Abstract
Complexes of formulation [Cu(TpPh)(L)](ClO4) (1-4), where TpPh is anionic tris(3-phenylpyrazolyl)borate and L is N,N-donor heterocyclic base, viz. 2,2′-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyridoquinoxaline (dpq, 3), and dipyridophenazine (dppz, 4), are prepared from a reaction of copper(II) acetate-hydrate with KTpPh and L in CH2Cl2 and isolated as perchlorate salts. The complexes are characterized by analytical, structural, and spectral methods. The crystal structures of complexes 1-4 show the presence of discrete cationic complexes having the metal, TpPh, and L in a 1:1:1 ratio and a noncoordinating perchlorate anion. The complexes have a square-pyramidal 4 + 1 coordination geometry in which two nitrogens of L and two nitrogens of the TpPh ligand occupy the basal plane and one nitrogen of TpPh binds at the axial site. Complexes 3 and 4 display distortion from the square-pyramidal geometry. The Cu-N distances for the equatorial and axial positions are ∼2.0 and 2.2 Å, respectively. The phenyl groups of TpPh form a bowl-shaped structure that encloses the {CuL} moiety. The steric encumbrance is greater for the bpy and phen ligands compared to that for dpq and dppz. The one-electron paramagnetic complexes (μ ≈ 1.8 μ6) exhibit axial EPR spectra in CH2Cl2 glass at 77 K giving gII and g⊥ values of ∼2.18 (AII = 128 G) and ∼2.07. The data suggest a {dx2x2-Y2}1 ground state. The complexes are redox-active and display a quasireversible cyclic voltammetric response for the Cu(II)/Cu(I) couple near 0.0 V versus SCE with an ipc/ipa ratio of unity in CH2Cl2 or DMF-0.1 M TBAP. The E1/2 values of the couple vary in the order 4 > 3 > 2 > 1. A profound effect of steric encumbrance caused by the TpPh ligand is observed in the reactivity of 1-4 with the calf thymus (CT) and supercoiled (SC) DNA. Complexes 2-4 show similar binding to CT DNA. The propensity for the SC DNA cleavage varies as 4 > 3 > 2. The bpy complex does not show any significant binding or cleavage of DNA. Mechanistic investigations using distamycin reveal minor groove binding for 2 and 3 and a major groove binding for 4. The scission reactions that are found to be inhibited by hydroxyl radical scavenger DMSO are likely to proceed through sugar hydrogen abstraction pathways.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 3469-3476 |
| Number of pages | 8 |
| Journal | Inorganic Chemistry |
| Volume | 41 |
| Issue number | 13 |
| DOIs | |
| State | Published - Jul 1 2002 |
| Externally published | Yes |
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ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
Cite this
Effect of steric encumbrance of tris(3-phenylpyrazolyl)borate on the structure and properties of ternary copper(II) complexes having N,N-donor heterocyclic bases. / Dhar, Shanta; Reddy, Pattubala A.N.; Nethaji, Munirathinam; Mahadevan, Subramony; Saha, Manas K.; Chakravarty, Akhil R.
In: Inorganic Chemistry, Vol. 41, No. 13, 01.07.2002, p. 3469-3476.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Effect of steric encumbrance of tris(3-phenylpyrazolyl)borate on the structure and properties of ternary copper(II) complexes having N,N-donor heterocyclic bases
AU - Dhar, Shanta
AU - Reddy, Pattubala A.N.
AU - Nethaji, Munirathinam
AU - Mahadevan, Subramony
AU - Saha, Manas K.
AU - Chakravarty, Akhil R.
