Suresh Tyagi

The crystal structure and electronic properties of catena-bis(2,2′-bipyridyl)-µ-tetrafluoroborato-copper(II) tetrafluoroborate and catena-bis(2,2′-bipyridyl)-µ-perchlorato-copper(II) perchlorate

The crystal structure of [Cu(bipy)2(F2BF2)][BF4](3)(bipy = 2,2′-bipyridyl) has been determined by X-ray analysis [triclinic, space group P, with a= 11.275(4), b= 14.760(5), c= 7.366(3)A, α= 96.44(3), β= 101.63(4), γ= 110.25(4)°, and Z= 2], and that of [Cu(bipy)2(O2ClO2)][ClO4](1) has been redetermined [triclinic, space group P, a= 11.238(4), b= 14.863(5), c= 7.403(3)A, α= 96.28(3), β= 99.49(4), γ= 110.21(4)°, and Z= 2]. The two structures are isomorphous with near isostructural, six-co-ordinate, elongated rhombic trans octahedral CuN4X2 chromophores. The co-ordination of the bipy ligands is approximately planar, with a tetrahedral twist of the CuN4 chromophore [dihedral angle 44.6 and 46.7° for (3) and (1), respectively]. The six-co-ordination is completed by one bridging (and one ionic) tetrafluoroborato and perchlorate anions, in (3) and (1), respectively, at non-equivalent copper–ligand distances consistent with semi-co-ordination. The structure of complex (3) represents the first crystallographic example of a bridging tetrafluoroborato anion and the i.r. spectrum at liquid-nitrogen temperature is consistent with this, showing clear splitting of the ν3 band. The electronic and e.s.r. spectra of the complexes are consistent with their elongated rhombic octahedral stereochemistries and are discussed as a ‘criterion of stereochemistry’ for this geometry in the structural pathway of [Cu(bipy)2X]Y complexes.

Electronic properties and crystal structure of (2,2′-bipyridyl)-catena-µ-(oxalato-O1O2: O1′O2′)-copper(II) dihydrate and aqua(2,2′-bipyridyl)-(oxalato-O1O2)copper(II) dihydrate

The crystal structure of the title compounds [Cu(bipy)(C2O4)]·2H2O (1) and [Cu(bipy)(C2O4)(OH2)]·2H2O (2) have been determined by X-ray analysis. Compound (1) crystallises in the triclinic space group P with a= 9.673(3), b= 6.940(3), c= 9.103(3)A, α= 105.718(3), β= 110.347(3), γ= 97.539(3)°, and Z= 2. The six-co-ordinate CuN2O2O′2 chromophore of (1) involves an elongated rhombic octahedral stereochemistry involving a symmetrically co-ordinated bipy ligand (mean Cu-N 2.007 A) and unsymmetrically co-ordinated bridging oxalate groups (mean Cu-O 1.988 and 2.320 A). Compound (2) crystallises in the triclinic space group P with a= 10.565(3), b= 7.246(3), c= 10.806(3)A, α= 102.467(3), β= 62.119(3), γ= 98.134(3)°, and Z= 2. The CuN2O2O′ chromophore of (2) is basically square pyramidal with a symmetrically co-ordinated bipy ligand (mean Cu-N 1.989 A), and a symmetrically co-ordinated oxalate group (mean Cu-O 1.953 A) in the plane of the square pyramid, and a water molecule at 2.341 A out of the plane. The electronic reflectance spectrum of (1) involves main band at 14 500 cm–1 with a resolved broad band at 9 300 cm–1, while that of (2) involves a single broad band at 15 600 cm–1, a difference that is consistent with the structures and suggests an ‘electronic criterion of stereochemistry’ to distinguish these two structures.

The crystal structure and electronic properties of bis(2,2′-bipyridyl)-copper(II) bis(hexafluorophosphate)

The crystal structure of the title compound, [Cu(bipy)2][PF6]2(1), has been determined by X-ray crystallographic methods, using diffractometer data collection; the structure was solved by the heavy-atom method and by successive Fourier syntheses. Compound (1) crystallises in the tetragonal space group I41/acd, a= 16.228(3), c= 18.954(3)A, Z= 8.319 unique reflections gave a final R= 0.0487. The structure of (1) involves a unique compressed tetrahedral CuN4 chromophore (dihedral angle 44.6°) with four additional non-bonding PF6– anions at 3.3 A. The e.s.r. spectrum is axial (g∥g⊥ > 2.0) and the dark green crystals have an electronic reflectance spectrum with a band maximum at 15 040 cm–1 with a high-frequency shoulder at 16 950 cm–1. This represents the highest electronic transition yet observed in the [Cu(bipy)2X]Y type complexes and establishes an ‘electronic criterion of stereochemistry’ for the compressed tetrahedral CuN4 chromophore.

