“…Many of these structures have been analyzed using principal component analysis (pca) and other methods. [30][31][32][33][34][35][36][37] When diethylenetriamine-type ligands bind to a metal center in a tridentate fashion, the pucker of the two five-membered chelate rings can have either δ or λ chirality (Chart 1), leading to four possible combinations of chelate-ring chirality: δλ, λδ, λλ, and δδ. In pca studies of X-ray structures from the Cambridge Structural Database (CSD) of [M(dien) 2 ] n+ (M ) Ni, Co, Zn, Cu, Cr, Rh, and Ir) 31 and of [M(dien)L n ] 32 complexes and M(dien) fragments, 30 the δλ and λδ conformation combinations were found much more frequently than combinations with the same pucker chirality (δδ and λλ).…”
Section: Introductionmentioning
confidence: 99%
“…Although chelate-ring pucker and factors affecting pucker have not been thoroughly examined for radiopharmaceuticals, extensive structural information exists for a large number of complexes with other metals containing chelate rings with an ethylene group bridge between ligating atoms. Many of these structures have been analyzed using principal component analysis (pca) and other methods. − When diethylenetriamine-type ligands bind to a metal center in a tridentate fashion, the pucker of the two five-membered chelate rings can have either δ or λ chirality (Chart ), leading to four possible combinations of chelate-ring chirality: δλ, λδ, λλ, and δδ. 1 …”
To achieve a net-neutral coordination unit in radiopharmaceuticals with a fac-M(CO)3+ core (M = Tc, Re), facially coordinated monoanionic tridentate ligands are needed. New neutral fac-Re(CO)3L complexes were obtained by treating fac-[Re(CO)3(H2O)3]+ with unsymmetrical tridentate NNN donor ligands (LH) based primarily on a diethylenetriamine (dien) moiety with an aromatic group linked to a terminal nitrogen through a sulfonamide. LHs contain 2,4,6-trimethylbenzenesulfonyl (tmbSO2) and 5-(dimethylamino)naphthalene-1-sulfonyl (DNS) groups. X-ray crystallographic and NMR analyses confirm that in both the solid and the solution states all L- in fac-Re(CO)3L complexes are bound in a tridentate fashion with one donor being nitrogen from a deprotonated sulfonamido group. Another fundamental property that is important in radiopharmaceuticals is shape, which in turn depends on ring pucker. For L- = tmbSO2-dien-, tmbSO2-N'-Medien-, and tmbSO2-N,N-Me2dien-, the two chelate rings have a different pucker chirality, as is commonly found for a broad range of metal complexes. However, for fac-Re(CO)3(DNS-dien), both chelate rings have the same pucker chirality because the sulfonamido ring has an unusual pucker for the absolute configuration at Re; a finding that is attributable to intramolecular and intermolecular hydrogen bonds from the sulfonamido oxygens to the NH2 groups. Averaging of tmb NMR signals, even at -90 degrees C for Re(CO)3(tmbSO2-N,N-Me2dien), indicates rapid dynamic motion in the complexes with this group. However, examination of the structures suggests that free rotation about the S-C(tmb) bond is not possible but that concerted coupled rotations about the N-S and the S-C bonds can explain the NMR data.