PY - 2002/7/1
Y1 - 2002/7/1
N2 - Complexes of formulation [Cu(TpPh)(L)](ClO4) (1-4), where TpPh is anionic tris(3-phenylpyrazolyl)borate and L is N,N-donor heterocyclic base, viz. 2,2′-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyridoquinoxaline (dpq, 3), and dipyridophenazine (dppz, 4), are prepared from a reaction of copper(II) acetate-hydrate with KTpPh and L in CH2Cl2 and isolated as perchlorate salts. The complexes are characterized by analytical, structural, and spectral methods. The crystal structures of complexes 1-4 show the presence of discrete cationic complexes having the metal, TpPh, and L in a 1:1:1 ratio and a noncoordinating perchlorate anion. The complexes have a square-pyramidal 4 + 1 coordination geometry in which two nitrogens of L and two nitrogens of the TpPh ligand occupy the basal plane and one nitrogen of TpPh binds at the axial site. Complexes 3 and 4 display distortion from the square-pyramidal geometry. The Cu-N distances for the equatorial and axial positions are ∼2.0 and 2.2 Å, respectively. The phenyl groups of TpPh form a bowl-shaped structure that encloses the {CuL} moiety. The steric encumbrance is greater for the bpy and phen ligands compared to that for dpq and dppz. The one-electron paramagnetic complexes (μ ≈ 1.8 μ6) exhibit axial EPR spectra in CH2Cl2 glass at 77 K giving gII and g⊥ values of ∼2.18 (AII = 128 G) and ∼2.07. The data suggest a {dx2x2-Y2}1 ground state. The complexes are redox-active and display a quasireversible cyclic voltammetric response for the Cu(II)/Cu(I) couple near 0.0 V versus SCE with an ipc/ipa ratio of unity in CH2Cl2 or DMF-0.1 M TBAP. The E1/2 values of the couple vary in the order 4 > 3 > 2 > 1. A profound effect of steric encumbrance caused by the TpPh ligand is observed in the reactivity of 1-4 with the calf thymus (CT) and supercoiled (SC) DNA. Complexes 2-4 show similar binding to CT DNA. The propensity for the SC DNA cleavage varies as 4 > 3 > 2. The bpy complex does not show any significant binding or cleavage of DNA. Mechanistic investigations using distamycin reveal minor groove binding for 2 and 3 and a major groove binding for 4. The scission reactions that are found to be inhibited by hydroxyl radical scavenger DMSO are likely to proceed through sugar hydrogen abstraction pathways.
AB - Complexes of formulation [Cu(TpPh)(L)](ClO4) (1-4), where TpPh is anionic tris(3-phenylpyrazolyl)borate and L is N,N-donor heterocyclic base, viz. 2,2′-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyridoquinoxaline (dpq, 3), and dipyridophenazine (dppz, 4), are prepared from a reaction of copper(II) acetate-hydrate with KTpPh and L in CH2Cl2 and isolated as perchlorate salts. The complexes are characterized by analytical, structural, and spectral methods. The crystal structures of complexes 1-4 show the presence of discrete cationic complexes having the metal, TpPh, and L in a 1:1:1 ratio and a noncoordinating perchlorate anion. The complexes have a square-pyramidal 4 + 1 coordination geometry in which two nitrogens of L and two nitrogens of the TpPh ligand occupy the basal plane and one nitrogen of TpPh binds at the axial site. Complexes 3 and 4 display distortion from the square-pyramidal geometry. The Cu-N distances for the equatorial and axial positions are ∼2.0 and 2.2 Å, respectively. The phenyl groups of TpPh form a bowl-shaped structure that encloses the {CuL} moiety. The steric encumbrance is greater for the bpy and phen ligands compared to that for dpq and dppz. The one-electron paramagnetic complexes (μ ≈ 1.8 μ6) exhibit axial EPR spectra in CH2Cl2 glass at 77 K giving gII and g⊥ values of ∼2.18 (AII = 128 G) and ∼2.07. The data suggest a {dx2x2-Y2}1 ground state. The complexes are redox-active and display a quasireversible cyclic voltammetric response for the Cu(II)/Cu(I) couple near 0.0 V versus SCE with an ipc/ipa ratio of unity in CH2Cl2 or DMF-0.1 M TBAP. The E1/2 values of the couple vary in the order 4 > 3 > 2 > 1. A profound effect of steric encumbrance caused by the TpPh ligand is observed in the reactivity of 1-4 with the calf thymus (CT) and supercoiled (SC) DNA. Complexes 2-4 show similar binding to CT DNA. The propensity for the SC DNA cleavage varies as 4 > 3 > 2. The bpy complex does not show any significant binding or cleavage of DNA. Mechanistic investigations using distamycin reveal minor groove binding for 2 and 3 and a major groove binding for 4. The scission reactions that are found to be inhibited by hydroxyl radical scavenger DMSO are likely to proceed through sugar hydrogen abstraction pathways.
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U2 - 10.1021/ic0201396
DO - 10.1021/ic0201396
M3 - Article
VL - 41
SP - 3469
EP - 3476
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 13
ER -