On the Origin of Electronic Term Splittings in Trigonally Distorted Metal Complexes.

Dingle, R.; Nordfält, Kjell; Bjare, Ulf; Hofsten, Bengt von; Williams, D. H.; Bunnenberg, E.; Djerassi, Carl; Records, Ruth

doi:10.3891/acta.chem.scand.20-1435

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“…It would appear, as has been suggested previously, that the ultimate origin of the trigonal splitting must be sought in the molecular orbital theory. [38][39][40] In this regard Schaffer41 has treated trigonal complexes using his angular overlap model, which is founded on the molecular orbital approach, and has predicted from it a negative K value for the Co(en)33+ complex based only on the known angular distortions of the coordinated nitrogens from octahedral positions. Similarly, O'Reilly and Offenbacher,42 performing a more in-depth molecular orbital calculation, were able to account successfully for the positive K values observed for the Ru3+ ion in the axially elongated Ru06 units in garnets.…”

Section: Discussionmentioning

confidence: 99%

Trigonal field splitting in tris(ethylenediamine) complexes. Evidence from the electron paramagnetic resonance spectrum of Ru(en)33+

Stanko¹,

Peresie²,

Bernheim³

et al. 1973

Inorg. Chem.

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related with steric interaction between the released chloride and the number of axial methyl groups,26 while the rate increase due to ring expansion has been attributed to steric interaction of boat or twist-boat ring conformations.' 327 The rate increase in the primary hydrolysis of trans-Co(en)-(tmd)Cl2+ relative to trans-Co(en)2Clz+ can also be accounted for on this basis and the positive value for the entropy of activation supports Tobe's t h e~r y , '~ as considerable stereochemical change is observed. Registry No. [Cr(en)(tmd)Clz] C104, 36904-25-3; cis-[Cr-(26) M. D. Alexander,Inorg. Chem., 5, 2084 (1966). (27) M. C. Couldwell and D. A. House, Znorg. Nucl. Chem. L e t t , 7,947 (1971). Stanko, et al. (en)aClz]The epr spectrum of the tris(ethylenediamine)ruthenium(III) complex, Ru(en), 3+, was measured at 4"K, diluted in single crystals of [Rh(en),C1,],.NaCl.6H2O and in powders of [Co(en),] Br3.3H2O, and employing K-band and X-band frequencies, respectively. The spectrum in both media can be described by an axial spin Hamiltonian with gl= 2.640 * 0.022 andgll= 0.330 f 0.007, defined with respect to the threefold symmetry axis of the complex. Interpretation of these g factors in terms of the theory of axial distortions for a low-spin d5 electronic configuration shows the ground electronic state t o be E'(2A,) and yields a value of the trigonal field splitting parameter, K , of -413 cm-'. The observed magnitude and sign of this latter quantity are discussed in terms of the known structure of the complex, crystal field theory predictions, and a comparison with the value for the same quantity in other tris(ethy1enediamine) complexes. IntroductionFor a transition metal ion immersed in a crystal field of predominantly octahedral symmetry, but with a superimposed component of trigonal ( D 3 ) symmetry, the lower lying,

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