Stereochemistry of tris(bidentate) complexes

Kepert, David L.

doi:10.1021/ic50113a022

Cited by 80 publications

(20 citation statements)

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“…The distortions of both octahedra, as measured by e (departure from the parallelism of the basal triangles) and ¢p (twist angle of these same triangles with respect to their antiprismatic position), are very similar (see Table 3). The tp values found are in excellent agreement with calculations based on Kepert's theoretical correlation with the bite of the ligand (Kepert, 1972(Kepert, , 1977 (2)]}. This is consistent with the hydrogen-bonding scheme observed (see below).…”

Section: Experimental Suitable Rectangular Prismatic Crystalssupporting

confidence: 87%

Structure of the active racemic complex [(±)Co(en)3](C2O4)I.1.5H2O: a hydrogen-bond-induced case of asymmetry

Fuertes¹,

Miravitlles²,

Ibáñez³

et al. 1988

Acta Crystallogr C

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Section: Experimental Suitable Rectangular Prismatic Crystalssupporting

confidence: 87%

Structure of the active racemic complex [(±)Co(en)3](C2O4)I.1.5H2O: a hydrogen-bond-induced case of asymmetry

Fuertes¹,

Miravitlles²,

Ibáñez³

et al. 1988

Acta Crystallogr C

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“…For monodentate ligands, q = 608 and q = 08 denote the ideal OC and TP limits, respectively. For three chelate ligands with bite angles b smaller than 908, [55,56] q = 08 still applies to the trigonal prism but the octahedral limit corresponds to q values smaller than 608 (48.2 and 36.08 for b = 80 and 708, respectively). [56] Another consequence of the presence of chelate ligands is that the O h symmetry cannot be reached for the OC structure.…”

Section: Resultsmentioning

confidence: 99%

2,2′‐Biphosphinines and 2,2′‐Bipyridines in Homoleptic Dianionic Group 4 Complexes and Neutral 2,2′‐Biphosphinine Group 6 d⁶ Metal Complexes: Octahedral versus Trigonal‐Prismatic Geometries

Lesnard¹,

Cantat²,

Floch³

et al. 2007

Chemistry A European J

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The geometric and electronic structure of formally d(6) tris-biphosphinine [M(bp)(3)](q) and tris-bipyridine [M(bpy)(3)](q) complexes were studied by means of DFT calculations with the B3LYP functional. In agreement with the available experimental data, Group 4 dianionic [M(bp)(3)](2-) complexes (1P-3P for M=Ti, Zr, and Hf, respectively) adopt a trigonal-prismatic (TP) structure, whereas the geometry of their nitrogen analogues [M(bpy)(3)](2-) (1N-3N) is nearly octahedral (OC), although a secondary minimum was found for the TP structures (1N'-3N'). The electronic factors at work in these systems are discussed by means of an MO analysis of the minima, MO correlation diagrams, and thermodynamic cycles connecting the octahedral and trigonal-prismatic limits. In all these complexes, pronounced electron transfer from the metal center to the lowest lying pi* ligand orbitals makes the d(6) electron count purely formal. However, it is shown that the bp and bpy ligands accommodate the release of electron density from the metal in different ways because of a change in the localization of the HOMO, which is a mainly metal-centered orbital in bp complexes and a pure pi* ligand orbital in bpy complexes. The energetic evolution of the HOMO allows a simple rationalization of the progressive change from the TP to the OC structure on successive oxidation of the [Zr(bp)(3)](2-) complex, a trend in agreement with the experimental structure of the monoanionic complex. The geometry of Group 6 neutral complexes [M(bp)(3)] (4P and 5P for M=Mo and W, respectively) is found to be intermediate between the TP and OC limits, as previously shown experimentally for the tungsten complex. The electron transfer from the metal center to the lowest lying pi* ligand orbitals is found to be significantly smaller than for the Group 4 dianionic analogues. The geometrical change between [Zr(bp)(3)](2-) and [W(bp)(3)] is analyzed by means of a thermodynamic cycle and it is shown that a larger ligand-ligand repulsion plays an important role in favoring the distortion of the tungsten complex away from the TP structure.