Crystal structure of bis(2,2′-bipyridyl)monochlorocopper(II) hexafluorophosphate monohydrate at 298 K and the electron spin resonance spectra of some bis(2,2′-bipyridyl)copper(II) complexes to 4.2 K

The crystal structure of the title compound [Cu(bipy)2Cl][PF6]·H2O (1)(bipy = 2,2′-bipyridyl) has been determined by X-ray diffraction, using diffractometer data collection. The structure was solved by the heavy-atom method and successive Fourier synthesis. Compound (1) crystallises in the monoclinic space group P21/n with a= 21.403(5), b= 12.235(3), c= 8.599(2)A, β= 92.68(2)°, and Z= 4. The CuN4Cl chromophore involves a near-regular trigonal bipyramidal stereochemistry, but with a significant distortion of the three in-plane angles from 120°(115.7, 123.8, and 120.5°). The poly-crystalline and single-crystal e.s.r. spectrum of (1) and a number of other 2,2′-bipyridyl complexes with [Cu(bipy)2X]n+ cations (X = Cl or I, n= 1; X = NH3, n= 2) are reported between 300 and 4 K. The molecular g tensors are consistent with a near-regular trigonal bipyramidal or square pyramidal distorted trigonal bipyramidal stereochemistry. As the e.s.r. spectra do not change significantly with temperature a dynamic behaviour in the sense of the pseudo-rotation of the Berry–Twist mechanism is not considered to operate.

Crystal structure and electronic properties of bis(2,2′-bipyridyl)-nitratocopper(II) nitrate monohydrate

The crystal structure of the title compound [Cu(bipy)2(ONO2)][NO3]·H2O (bipy = 2,2′-bipyridyl) has been redetermined by X-ray analysis in the triclinic space group P with a= 7.488(2), b= 10.017(2), c= 15.061 (2)A, α= 106.183(4), β= 91.335(3), γ= 89.662(3)°, and Z= 2. The six-co-ordinate CuN2N′2OO′ chromophore has a (4 + 1 + 1*) stereochemistry related to the original square-based pyramidal stereochemistry by an asymmetrically co-ordinated nitrate group to give an unsymmetrical bicapped square-pyramidal structure. The single-crystal e.s.r. and polarised electronic spectra are reported and together are shown to offer the possibility of distinguishing this bicapped square-pyramidal structure from that of a (4 + 1 + 1*) distorted square-pyramidal structure or cis-distorted octahedral structure. A structural pathway is suggested to connect these three geometries of the [Cu(bipy)2(OXO)]+(OXO = ONO–, O2CMe–, or O2CH–) cation by a linear combination of the S1a and S2a modes of vibration of the parent tris(chelate)copper(II) complex.

Crystal structure and electronic properties of bis(2,2′-bipyridyl)-thiocyanatocopper(II) tetrafluoroborate

The crystal structure of the title compound, [Cu(bipy)2(NCS)][BF4](1)(bipy = 2,2′-bipyridyl), has been determined by X-ray analysis. It crystallises in the monoclinic space group C2/c with a= 12.791 (3), b= 24.641 (4), c= 15.456(3)A, β= 107.4(1)°, and Z= 8. The five-co-ordinate CuN2N′2N″ chromophore has a distorted bipyramidal stereochemistry related to a regular trigonal-bipyramidal stereochemistry by a distortion towards square pyramidal. The single-crystal e.s.r. spectra involve rhombic g values, R= 1.21 [(g2–g1)/(g3–g2) where g1 < g2 < g3], and cannot be used to distinguish between a dz2 or dx2–y2 ground state, but the direction of the highest g value establishes that it correlates with the elongated Cu–N direction of the square-pyramidal distortion of the CuN2N′2N″ chromophore. This, together with the twin-peaked electronic reflectance spectra (11 170 and 14 120 cm–1), suggests that the structure of (1) is best described as square-pyramidal distorted trigonal bipyramidal.

Crystal structure and electronic properties of bis(2,2′-bipyridyl)-cyanocopper(II) nitrate dihydrate: a correlation of the in-plane angular distortion with the splitting of the electronic spectrum

The crystal structure of the title compound [Cu(bipy)2(CN)][NO3]·2H2O has been determined by X-ray analysis. It crystallises in the monoclinic space group, P21/n with a= 9.263(3), b= 24.678(4), c= 10.123(3)A, β= 109.83(8)°, and Z= 4. The five-co-ordinate CuN2N2C chromophore has a distorted trigonal-bipyramidal stereochemistry related to a regular trigonal-bipyramidal stereochemistry by distortion towards square pyramidal. The cyanide ion is bonded to the copper atom in the trigonal plane, via the carbon atom at a distance of 1.974(5)A. The three in-plane trigonal angles of 138.0, 126.5, and 95.4° show considerable distortion from 120°, and are considered responsible for the splitting in the twin-peaked electronic reflectance spectrum (12 820 and 14 920 cm–1).

