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.

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).

X-ray magnetic circular dichroism (XMCD) study of a methoxide-bridged Dy(III)-Cr(III) cluster obtained by fluoride abstraction from cis-[Cr(III)F2(phen)2](+).

An isostructural series of dinuclear chromium(III)-lanthanide(III) clusters is formed by fluoride abstraction of cis-[CrF2(phen)2](+) by Ln(3+) resulting in LnF3 and methoxide-bridged Cr-Ln clusters (Ln = Nd (1), Tb (2), Dy (3)) of formula [Cr(III)(phen)2(µ-MeO)2Ln(NO3)4]·xMeOH (x = 2-2.73). In contrast to fluoride, methoxide bridges in a nonlinear fashion, which facilitates chelation. For 3, X-ray magnetic circular dichroism (XMCD) provides element-specific magnetization curves that are compared to cluster magnetization and susceptibility data acquired by SQUID magnetometry. The combination of XMCD and SQUID is able to resolve very small magnetic coupling values and reveals a weak Cr(III)-Dy(III) coupling of j = -0.04(3) cm(-1). The Dy(III) ion has a ground-state Kramers doublet of mJ = ±13/2, and the first excited doublet is found to be mJ = ±11/2 at an energy of δ = 57(21) cm(-1). The Cr(III) ion exhibits a uniaxial anisotropy of DCr = -1.7(1.0) cm(-1). Further, we observe that a weak anisotropic coupling of dipolar origin is sufficient to model the data, suggesting that methoxide bridges do not play a significant role in the magnetic coupling for the present systems.

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).

cyclo-Tetra-µ-fluorido-1:2κF;2:3κF;3:4κF;1:4κF-octa-nitrato-1κO,O';3κO,O'-tetra-kis-(1,10-phenanthroline)-2κN,N';4κN,N'-2,4-dichromium(III)-1,3-dineodymium(III) methanol tetra-solvate monohydrate.

In the title compound, [Cr(2)Nd(2)F(4)(NO(2))(8)(C(12)H(8)N(2))(4)]·4CH(3)OH·H(2)O, two cis-difluoridobis(1,10-phenanthroline)chromium(III) fragments containing octa-hedrally coordinated chromium(III) bridge via fluoride ions to two tetra-nitratoneodymate(III) fragments, forming an uncharged tetra-nuclear square-like core. The fluoride bridges are fairly linear, with Cr-F-Nd angles of 168.74 (8)°. Cr-F bond lengths are 1.8815 (15) Å, slightly elongated compared to those of the parent chromium(III) complex, which has bond lengths ranging from 1.8444 (10) to 1.8621 (10) Å. The tetra-nuclear complex is centered at a fourfold rotoinversion axis, with the Cr and Nd atoms situated on two perpendicular twofold rotation axes. The uncoordinated water mol-ecule resides on a fourfold rotation axis. The four methanol solvent mol-ecules are located around this axis, forming a cyclic hydrogen-bonded arrangement. The title compound is the first structurally characterized example of unsupported fluoride bridges between lanthanide and transition metal ions.

cis-Aqua-bis(2,2'-bipyridine-κN,N')fluoridochromium(III) bis-(perchlorate) dihydrate.

The title mixed aqua-fluoride complex, [CrF(C(10)H(8)N(2))(2)(H(2)O)](ClO(4))(2)·2H(2)O, has been synthesized by aqua-tion of the corresponding difluoride complex using lanthan-ide(III) ions as F(-) acceptors. The complex crystallizes with a Cr(III) ion at the center of a distorted octa-hedral coordination polyhedron with a cis arrangement of ligands. The crystal packing shows a hydrogen-bonding pattern involving water mol-ecules, the coordinated F atom and the perchlorate anions.

cis-Difluoridobis(1,10-phenanthroline)chromium(III) perchlorate monohydrate.

The title complex, [CrF(2)(C(12)H(8)N(2))(2)]ClO(4)·H(2)O, displays a slightly distorted octa-hedral coordination geometry around the central chromium(III) ion. The Cr environment is composed of a cis arrangement of two 1,10-phenanthroline [average Cr(III)-N = 2.0726 (10) Å] and two fluoride [average Cr(III)-F = 1.8533 (6) Å] ligands. The water molecule forms a hydrogen bond to fluorine in a neighbouring cation.

Molecular and electronic structure of chromium(V) nitrido complexes with azide and isothiocyanate ligands.

