Magnetic interactions through fluoride: magnetic and spectroscopic characterization of discrete, linearly bridged [Mn(III)2(µ-F)F4(Me3tacn)2](PF6).

The nature of the magnetic interaction through fluoride in a simple, dinuclear manganese(III) complex (1), bridged by a single fluoride ion in a perfectly linear fashion, is established by experiment and density functional theory. The magnitude of the antiferromagnetic exchange interaction and the manganese(III) zero-field-splitting parameters are unambiguously determined by inelastic neutron scattering to yield J = 33.0(2) cm(-1) (H = JS1·S2 Hamiltonian definition) and single-ion D = -4.0(1) cm(-1). Additionally, high-field, high-frequency electron paramagnetic resonance and magnetic measurements support the parameter values and resolve |E| ≈ 0.04 cm(-1). The exchange coupling constant (J) is 1 order of magnitude smaller than that found in comparable systems with linear oxide bridging but comparable to typical magnitudes through cyanide, thus underlining the potential of fluoride complexes as promising building blocks for novel magnetic systems.

[ReF(6)](2-) : a robust module for the design of molecule-based magnetic materials.

A facile synthesis of the [ReF6 ](2-) ion and its use as a building block to synthesize magnetic systems are reported. Using dc and ac magnetic susceptibility measurements, INS and EPR spectroscopies, the magnetic properties of the isolated [ReF6 ](2-) unit in (PPh4 )2 [ReF6 ]⋅2 H2 O (1) have been fully studied including the slow relaxation of the magnetization observed below ca. 4 K. This slow dynamic is preserved for the one-dimensional coordination polymer [Zn(viz)4 (ReF6 )]∞ (2, viz=1-vinylimidazole), demonstrating the irrelevance of low symmetry for such magnetization dynamics in systems with easy-plane-type anisotropy. The ability of fluoride to mediate significant exchange interactions is exemplified by the isostructural [Ni(viz)4 (ReF6 )]∞ (3) analogue in which the ferromagnetic Ni(II) -Re(IV) interaction (+10.8 cm(-1) ) dwarfs the coupling present in related cyanide-bridged systems. These results reveal [ReF6 ](2-) to be an unique new module for the design of molecule-based magnetic materials.

Fluoride bridges as structure-directing motifs in 3d-4f cluster chemistry.

The use of kinetically robust chromium(III) fluorido complexes as synthons for mixed 3d-4f clusters is reported. The tendency toward linear {Cr(III)-F-Ln(III)} units dictates the cluster topology. Specifically, we show that reaction of cis-[Cr(III)F(2)(NN)(2)]NO(3) (NN = 1,10-phenanthroline ("phen") or 2,2'-bipyridine ("bpy")) with Ln(NO(3))(3)·xH(2)O produces isostructural series of molecular {Ln(2)Cr(2)} squares (1-9) with linear fluoride bridges. In a parallel fashion, fac-[Cr(III)F(3)L], where L = N,N',N″-trimethyl-1,4,7-triazacyclononane ("Me(3)tacn"), reacts with Nd(NO(3))(3)·6H(2)O to form a fluoride-centered penta-nuclear complex and fac-[Cr(III)F(3)L'], with L' = 1,1,1-tris-((methylamino)methylethane) ("Me(3)tame"), reacts with [Ln(hfac)(3)(H(2)O)(2)] (hfacH = 1,1,1,5,5,5-hexafluoroacetylacetone) to yield an isostructural series of {Ln(3)Cr(2)} (10-14) trigonal bipyramids with no central ligand. The formation of the latter is accompanied by a partial solvolysis of the Cr(III) precursor but without formation of insoluble LnF(3). The magnetic properties of the gadolinium containing clusters allow quantification of fluoride-mediated, antiferromagnetic Gd-Cr exchange interactions of magnitude between 0.14 cm(-1) and 0.71 cm(-1) (H = J(12)S(1)·S(2) formalism) and vanishingly small J(Gd-Gd) of 0.06(0) cm(-1). The large spin and small anisotropy together with weak exchange interactions in the {Gd(3)Cr(2)} (11) cluster give rise to a very large magneto-caloric effect of -ΔS(m) = 28.7 J kg(-1) K(-1) (µ(0)H = 90 to 0 kOe).

Magnetic properties of a manganese(III) Chain with monoatomic bridges: catena-MnF(salen).

In the solid state, MnF(salen) forms chains wherein fairly linear fluoride bridges between high-spin Mn(III) centers are observed. We interpret the magnetic properties of these chains by use of the classical Fisher model and by use of the high-temperature expansion approach, as well as by exact matrix diagonalization of the spin Hamiltonian, of model rings. In solution, electron paramagnetic resonance shows the chains to be symmetrically cleaved to monomeric MnF(salen).

Angular dependence of the exchange interaction in fluoride-bridged Gd(III)-Cr(III) complexes.

The observed angular variation of the magnetic exchange coupling parameter in a series of fluoride-bridged chromium(III)-gadolinium(III) complexes is explained by DFT calculations.

Fluoride-bridged {Ln2Cr2} polynuclear complexes from semi-labile mer-[CrF3(py)3] and [Ln(hfac)3(H2O)2].

The trifluorido complex mer-[CrF(3)(py)(3)] (py = pyridine) reacts with 1 equiv. of [Ln(hfac)(3)(H(2)O)(2)] and depending on the solvent forms the tetranuclear clusters [Cr(2)Ln(2)(µ-F)(4)(µ-OH)(2)(py)(4)(hfac)(6)], 1Ln, and [Cr(2)Ln(2)(µ-F)(4)F(2)(py)(6)(hfac)(6)], 2Ln, in acetonitrile and 1,2-dichloroethane, respectively (Ln = Y, Gd, Tb, Dy, Ho, and Er; hfacH = 1,1,1,5,5,5-hexafluoroacetylacetone). Reaction with [Dy(hfac)(3)(H(2)O)(2)] in dichloromethane produces the dinuclear cluster [CrDy(µ-F)F(OH(2))(py)(3)(hfac)(4)], 3Dy. All the clusters feature fluoride bridges between the chromium(III) and lanthanide(III) centres. Fits of susceptibility data for 1Gd and 2Gd reveal the fluoride-mediated chromium(III)-lanthanide(III) exchange interactions to be 0.43(5) cm(-1) and 0.57(7) cm(-1), respectively (in the H = JS1· S2 convention). Heat capacity measurements on 2Gd reveal a moderate magneto-caloric effect (MCE) reaching -ΔS(m)(T) = 11.4 J kg(-1) K(-1) for ΔB(0) = 9 T → 0 T at T = 4.1 K. Out-of-phase alternating-current susceptibility (χ'') signals are observed for 1Dy, 2Dy and 2Tb, demonstrating slow relaxation of the magnetization.