Ferromagnetic exchange in the ground and (4)A(1) excited states of (Et(4)N)(3)Fe(2)F(9). A magnetic and optical spectroscopic study

The synthesis, crystal growth, magnetic susceptibility, and polarized optical absorption spectra in the visible and near UV of (Et(4)N)(3)Fe(2)F(9) are reported. From single-crystal magnetic susceptibility data and high-resolution absorption spectra in the region of the (6)A(1) --> (4)A(1) spin-flip transition, exchange splittings in the ground and excited states are derived. Ferromagnetic ground and excited state exchange parameters J(GS) = -1.55 cm(-1) and J(ES) = -0.53 cm(-1) are determined, respectively, and the relevant orbital contributions to the net exchange are derived from the spectra. The results are compared with those reported earlier for the structurally and electronically analogous [Mn(2)X(9)](5-) pairs in CsMgX(3):Mn(2+) (X = Cl(-), Br(-)), in which the splittings are antiferromagnetic. This major difference is found to be due to the increased metal charge of Fe(3+) compared to Mn(2+), leading to orbital contraction and thus to a strong decrease of the orbital overlaps and hence the antiferromagnetic interactions.     

Darstellung und Strukturen von (Et4N)2[Re(CO)3(NCS)3] und (Et4N)[Re(CO)2Br4]

Syntheses and Structures of (Et₄N)₂[Re(CO)₃(NCS)₃] and (Et₄N)[Re(CO)₂Br₄] Rhenium(I) and rhenium(III) carbonyl complexes can easily be prepared by ligand exchange reactions starting from (Et₄N)₂[Re(CO)₃Br₃]. Using nonoxidizing reagents the facial Re^I(CO)₃ unit remains and only the bromo ligands are exchanged. Following this procedure, (Et₄N)₂[Re(CO)₃(NCS)₃] can be obtained in high yield and purity using trimethylsilylisothiocyanate. The compound crystallizes in the monoclinic space group P2₁/n, a = 18.442(5), b = 17.724(3), c = 18.668(5) Å, β = 92.54(1)°, Z = 8. The NCS^? ligands are coordinated via nitrogen. The reaction of [Re(CO)₃Br₃]^2? with Br₂ yields the rhenium(III) anion [Re(CO)₂Br₄]^?. The tetraethylammonium salt of this complex crystallizes in the noncentrosymmetric, orthorhombic space group Cmc2₁, a = 8.311(1), b = 25.480(6), c = 8.624(1) Å, Z = 4. The carbonyl ligands are positioned in a cis arrangement. Their strong trans influence causes a lengthening of the Re? Br bond distances by at least 0.05 Å.     

Crystal Structures of (Et4N)3M2F9 (M = V,Cr, Fe) determined by X‐Ray Single‐Crystal and Powder Diffraction: A New Structure Type for A3M2X9 Compounds

The syntheses and X‐ray structure determinations of single crystals and powders are reported for the compounds (Et₄N)₃M₂F₉ (M = V³⁺, Cr³⁺, Fe³⁺). The compounds are isostructural and represent a new structure type for A₃M₂X₉ compounds. They crystallize in the hexagonal space group P6₃/m with Z = 2. Their lattice parameters are (Et₄N)₃V₂F₉: a = 13.3017(3), c = 10.7714(2) Å; (Et₄N)₃Cr₂F₉: a = 13.2691(3), c = 10.7148(3) Å; and (Et₄N)₃Fe₂F₉: a = 13.3040(3), c = 10.7650(3) Å.     

Direct chemical synthesis of the beta-D-mannans: the beta-(1-->2) and beta-(1-->4) series

The direct syntheses of a beta-(1-->2)-mannooctaose and of a beta-(1-->4)-mannohexaose are reported by means of 4,6-O-benzylidene-protected beta-mannosyl donors. The synthesis of the (1-->2)-mannan was achieved by means of the sulfoxide coupling protocol, whereas the (1-->4)-mannan was prepared using the analogous thioglycoside/sulfinamide methodology. In the synthesis of the (1-->4)-mannan, the glycosylation yields and stereoselectivities remain approximately constant with increasing chain length, whereas those for the (1-->2)-mannan consist of two groups with the formation of the tetra- and higher saccharides giving yields and selectivities consistently lower than those of the lower homologues. The decrease in yield after the trisaccharide in the (1-->2)-mannan synthesis is attributed to steric interference by the n-3 residue and is consistent with the collapsed, disordered structure predicted by early computational work. The consistently high yields and selectivities seen in the synthesis of the (1-->4)-mannan are congruent with the more open, ordered structure originally predicted for this polymer. The lack of order in the structure of the (1-->2)-mannan, as compared to the high degree of order in the (1-->4)-mannan, is also evident from a comparison of the NMR spectra of the two polymers and even from their physical nature: the (1-->2)-mannan is a gum and the (1-->4)-mannan is a high melting solid.     

