Syntheses of Monomeric, Dimeric, and Trimeric Complexes of Tungsten(VI), (V), (IV), and (III) with the 1,4,7‐Triazacyclononane (L) Ligand. Crystal Structures of Dimeric [W2L2(μ2OH)2Br2]Br2 · 2H2O and of Trimeric [W3L3(μ30)(μ2‐0)3][ZnBr4]2

Reactions of WL(CO)3 (L = 1, 4, 7-triazacyclononane; C6H15N3) with bromine under different conditions afford the monomeric WVI compound, WO2LBr2, or the monomeric WV complex, WOLBr3. The former dimerizes in aqueous solution, yielding the [W2O5L2]2+ cation. Two diamagnetic isomers of the WV -dimer, [W2O4L2]2+, have been prepared : a yellow form with terminal oxo groups in cis-positions with respect to each other and a red species containing two terminal oxo-groups in trans-positions. The cationic WIV -trinuclear cluster, [W3O4L3]4+, has been isolated as the tetrabromozincate(2-) salt and its structure has been determined by single crystal X-ray diffraction. [W3O4L3][ZnBr4]2 crystallizes in the monoclinic space group P21/c with a = 12.698(2) A, b = 21.267(6) A, c = 15.687(7) A, β = 92.94(3)0, and V = 4222 A3, dealed. = 2.79 g cm−3 for Z = 4, and mol wt 1773.2. The structure was solved by direct methods using 7399 unique reflections with I≥ 2.5 σ (I). Final residuals were R1 = 0.089 and R2 = 0.096. The structure consists of [W3L3O4]4+ cations of the M3X13 cluster type and isolated ZnBr42− anions. Three tungsten atoms occupy the corners of an equilateral triangle bridged by three μ2-oxo- and one μ3-oxo-ligands; each tungsten atom has a distorted octahedral environment of three oxygen and three nitrogen atoms. The short W - W distances of 2,52 A and the diamagnetism indicate metal-metal bonding. The green, diamagnetic binuclear WIII complex, [W2L2(μOH)2Br2]Br2 · 2 H2O, has been prepared by reduction of monomeric WLOBr3 in strongly acidic solution with zinc powder. The complex has been characterized by a single-crystal X-ray diffraction study; it crystallized in the orthorhombic space group Pnnm with a = 13.837(5) A, b = 11.657(6) A, c = 7.832 A, and V = 1263 A3, dcalcd. = 2.67 g cm−3 for Z = 2, and mol wt 1015.8. The structure was solved by direct methods using 783 unique reflections with I ⩾ 2.5 σ(1). Final residuals were R1 = 0.062 and R2 = 0.084. The structure consists of dimeric cations [W2L2(μOH)2Br2]2+, bromide anions and molecules of water of crystallization. The tungsten centers are in a distorted octahedral environment of the tridentate N-donor igand, one coordinated bromide and two μ2-hydroxo bridges (edge sharing), respectively. The bromide ligands are in trans-positions with respect to each other. The four-membered W2(μOH)2 ring is planar. The WW distance of 2.477(3) A together with its diamagnetism imply the presence of a strong metal-metal bond between the tungsten(II1) centers (σ2π2δ2).

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