Functionalization of Krebs-Type Polyoxometalates with N,O-Chelating Ligands: A Systematic Study

Abstract

The first organic derivatives of 3d-metal-disubstituted Krebs-type polyoxometalates have been synthesized under mild bench conditions via straightforward replacement of labile aqua ligands with N,O-chelating planar anions on either preformed or in situ-generated precursors. Nine hybrid clusters containing carboxylate derivatives of five- or six-membered aromatic N-heterocycles as antenna ligands have been obtained as pure crystalline phases and characterized by elemental and thermal analyses, infrared spectroscopy, and single-crystal X-ray diffraction. They all show the general formula [{M(II)L(H2O)}2(WO2)2(B-β-XW9O33)2](n-) and can be classified as follows: 1-SbM, where L = 1H-imidazole-4-carboxylate (imc), X = Sb(III), n = 12, and M(II) = Mn, Co, Ni, Zn; 1-TeM, where L = imc, X = Te(IV), n = 10, and M(II) = Mn, Co; 2-SbNi, where L = 1H-pyrazole-3-carboxylate (pzc), X = Sb(III), n = 12, and M(II) = Ni; and 3-SbM, where L = pyrazine-2-carboxylate (pyzc), X =Sb(III), n = 12, and M(II) = Co, Zn. The 3d-metal-disubstituted tungstotellurate(IV) skeleton of compounds 1-TeM is unprecedented in polyoxometalate chemistry. The stability of these hybrid Krebs-type species in aqueous solution has been confirmed by (1)H NMR spectroscopy performed on the diamagnetic 1-SbZn and 3-SbZn derivatives. Our systematic study of the reactivity of disubtituted Krebs-type polyoxotungstates toward diazole-, pyridine-, and diazinecarboxylates demonstrates that organic derivatization is strongly dependent on the nature of the ligand, as follows: imc displays a "universal ligand" character, as functionalization takes place regardless of the external 3d metal and heteroatom; pzc and pyzc show selectivity toward specific 3d metals; pyridazine-3-carboxylate and pyrimidine-4-carboxylate promote partial decomposition of specific precursors, leading to [M(II)L2(H2O)2] complexes; and picolinate is inert under all conditions tested.

Crystal structure, solvothermal synthesis, thermogravimetric studies and DFT calculations of a five-coordinate cobalt(II) compound based on the N,N-bis(2-hydroxyethyl)glycine anion

“…There are several coordination modes for the cobalt ion. The common mode is six-coordinate (Bryant et al, 2015;Artetxe et al, 2015), and only relatively few four-coordinate (Gupta et al, 2015) and five-coordinate (Lee et al, 2015) cobalt complexes have been recorded. Generally, five-coordinate compounds have two classical configurations, trigonal-bipyramidal and square-pyramidal, and the extent of each geometry each can be determined by the value (Addison et al, 1984).…”

Naphthyl-Containing Organophosphonate Derivatives of Keggin-Type Polyoxotungstates

“…The spin system, determined as two singlets at 3.47 and 3.51 ppm in the phosphonic acid, becomes diastereotopic in the hybrid POM structure in such a way that four different protons can be differentiated: H a and H b from one of the P(O)CH 2 C 10 H 7 moieties and H c and H d from the other one ( Figure 10). These four resonances appear as doublets with a geminal coupling constant of about J = 15.2 Hz and arrange into two well-separated groups of signals because those that originate from the two H atoms pointing at the POM surface undergo significantly larger shift downfield due to the intramolecular C-H¨¨¨O POM interactions, which promote the deshielding of the protons [15] (H a and H c : ∆δ = 0.69-0.76 ppm for TBA-1 and ∆δ = 0.62-0.66 ppm for TBA-2; H b and H d : ∆δ = 0.42-0.47 ppm for TBA-1 and ∆δ = 0.34-0.38 ppm for TBA-2). It is also worth noting the roof effect of the signals, which is characteristic of almost overlapping resonances showing similar intensity.…”

Crystal structure oftrans-diaquabis(1H-pyrazole-3-carboxylato-κ2N,O)copper(II) dihydrate

“…Data collection: CrysAlis PRO (Agilent, 2011); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: OLEX2 (Dolomanov et al, 2009); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2009). Zn(II) analogues (Artetxe et al, 2015;López-Viseras et al, 2014). However, the axial bond lenghts are much longer due to the Jahn-Teller effect operating in Cu (…”