Facile syntheses and characterization of pentaamminechromium(III) complexes with neutral O- and N-bound ligands

Curtis, Neville J.; Lawrance, Geoffrey A.

doi:10.1016/s0020-1693(00)85297-4

Cited by 13 publications

(3 citation statements)

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“…Figure displays the UV−vis features of (pyridine)pentaamminechromium(III) in aqueous solution. The two LF maxima at 467 and 352 nm, associated with the 4 A 2g → 4 T 2g and 4 A 2g → 4 T 1g transitions in the O h approximation, are compared in Table with literature data for the closely related imidazole (im) complex and for Cr(NH 3 ) 6 3+ …”

Section: Resultsmentioning

confidence: 99%

(Pyridine)pentaamminechromium(III). Synthesis, Characterization, and Photochemistry

Riccieri

Zinato

1996

Inorg. Chem.

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The Cr(NH(3))(5)(py)(3+) ion has been obtained by metathesis of Cr(NH(3))(5)(Me(2)SO)(3+) in pyridine, isolated as the perchlorate salt, and characterized by absorption (lambda(max) at 467, 352, and 260 nm) and emission spectra (lambda(max) at 668 nm, tau = 2.0 &mgr;s at 20 degrees C in water) and by the py aquation rate (k = 5 x 10(-)(4) s(-)(1) at 80 degrees C). Ligand-field (LF) band irradiation in acid aqueous solution (10(-)(2) M HClO(4)) induces photoaquation of py (Phi = 0.26) and NH(3) (Phi = 0.16). HPLC indicates that the latter reaction gives rise to both cis- and trans-Cr(NH(3))(4)(py)(H(2)O)(3+), with the predominance of the cis isomer. This is the first Cr(NH(3))(5)X(z+)() species where Phi(x) > Phi(NH)3: the result is compared with the predictions of various photolysis models and is taken as chemical evidence for pi-acceptance by the py ligand. The photostereochemistry is also discussed. The phosphorescence is totally quenched by Cr(C(2)O(4))(3)(3)(-) (k(q) = 2.7 x 10(9) M(-)(1) s(-)(1)), while the photoreactions are only in part. On 470-nm excitation, the Phi(py)/Phi(NH)()3 ratio is approximately 1 and approximately 2 for the unquenchable and the quenchable contributions, respectively. Such a difference, suggesting at least two reactive precursors, can be interpreted in terms of the photochemistry proceeding from either the lowest doublet and quartet excited states or, alternatively, from the (4)E and (4)B(2) states. Irradiation of the very distinct absorption of coordinated pyridine results in both doublet-state emission and loss of py and NH(3). Comparison of this photobehavior with the LF results gives an efficiency of 0.7 for conversion of the py-localized pipi states into the Cr-localized LF states, confirmed by the wavelength dependence of the relative emission yields. Some py release (Phi = 0.03) is concluded to originate in the pipi states.

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Section: Resultsmentioning

confidence: 99%

(Pyridine)pentaamminechromium(III). Synthesis, Characterization, and Photochemistry

Riccieri

Zinato

1996

Inorg. Chem.

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“…The situation is far more complex than this though. Macrocyclic −NH− and −S− donors are chirotopic and may exist in one of two forms ( R / S ) which leads to the proliferation of diastereomeric forms. , Some interesting results concerning the involvement of donor-atom-based diastereomers in biologically relevant processes have appeared recently. , The use of pentadentate ligands that leave only a single coordination site capable of undergoing substitution processes is less common because of the more sophisticated nature of the ligands. ,,, In most cases, a pentadentate ligand bearing predominantly strong field atoms is employed with a weakly bound monodentate ligand (e.g., chloro) completing the coordination sphere. − …”

Section: Introductionmentioning

confidence: 99%

“…3,10,15,16 In most cases, a pentadentate ligand bearing predominantly strong field atoms is employed with a weakly bound monodentate ligand (e.g., chloro) completing the coordination sphere. [17][18][19][20][21][22][23][24][25][26][27] We have been involved in the chemistry of cobalt(III) complexes with pentadentate macrocyclic ligands containing a pendant primary amine arm (Scheme 1). [28][29][30][31] The complexes have been prepared and characterized in pure isomeric forms in a neutral or acidic medium, and their cis/trans isomerism has been established by X-ray crystallography.…”

Section: Introductionmentioning

confidence: 99%

Isomeric Distribution and Catalyzed Isomerization of Cobalt(III) Complexes with Pentadentate Macrocyclic Ligands. Importance of Hydrogen Bonding

et al. 2006

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We have investigated the isomeric distribution and rearrangement of complexes of the type [CoXLn]2+,3+ (where X = Cl-, OH-, H2O, and Ln represents a pentadentate 13-, 14-, and 15-membered tetra-aza or diaza-dithia (N4 or N2S2) macrocycle bearing a pendant primary amine). The preparative procedures for chloro complexes produced almost exclusively kinetically preferred cis isomers (where the pendant primary amine is cis to the chloro ligand) that can be separated by careful cation-exchange chromatography. For L13 and L14 the so-called cis-V isomer is isolated as the kinetic product, and for L15 the cis-VI form (an N-based diastereomer) is the preferred, while for the L14(S) complex both cis-V and trans-I forms are obtained. All these complexes rearrange to form stable trans isomers in which the pendent primary amine is trans to the monodentate aqua or hydroxo ligand, depending on pH and the workup procedure. In total 11 different complexes have been studied. From these, two different trans isomers of [CoClL14(S)]2+ have been characterized crystallographically for the first time in addition to a new structure of cis-V-[CoClL14(S)]2+; all were isolated as their chloride perchlorate salts. Two additional isomers have been identified and characterized by NMR as reaction intermediates. The remaining seven forms correspond to the complexes already known, produced in preparative procedures. The kinetic, thermal, and baric activation parameters for all the isomerization reactions have been determined and involve large activation enthalpies and positive volumes of activation. Activation entropies indicate a very important degree of hydrogen bonding in the reactivity of the complexes, confirmed by density functional theory studies on the stability of the different isomeric forms. The isomerization processes are not simple and even some unstable intermediates have been detected and characterized as part of the above-mentioned 11 forms of the complexes. A common reaction mechanism for the isomerization reactions has been proposed for all the complexes derived from the observed kinetic and solution behavior.

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ChemInform Abstract: FACILE SYNTHESES AND CHARACTERIZATION OF PENTAAMMINECHROMIUM(III) COMPLEXES WITH NEUTRAL OXYGEN‐ AND NITROGEN‐BOUND LIGANDS

Curtis¹,

Lawrance²

1985

Chemischer Informationsdienst

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Facile syntheses and characterization of pentaamminechromium(III) complexes with neutral O- and N-bound ligands

Cited by 13 publications

References 14 publications

(Pyridine)pentaamminechromium(III). Synthesis, Characterization, and Photochemistry

(Pyridine)pentaamminechromium(III). Synthesis, Characterization, and Photochemistry

Isomeric Distribution and Catalyzed Isomerization of Cobalt(III) Complexes with Pentadentate Macrocyclic Ligands. Importance of Hydrogen Bonding

ChemInform Abstract: FACILE SYNTHESES AND CHARACTERIZATION OF PENTAAMMINECHROMIUM(III) COMPLEXES WITH NEUTRAL OXYGEN‐ AND NITROGEN‐BOUND LIGANDS

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