Functionalization of Krebs-type polyoxometalates with N,O-chelating ligands: a systematic study.
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.
Departamento de Química Inorgánica, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU , P.O. Box 644, 48080 Bilbao, Spain.
Beñat
B
Artetxe
Santiago
S
Reinoso
Leire
L
San Felices
Pablo
P
Vitoria
Aroa
A
Pache
Jagoba
J
Martín-Caballero
Juan M
JM
Gutiérrez-Zorrilla
D000965:Antimony / Q000737:chemistry; D002264:Carboxylic Acids / Q000737:chemistry; D002614:Chelating Agents / Q000138:chemical synthesis / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D009584:Nitrogen / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D011719:Pyrazines / Q000737:chemistry; D011720:Pyrazoles / Q000737:chemistry; D013691:Tellurium / Q000737:chemistry; D017973:Tungsten Compounds / Q000138:chemical synthesis / Q000737:chemistry*
D002264:Carboxylic Acids; D002614:Chelating Agents; D007093:Imidazoles; D008024:Ligands; D011719:Pyrazines; D011720:Pyrazoles; D017973:Tungsten Compounds; D000965:Antimony; D009584:Nitrogen; D013691:Tellurium; D010100:Oxygen