Syntheses, Structures, and Properties of Tetrakis(μ-acetato)dirhodium(II) Complexes with Axial Pyridine Nitrogen Donor Ligands with or without Assistance of Hydrogen Bonds

Abstract

Eight adducts of Rh2(O2CCH3)4 with axial pyridine derivatives that contain hydrogen-bonding amino and/or steric methyl substituents in the 2- and 6-positions have been prepared and examined by electronic absorption and 1H NMR spectroscopy in solution and by elemental, IR, thermogravimetric, and X-ray diffraction analyses in the solid state. The results indicated that strong hydrogen bonding interactions between Rh2(O2CCH3)4 and axially coordinated pyridine derivatives with a 2- or 6-amino group occur in both solution and the solid state and contribute to the higher thermal stability of the molecular assembly of dirhodium complexes. It was demonstrated that such a combination of coordinate and hydrogen bonds is useful as a building tool in designing and constructing new organic-inorganic hybridized compounds and supramolecular architectures.

Synthesis, spectral and structural characterization of dinuclear rhodium (II) complexes of the anticonvulsant drug valproate with theophylline and caffeine

“…The adducts formed are green or blue-green for oxygen donor ligands, rose-red, violet, purple or pink for nitrogen donors, and violet, purple, or orange for sulfur donors [35]. The purple or violet color and the shift of the absorption peak of band I to higher energy for the bis-adducts 4 and 5 compared with the absorption peak of the binary Rh 2 (valp) 4 complex ( Table 1) is in agreement with an axial nitrogen donor ligands [1,14]. Band II in the visible region of dirhodium tetracarboxylates does not depend on the nature of axial ligands but it depends on the nature of the equatorial ligands, i.e.…”

“…r * (RhRh) transition and the higher energy band (II) as the p * (RhRh) ? r * (Rh-O) [1,14,33], or as the p(Rh-O) ? r * (Rh-O) transition [37].…”

“…The antitumor activity of these complexes was first discovered by Bear et al [4,5] and it was found that the activity of dirhodium tetracarboxylate, Rh 2 (OOCR) 4 , to be in the order: methoxyacetate < acetate < propionate < butyrate [5]. The ability of these complexes to function as antitumor agents against many types of tumors, by inhibiting DNA and protein synthesis, has prompted several studies on the nature of rhodium carboxylates formed with various nucleic acids and their constituent bases in order to elucidate their inhibition properties [1,2,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. These investigations have shown that dirhodium tetracarboxylates form stable mono and bis-adducts as well as bridging and/or chelating adducts with a wide variety of ligand types involving donor atoms such as nitrogen, oxygen and sulfur [1,2,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24].…”

Synthesis, crystal structures and catalytic activity of tetrakis(acetato)dirhodium(II) complexes with axial picoline ligands

“…There is a The Rh-Rh bond length, 2.4121(5) Å, is slightly longer than that of Rh 2 (O 2 CCH 3 ) 4 (pyridine) 2 (2.3963(2) Å) [25], whereas the Rh-N bond length (2.317(3) Å) shows a significantly longer than the value of Rh 2 (O 2 CCH 3 ) 4 (pyridine) 2 (2.227(3) Å). The longer Rh-N bond found in 1 is obviously due to the steric repulsion between the 2-methyl groups and acetate oxygens, which have been reported for Rh 2 (O 2 CCH 3 ) 4 with axial pyridine derivatives having 2-or 6-methyl groups, Rh 2 (O 2 CCH 3 ) 4 (2,6-dimethylpyridine) 2 (2.403(4) Å) [26], Rh 2 (O 2 CCH 3 ) 4 (2-amino-6-ethylyridine) 2 (2.36(1) Å [27], bound to Rh atoms by the pyridine nitrogens) and Rh 2 (O 2 CCH 3 ) 4 (2-acetylamino-6-methylpyridine) 2 (2.439(4) Å, bound to Rh atoms by the pyridine nitrogens). The Rh-N bond length increases in the following sequence of the ligand: pyridine < 2-picoline < 2-amino-6-methylpyridine < 2,6-dimethylpyridine < 2-acetylamino-6-methylpyridine.…”

A pyrazine bis-adduct of a binuclear rhodium(II) carboxylate containing 3,4,5-triethoxybenzoate as the equatorial ligand

“…Lantern-type dirhodium carboxylates of the general formula [Rh 2 II,II (O 2 CR) 4 L 2 ] (L are axial ligands) have been the subject of numerous investigations focusing on their catalytic properties, antitumour activity, molecular and electronic structure, spectroscopic features and chemical reactivity (Norman et al, 1979;Christoph & Koh, 1979;Boyar & Robinson, 1983;Cotton & Walton, 1992;Kitamura et al, 2000). Moreover, their use as building blocks in the synthesis of advanced materials has received increasing attention (Marchon et al, 1992;Barbera  et al, 1992;Bonar-Law et al, 2000;Rusjan et al, 2002).…”