Geometry optimization for a series of ten, two-ring diimine Ru(II) complexes was effected using the Gaussian 98 protocol at density functional theory (DFT) B3LYP level with basis sets 3-21G(*) and ...3-21G(*)(*). HOMO−LUMO energy difference values compared favorably to the experimental data from electrochemistry ΔE 1/2 = (E 1/2ox − E 1/2red) and the lowest energy absorption maxima, which for these complexes correspond to the metal-to-ligand charge transfer (MLCT) band. The HOMO and LUMO distributions from DFT support the idea that the lowest energy transitions are metal-to-ligand charge transfer and that the lowest energy LUMO for the mixed ligand complexes is located on 2,2‘-bipyrazine (bpz), followed by 2,2‘-bipyrimidine (bpm) and then 2,2‘-bipyridine (bpy).
This study focuses on a series of PtII(L−L‘)(dppm) n + complexes, where dppm is bis(diphenylphosphino)methane and L−L‘ are C∧C‘ (n = 0), C∧N (n = 1), and N∧N‘ (n = 2) aromatic ligands. Structural ...characteristics are as follows: for Pt(phen)(dppm)(PF6)2, a N∧N‘ derivative, monoclinic, C2/c, a = 33.583(6) Å, b = 11.399(2) Å, c = 22.158(4) Å, Z = 8; for Pt(phq)(dppm)(PF6), a C∧N derivative, triclinic, P1̄, a = 11.415(3) Å, b = 13.450(3) Å, c = 14.210(4) Å, Z = 2; for Pt(phpy)(dppm)(PF6), a C∧N derivative, triclinic, P1̄, a = 10.030(3) Å, b = 13.010(2) Å, c = 15.066(4) Å, Z = 2; and for Pt(bph)(dppm), a C∧C‘ derivative, P21/c, a = 17.116(7) Å, b = 21.422(6) Å, c = 26.528(6) Å, Z = 12, where phen is 1,10-phenanthroline, phq is 2-phenylquinoline, phpy is 2-phenylpyridine, and bph is 2,2‘-biphenyl. Structural features indicate that the Pt−C bond distance is shorter than the Pt−N bond distance in symmetrical complexes and that the Pt−P bond distance trans to N is shorter than the Pt−P bond trans to C. This is consistent with the 31P NMR spectra where the chemical shift of the P trans to C is ∼10 ppm less than found for P trans to N. The energy maxima of the metal-to-ligand charge-transfer band for the complexes containing various L−L‘ ligands occur in the near-UV region of the spectrum and fall into the energy series bpy > bph > phen > 2-phpy > 2-ptpy > 2-phq > 7,8-bzq, where bpy is 2,2‘-bipyridine, 2-phpy is 2-phenylpyridine, 2-ptpy is 2-p-tolylpyridine, and 7,8-bzq is 7,8-benzoquinoline. The emission energy maxima, ascribed to variance in metal-perturbed triplet ligand centered emission, commence near 500 nm and follow the series phen > bpy > 7,8-bzq > 2-phpy > 2-ptpy > bph > 2-phq. In general, emission is observed at 77 K and in solution at low temperatures, but the temperature dependence of the emission lifetimes indicates thermal activation to another state occurs with an energy of ∼1800 cm-1 for the complexes, with the exception of Pt(bph)(dppm), which has an activation energy of ∼2300 cm-1.
Density functional theory (DFT) calculations show the higher energy HOMO (highest occupied molecular orbital) orbitals of four iron(II) diimine complexes are metal centered and the lower energy LUMO ...(lowest unoccupied molecular orbitals) are ligand centered. The energy of the orbitals correlates with electrochemical redox potentials of the complexes. Time-dependent density functional theory (TDDFT) calculations reveal ligand centered (LC) and metal-to-ligand charge transfer (MLCT) at higher energy than experimentally observed. TDDFT calculations also reveal the presence of d−d transitions which are buried under the MLCT and LC transitions. The difference in chemical and photophysical behavior of the iron complexes compared to that of their ruthenium analogues is also addressed.
