Secondary-Sphere Chlorolanthanide(III) Complexes with a 1,3,5-Triazine-Based Ligand Supported by Anion-π, π-π, and Hydrogen-Bonding Interactions.

2,4,6-Dipicolylamine-functionalized 1,3,5-triazine (dpat) was isolated. When reacted with LaCl3, compound [(LaCl6)(H3dpat)][H2O]2 (1) formed, which crystallized in the monoclinic P21/n space group with parameters a = 11.47 Å, b = 19.22 Å, c = 20.98 Å, V = 4652.02 Å, and ß = 90.53°. When reacted with NdCl3, the complex [NdCl3(H2O)4(H3dpat)][Cl]3(MeOH)2 (2) crystallized in the monoclinic P21/n space group with unit cell parameters a = 20.05 Å, b = 12.81 Å, c = 20.64 Å, V = 5004.40 Å, and ß = 110.20°. In both cases, the dpat ligand forms a bowl-shaped cavity that partially envelops the LnIII-containing central unit, which is anionic in 1 and neutral in 2. The formation of these outer-sphere complexes is supported by secondary interactions, including π-π stacking, hydrogen bonding, and anion-π between the chlorolanthanide(III) fragment and the electron-deficient 1,3,5-triazine ring. Evidence of protonation of the pyridine rings in dpat was substantiated through the isolation of [H2dpat][Cl]2 (3). This compound crystallized in the monoclinic C2/c space group with parameters a = 11.93 Å, b = 20.22 Å, c = 15.28 Å, V = 3664.97 Å, and ß = 94.35°. Four pyridine rings are pairwise protonated in 3. dpat showed a moderate ability to extract LaIII from an aqueous to an organic phase, indicating its potential, through judicious manipulation of secondary-sphere interactions, as the starting point for efficient extractants for LnIII ions.

Anion-π and H-Bonding Interactions Supporting Encapsulation of [Ln(NO3)6/5]3-/2- (Ln = Nd, Er) with a Triazine-Based Ligand.

Reaction of NdIII and ErIII nitrate salts with a 1,3,5-tris(dipicolylamine)-triazine (dpat) ligand yielded two unprecedented examples of [Ln(NO3)6/5]3-/2- (Ln = Nd, Er) moieties completely encapsulated by the ligands. They are found in the two new complexes, [(H3dpat)2][(Nd(NO3)6)2]·2CH3CN (1), and the related [(H3dpat)2][(Er(NO3)5)3]·3CH3CN·2H2O (2). The structures of the complexes are similar and they crystallize in the triclinic P-1 space group with a = 12.1630(3), b = 12.2694(3), c = 17.6357(5) Å, V = 2611.10(12) Å3, and a = 14.3372(4), b = 17.1271(4), c = 25.2207(7) Å, V = 5934.7(3) Å3, respectively. Anion-π interactions, which are reported here for the first time for LnIII ion complexes, hydrogen bonding interactions and π-π stacking support the formation of the encapsulated species. Evidence of the protonated dpat ligand in 1 and 2 was found through isolation of (H2dpat)(NO3)2. Finally, the pH-dependent ability of the ligand to extract LaIII and nitrate ions from aqueous into toluene solution is demonstrated.

Tridentate N(2)S ligand from 2,2'-dithiodibenzaldehyde and N,N-dimethylethylenediamine: Synthesis, structure, and characterization of a Ni(II) complex with relevance to Ni Superoxide Dismutase.

Nickel Superoxide Dismutase (NiSOD) and the A-cluster of Carbon Monoxide Dehydrogenase/Acetyl Coenzyme A Synthase (CODH/ACS) both feature active sites with Ni coordinated by thiolate and amide donors. It is likely that the particular set of donors is important in tuning the redox potential of the Ni center(s). We report herein an expansion of our efforts involving the use of 2,2'-dithiodibenzaldehyde (DTDB) as a synthon for metal-thiolate complexes to reactions with Ni complexes of N,N-dimethylethylenediamine (dmen). In the presence of coordinating counterions, these reactions result in monomeric square-planar complexes of the tridentate N(2)S donor ligand derived from the Schiff-base condensation of dmen and DTDB. In the absence of a coordinating counterion, we have isolated a Ni(II) complex with an asymmetric N(2)S(2) donor set involving one amine and one imine N donor in addition to two thiolate donors. This latter complex is discussed with respect to its relevance to the active site of NiSOD.