8K above the S T =3 ground state. Analysis of the ac susceptibility suggests that 1 exhibits fast quantum tunneling of the magnetization above ca. 1.8K while 2 displays slow relaxation in the range seen for many SMMs; at H dc =2.2kOe an SMM energy barrier of Δeff =15.7K is estimated for 2. Upon prolonged standing in air, 1 is readily transformed into a new system that exhibits a respectable energy barrier (Δeff =20.4K) suggesting that the desolvation is able to dramatically alter the dynamics and the quantum properties of the square-shaped {FeIII 2(μ-CN)4NiII 2}SMM. [Copyright &y& Elsevier]