Studies on metal carboxylates. Part III. Pyridine-2,6-dicarboxylates of the lanthanides. Synthesis and spectral studies and the X-ray photoelectron spectra of several pyridine carboxylate complexes

Abstract

The lanthanide( 111) acetates react with aqueous solutions of pyridine-2.6-dicarboxylic acid (dipicoiinic acid, dpcH,) to afford two series of complexes, Ln(dpc)(dpcH).GH,O (Ln = La, Ce, Pr, Nd, Sm, Gd, and Tb) and Ln(dpcH),,H,O (Ln = Sm, Gd, Tb, Dy, Ho, or Yb). The samarium complex Sm(dpc)(dpcH).GH,O was isolated in a-and @-forms. X-Ray powder data show that within each series the complexes are isostructural. The electronic absorption spectra of the complexes have also been recorded. The X-ray photoelectron spectra of the dehydrated species Ln(dpc)(dpcH) (Ln = Ce or Pr) and Dy(dpcH), have been investigated and the C(ls), N(1s). and O ( l s ) binding energies measured. Attempts to determine the Ce, Pr, and Dy 4s binding energies were unsuccessful. Related measurements of the C ( 1s). N (Is), and O(1s) binding energies of several pyridine carboxylates of manganese(ll), cobalt(i1). nickel(ii), and silver(i1) are also described.PYRIDINE-2,6-DICARBoxYLIc ACID (dipicolinic acid) can co-ordinate as a neutral (dpcH,), monoanionic (dpcH), or dianionic (dpc) terdentate donor. Our interest in this molecule arose from its stabilization of the silver@) oxidation state to form a complex which can be formulated as Ag(dpc)(dpcH,),xH,O (x = 1 or 4).2-4 Subsequently, we found that its complex with nickel(II), bis-(pyridine-2,6-dicarboxylat 0) nickel( 11) trih ydrate, is best represented as Ni(dpcH),,SH,O. The versatile bonding characteristics of this ligand prompted us to investigate its metal complexes in some detail and in the present report we describe our studies on several of the lanthanide (111) derivatives. EXPERIMENTALThe hydrated lanthanide acetates, of general formula Ln(OAc),,xH,O, were obtained from Apache Chemicals, Inc., Illinois or Bradford Scientific, Massachusetts, and pyridine-2,6-dicarboxylic acid was from the Aldrich Chemical Company. These reagents were used without further purification.Complexes of General Formula Ln(dpc) (dpcH), 6H20.-These complexes were prepared for Ln = La, Ce, Pr, Nd,

Synthesis and characterization of some metal complexes of a proton transfer salt, and their inhibition studies on carbonic anhydrase isozymes and the evaluation of the results by statistical analysis

“…[177.01 (6) ] and the dihedral angle defined by the mean planes of two dipic ligands is 86.97 (14) showing that they fall almost perpendicular. The Ni-N (1.9671(17) and 1.9763(17) Å ) and Ni-O (2.1210(17)-2.1698(17) Å ) bond distances lie within expected range (Table 2).…”

“…Continuing the path to synthesize water soluble proton transfer compounds, our group has focused on forming ion pairs between H 2 DPC and various organic bases, such as 2-aminobenzothiazole 2 , 2-amino-6-methylbenzothiazole 3 , 2-(piperazin-1-yl)ethanol 4 , 2-amino-4-methylpyridine 5 . The interest of metal complexes for H 2 DPC and its deprotonated forms, HDPC À and DPC 2À , stems from their interesting structural features with various coordination modes 1 , stabilization of unusual oxidation states 6 and insulinmimetic effects 7,8 . Benzothiazoles and their simple metal complexes are well known for their biological activities 2,3, 9,10 .…”

Synthesis and characterization of complexes of a novel proton transfer salt and their inhibition studies on carbonic anhydrase isoenzymes

“…Continuing the path to synthesize proton transfer compounds, our group has focused on forming ion pairs between H 2 DPC and various organic bases, such as 2-aminobenzothiazole 2 , 2-amino-6-methylbenzothiazole 3 , 2-amino-6-methoxybenzothiazole 4 , 2-amino-4-methylpyridine 5 , 2-hydroxyethylpiperazine 6 . The interest of metal complexes for H 2 DPC and its deprotonated forms, HDPC À and DPC 2À , stems from their interesting structural features with various coordination modes 1 , stabilization of unusual oxidation states 7 and insulin-mimetic effects 8,9 . Benzothiazoles and their simple metal complexes are well known for their biological activities, such as antitumor agents, antimicrobial, antifungal, analgesics, anti-inflammatory, anti HIV, carbonic anhydrase inhibition and local anesthestic 2-4, [10][11][12][13][14][15] .…”

Polymeric and monomeric dipicolinate complexes with 4-hydroxymethyl pyridine: spectral, structural, thermal and electrochemical characterization

“…During the past few years, these properties have attracted the scientists not only in the field of coordination chemistry but also in both inorganic and bioinorganic chemistries [8,9]. The interest of metal complexes with dpc and its protonated forms, Hdpc and H 2 dpc, stems from their interesting structural features with various coordination modes [10], stabilization of unusual oxidation states [11], chemical analysis of iron at low concentration [12] and catalysis [13]. It is known that there are a range of different coordination modes with possible monodentate [14], bidentate [15,16], tridentate [17,18] or bridging (polymeric, trimeric or dimeric) [19,20] in transition metal-dipicolinate complexes depending on whether the divalent anionic dpc, protonated anionic Hdpc or diprotonated H 2 dpc forms are coordinated to metal ions ( Fig.…”