Pyrazine‐Assisted Dimerization of Molybdenum(V): Synthesis and Structural Characterization of Novel Dinuclear and Tetranuclear Complexes

Abstract

12 pagesInternational audienceReactions of pyrazine (Pyz = C4H4N2) with [MoOCl4(H2O)]– or [MoOBr4]– afforded a series of complexes, dinuclear [(MoOX4)2(Pyz)]2– (X = Cl, Br), [{MoOCl3(Pyz)}2O]2– and tetranuclear [(Mo2O4Cl4)2(Pyz)2]4– anions, with N-donor ligands engaged either in monodentate or bidentate bridging coordination. A dinuclear [(MoOX4)2(Pyz)]2– ion, which may be viewed as a linkage of two mononuclear subunits with a bidentate pyrazine, crystallizes either as a PyH+ (pyridinium cation, C5H5NH+; compound 1), a {(C2H5)4N}+ (compound 2) or a {(C6H5)4P}+ salt (compounds 3 and 4). In (PyH)2- [{MoOCl3(Pyz)}2O] (5) with an anti-{Mo2O3}4+ core, pyrazine is bound to the metal through only one nitrogen atom. The tetranuclear [(Mo2O4Cl4)2(Pyz)2]4– ion, a linkage of two metal–metal bonded {Mo2O4}2+ cores with a pair of bidentate pyrazines, is found in two compounds, (MeNC5H5)2(PyzH2)- [(Mo2O4Cl4)2(Pyz)2] (6) [MeNC5H5 + = N-methylpyridinium cation, PyzH2 2+ = pyrazinium(2+) cation] and (PyH)4- [(Mo2O4Cl4)2(Pyz)2]·2CH3CN (7). In the presence of methanol, dinuclear {(C6H5)4P}2[(MoOBr4)2(Pyz)]·2CH3CN (4) was transformed directly into tetranuclear (PyH)4[(Mo2O4Br4)2- (Pyz)2]·2CH3CN (8). All compounds were fully characterized by X-ray crystallography and IR spectroscopy. The compounds containing the [(MoOX4)2(Pyz)]2– ions display an irreversible electrochemical reduction behaviour. Temperature- dependent magnetic measurements on {(C6H5)4P}2- [(MoOX4)2(Pyz)]·2CH3CN (X = Cl for 3, X = Br for 4) reveal a weak ferromagnetic coupling across the pyrazine bridge between a pair ofMoV S = 1/2 spins. The magnetic properties of {(C2H5)4N}2[(MoOCl4)2(Pyz)] (2), another compound with dinuclear complex anions, are dominated by antiferromagnetic intermolecular interactions

Spectroscopically and/or Structurally Intriguing Phthalocyanines and Related Compounds. Part 2. Monomeric Systems

“…The Mo−O bonding distance of 1.66 Å in the crystal structure is in the range of lengths for Mo=O double bonds [18] The interatomic distance between the two Mo ions is 2.64 Å, which corresponds to the distance of a Mo−Mo single bond [19]. Each Mo ion is further coordinated by two pyrrole nitrogen atoms and two amino nitrogen atoms of the macrocycle (5A in Fig.…”

Polymerization of MoV: Synthesis and Characterization of a Dinuclear MoV and a Hexanuclear Mixed‐Valence MoV/MoVI Complex

“…On the basis of an analysis of the bond lengths ( Table 1) with values of 2.625(1) Å for the Mo-Mo single bond, 1.698(4), 1.701(4) Å for the Mo=O oxo double bonds, and 1.945(4)-1.961(4) Å for µO-Mo bridges, the +5 state is the only chemically sensible oxidation number for the two Mo centers in this complex. [22][23][24][25][26][27][28] Consequently, one of the tdci entities must bear a positive charge. Inspection of the Mo-O bond lengths for the two tdci ligands revealed values of 2.045(4)-2.079(4) Å (mean: 2.054 Å) for the four tdci oxygen donors in the cis position of O oxo .…”

“…The molecular structure of the uncharged complex [(MoO) 4 (µ 2 -O) 2 (µ 3 -O) 2 (tdci) 2 (MoO 4 ) 2 ] (2) is depicted in Figure 4. It represents a mixed-valence Mo V -Mo VI species consisting of the well-known [Mo 4 O 8 ] 4+ core, [22][23][24][25][26][27][28] which is ligated by two facially coordinating tdci entities and by two [Mo VI O 4 ] 2units coordinating in a monodentate fashion. The oxidation state of +6 for Mo3 was confirmed by bondvalence calculations (5.95).…”

“…The various Mo-O bond lengths are summarized in Table 1 and correspond to expectations. [8,[22][23][24][25][26][27][28] The observed order: bonding ability of the different types of oxygen donors, and the observed differences within the same donor class can simply be discussed in terms of a trans influence (push-pull mechanism): strong π-bonding generally results in a more significant weakening of the Mo-O bond in the trans position. [47] Formation of the [Mo 4 O 8 ] 4+ core was further confirmed by FAB mass spectrometry (Figure 2c).…”

“…The polymerization reaction, which starts from mononuclear Mo V , yielding dinuclear species of the [Mo 2 O 4 ] 2+ core which assemble to tetranuclear complexes and further to aggregates of even higher nuclearity, is well known. [22][23][24][25][26][27][28][29][30] Even the formation of very large clusters, still containing the basic [Mo 2 O 4 ] 2+ unit as building block, [17] has been observed. Modec and Brencic stated in their review on [Mo 2 O 4 ] 2+ aggregation that "traces of water have been found to severely change the reaction course, leading to mixed-valence, Mo V / Mo VI clusters.…”