The employment of the anion of methyl 2-pyridyl ketone oxime (mpko(-)) as a tridentate chelating/bridging ligand in manganese chemistry is described. The inorganic anion (Br(-), ClO(4)(-)) used in the reaction affects the identity of the product. The reaction of MnBr(2) and one equivalent of mpkoH in the presence of a base affords [Mn(3)(OMe)(2)(mpko)(4)Br(2)] (3), which is mixed-valence (2Mn(II), Mn(IV)). The central Mn(IV) atom in each of the two, crystallographically independent, centrosymmetric molecules is coordinated by four oximate oxygen atoms belonging to the eta(1):eta(1):eta(1):mu mpko(-) ligands, and two eta(1):mu MeO(-) groups, while six coordination at each terminal Mn(II) atom is completed by four nitrogen atoms belonging to the 'chelating' part of two mpko(-) ligands, and one Br(-) ion. The Mn(II) atoms have trigonal prismatic coordination geometry. The reaction of Mn(ClO(4))(2).6H(2)O, mpkoH and OH(-) (1:2:1) in MeOH gives [Mn(8)O(4)(OMe)(mpko)(9)(mpkoH)](ClO(4))(4) (4), which is also mixed-valence (2Mn(II), 6Mn(III)) and possesses the novel [Mn(8)(mu(3)-O)(4)(mu-OMe)(mu-OR'')(2)](11+) core. The latter possesses a U-shaped sequence of four fused {Mn(II)Mn(III)(2)(mu(3)-O)}(6+) triangular units, with a Mn(III)-Mn(III) edge being shared between the central triangles. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on complexes 3 and 4 . The dc susceptibility data for 3 in the 5.0-300 K range have been fit to a model with two J values, revealing weak ferromagnetic Mn(II)Mn(IV) (J = +3.4 cm(-1)) and Mn(II)Mn(II) (J' = +0.3 cm(-1)) exchange interactions. Fitting of the magnetization vs. H/T data by matrix diagonalization and including only axial anisotropy (ZFS, D) gave ground state spin (S) and D values of S = 13/2, D = +0.17 cm(-1) for and S = 3, D = -0.09 cm(-1) for 4 . The combined work demonstrates the usefulness of mpko(-) in the preparation of interesting Mn clusters, without requiring the co-presence of carboxylate ligands.
The use of phenyl-2-pyridyl ketone oxime and di-2-pyridyl ketone oxime in Mn chemistry has led to hexanuclear clusters with unprecedented (Mn(II)(4)Mn(III)Mn(IV)) or extremely rare (Mn(II)Mn(III)(5) and Mn(II)(3)Mn(III)(3)) metal oxidation-state combinations and uncommon structural motifs.
A novel metal ion-mediated reaction of pyridine-2-amidoxime has led to an 1:3 mononuclear Mn(III) complex containing the 2,4-bis(2-pyridyl)-1,3,5-triazapentanedienate(-1) ligand; the high-spin Mn III in the complex is "EPR silent" at X-band. Upon coordination of a ligand (L) to a metal center (M), the former's properties (acidity, electrophilic or nucleophilic character, susceptibility to reduction or oxidation, etc.) can be significantly altered and therefore its reactivity can be enhanced or inhibited; coordination to M can even enable a reaction that would otherwise not take place. Thus the reactivity chemistry of coordinated ligands is a "hot" research theme in contemporary transition-metal chemistry [1]. Oxime (C═N-OH) and oximate (C═N-O-) groups can bind an M in a variety of coordination modes and are thus ideal candidates for reactivity chemistry [2]. Nucleophilic reagents can add to the C-atom (a reaction that is promoted by coordination of the N-atom), whereas electrophilic reagents can attack the O-or the N-sites [2]. Scheme 1. Structural formulae and abbreviations of the ligands discussed in the text. The initially used ligand is pyridine-2-amidoxime, (py)C(NH 2)NOH, and the anionic ligand present in the Mn(III) complex is 2,4-bis(2-pyridyl)-1,3,5-triazapentanedienate(-1), bptzpd-; py is the general abbreviation for the 2-pyridyl moiety.
rH2O where p, q, r = [2,3,8] for 1 and [4,1,4] Polyoxometalates (POMs) are anionic molecular metal oxides constructed from W, Mo, V or Nb. They attract much attention due to their structures, electronic properties [1] and applications in catalysis, [2] magnetism, [3] as well as medicine [4] and molecular electronics. [5] The first polyoxometalate compound was reported by Berzelius [6] in 1826 but it was not until the 1930s that the XRay structure of this iconic compound, the Keggin ion, was first elucidated. [6] This ion has a tetrahedral symmetry with the general formula [XM12O40] n-, where X is a heteroatom (P, Si, S, Ge, As, Co, Fe) [7] with four O atoms completing the tetrahedral geometry. Investigations of the Keggin structure revealed four additional isomers, each resulting from the 60 o rotation of the four basic {M3O13} units, giving α, β, γ, δ and ε isomers as reported by Baker and Figgis, see Figure 1. [8] With the α and β -isomers, the four building blocks are linked together in a corner-shared fashion, whilst in the case of γ, δ and ε the corner-shared linkages are replaced by one, three and six edge-shared, respectively. [9] Since the first report of the most common α-and β-Keggin isomers, [10] many researchers have investigated their properties, [11] whilst others reported families of transition metal substituted derivatives of α-, β-and γ-isomers. [12] The first Keggin species containing an ε-core was reported almost 60 years later as a Rh-substituted oxomolybdenum(V) complex, [13] followed by the report of a mixed-valence Mo(V)/Mo(VI) isopolyanion [14] , the La and Ni-substituted oxomolybdenum ε-Keggin isomers [15] and recently the Bi substituted vanadiumbased ε isomer [16] , respectively. However, the only related δ-Keggin structures observed so far are not POM anions but cationic species e.g. the {Al13} cation [17] and the "reverse-Keggin" ions incorporating either p-block elements (Sb 5+ ) or first row transition metal ions (Co 2+ , Mn 2+ or Zn 2+ ). [18] Herein, we report the synthesis and characterization of the first members of the δ-Keggin polyanionic isomers to be isolated, compounds 1 and 2, with the general formula: TEAHpNaq[H2M12(XO4)O33 ( Supporting information for this article is given via a link at the end of the document.
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