| Title
| - 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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| Abstract
| - The clathrochelates of general formula[LCr{μ-(dmg)3M}CrL]1+/2+/3+/4+have been synthesized, and their spectroscopic (EPR, Mössbauer,UV−vis), magnetic, electrochemical, and mass spectrometric propertiestogether with their linear nature, revealed by X-ray structures, arereported. There are two exchange coupling constants, Jand J13, operative in these clathrochelates.J13 represents the exchange interactionbetween the terminal Cr(III) centers separated by a large distanceof ∼7 Å. The spin-level ordering is a result of the mutualinfluence of two different exchange interactions, which might lead toground-state variability.
- Synthesis of linear trinuclear complexes containingthe[tris(dimethylglyoximato)-metalate(II)]4-anion as bridgingligand 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 stepwisereactions of the LCr unit with in situ preparedM(dmg)3n-ions,where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane anddmg2- is the dimethylglyoximato dianion.Theclathrochelate complexes 1−13 have beencharacterized on the basis of elemental analysis, massspectrometry,IR, UV−vis, Mössbauer, and EPR spectroscopies, andvariable-temperature (2−295 K) magnetic susceptibilitymeasurements. They are quasi-isostructural with the terminalchromium(III) ions in a distorted octahedralenvironment, CrN3O3, and the central metal ionsM are six-coordinate, mostly trigonal prismatic, with theMN6core. The crystal structures of the perchlorate salts of7, 8, and 11 have been determined bysingle-crystal X-raycrystallography. They crystallize in the monoclinic system, spacegroup C2/c with the following cellparameters: 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 oftris(dimethylglyoximato)-bridgedCrIIIMIICrIII dicationsandnoncoordinated perchlorate anions, with an intramolecularCr···Cr distance of ∼7.1 Å. The trinuclear unitCr−M−Cr is nearly planar exhibiting angles at M in the range179.0−178.6°, except 7, with a Cr−Cu−Cr angleof175.1°. Analysis of the susceptibility data indicates thepresence of weak to moderate exchange interactions,both ferro- and antiferromagnetic, between the paramagnetic centers.There are indeed two different couplingconstants, J (=J12 =J23) and J13, operativein these clathrochelates. J13 representsthe exchange interactionbetween the two terminal Cr(III) centers separated by a largedistance of ∼7.1 Å. An analysis of the interactingmagnetic orbitals in complexes containing three metal centers ispresented. The cyclic voltammograms of thecomplexes reveal both oxidation and reduction processes and indicatethe formation of the uncommon speciessuch as Cu(III), Ni(III), Ni(IV), and low-spinFe(III). Liquid secondary ion mass spectrometry(L-SIMS)demonstrates the nonfragile character of the complexes examined,together with their nuclearity.
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