Inorganic Stereochemistry

Kepert, David L.

doi:10.1007/978-3-642-68046-5

Cited by 320 publications

(170 citation statements)

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“…At first glance, the fact that the Ln III centers in the isomorphous complexes 1·2MeOH, 2·2MeOH and 4·2MeOH have different coordination geometries (and not consistent CShM values) seems strange. We attribute this to two factors: (i) For a given ligand set of nine donor atoms, the tricapped trigonal prism, capped square antiprism and capped cube polyhedra have comparable energies [48,49] and there exist minimal distortion interconversion paths between them; thus many structures are intermediate between two ideal shapes [48], and (ii) the Ln III -donor atom distances are slightly different due to lanthanide(III) contraction and this can affect the shape. For example, the CShM values of the Dy III center in 4·2MeOH for the spherical capped square antiprism (3.263), spherical-relaxed capped cube (4.016) and tricapped trigonal prism (4.165) are all low and similar (Table S1), and its polyhedron could be equally well described as spherical-relaxed capped cube (a polyhedron that gives the lowest CShM value for the Pr III center in 1·2MeOH, Table S3).…”

Section: Interatomic Distances (å) Amentioning

confidence: 99%

Using the Singly Deprotonated Triethanolamine to Prepare Dinuclear Lanthanide(III) Complexes: Synthesis, Structural Characterization and Magnetic Studies

et al. 2017

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Abstract:The 1:1 reactions between hydrated lanthanide(III) nitrates and triethanolamine (teaH 3 ) in MeOH, in the absence of external bases, have provided access to the dinuclear complexes [Ln 2 (NO 3 ) 4 (teaH 2 ) 2 ] (Ln = Pr, 1; Ln = Gd, 2; Ln = Tb, 3; Ln = Dy, 4; Ln = Ho, 5) containing the singly deprotonated form of the ligand. Use of excess of the ligand in the same solvent gives mononuclear complexes containing the neutral ligand and the representative compound [Pr(NO 3 )(teaH 3 ) 2 ](NO 3 ) 2 (6) was characterized. The structures of the isomorphous complexes 1·2MeOH, 2·2MeOH and 4·2MeOH were solved by single-crystal X-ray crystallography; the other two dinuclear complexes are proposed to be isostructural with 1, 2 and 4 based on elemental analyses, IR spectra and powder XRD patterns. The IR spectra of 1-6 are discussed in terms of structural features of the complexes. The two Ln III atoms in centrosymmetric 1·2MeOH, 2·2MeOH and 4·2MeOH are doubly bridged by the deprotonated oxygen atoms of the two η 1 :η 1 :η 1 :η 2 :µ 2 teaH 2 − ligands. The teaH 2 − nitrogen atom and six terminal oxygen atoms (two from the neutral hydroxyl groups of teaH 2 − and four from two slightly anisobidentate chelating nitrato groups) complete 9-coordination at each 4f-metal center. The coordination geometries of the metal ions are spherical-relaxed capped cubic (1·2MeOH), Johnson tricapped trigonal prismatic (2·2MeOH) and spherical capped square antiprismatic (4·2MeOH). O-H···O H bonds create chains parallel to the a axis. The cation of 6 has crystallographic two fold symmetry and the rotation axis passes through the Pr III atom, the nitrogen atom of the coordinated nitrato group and the non-coordinated oxygen atom of the nitrato ligand. The metal ion is bound to the two η 1 :η 1 :η 1 :η 1 teaH 3 ligands and to one bidentate chelating nitrato group. The 10-coordinate Pr III atom has a sphenocoronal coordination geometry. Several H bonds are responsible for the formation of a 3D architecture in the crystal structure of 6. Complexes 1-6 are new members of a small family of homometallic Ln III complexes containing various forms of triethanolamine as ligands. Dc magnetic susceptibility studies in the 2-300 K range reveal the presence of a weak to moderate intramolecular antiferromagnetic exchange interaction (J = −0.30(2) cm −1 based on the spin HamiltonianĤ = −J(Ŝ Gd1 ·Ŝ Gd1 )) for 2 and probably weak antiferromagnetic exchange interactions within the molecules of 3-5. The antiferromagnetic Gd III ···Gd III interaction in 2 is discussed in terms of known magnetostructural correlations for complexes possessing the {Gd 2 (µ 2 -OR) 2 } 4+ core. Ac magnetic susceptibility measurements in zero dc field for 3-5 do not show frequency dependent out-of-phase signals; this experimental fact is discussed and rationalized for complex 4 in terms of the magnetic anisotropy axis for each Dy III center and the oblate electron density of the metal ion.

