Complexation Behavior of Pinene–Bipyridine Ligands towards Lanthanides: The Influence of the Carboxylic Arm

The complexation behavior of two novel, chiral pinene–bipyridine-type ligands ((–)-HL1 and (–)-HL2) containing a carboxylic arm towards lanthanide Ln(III) (Ln = La, Eu, Lu) ions was investigated through spectroscopic methods. The association constants of the mononuclear complexes determined from the UV-Vis titrations indicated that the ligand (–)-HL1 possessing a shorter carboxylic arm formed more stable complexes compared with (–)-HL2, whose carboxylic arm had one more methylene unit. This is due to the formation of more stable seven-member metal chelate rings in the first case as compared with the eight-member metal chelate rings in the second. IR and fluorescence spectroscopy provided additional information about the structure of these complexes.

An Investigation of Some Aspects of the Coordination Chemistry of Synthetic Macroheterocyclic Ligands

<p>The preparation of a range of fully saturated, unsubstituted pentaazamacrocycles is described. The macrocycles vary in ring size from fifteen to twenty members, and comprise every possible arrangement of dimethylene and trimethylene linkages between five nitroqens in a monocyclic arrangement. A new linear homologue of tetraethylene pentamine with trimethylene linkages between nitrogens is also reported. The copper(II) and nickel(II) complexes of these amines have been prepared; the conductivity and spectral properties have been determined in order to investigate their stereochemistry. The nickel(II) complexes of the two largest macrocycles appear to be five-coordinate both in the solid state and in solution. The remainder of the complexes are either five-coordinate (as the perchlorate salts in the solid state or in non-coordinating solvents) or six-coordinate (with a coordinated nitrate). Cobalt(III) complexes of the fifteen to eighteen membered macrocycles have been prepared with a variety of ligands occupying the sixth coordination site. Ligand field parameters have been derived from the electronic spectra of the complexes. The stereochemistry of the complexes and their behaviour on ligand substitution have been investigated principally by 13C n.m.r. Only a few of the numerous possible isomers of each species were formed. The structures of [Co(1, 4, 7, 10, 14-pentaazacycloheptadecane) Cl]Br0.33 Cl1.67. H2O and [Co(1, 4, 7, 11, 15-pentaazacyclooctadecane)Br]Br2, which were determined by single-crystal x-ray diffraction studies, are described. The spontaneous aquation rates of the bromo complexes have been investigated semi-quantitatively, and found to span many orders of magnitude. The most labile bromo complex [Co(1, 4, 8, 11, 15-pentaazacyclooctadecane)Br]Br2 spontaneously aquates in a matter of seconds at room temperature. The increasing strain and steric crowding caused by successive replacement of five-membered chelate rings by six-membered chelate rings, or by simply altering the sequence of five- and six-membered chelate rings is manifested in a progressive increase in the instability of the complexes. In the case of the nineteen- and twenty-membered macrocycles, this crowding and strain results in the formation of stable five-coordinate cobalt(II) complexes; for these ligands, no stable complexes were formed with the smaller cobalt(III) cation. The acid-dissociation kinetics of the copper(II) complexes have been examined in nitric acid at 298 K. A variable temperature study has also been performed on the complex of l, 4, 7, 10, 14-pentaazacycloheptadecane in order to determine the activation parameters. The complexes are labile by comparison with most tetraazamacrocyclic complexes. The dissociation reactions are first-order in complex concentration, but the acid-dependence varies. The observed rate constant is second-order in hydrogen ion concentration for the complex of 1, 4, 7, 10, 13-pentaazacyclopentadecane, first-order in hydrogen ion concentration for 1, 4, 7, 10, 14-pentaazacycloheptadecane and takes the form kobs = a[H+]2/(l+b[H+]2) for the complex of 1, 4, 7, 10, 13-pentaazacyclohexadecane. For the remainder of the complexes, the observed rate constant takes the form kobs = (c[H+] + d[H+]2)/(e + [H+]). Possible mechanisms that are consistent with the above behaviour are presented.</p>

An Investigation of Some Aspects of the Coordination Chemistry of Synthetic Macroheterocyclic Ligands