The first use of [Cr(N)Cl4]2- as a starting material in chromium(v) nitrido chemistry is demonstrated in simple, high yield, metathesis reactions with the pseudohalogens SCN- and N3- yielding five-coordinate, labile complexes: [Cr(N)(NCS)4]2- and [Cr(N)(N3)4]2-, which have been crystallized and characterized by single-crystal X-ray diffraction. Reaction of [Cr(N)(NCS)4]2- with 1,10-phenanthroline furnishes six-coordinate [Cr(N)(NCS)3(phen)]- wherein phenanthroline coordinates to the position trans to the nitrido ligand. The trans influence of the nitrido ligand leads to a bond length difference of 0.223 A between the axial and equatorial ligators from the phenanthroline ligand. The absorption band with lowest energy in these pseudo-linear complexes is assigned as the electric dipole forbidden transition d(xy) --> d(x-y) based on intensities and its variation with the nature of the equatorial ligators. This absorption provides the spectrochemical series for the equatorial ligands, which is found to be numerically almost identical to that determined for chromium(III). DFT calculations reproduce the observed structures and corroborate the ligand field picture of the electronic structure of these complexes.

Two square-pyramidal chromium(V)-nitride complexes: bis(2-methylquinolin-8-olato)nitridochromium(V) and nitridobis(2-sulfidopyridine N-oxide)chromium(V).

Two new chromium(V)-nitride complexes with a coordination sphere completed by bidentate ligands have been synthesized and structurally characterized. Bis(2-methylquinolin-8-olato)nitridochromium(V), [Cr(C10H8NO)2(N)], has the coordination sphere completed by an equatorial N2O2 set of ligators. The compound crystallizes with the five-coordinate complexes at sites with twofold rotational symmetry and all Cr-N bond directions aligned with the crystallographic b axis. Nitridobis(2-sulfidopyridine N-oxide)chromium(V), [Cr(C5H4NOS)2(N)], crystallizes with the molecules on general positions and has an equatorial S2O2 coordination environment, which is unprecedented among nitride complexes of the first-row transition metals. In both systems, Cr[triple-bond]N bonds are short at ca 1.56 A.

Atom transfer as a preparative tool in coordination chemistry. Synthesis and characterization of Cr(V) nitrido complexes of bidentate ligands.

The transfer of a terminal nitrido ligand from Mn(V)(N)(salen) to Cr(III) complexes is explored as a new preparative route to Cr(V) nitrido complexes. Reaction of Mn(V)(N)(salen) with labile CrCl(3)(THF)(3) in acetonitrile solution precipitates [Mn(Cl)(salen)].(CH(3)CN) and yields a solution containing a mixture of Cr(V) nitrido species with only labile auxiliary ligands. From this solution Cr(V) nitrido complexes with bidentate monoanionic ligands can be obtained in high yields. Five coordinate complexes of 8-hydroxoquinolinate (quin), 1,3-diphenylpropane-1,3-dionate (dbm), and pyrrolidinedithiocarbamate (pyr-dtc) have been structurally characterized: Cr(N)(quin)(2) (1) crystallizes as compact orange prisms in the triclinic space group P with cell parameters a = 7.2450(6) A, b = 8.1710(4) A, c = 13.1610(12) A, alpha = 80.519(6) degrees, beta = 75.721(7) degrees, gamma = 75.131(5) degrees, V = 725.47(10) A(3), Z = 2. Cr(N)(dbm)(2) (2) crystallizes as green rhombs in the orthorhombic space group Pbca with cell parameters a = 14.6940(6) A, b = 16.4570(18) A, c = 19.890(3) A, V = 4809.8(8) A(3), Z = 8. Cr(N)(pyr-dtc)(2) (3) crystallizes as orange prisms in the monoclinic space group P21/c with cell parameters a = 14.8592(14) A, b = 8.5575(5) A, c = 11.8267(12) A, beta = 106.528(7) degrees, V = 1441.7(2) A(3), Z = 4. Complexes 2 and 3 represent new coordination environments for first row transition metal nitrido complexes. The d-orbital energy splitting in these systems with relatively weak equatorial donors differs significantly from the pattern in vanadyl and the previously known first row transition metal nitrido complexes. The d(x)2(-)(y)2 orbital in 2 and 3 is lower in energy and well resolved from the M-N pi orbitals [d(zx),d(yz)].