Na(THF)2Cr(N3N)]: The first trigonal monopyramidal chromium(II) complex

Reduction of [Cr(N(3)N)] (1) [(N(3)N)(3)(-) = ((SiMe(3)NCH(2)CH(2))(3)N)(3)(-)] with sodium powder in THF affords the yellow, extremely air-sensitive amidochromate(II) [Na(THF)(2)Cr(N(3)N)] (2) in good yield. Complex 2 has an effective magnetic moment of 5.1 mu(B) indicative of a d(4) high-spin electronic configuration. (1)H NMR spectroscopy in solution and single-crystal X-ray crystallography show that compound 2 is composed of idealized C(s) symmetric contact ion pairs, in which trigonal-monopyramidal [Cr(II)(N(3)N)](-) anions are linked to the [Na(THF)(2)](+) countercations by two bridging amide ligands. DFT calculations of 1, 2, and the anion [Cr(N(3)N)](-) at the RI-BP86/TZVPP level of theory provide in combination with extended Hückel calculations a rationale for the observed structural changes from 1 to 2.     

Rotationally selected product pair correlation: F+CD4 --> DF(nu')+CD3(nu2 = 0 and 2, N)

The product pair correlation of the title reaction was measured with rotational selection for both the vibrationally ground CD3(nu = 0) and umbrella-excited CD3(nu2 = 2) products. A striking linear relationship was found between the rotational energy of the selected CD3 product and the correlated kinetic energy release (or the average vibrational energy of the DF coproduct). Such a linearly correlated (or anticorrelated) dependence appears to be stronger for CD3(nu2 = 2,N) than for CD3(nu = 0,N). The mechanistic implication of the observation is that the rotational motion N of the CD3 product tends to lie antiparallel to the orbital angular momentum l' of the two departing products. The dependency on the K quantum number--the projection of N on the top axis--is, on the other hand, less significant yet noticeable.     

Nonvalent interactions in the crystal structures of (Et4N)2[Mo3S7Br6] and (Et4N)(H9O4)[Mo3S7Cl6] clusters

Crystal structures of (Et₄N)₂[Mo₃S₇Br₆] (I) and (Et₄N)(H₉O₄)[Mo₃S₇Cl₆] (II) clusters belonging to the class of Mo₃S ₇ ⁴⁺ were determined by X-ray diffraction analysis. Crystals I are orthorhombic a=19.106(3), b=12.930(2), c=29.887(5) Å, V=7383(2) ų, space group Pbca, Z=8, d_calc=2.253 g/cm³, R(F)=0.0402, wR(F²)=0.0587 for 2493 F_hkl>4σ. Crystals II are monoclinic, a=17.106(3), b=18.882(4), c=11.006(2), Å, β=126.13(3)°, V=2871.2(9) ų, space group Cc, Z=4, d_calc=2.147 g/cm³, R(F)=0.0181, wR(F²)=0.0445 for 2307 F_hkl>4σ. Structure I has an anion dimer with 3S_ax…Cl=3.258(4)–3.404(4) Å; the dimer is similar to that observed in the structures of A₂[M₃X₇Hal₆], A=Ph₄P⁺, Ph₃EtP⁺, and PPN⁺. In structure II, infinite chains of anions bonded by 3S_ax…Cl contacts of 3.183(3)–3.394(3) Å were found. A similar phenomenon was established earlier for the structure of (Et₄N)(H₉O₄)[Mo₃S₇Br₆] (III), which is not isostructural to II. Compounds II and III also differ in the structure of the H₉O₄ ⁺ cation: infinite helix in II and pyramid in III.     

Crystal structure of (Et4N) [(µ-H)Fe3(µ3-Se)(CO)9]

The crystal structure of (Et₄N)[(μ-H)Fe₃(μ₃-Se)(CO)₉] is determined;the crystals are monoclinic, a = 11.172(2), b =32.332(5), c =13.552(3) ?, μ =91.86(2)‡, V _cell =4893(2) ? ³, space group P2₁/n, Z =8, d _calc =1.710 g/cm ³, CAD-4 diffractometer, MoK_α radiation;the total number of data collected 4395,including 4086 independent reflections(R_int =0.0701), R(F) =0.0566, wR(F ²) =0.1202 for 1963 F _hkl > 4Σ(F). The data were corrected for the 37.8% linear drop of intensities of the control reflections due to crystal decay. The Fe-H bond lengths are 1.5(1)-1.72(9) ?. As in the case of three-osmium clusters,the presence of the Μ-H ligand leads to a lengthening of the Fe-Fe bond by approximately 0.1 ? and to push-away of the equatorial carbonyl ligands leading to an increase in the FeFeC angle by approximately 5–10‡, whereas the axial CO and (Μ ₃-Se) remain unchanged.     

(Et4N)4[V4O12]·2H2O

The title compound, tetrakis(tetraethylammonium) cyclo‐tetra‐μ‐oxo‐tetrakis[dioxovanadium(V)] dihydrate, (C₈H₂₀N)₄[V₄O₁₂]·2H₂O, was obtained by reacting V₂O₅ with (C₂H₅)₄NOH. It consists of a discrete centrosymmetric molecular anion, [V₄O₁₂]^4?, where four tetrahedral VO₄ units share two vertices with each other to form a ring. A water mol­ecule is attached on each side of the ring through hydrogen bonds.     

