title: Metal Ion Complexes of N,N'-Bis(2-Pyridylmethyl)-trans-1,2-Diaminocyclohexane-N,N'-Diacetic Acid, H2bpcd: Lanthanide(III)-bpcd2-Cationic Complexes.
abstract: The synthesis and characterization of N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetic acid (H2bpcd) cationic complexes of La(III), Nd(III), and Sm(III) are reported. The Ln(III)-bpcd2-complex ions, where bpcd2-stands for N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetate, were isolated as PF6-salts. These salts were characterized by elemental analysis, X-ray crystallography, IR, and1H and13C NMR spectroscopy. Binuclear [La2(bpcd)2(H2O)2]2+crystallized from an aqueous solution in the monoclinic P21/c space group as a cocrystallate with Na2bpcd and NaPF6, nominally Na2.34[La1.22(C22H26N4O4)2(H2O)2][PF6]2·2H2O, 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 N4O4donor atom set. In addition to four N atoms from the bpcd2-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). The1H and13C assignments for H2bpcd and the metal-bpcd2-complexes were made on the basis of 2D COSY and HSQC experiments, which established1H-1H and1H-13C 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)-bpcd2-and Sm(III)-bpcd2-complexes are present in solution as a single species with C2symmetry. The1H NMR spectrum of [Nd(bpcd)]PF6in D2O 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)-bpad2-complex ions, were used to determine the relative free energies of the geometric isomers possible for eight- and nine-coordinate La(III)-bpcd2-cationic aqua complexes in aqueous solution, i.e., [La(bpcd)(H2O)2]+and La(bpcd)(H2O)3]+.
authors.affiliation: Department of Chemistry, Illinois State University , Campus Box 4160, Normal, Illinois 61790-4160, United States.
authors.forename: Craig C
authors.initials: CC
authors.lastname: McLauchlan
authors.affiliation: Department of Chemistry and Biochemistry, Loyola University Chicago , 1032 W. Sheridan Road, Chicago, Illinois 60660, United States.
authors.forename: Jan
authors.identifier: http://orcid.org/0000-0003-2669-4293
authors.initials: J
authors.lastname: Florián
authors.affiliation: Department of Chemistry and Biochemistry, Loyola University Chicago , 1032 W. Sheridan Road, Chicago, Illinois 60660, United States.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Kissel
authors.affiliation: Department of Chemistry and Biochemistry, Loyola University Chicago , 1032 W. Sheridan Road, Chicago, Illinois 60660, United States.
authors.forename: Albert W
authors.initials: AW
authors.lastname: Herlinger