<p>The preparation of a range of fully saturated, unsubstituted pentaazamacrocycles is described. The macrocycles vary in ring size from fifteen to twenty members, and comprise every possible arrangement of dimethylene and trimethylene linkages between five nitroqens in a monocyclic arrangement. A new linear homologue of tetraethylene pentamine with trimethylene linkages between nitrogens is also reported. The copper(II) and nickel(II) complexes of these amines have been prepared; the conductivity and spectral properties have been determined in order to investigate their stereochemistry. The nickel(II) complexes of the two largest macrocycles appear to be five-coordinate both in the solid state and in solution. The remainder of the complexes are either five-coordinate (as the perchlorate salts in the solid state or in non-coordinating solvents) or six-coordinate (with a coordinated nitrate). Cobalt(III) complexes of the fifteen to eighteen membered macrocycles have been prepared with a variety of ligands occupying the sixth coordination site. Ligand field parameters have been derived from the electronic spectra of the complexes. The stereochemistry of the complexes and their behaviour on ligand substitution have been investigated principally by 13C n.m.r. Only a few of the numerous possible isomers of each species were formed. The structures of [Co(1, 4, 7, 10, 14-pentaazacycloheptadecane) Cl]Br0.33 Cl1.67. H2O and [Co(1, 4, 7, 11, 15-pentaazacyclooctadecane)Br]Br2, which were determined by single-crystal x-ray diffraction studies, are described. The spontaneous aquation rates of the bromo complexes have been investigated semi-quantitatively, and found to span many orders of magnitude. The most labile bromo complex [Co(1, 4, 8, 11, 15-pentaazacyclooctadecane)Br]Br2 spontaneously aquates in a matter of seconds at room temperature. The increasing strain and steric crowding caused by successive replacement of five-membered chelate rings by six-membered chelate rings, or by simply altering the sequence of five- and six-membered chelate rings is manifested in a progressive increase in the instability of the complexes. In the case of the nineteen- and twenty-membered macrocycles, this crowding and strain results in the formation of stable five-coordinate cobalt(II) complexes; for these ligands, no stable complexes were formed with the smaller cobalt(III) cation. The acid-dissociation kinetics of the copper(II) complexes have been examined in nitric acid at 298 K. A variable temperature study has also been performed on the complex of l, 4, 7, 10, 14-pentaazacycloheptadecane in order to determine the activation parameters. The complexes are labile by comparison with most tetraazamacrocyclic complexes. The dissociation reactions are first-order in complex concentration, but the acid-dependence varies. The observed rate constant is second-order in hydrogen ion concentration for the complex of 1, 4, 7, 10, 13-pentaazacyclopentadecane, first-order in hydrogen ion concentration for 1, 4, 7, 10, 14-pentaazacycloheptadecane and takes the form kobs = a[H+]2/(l+b[H+]2) for the complex of 1, 4, 7, 10, 13-pentaazacyclohexadecane. For the remainder of the complexes, the observed rate constant takes the form kobs = (c[H+] + d[H+]2)/(e + [H+]). Possible mechanisms that are consistent with the above behaviour are presented.</p>

A homochiral coordination polymer of cobalt(II) and L-serine

A one-dimensional chiral cobalt(II) coordination polymer, namely, catena-poly[[[(S)-2-amino-3-hydroxypropanoato-κ2 N,O 1]cobalt(II)]-μ-(S)-2-amino-3-hydroxypropanoato-κ4 O 1,O 3:N,O 1′], [Co(C3H6NO3)2] n or Δ-[Co(L-Ser-κ2 N,O)2] n (L-Ser = L-serine) (1), has been synthesized and characterized using elemental and thermal analyses, IR spectroscopy and single-crystal and powder X-ray diffraction techniques. The asymmetric unit of 1 consists of two serine anions which are coordinated to a Co2+ ion to give three chelate rings. These extend the structure into a helical chain with pendant chelate rings which participate in interchain hydrogen bonding. The ability of 1 to undergo transmetallation was evaluated. Among a range of divalent metal ions, only copper(II) partially replaced cobalt(II).

Heterotridentate organodiphosphines in Pt(η3–P1X1P2)(Y) derivatives-structural aspects

This review covers over 30 examples of monomeric Pt(II) complexes of the types: Pt(η3–P1O1P2)(Y) (Y = PL, CL, OL), Pt(η3–P1N1P2)(Y) (Y = H, NL, CL, Cl, PL) and Pt(η3–P1P2N1)(Y) (Y = Cl). The heterotridentate donor ligands create 11 types of a couple chelate rings with common central atom O1 (η3–P1O1P2), N1 (η3–P1N1P2) and P2 (η3–P1P2N1). The most frequent is P1C2N1C2P2. Some cooperative effects between chelate rings and Y donor ligands were found and discussed. A degree of distortions of square-planar geometry about Pt(II) were also calculated.

Au(III) complexes with tetradentate-cyclam-based ligands

Chiral cyclam (1,4,8,11-tetraazacyclotetradecane) derivatives were synthesized stepwise from chiral mono-Boc-1,2-diamines and (dialkyl)malonyl dichloride via open diamide-bis(N-Boc-amino) intermediates (65–91%). Deprotection and ring closure with a second malonyl unit afforded the cyclam tetraamide precursors (80–95%). The new protocol allowed the preparation of the target cyclam derivatives (53–59%) by a final optimized hydride reduction. Both the open tetraamine intermediates and the cyclam derivatives successfully coordinated with AuCl3 to give moderate to excellent yields (50–96%) of the corresponding novel tetra-coordinated N,N,N,N-Au(III) complexes with alternating five- and six-membered chelate rings. The testing of the catalytic ability of the cyclam-based N,N,N,N-Au(III) complexes demonstrated high catalytic activity of some complexes in selected test reactions (full conversion in 1–24 h, 62–97% product yields).

Grafting chelating groups on 2D carbon for selective heavy metal adsorption

Iminodiacetic acid (IDA) is a tridentate ligand, which can capture metal ions by forming two fused five-membered chelate rings. In this study, we fixed IDA moieties onto a two-dimensional nanocarbon,...

Au(III) Complexes with tetradentate cyclam based ligands

Chiral cyclam (1,4,8,11-tetraazacyclotetradecane) derivatives were synthesized stepwise from chiral mono-Boc-1,2-diamines and (dialkyl)malonyl dichloride via the open diamide-di-(N-Boc-amino) intermediates (65-91%). Deprotection and ring closure with a second malonyl unit afforded the cyclam tetraamide precursors (80-95%). The new protocol allowed preparation of the target cyclam derivatives (53-59%) by a final optimized hydride reduction. Both the open tetraamine intermediates and the cyclam derivatives successfully coordinated with AuCl3 to give moderate to excellent yields (50-96%) of the corresponding novel tetracoordinated N,N,N,N-Au(III) complexes with alternating five- and six-membered chelate rings. Testing of catalytic ability of the cyclam based N,N,N,N-Au(III) complexes demonstrated high catalytic activity of some complexes in selected test reactions (full conversion in 1-24h, 62-97% product yields).