Metal Ion Complexes of N,N′-Bis(2-Pyridylmethyl)-trans-1,2-Diaminocyclohexane-N,N′-Diacetic Acid, H₂bpcd: Lanthanide(III)–bpcd^2– Cationic Complexes

Abstract

The synthesis and characterization of N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetic acid (Hbpcd) cationic complexes of La(III), Nd(III), and Sm(III) are reported. The Ln(III)-bpcd complex ions, where bpcd stands for N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetate, were isolated as PF salts. These salts were characterized by elemental analysis, X-ray crystallography, IR, and H andC NMR spectroscopy. Binuclear [La(bpcd)(HO)] crystallized from an aqueous solution in the monoclinic P2/c space group as a cocrystallate with Nabpcd and NaPF, nominally Na[La(CHNO)(HO)][PF]·2HO, with a = 11.3343(6) Å, b = 17.7090(9) Å, c = 15.0567(8) Å, β = 110.632(3)°, and Z = 4 (Z' = 2). La is eight-coordinate with distorted dodecahedral coordination geometry provided by a NO donor atom set. In addition to four N atoms from the bpcd ligand, La's coordination sphere includes O atoms from a water molecule and three acetate groups (one O atom from singly bound acetate and two O atoms from acetate groups that bridge the La centers). The H andC assignments for Hbpcd and the metal-bpcd complexes were made on the basis of 2D COSY and HSQC experiments, which established H-H and H-C correlations. The NMR spectral data were used to establish the symmetry of the cationic complexes present in aqueous solution. The data indicate that the La(III)-bpcd and Sm(III)-bpcd complexes are present in solution as a single species with C symmetry. The H NMR spectrum of [Nd(bpcd)]PF in DO consists of eight considerably line-broadened, paramagnetic-shifted singlets. The ab initio quantum mechanical calculations at the PCM/MP2/SDD//HF/SDD level, which were established previously for determining isomerization energies for octahedral M(III)-bpad complex ions, were used to determine the relative free energies of the geometric isomers possible for eight- and nine-coordinate La(III)-bpcd cationic aqua complexes in aqueous solution, i.e., [La(bpcd)(HO)] and La(bpcd)(HO)].

Influence of a Heterocyclic Nitrogen-Donor Group on the Coordination of Trivalent Actinides and Lanthanides by Aminopolycarboxylate Complexants

“…study byMcLauchlan et al, who reported shorter bond lengths between the lanthanum ion and the pyridine nitrogen atoms of N,N′-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N′diacetic acid, relative to the nitrogen atoms of the ethylenediamine backbone 57. The M−N 4 bond in [EuDTTA-PyM] − is still substantially longer than a typical metal−oxygen bond, however.…”

Circularly Polarized Luminescence from New Heteroleptic Eu(III) and Tb(III) Complexes

“…DFT calculations were carried out to obtain structural information about the [Ln(bpcd)L] complexes by studying the diamagnetic analogues of the Eu and Tb complexes. As previously described, 30,58 several isomeric forms can be present, depending on the arrangement of the pyridine and acetate groups in the bpcd ligand, namely, trans-OO, trans-NN, and cis-OO,NN. These isomers can host either the Coum (Figure 8a−c) or tta (Figure 8d−f) ligand, which replaces the coordinated solvent molecules.…”

Lanthanide‐Based Complexes Containing a Chiral trans‐1,2‐Diaminocyclohexane (DACH) Backbone: Spectroscopic Properties and Potential Applications

“…McLauchlan et al. showed that, although the [Ln(bpcd)]PF 6 complexes are C 2 ‐symmetric single species in solution, the La‐based derivative crystallizes as binuclear complex with [La 2 (bpcd) 2 (H 2 O) 2 ] 2+ formula [64] …”