Chromium(III) complexes containing macrocyclic ligands

Swisher, Robert G.; Brown, George; Smierciak, R. C.; Blinn, Elliott L.

doi:10.1021/ic50225a069

Cited by 22 publications

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“…Electronic Spectra. The visible range and infrared absorption spectra of 4a − d are consistent with those expected for the cis configurations demonstrated by X-ray crystallography (see details in a following paragraph). The visible range absorption spectra in solution (Table ) each display a broad band at λ max 592 nm for 4a , 4b , and 4c and at 584 nm for 4d (Figure ) that can be assigned to the spin-allowed Q 1 ← Q 0 ligand field transition .…”

Section: Resultssupporting

confidence: 82%

“…The visible range absorption spectra in solution (Table ) each display a broad band at λ max 592 nm for 4a , 4b , and 4c and at 584 nm for 4d (Figure ) that can be assigned to the spin-allowed Q 1 ← Q 0 ligand field transition . Although there is little sensitivity to the different pendant groups, it is notable that in all four cases this band is shifted to a significantly longer wavelength from the Q 1 ← Q 0 band of the analogous cis -Cr(cyclam)Cl 2 + ion. 15a, There is a smaller shift of the Q 2 bands to lower energy relative to the cyclam complex. The shifts can be attributed to the weaker ligand field strengths of the R 2 cyclam ligand owing to the longer Cr−N bond lengths for the two tertiary nitrogens (see details in a following paragraph).…”

Section: Resultsmentioning

confidence: 85%

“…b Q 2 band hidden by anthracene absorption. c Optical spectrum of c is -[Cr(cyclam)Cl 2 ]Cl in H 2 O according to refs a and .…”

Section: Resultsmentioning

confidence: 99%

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Synthesis and Photophysical Properties of New Chromium(III) Complexes of N-Derivatized 1,4,8,11-Tetraazacyclotetradecane Ligands cis-[Cr(1,8-R₂cyclam)Cl₂]Cl, Where R Is a Pendant Chromophore. Exclusive Formation of the cis Isomer

DeRosa

Ford

2003

Inorg. Chem.

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Several new chromium(III) complexes have been synthesized utilizing derivatives of the macrocyclic ligand cyclam (1,4,8,11-tetraazacyclotetradecane) with various N-substituted chromophores in the 1 and 8 positions (1,8-R(2)cyclam) where R = CH(3), CH(2)Ph, CH(2)Nph (Nph = naphthyl), and CH(2)Anth (Anth = anthracyl). X-ray crystal structures were determined for all four complexes, and these are formed exclusively in the cis configuration with the two tertiary amines in the "hinge" positions (i.e., along the folding axis) of the coordinated ligand. As a result, the cis isomers appear to be inert to isomerization under conditions dramatically more forcing than needed to effect the cis to trans isomerization of the unsubstituted Cr(cyclam)Cl(2)(+) ion. Photophysical studies demonstrated that emission occurs solely from the metal-centered ligand field doublet excited states regardless of whether initial excitation is into the quartet ligand field bands or into the pi-pi bands of the pendant chromophore. Thus, excitation of the pendant chromophore results in efficient intramolecular energy transfer to the metal centered ligand field excited states.

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Section: Resultssupporting

confidence: 82%

Section: Resultsmentioning

confidence: 85%

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Synthesis and Photophysical Properties of New Chromium(III) Complexes of N-Derivatized 1,4,8,11-Tetraazacyclotetradecane Ligands cis-[Cr(1,8-R₂cyclam)Cl₂]Cl, Where R Is a Pendant Chromophore. Exclusive Formation of the cis Isomer

DeRosa

Ford

2003

Inorg. Chem.

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Molecular Mechanics Calculations as a Tool in Coordination Chemistry

Hancock

1989

Progress in Inorganic Chemistry

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Synthesis and Characterization of Copper, Nickel and Cobalt Complexes of N,N′‐Dimethyl‐2,11‐diaza[3,3](2,6)pyridinophane

Krüger

1995

Chem. Ber.

