ChemInform Abstract: STRUCTURAL AND MAGNETIC CHARACTERIZATION OF T

Cline, Susan J.; Kallesoee, S.; Pedersen, E.; Hodgson, Derek J.

doi:10.1002/chin.197924075

Cited by 2 publications

(2 citation statements)

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“…As expected from structural studies on other transition metal dipicolinate complexes [21][22][23][24][25], the dipicolinate ligand is bound to the Ti centre by its pyridine N atom and two of the carboxylate 0 atoms, which occupy the central and the two lateral coordination sites of the titanocene fragment. The Ti-N and Ti-O distances of 216 and 211 pm are significantly longer than Ti-N= bonds (196-202 pm) [2,26,27] and Ti-O bonds (186-190 pm) [28][29][30] in comparable, tetracoordinate titanocene complexes.…”

Section: Resultsmentioning

confidence: 83%

Dicyclopentadienyltitanium(IV) pyridine-2,6-dicarboxylate complexes. Synthesis and structural characterization as pentacoordinate titanocene derivatives

Leik

Zsolnai

Hüttner

et al. 1986

Journal of Organometallic Chemistry

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Reaction of (CsHs)2Ti(CH3)2 or (CH3).C2(C,H4)2Ti(CH3)2 with pyridine-2,6dicarboxylic acid (dipicolinic acid) yields titanocene dipicolinate derivatives. The molecular structure of (C,H,),Ti dipicolinate is that of an axially symmetric, pentacoordinate titanocene derivative with two carboxyl oxygen atoms and the pyridine nitrogen atom as ligating atoms. Two identical chelate bite angles of only 71 0 make the dipicolinate ligand particularly suited to form a remarkably stable titanocene derivative with unprecedented pentacoordinate geometry. '" To whom correspondence should be addressed. ** Cf. ref. 1 and references therein. At the titanium-(II) and-(III) levels, titanocene derivatives with tricoordinate geometry have been reported in a few instances [2-51. *** Whether complexes with '12-coordinated ligands, such as (CsRshTi(CO)C2(C6Hsh [12] or (CsHshTi(CI)OCCH3 [13] should be considered as examples of pseudotetrahedral geometry or as exceptions to this rule is debatable. In a number of instances, pentacoordinate or hexacoordinate dicyc1opentadienyltitanium(lV) species have been proposed without support from crystal structure determinations [14-19}.

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Section: Resultsmentioning

confidence: 83%

Dicyclopentadienyltitanium(IV) pyridine-2,6-dicarboxylate complexes. Synthesis and structural characterization as pentacoordinate titanocene derivatives

Leik

Zsolnai

Hüttner

et al. 1986

Journal of Organometallic Chemistry

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“…The magnitude of the exchange parameter depends upon the Cr-O-Cr bridging angle [68], the Cr-O bond length [69] and the dihedral angle between the bridge planes [70]. A number of data have been summarized [71,72] and applied to a model which has been constructed to include the different structural parameters.…”

Section: Some Other Dimersmentioning

confidence: 99%

Introduction to Magnetic Exchange: Dimers and Clusters

Carlin

1986

Magnetochemistry

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Energy Levels and Specific Heats 71configurational mixing of states such as M+ F M2+. The electron on Fin (c) and (d) can now couple with the lone electron in a d z 2 orbital on an adjoining Ni2+ . The preferred coupling is to give a singlet state [(c), called antiferromagnetic] rather than a triplet, (d). This in turn stabilizes the singlet state (a) with respect to the triplet (b). The strength of the interaction will depend on the amount of overlap, and we present here only a model of 180° superexchange. Metal ion orbitals can also overlap with p" ligand orbitals at a 90° angle, and much recent research effort has gone into finding the factors which influence this superexchange interaction.This model, which has been applied to a variety of systems [1,2] is somewhat similar to that which is used for explaining spin-spin coupling in NMR spectroscopy [3]. The Hamiltonian in use for metal-metal exchange interaction in magnetic insulators is of the form (5.2) where the sum is taken over all pair-wise interactions of spins i and j in a lattice. For the moment, we shall restrict our attention to dimers, and thereby limit the summation to the two atoms 1 and 2 in the dimeric molecule, so thatThis is called an isotropic (note the dot product between the two spins, S) or Heisenberg Hamiltonian, and we adopt the convention that negative J refers to antiferromagnetic (spin-paired or singlet ground state in a dimer) interactions, and positive J refers to ferromagnetic (spin-triplet ground state) interactions. The exchange constant J is given in energy units (Kelvins) and measures the strength ofthe interaction. The reader must be careful in comparing different authors, for a variety of conventions (involving the negative sign and even the factor of 2) are in use. (The symbol J now takes a different meaning from its earlier use as the quantum operator for total angular momentum.) Energy Levels and Specific HeatsAn antiferromagnetic interaction ofthe type given in Eq. (5.3), when applied to two ions each of!/ = t gives a spin-singlet ground state and a spin-triplet 2J in energy above the singlet ( Fig. 5.2). Naturally, ifthe interaction were ferromagnetic, the diagram is simply inverted. For an external field applied along the z-axis of the pair, the complete Hamiltonian will be taken as

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ChemInform Abstract: STRUCTURAL AND MAGNETIC CHARACTERIZATION OF T

Cited by 2 publications

References 1 publication

Dicyclopentadienyltitanium(IV) pyridine-2,6-dicarboxylate complexes. Synthesis and structural characterization as pentacoordinate titanocene derivatives

Dicyclopentadienyltitanium(IV) pyridine-2,6-dicarboxylate complexes. Synthesis and structural characterization as pentacoordinate titanocene derivatives

Introduction to Magnetic Exchange: Dimers and Clusters

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