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Section: Interatomic Distances (å) Amentioning

confidence: 99%

Using the Singly Deprotonated Triethanolamine to Prepare Dinuclear Lanthanide(III) Complexes: Synthesis, Structural Characterization and Magnetic Studies

et al. 2017

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“…The basal pinacoid face of the square pyramid forms together with two sulphur atoms Table 2. Geometric conditions for an ideal single-capped trigonal prism [31]. Five different edges with index i have to be distinguished occurring with frequency ni and different edge lengths di.…”

Section: Compression Mechanismmentioning

confidence: 99%

The high-pressure ?/? phase transition in lead sulphide (PbS)

Knorr

Ehm

Hytha

et al. 2003

The European Physical Journal B - Condensed Matter

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Abstract. The high-pressure behaviour of PbS was investigated by angular dispersive X-ray powder diffraction up to pressures of 6.8 GPa. Experiments were accompanied by first principles calculations at the density functional theory level. By combining both methods reliable data for the elastic properties of rock-salt type α-and high-pressure β-PbS could be obtained. β-PbS could be determined to crystallise in the CrB-type (B33), with space group Cmcm. The reversible ferro-elastic α/β transition is of first order. It is accompanied by a large volume discontinuity of about 5% and a coexistence region of the two phases. A gliding mechanism of {001} bilayers along one of the cubic 110 directions governs the phase transition which can be described in terms of group/subgroup relationships via a common subgroup, despite its reconstructive

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“…First we look for the best-fitting MSA or TTP for a given structure (MD snapshot) by applying the symmetry operations of the point group to all donor atoms and estimating a quality factor related to the root mean square displacements [25]. In order to confirm our symmetry assignment, we calculate the angles defined by Kepert [35] (Fig. 2).…”

Section: Coordination Polyhedron Dynamicsmentioning

confidence: 99%

Molecular Dynamics Simulations of the Internal Mobility of Gd3+-Based MRI Contrast Agents: Consequences for Water Proton Relaxivity

Borel¹,

Yerly²,

Helm³

et al. 2004

Chimia

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Abstract:The increasing use of contrast agents in magnetic resonance imaging (MRI) for medical diagnosis is due to the ability, called relaxivity, of these paramagnetic compounds to accelerate the relaxation of the surrounding water proton spins. A new classical force field for molecular dynamics simulations of Gd 3+ polyaminocarboxylates has recently been published, which allows the study of the chelate internal mobility. We present two selected examples where such motions can affect relaxivity. Knowing the relationship between the bound water proton and oxygen mobility is important for the combined analysis of multinuclear NMR studies, and we show that they differ significantly. Next, we observe symmetry changes over time in the Gd 3+ coordination polyhedron of the acyclic complexes. We propose that such rearrangements can play a role in the electron spin relaxation of Gd 3+ chelates, an important result considering the uncertainty still attached to this particular factor.

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Inorganic Stereochemistry

Cited by 320 publications

References 0 publications

Using the Singly Deprotonated Triethanolamine to Prepare Dinuclear Lanthanide(III) Complexes: Synthesis, Structural Characterization and Magnetic Studies

Using the Singly Deprotonated Triethanolamine to Prepare Dinuclear Lanthanide(III) Complexes: Synthesis, Structural Characterization and Magnetic Studies

The high-pressure ?/? phase transition in lead sulphide (PbS)

Molecular Dynamics Simulations of the Internal Mobility of Gd3+-Based MRI Contrast Agents: Consequences for Water Proton Relaxivity

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