Synthesis, structure, and dynamic properties of the lanthanum(III) complex of 1,4,7,10-tetrakis(2-carbamoylethyl)-1,4,7,10-tetraazacyclododecane

Journal Article · Wed Oct 13 04:00:00 EDT 1993 · Inorganic Chemistry; (United States)

DOI:https://doi.org/10.1021/ic00073a017· OSTI ID:7283794

Morrow, J R; Amin, S; Lake, C H; Churchill, M R ^[1]

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1. State Univ. of New York, Buffalo, NY (United States)

The synthesis, structure and dynamic properties of the lanthanum(III) complex of macrocycle 1 (1=1,4,7,10-tetrakis(2-carbamoylethyl)-1,4,7,10-tetraazacyclododecane) are reported. The eight-coordinate La[sup 3+] cation is encapsulated by the macrocyclic ligand and has a distorted square antiprismatic coordination geometry. The macrocyclic ligand coordinates strongly with the four oxygen atoms of the amide groups (average distance = 2.423 [+-] 0.032 [angstrom]) and weakly with the four nitrogen atoms within the macrocyclic ring (average distance = 2.718 [+-] 0.009 [angstrom]). The hydrogen atoms of the amide groups form a hydrogen-bonded system with the triflate counteranions. In acetonitrile or methanol solutions, [sup 13]C NMR resonances for the amide C(O) carbons in the complex are shifted by greater than 2 ppm from those of 1, suggesting that the amide groups are coordinated in these solvents. At low temperatures (O[degrees]C) the ethylenic groups of the 12-membered tetraazamacrocyclic are rigid on the NMR time scale. Variable-temperature [sup 13]C NMR studies suggest that rigidity of the macrocyclic is lost at higher temperatures. A dynamic process involving conformational changes about the cyclen ethylenic groups is consistent with [sup 13]C NMR data, and an activation barrier of 58.9 [+-] 0.3 kJ mol[sup [minus]1] is calculated for this process. A second dynamic process that averages protons on the amide nitrogens may involve free rotation about the amide C-N bond. An activation barrier of 69.8 [+-] 0.5 kJ mol[sup [minus]1] is calculated for this process for the lanthanum complex in dimethyl-d[sub 6] sulfoxide. The activation barrier calculated for the free ligand 1 is 70.5 [+-] 0.5 kJ mol[sup [minus]1]. The close correspondence of these values in conjunction with [sup 13]C NMR data for the amide C(O) resonance suggests that, in dimethyl sulfoxide solution, the amide groups of the complex are not bound.

• OSTI ID: 7283794
• Journal Information: Inorganic Chemistry; (United States), Journal Name: Inorganic Chemistry; (United States) Vol. 32:21; ISSN 0020-1669; ISSN INOCAJ
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACTIVATION ENERGY
CARBON 13
CARBON ISOTOPES
CHEMICAL PREPARATION
COMPLEXES
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DYNAMICS
ENERGY
EVEN-ODD NUCLEI
ISOTOPES
LANTHANUM COMPLEXES
LIGHT NUCLEI
MAGNETIC RESONANCE
MECHANICS
MOLECULAR STRUCTURE
NUCLEAR MAGNETIC RESONANCE
NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORTHORHOMBIC LATTICES
RARE EARTH COMPLEXES
RESONANCE
STABLE ISOTOPES
SYNTHESIS