The single-crystal electronic and electron spin resonance spectra of copper(II) doped bis(2,2′-bipyridyl)nitritozinc(II) nitrate and bis(2,2′-bipyridyl)nitritocopper(II) tetrafluoroborate: a fluxional CuN2N′2O2 chromophore

The single-crystal e.s.r. spectra and polarised electronic spectra of the copper(II) doped [Zn(bipy)2(ONO)][NO3] system are shown to be closely comparable to those previously reported for [Cu(bipy)2(ONO)][NO3]. The observation of more than four copper hyperfine lines in the single-crystal e.s.r. spectrum measured in the approximate bc plane is consistent with a two-dimensional misalignment of the CuN2N′2O2 chromophore and the temperature variability of the g and A factors are consistent with a two-dimensional fluxional model of the CuN2N′2O2 chromophore with a distorted square-pyramidal 4 + 1 + 1* structure and not with static disorder. This suggests that the structures of [Cu(bipy)2(ONO)][NO3] and [Cu(bipy)2(ONO)][BF4] are not genuine static stereochemistries of the copper(II) ion, but arise as a consequence of the fluxional model and are best referred to as pseudo cis distorted-octahedral structures. The electronic properties of 0.1–100% copper(II) doped [Zn(bipy)2(ONO)][NO3] are shown to be independent of the copper(II) concentration, and this suggests that the structure of the doped CuN2N′2O2 chromophore is independent of the structure of the ZnN2N′2O2 chromophore of the zinc host lattice, but correlates with the known structure of the [Cu(bipy)2(ONO)][NO3] complex, an example of the Non-co-operative Jahn–Teller Effect. The electronic reflectance spectrum of [Cu(bipy)2(ONO)][BF4] is closely comparable to that of the nitrate, despite having a significantly different, (4 + 1 + 1*) type, fluxional CuN4O2 chromophore structure.

Studies on the kinetics and mechanism of the interaction of hexaaquochromium(III) with acetate ions

The composition of the complex formed by the interaction of hexaaquochromium(III) with acetate ions was determined by Jobs method of continuous variations and by conductivity measurements. It was found to be (1:2). Kinetic studies were carried out at 30, 35 and 40°C while the [H+] of the medium was varied from 0.1 × 10−4 M to 31.6 × 10−4 M. The variation of the pseudo-first order rate constant (kobs) with [H+] and the ligand concentration indicated a mechanism based on ion-pair formation and the following rate equation was derived on this basis: kobs=[kanKIKa[H+]+k′anK′IKa][acetate]T[H+]2[H+]Ka+[H+]K′I+KaK′I+[KIKa+[H+]+K′IK′aKa][acetate]T The reaction was found to be of the associative interchange (Ia) type for the reaction of Cr(H2O)63+ and dissociative interchange (Id) type for that of Cr(H2O)5OH2+ with acetate ions. The activation parameters, calculated using the Eyring equation are: ΔH∗ = 103 kJ mol−1; ΔS∗ = 31 JK−1mol−1 for the formation of Cr(H2O)5(OOCCH3)2+ and ΔH = 104 kJ mol−1; ΔS∗ = 41(±2)JK−1mol−1 for the formation of Cr(H2O)4OH(OOCCH3)+.

The studies on the composition and kinetics of the complex formed by the interaction of hexaaquochromium(III) with salicylic acid

Abstract The interaction of hexaaquochromium(III) with salicylic acid was studied in the pH range 2.5-4.2. The composition of the complex formed was one mole of salicylic acid to one mole of hexaaquochromium(III). The variation of pseudo first order rate constant with pH, ionic strength and ligand concentrations indicated a mechanism based on ion-pair formation. The rate equation derived on the basis of this mechanism is: k obs = k an K 1 K a [salicylic] T [H + +K a +K 1 K a [salicylic] T An associative interchange mechanism is suggested for the reaction. The activation parameters calculated by Eyring equation are ΔH ∗ = 74.48 (±0.33) kJ mol−1; ΔS ∗ = −60.49 (±1.11) JK−1 mol−1 for anation and ΔH = −9.00 (±0.43) kJ mol−1; ΔS = −13.60(±1.42) KJ−1 mol−1 for ion-pairing.