“…Many of these structures have been analyzed using principal component analysis (pca) and other methods. [30][31][32][33][34][35][36][37] When diethylenetriamine-type ligands bind to a metal center in a tridentate fashion, the pucker of the two five-membered chelate rings can have either δ or λ chirality (Chart 1), leading to four possible combinations of chelate-ring chirality: δλ, λδ, λλ, and δδ. In pca studies of X-ray structures from the Cambridge Structural Database (CSD) of [M(dien) 2 ] n+ (M ) Ni, Co, Zn, Cu, Cr, Rh, and Ir) 31 and of [M(dien)L n ] 32 complexes and M(dien) fragments, 30 the δλ and λδ conformation combinations were found much more frequently than combinations with the same pucker chirality (δδ and λλ).…”
Section: Introductionmentioning
confidence: 99%
“…Although chelate-ring pucker and factors affecting pucker have not been thoroughly examined for radiopharmaceuticals, extensive structural information exists for a large number of complexes with other metals containing chelate rings with an ethylene group bridge between ligating atoms. Many of these structures have been analyzed using principal component analysis (pca) and other methods. − When diethylenetriamine-type ligands bind to a metal center in a tridentate fashion, the pucker of the two five-membered chelate rings can have either δ or λ chirality (Chart ), leading to four possible combinations of chelate-ring chirality: δλ, λδ, λλ, and δδ. 1 …”
To achieve a net-neutral coordination unit in radiopharmaceuticals with a fac-M(CO)3+ core (M = Tc, Re), facially coordinated monoanionic tridentate ligands are needed. New neutral fac-Re(CO)3L complexes were obtained by treating fac-[Re(CO)3(H2O)3]+ with unsymmetrical tridentate NNN donor ligands (LH) based primarily on a diethylenetriamine (dien) moiety with an aromatic group linked to a terminal nitrogen through a sulfonamide. LHs contain 2,4,6-trimethylbenzenesulfonyl (tmbSO2) and 5-(dimethylamino)naphthalene-1-sulfonyl (DNS) groups. X-ray crystallographic and NMR analyses confirm that in both the solid and the solution states all L- in fac-Re(CO)3L complexes are bound in a tridentate fashion with one donor being nitrogen from a deprotonated sulfonamido group. Another fundamental property that is important in radiopharmaceuticals is shape, which in turn depends on ring pucker. For L- = tmbSO2-dien-, tmbSO2-N'-Medien-, and tmbSO2-N,N-Me2dien-, the two chelate rings have a different pucker chirality, as is commonly found for a broad range of metal complexes. However, for fac-Re(CO)3(DNS-dien), both chelate rings have the same pucker chirality because the sulfonamido ring has an unusual pucker for the absolute configuration at Re; a finding that is attributable to intramolecular and intermolecular hydrogen bonds from the sulfonamido oxygens to the NH2 groups. Averaging of tmb NMR signals, even at -90 degrees C for Re(CO)3(tmbSO2-N,N-Me2dien), indicates rapid dynamic motion in the complexes with this group. However, examination of the structures suggests that free rotation about the S-C(tmb) bond is not possible but that concerted coupled rotations about the N-S and the S-C bonds can explain the NMR data.
“…In the mer- [Co(dien) 2 ] 3+ structure, all but one of the C−N bond lengths were less than 1.48 Å. In addition, there were some unusually short Co−N bond lengths (∼1.91 to 1.93 Å) even though nothing unusual was noted in the publication of this structure . However, disorder does not account for unusually long observed values.…”
Section: Discussionmentioning
confidence: 84%
“…In addition, there were some unusually short Co-N bond lengths (∼1.91 to 1.93 Å) even though nothing unusual was noted in the publication of this structure. 69 However, disorder does not account for unusually long observed values. In the report on the structure of Co[(lel 3 -R-pn) 3 ] 3+ , it is noted that the C-C bond lengths are longer in this structure than in the ob 3 structure.…”
The ability of available molecular mechanics programs to calculate structures and relative energies of metal complexes is examined via a comparative study of five different force fields: Molmec, Momec91(H), Momec91(C), Xnviron, and Spartan. The method used for assessing the validity of the force fields showed that four of the force fields were able to reproduce successfully the structures of various Co(III) hexaamine cations determined by X-ray analysis, even when these structures were considerably distorted. In certain cases, the calculated relative steric energies were not reliable. Small variations in force fields parameters sometimes led to large changes in the calculated steric energies, and in some instances, in the order of steric strain for different isomers. The most notable changes occurred when metal-dependent parameters were altered.
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