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The properties of the tetraazamacrocyclic compound N, N'-dimethyl-2,11 -diaza[ 3,3] (2,G)pyridinophane (L-N4Mez) as a ligand for some selected metal chlorides have been examined. The crystal structure of the uncoordinated ligand reveals a syn chair-chair conformation. In solution, the ligand displays fluctional behavior. Reaction of L-N4Mez with the chlorides of copper(II), nickel(II), and cobalt(I1) affords the com-. HzO (4), and [Co(L-N4Me2)Cl2] . 2 HzO (5) in which the ligand adopts a syn boat-boat conformation. The crystal structures of 4 and 5 are presented. Due to the small cavity of the 12-membered ring of the ligand, exclusively distorted cis-octahedral coordination geometries are found at the metal sites. A comparison of structural data of several complexes with this ligand shows that the extent of the distortions from ideal octahedral geometry is mainly determined by the M-N,, bond strength. The electronic as well as the solution properties of the described complexes have been investigated by electronic absorption spectroscopy, ESR spectroscopy, and electrochemical methods.As a part of our research efforts in investigating the effects of structural aspects from a coordinated ligand on the reactivity occurring at the metal site of a complex, we searched for a suitable tetradentate ligand which fulfills several requirements. First, it should contain nitrogenous donor atoms. In addition, the ligand needs to form octahedral complexes with various metal ions where two cis coordination sites can be occupied by a wide variety of additional ligands. Further, the ligand should have some functional options for implementation of steric hindrance to avoid formation of dinuclear complexes. To ensure coordination of all four nitrogen atoms at any time, the ligand should also be macrocyclic. Acyclic ligands with four potential donor atoms like tpa"] have been shown in some cases to act as tridentate ligandsw. In other instances, lbmembered tetraazamacrocyclic rings like cyclam can coordinate to metal ions in the required fashion to leave two cis coordination sites at the disposal of additional ligand However, this cis-octahedral geometry occurs only in the presence of bidentate ligands or due to specific synthetic procedures. In the vast majority of complexes, cyclam acts as an equatorial ligandr'll. Smaller rings, like the 12-membered macrocycle cyclen, usually afford cavities which are too small to allow coordination of the ligand in an equatorial lane [^,^]. The utilization of cyclen for our purposes was impeded by two considerations. First, cyclen is a very flexible ligand and, although unusual, allows accommodation of square-planar nickel ionsL71. Further, attachment of sterically demanding substituents to the nitrogen atoms results in the formation of square-pyramidal rather than octahedral comp l e x e~[~~~~'~] . Therefore, 2,11 -diaza[3,3](2,6)pyridinophane (L-N4H2) was chosen as a starting point for our research. Similar to cyclen, L-N4H2 consists of a 12-membered macrocyclic ring. However, in contrast to c...

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Chromium(III) complexes containing macrocyclic ligands

Cited by 22 publications

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Synthesis and Photophysical Properties of New Chromium(III) Complexes of N-Derivatized 1,4,8,11-Tetraazacyclotetradecane Ligands cis-[Cr(1,8-R₂cyclam)Cl₂]Cl, Where R Is a Pendant Chromophore. Exclusive Formation of the cis Isomer

Synthesis and Photophysical Properties of New Chromium(III) Complexes of N-Derivatized 1,4,8,11-Tetraazacyclotetradecane Ligands cis-[Cr(1,8-R₂cyclam)Cl₂]Cl, Where R Is a Pendant Chromophore. Exclusive Formation of the cis Isomer

Molecular Mechanics Calculations as a Tool in Coordination Chemistry

Synthesis and Characterization of Copper, Nickel and Cobalt Complexes of N,N′‐Dimethyl‐2,11‐diaza[3,3](2,6)pyridinophane

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Chromium(III) complexes containing macrocyclic ligands

Cited by 22 publications

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Synthesis and Photophysical Properties of New Chromium(III) Complexes of N-Derivatized 1,4,8,11-Tetraazacyclotetradecane Ligands cis-[Cr(1,8-R2cyclam)Cl2]Cl, Where R Is a Pendant Chromophore. Exclusive Formation of the cis Isomer

Synthesis and Photophysical Properties of New Chromium(III) Complexes of N-Derivatized 1,4,8,11-Tetraazacyclotetradecane Ligands cis-[Cr(1,8-R2cyclam)Cl2]Cl, Where R Is a Pendant Chromophore. Exclusive Formation of the cis Isomer

Molecular Mechanics Calculations as a Tool in Coordination Chemistry

Synthesis and Characterization of Copper, Nickel and Cobalt Complexes of N,N′‐Dimethyl‐2,11‐diaza[3,3](2,6)pyridinophane

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Synthesis and Photophysical Properties of New Chromium(III) Complexes of N-Derivatized 1,4,8,11-Tetraazacyclotetradecane Ligands cis-[Cr(1,8-R₂cyclam)Cl₂]Cl, Where R Is a Pendant Chromophore. Exclusive Formation of the cis Isomer

Synthesis and Photophysical Properties of New Chromium(III) Complexes of N-Derivatized 1,4,8,11-Tetraazacyclotetradecane Ligands cis-[Cr(1,8-R₂cyclam)Cl₂]Cl, Where R Is a Pendant Chromophore. Exclusive Formation of the cis Isomer