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“…The restrained non-bonded model is similar to the points-on-asphere (POS) model, frequently used for coordination compounds. 17,38,39 Both methods include metal-ligand bonds, exclude ligand-metal-ligand angles, and include ligand-ligand nonbonded interactions. However, the POS model normally retains all the other bonded terms involving the metal, whereas the restrained model excludes them.…”

Section: Discussionmentioning

confidence: 99%

Comparison of Methods to Obtain Force-Field Parameters for Metal Sites

Ryde

2011

J. Chem. Theory Comput.

119

173

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We have critically examined and compared various ways to obtain standard harmonic molecular-mechanics (MM) force-field parameters for metal sites in proteins, using the twelve most common Zn 2+ sites as test cases. We show that the parametrisation of metal sites is hard to treat with automatic methods. The choice of method is a compromise between speed and accuracy, and therefore depends on the intended use of the parameters. If the metal site is not of central interest in the investigation, e.g. a structural metal, far from the active site, a simple and fast parametrisation is normally enough, using either a non-bonded model with restraints or a bonded parametrisation based on the method of Seminario. On the other hand, if the metal site is of central interest in the investigation, a more accurate method is needed to give quantitative results, e.g. the method by Norrby and Liljefors. The former methods are semiautomatic and can be performed in seconds, once quantum mechanical (QM) geometry optimisation and frequency calculations have been performed, whereas the latter method typically takes several days and requires significant human intervention. All approaches require a careful selection of the atom types used. For a non-bonded model, standard atom types can be used, whereas for a bonded-model, it is normally wise to use special atom types for each metal ligand. For accurate results, new atom types for all atoms in the metal site can be used. Atomic charges should also be considered. Typically, QM restrained electrostatic potential charges are accurate and easy to obtain once the QM calculation is performed, and they allow for charge transfer within the complex. For negatively charged complexes, it should be checked that hydrogen atoms of the ligands get proper charges. Finally, water ligands pose severe problems for bonded models in force fields that ignore non-bonded interactions for atoms separated by two bonds. Complexes with a single water ligand can normally be accurately treated with a bonded potential, once it is ensured that the water H atoms have non-zero Lennard-Jones parameters. However, for metal sites with several water molecules, a non-bonded model with restraints (taken from the QM calculations) is more stable.

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Stereochemistry of tris(bidentate) complexes

Cited by 80 publications

References 0 publications

Structure of the active racemic complex [(±)Co(en)3](C2O4)I.1.5H2O: a hydrogen-bond-induced case of asymmetry

Structure of the active racemic complex [(±)Co(en)3](C2O4)I.1.5H2O: a hydrogen-bond-induced case of asymmetry

2,2′‐Biphosphinines and 2,2′‐Bipyridines in Homoleptic Dianionic Group 4 Complexes and Neutral 2,2′‐Biphosphinine Group 6 d⁶ Metal Complexes: Octahedral versus Trigonal‐Prismatic Geometries

Comparison of Methods to Obtain Force-Field Parameters for Metal Sites

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Stereochemistry of tris(bidentate) complexes

Cited by 80 publications

References 0 publications

Structure of the active racemic complex [(±)Co(en)3](C2O4)I.1.5H2O: a hydrogen-bond-induced case of asymmetry

Structure of the active racemic complex [(±)Co(en)3](C2O4)I.1.5H2O: a hydrogen-bond-induced case of asymmetry

2,2′‐Biphosphinines and 2,2′‐Bipyridines in Homoleptic Dianionic Group 4 Complexes and Neutral 2,2′‐Biphosphinine Group 6 d6 Metal Complexes: Octahedral versus Trigonal‐Prismatic Geometries

Comparison of Methods to Obtain Force-Field Parameters for Metal Sites

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2,2′‐Biphosphinines and 2,2′‐Bipyridines in Homoleptic Dianionic Group 4 Complexes and Neutral 2,2′‐Biphosphinine Group 6 d⁶ Metal Complexes: Octahedral versus Trigonal‐Prismatic Geometries