A pair of uranyl complexes incorporating tetrahydrosalen and N,N-dimethyltetrahydrosalen ligands are synthesized and studied. These new ligands, with saturated secondary and tertiary amines, exhibit higher chemostability than the prototype Schiff base (salen) structure, especially under acidic conditions. As shown by X-ray diffraction crystallography, the coordination geometry of uranium in these new complexes is a distorted pentagonal bipyramid. Interestingly, UO 2 ([H 4 ]salen), comprising the tetrahydrosalen ligand, forms a dimeric structure in the crystals, with two subunits held together by [a]
Because of their versatile coordination modes and strong coordination ability for metals, triazole ligands can provide a wide range of possibilities for the construction of metal-organic frameworks. Three transition-metal complexes, namely bis(μ-1,2,4-triazol-4-ide-3-carboxylato)-κN,O:N;κN:N,O-bis[triamminenickel(II)] tetrahydrate, [Ni(CHNO)(NH)]·4HO, (I), catena-poly[[[diamminediaquacopper(II)]-μ-1,2,4-triazol-4-ide-3-carboxylato-κN:N,O-[diamminecopper(II)]-μ-1,2,4-triazol-4-ide-3-carboxylato-κN,O:N] dihydrate], {[Cu(CHNO)(NH)(HO)]·2HO}, (II), (μ-5-amino-1,2,4-triazol-1-ide-3-carboxylato-κN:N)di-μ-hydroxido-κO:O-bis[triamminecobalt(III)] nitrate hydroxide trihydrate, [Co(CHNO)(OH)(NH)](NO)(OH)·3HO, (III), with different structural forms have been prepared by the reaction of transition metal salts, i.e. NiCl, CuCl and Co(NO), with 1,2,4-triazole-3-carboxylic acid or 3-amino-1,2,4-triazole-5-carboxylic acid hemihydrate in aqueous ammonia at room temperature. Compound (I) is a dinuclear complex. Extensive O-H...O, O-H...N and N-H...O hydrogen bonds and π-π stacking interactions between the centroids of the triazole rings contribute to the formation of the three-dimensional supramolecular structure. Compound (II) exhibits a one-dimensional chain structure, with O-H...O hydrogen bonds and weak O-H...N, N-H...O and C-H...O hydrogen bonds linking anions and lattice water molecules into the three-dimensional supramolecular structure. Compared with compound (I), compound (III) is a structurally different dinuclear complex. Extensive N-H...O, N-H...N, O-H...N and O-H...O hydrogen bonding occurs in the structure, leading to the formation of the three-dimensional supramolecular structure.
Due to their versatile coordination modes and metal-binding conformations, triazolyl ligands can provide a wide range of possibilities for the construction of supramolecular structures. Seven mononuclear transition metal complexes with different structural forms, namely aquabis[3-(4-methylphenyl)-5-(pyridin-2-yl)-1H-1,2,4-triazolato-κN,N]zinc(II), [Zn(CHN)(HO)], (I), bis[5-(4-methylphenyl)-3-(pyridin-2-yl)-1H-1,2,4-triazole-κN,N]bis(nitrato-κO)zinc(II), [Zn(NO)(CHN)], (II), bis(methanol-κO)bis[3-(4-methylphenyl)-5-(pyridin-2-yl)-1H-1,2,4-triazolato-κN,N]zinc(II), [Zn(CHN)(CHO)], (III), diiodidobis[5-(4-methylphenyl)-3-(pyridin-2-yl)-1H-1,2,4-triazole-κN,N]cadmium(II), [CdI(CHN)], (IV), bis[5-(4-methylphenyl)-3-(pyridin-2-yl)-1H-1,2,4-triazole-κN,N]bis(nitrato-κO)cadmium(II), [Cd(NO)(CHN)], (V), aquabis[3-(4-methylphenyl)-5-(pyridin-2-yl)-1H-1,2,4-triazolato-κN,N]cobalt(II), [Co(CHN)(HO)], (VI), and diaquabis[3-(4-methylphenyl)-5-(pyridin-2-yl)-1H-1,2,4-triazolato-κN,N]nickel(II), [Ni(CHN)(HO)], (VII), have been prepared by the reaction of transition metal salts (Zn, Cd, Co and Ni) with 3-(4-methylphenyl)-5-(pyridin-2-yl)-1H-1,2,4-triazole (pymphtzH) under either ambient or hydrothermal conditions. These compounds have been characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. All the complexes form three-dimensional supramolecular structures through hydrogen bonds or through π-π stacking interactions between the centroids of the pyridyl or arene rings. The pymphtzH and pymphtz entities act as bidentate coordinating ligands in each structure. Moreover, all the pyridyl N atoms are coordinated to metal atoms (Zn, Cd, Co or Ni). The N atom in the 4-position of the triazole group is coordinated to the Zn and Cd atoms in the crystal structures of (II), (IV) and (V), while the N atom in the 1-position of the triazolate group is coordinated to the Zn, Co and Ni atoms in (I), (III), (VI) and (VII).
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