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Encapsulation by a Chromium(III)-Containing Bicyclic Ligand Cage. Synthesis, Structures, and Physical Properties of Heterometal Complexes CrIIIMCrIII [M = (H+)2, Li(I), Mg(II), Cu(II), Ni(II), Ni(IV), Co(III), Fe(II), Fe(III), Mn(II)]

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journal contribution
posted on 14.02.1998, 00:00 by Dirk Burdinski, Frank Birkelbach, Thomas Weyhermüller, Ulrich Flörke, Hans-Jürgen Haupt, Marek Lengen, Alfred X. Trautwein, Eckhard Bill, Karl Wieghardt, Phalguni Chaudhuri
Synthesis of linear trinuclear complexes containing the [tris(dimethylglyoximato)-metalate(II)]4- anion as bridging ligand of general formula [LCrIII{μ-(dmg)3M}CrIIIL]1+/2+/3+/4+ as perchlorate salts, where M = (H+)2 (1 and 2), absent (3), (H+)4 (4), Li(I) (5), Mg(II) (6), Cu(II) (7), Ni(II) (8), Ni(IV) (9), Co(III) (10), Fe(II) (11), Fe(III) (12) and Mn(II) (13), has been achieved by stepwise reactions of the LCr unit with in situ prepared M(dmg)3n- ions, where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane and dmg2- is the dimethylglyoximato dianion. The clathrochelate complexes 113 have been characterized on the basis of elemental analysis, mass spectrometry, IR, UV−vis, Mössbauer, and EPR spectroscopies, and variable-temperature (2−295 K) magnetic susceptibility measurements. They are quasi-isostructural with the terminal chromium(III) ions in a distorted octahedral environment, CrN3O3, and the central metal ions M are six-coordinate, mostly trigonal prismatic, with the MN6 core. The crystal structures of the perchlorate salts of 7, 8, and 11 have been determined by single-crystal X-ray crystallography. They crystallize in the monoclinic system, space group C2/c with the following cell parameters:  7, a = 29.029(7) Å, b = 12.239(4) Å, c = 14.850(4) Å, β = 118.90(2)°, Z = 4; 8, a = 32.333(6) Å, b = 8.772(2) Å, c = 16.716(3) Å, β = 109.51(3)°, Z = 4; 11, a = 30.941(6) Å, b = 8.777(2) Å, c = 16.801(3) Å, β = 96.22(3)°, Z = 4. The structures consist of tris(dimethylglyoximato)-bridged CrIIIMIICrIII dications and noncoordinated perchlorate anions, with an intramolecular Cr···Cr distance of ∼7.1 Å. The trinuclear unit Cr−M−Cr is nearly planar exhibiting angles at M in the range 179.0−178.6°, except 7, with a Cr−Cu−Cr angle of 175.1°. Analysis of the susceptibility data indicates the presence of weak to moderate exchange interactions, both ferro- and antiferromagnetic, between the paramagnetic centers. There are indeed two different coupling constants, J (=J12 = J23) and J13, operative in these clathrochelates. J13 represents the exchange interaction between the two terminal Cr(III) centers separated by a large distance of ∼7.1 Å. An analysis of the interacting magnetic orbitals in complexes containing three metal centers is presented. The cyclic voltammograms of the complexes reveal both oxidation and reduction processes and indicate the formation of the uncommon species such as Cu(III), Ni(III), Ni(IV), and low-spin Fe(III). Liquid secondary ion mass spectrometry (L-SIMS) demonstrates the nonfragile character of the complexes examined, together with their nuclearity.

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