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Low-spin states

Derived from the German word meaning devil s copper, nickel is found predominantly in two isotopic forms, Ni (68% natural abundance) and Ni (26%). Ni exists in four oxidation states, 0, I, II, III, and IV. Ni(II), which is the most common oxidation state, has an ionic radius of —65 pm in the four-coordinate state and —80 pm in the octahedral low-spin state. The Ni(II) aqua cation exhibits a pAa of 9.9. It forms tight complexes with histidine (log Af = 15.9) and, among the first-row transition metals, is second only to Cu(II) in its ability to complex with acidic amino acids (log K( = 6-7 (7). Although Ni(II) is most common, the paramagnetic Ni(I) and Ni(III) states are also attainable. Ni(I), a (P metal, can exist only in the S = state, whereas Ni(lll), a cT ion, can be either S = or S =. ... [Pg.284]

The energy calculations show that the low spin state of C54 is indeed about 1.3 eV lower in energy than the high spin state, at least for the molecular geometries used here, whereas for C24 nearly identical energies for the two states are found. Inclusion of electron correlation would favor the low spin form further, possibly... [Pg.38]

Photoionization can also access excited electronic states of the ion that are difficult to study by optical methods. The photoionization yield of FeO increases dramatically 0.36 eV above the ionzation energy. This result corresponds to the threshold for producing low spin quartet states of FeO. These states had not been previously observed, as transitions to them are spin forbidden and occur at inconveniently low energy. Because the FeO + CH4 reaction occurs via low spin intermediates, accurately predicting the energies of high and low spin states is critical. [Pg.352]

Fig. 4.3 Ranges of isomer shifts observed for Fe compounds relative to metallic iron at room temperature (adapted from [24] and complemented with recent data). The high values above 1.4-2 mm s were obtained from Co emission experiments with insulators like NaCl, MgO or Ti02 [25-28], which yielded complex multi-component spectra. However, the assignment of subspectra for Fe(I) to Fe(III) in different spin states has never been confirmed by applied-field measurements, or other means. More recent examples of structurally characterized molecular Fe (I)-diketiminate and tris(phosphino)borate complexes with three-coordinate iron show values around 0.45-0.57 mm s [29-31]. The usual low-spin state for Fe(IV) with 3d configuration is 5 = 1 for quasi-octahedral or tetrahedral coordination. The low-low-spin state with S = 0 is found for distorted trigonal-prismatic sites with three strong ligands [30, 32]. Occurs only in ferrates. There is only one example of a molecular iron(VI) complex it is six-coordinate and has spin S = 0 [33]... Fig. 4.3 Ranges of isomer shifts observed for Fe compounds relative to metallic iron at room temperature (adapted from [24] and complemented with recent data). The high values above 1.4-2 mm s were obtained from Co emission experiments with insulators like NaCl, MgO or Ti02 [25-28], which yielded complex multi-component spectra. However, the assignment of subspectra for Fe(I) to Fe(III) in different spin states has never been confirmed by applied-field measurements, or other means. More recent examples of structurally characterized molecular Fe (I)-diketiminate and tris(phosphino)borate complexes with three-coordinate iron show values around 0.45-0.57 mm s [29-31]. The usual low-spin state for Fe(IV) with 3d configuration is 5 = 1 for quasi-octahedral or tetrahedral coordination. The low-low-spin state with S = 0 is found for distorted trigonal-prismatic sites with three strong ligands [30, 32]. Occurs only in ferrates. There is only one example of a molecular iron(VI) complex it is six-coordinate and has spin S = 0 [33]...
In 2005, Matsuda and co-workers [20] investigated the magnetic properties of complex 93. The magnetic susceptibility measurement reveals the Mnm ion in the low-spin state (d45 = 1). However, the jJ.es at room temperature is 3.28pB, which is considerably higher than the calculated spin-only value of 2.83 pB for 5 = 1. The extraordinary pe i value should be due to the spin-orbit coupling effect. [Pg.86]

In the reaction shown in Eq. (20.93), the dA complex containing Cr2+ is inert owing to electron pairing giving the low-spin state. There is an extreme variation in rates from very slow to very fast depending on the nature of the ligands present, and rate constants may vary from 10 6 to 108 M-1 s 1. [Pg.726]


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See also in sourсe #XX -- [ Pg.406 , Pg.493 ]

See also in sourсe #XX -- [ Pg.50 , Pg.67 ]

See also in sourсe #XX -- [ Pg.119 , Pg.120 ]




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High- and low-spin states

Low versus high spin state

Low-spin ground state

Low-versus High-Spin States in Polyenes

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