Synthese und Kristallstruktur von [Cr(NH3)6][Cr(NH3)2F4][BF4]2

Synthesis and Crystal Structure of [Cr(NH₃)₆][Cr(NH₃)₂F₄][BF₄]₂ The action of ammonium fluoride on a mixture of boron and chromium in a sealed Monel ampoule at 300 °C yields single crystals of [Cr(NH₃)₆][Cr(NH₃)₂F₄][BF₄]₂. The crystal structure (tetragonal, P4/mbm, Z = 2, a = 1056.0(1), c = 781.7(1) pm; R₁ = 0.0414; wR₂ = 0.1087 for 411 reflections with I₀ > 2σ(I)) contains [Cr(NH₃)₆]³⁺ and [Cr(NH₃)₂F₄]^– octahedra and twice as many [BF₄]^– tetrahedra that are arranged in a quadrupled super‐structure of the CsCl‐type of structure.     

Acetic acid induced self-assembly of supramolecular compounds [Et4N]3[(WS4Cu2)2(mu-CN)3].2MeCN and [PPh4][WS4Cu3(mu-CN)2].MeCN from preformed clusters [A]2[WS4(CuCN)2] (A = Et4N, PPh4)

Reactions of two preformed trinuclear W/Cu/S clusters, [A](2)[WS(4)(CuCN)(2)] (1: A = Et(4)N; 2: A = PPh(4)), with different concentrations of acetic acid in MeCN generate two interesting 2D polymeric clusters [Et(4)N](3)[(WS(4)Cu(2))(2)(mu-CN)(3)].2MeCN (3), and [PPh(4)][WS(4)Cu(3)(mu-CN)(2)].MeCN (4), respectively. Compound 4 can also be readily obtained in a high yield from the reaction of 2 with equimolar [Cu(MeCN)(4)]PF(6) in MeCN. These compounds have been characterized by elemental analysis, IR spectra, thermal analysis, and single-crystal X-ray diffraction. An X-ray analysis reveals that compound 3 retains the WS(4)Cu(2) cluster core, which serves as a 3-connecting node to link equivalent nodes via single cyanide bridges, forming an anionic 2D (6,3) net. Compound 4 consists of a T-shaped WS(4)Cu(3) core, which also acts as a 3-connecting node, with links to 3 equivalent clusters either through single or double cyanide bridges, affording a different anionic 2D (6,3) network. The acetic acid induced aggregation of 3 and 4 from the two cluster precursors 1 and 2 suggests that this simple synthetic strategy is likely to be applicable to many related systems.     

A first transition series pseudotetrahedral oxynitride anion: synthesis and characterization of Ba(2)VO(3)N

Ammonolysis of reactive oxide precursors affords the vanadium(V) phase Ba(2)VO(3)N that is shown by X-ray and neutron powder diffraction and Raman spectroscopy to contain pseudotetrahedral VO(3)N(4-) anions. This is the first example of such species for the first transition series metals.     

Ein- und zweikernige Fluorokomplexe des Titan(III), Chrom(III) und Eisen(III) Darstellung und Struktur von (NMe4)(Ti(H2O)4F2)TiF6 · H2O, (NMe4)3Cr2F9 und (NMe4)3Fe2F9

Mono- and Dinuclear Fluoro Complexes of Titanium (III), Chromium (III), and Iron(III). Syntheses and Structures of (NMe₄) (Ti(H₂O)₄F₂)TiF₆ · H₂O, (NMe₄)₃Cr₂F₉, and (NMe₄)₃Fe₂F₉ The title compounds have been prepared by reaction of MCl₃ (M = Ti, Cr, Fe) with NMe₄F in dimethylformamide. (NMe₄)₃Cr₂F₉ and (NMe₄)₃Fe₂F₉ contain the face-sharing biocathedral M₂F₉^3? unit. The M…M distances are 277.1(1) and 289.8(3) pm in (NMe₄)₃Cr₂F₉ and (NMe₄)Fe₂F₉, respectively. (NMe₄)(Ti(H₂O)₄F₂)TiF₆ · H₂O contains trans-Ti^III(H₂O)₄F₂⁺ cations and Ti^IVF₆^2? anions. Crystal data: (NMe₄)₃Cr₂F₉: hexagonal, space group P6₃/m, a = 804.1(3), c = 1857.5(4) pm, Z = 2, 529 reflections, R = 0.049; (NMe₄)₃Fe₂F₉: hexagonal, space group P6₃/m, a = 804.7(5), c = 1 861.6(5) pm, Z = 2, 635 reflections, R = 0,046; (NMe₄)(Ti(H₂O)₄F₂)TiF₆ · H₂O: orthorhombic, space group Pbca, a = 776.9(2), b = 1 616.3(3), c = 2 428.6(7) pm, Z = 8, 2 784 reflections, R = 0,056.