The preparation, crystal structures and magnetic properties of the copper(II) complexes of formula Cu(pyim)(tcm)(2)(n) (1), Cu(bpy)(tcm)(2)(n) (2), Cu(4)(bpz)(4)(tcm)(8) (3), {Cu(terpy)(tcm).tcm}(n) ...(4) and {Cu(2)(tppz)(tcm)(4).3/2H(2)O}(n) (5) pyim = 2-(2-pyridyl)imidazole, tcm = tricyanomethanide, bpy = 2,2'-bipyridine, bpz = 2,2'-bipyrazine, terpy = 2,2':6',2''-terpyridine and tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine are reported. Complexes, 1, 2 and 4 are uniform copper(II) chains with single- (1 and 4) and double-(2) micro-1,5-tcm bridges with values of the intrachain copper-copper separation of 7.489(1) (1), 7.520(1) and 7.758(1) (2) and 7.469(1) A (4). Each copper atom in 1, 2 and 4 is five-coordinate with bidentate pyim (1)/bpy (2) and tridentate terpy (4) ligands and nitrile-nitrogen atoms from bridging (1,2 and 4) and terminal (1) tcm groups building a distorted square pyramidal surrounding. The structure of 3 is made up of neutral centrosymmetric rectangles of (2,2'-bipyrazine)copper(II) units at the corners, the edges being built by single- and double-micro-1,5-tcm bridges with copper-copper separations of 7.969(1) and 7.270(1) A, respectively. Five- and six-coordinated copper atoms with distorted square pyramidal and elongated octahedral environments occur in . Compound 5 is a neutral copper(II) chain with regular alternating bis-tridentate tppz and double micro-1,5-tcm bridges, the intrachain copper-copper distances being 6.549(7) and 7.668(1) A, respectively. The two crystallographically independent copper atoms in 5 have an elongated octahedral geometry with three tppz nitrogen atoms and a nitrile-nitrogen atom from a bridging tcm group in the equatorial positions, and two nitrile nitrogen atoms from a terminal and a bridging tcm ligand occupying the axial sites. The investigation of the magnetic properies of 1-5 in the temperature range 1.9-295 K has shown the occurrence of weak ferro- J = +0.11(1) cm(-1) (2) and antiferromagnetic interactions J = -0.093(1) (1), -0.083(1) (4), -0.04(1) and 1.21(1) cm(-1) (3) across the micro-1,5-tcm bridges and intermediate antiferromagnetic coupling -J = 37.4(1) cm(-1) (5) through bis-tridentate tppz. The values of the magnetic interactions are analyzed through simple orbital symmetry considerations and compared with those previously reported for related systems.
Density functional theory and time-dependent density functional theory calculations provide pictures of the molecular orbitals involved in the ground and excited states of two cyano derivatives of ...8′-apo-β-caroten-8′-al synthesized via an acid−base-catalyzed Knoevenagel condensation reaction. Population analysis shows that the symmetry-allowed transition, S0 (1Ag) → S2 (1Bu) based on the C 2h symmetry is a HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) π → π* transition with electron densities located mostly on the polyene chain. Calculated and actual steady-state absorption spectra show similar features with low-energy peak maxima between 550 and 600 nm.
Two new derivatives of all-trans retinal, one containing a pyridine and a cyanide substituent, all-trans-15-cyano-15′-pyridylretinal (2), and the other containing two cyanide substituents, ...all-trans-15,15′-dicyanoretinal (3), have been synthesized from all-trans-retinal (1) by the Knoevenagel reaction. Compound 2 crystallizes in the space group P1̅; compound 3 crystallizes in the space group P21/n. The polyene chains are bowed. The compounds exhibit CN vibrations in the infrared and Raman regions and undergo irreversible oxidations. Compounds 2 and 3 display electronic absorptions with maxima located at 442 and 487 nm and emission peaks located at 583 and 500 nm, respectively. Density Functional Theory and Time Dependent Density Functional Theory calculations reveal that the electronic transition from the HOMO to the LUMO can be associated with the Ag → Bu electronic transition and a peak corresponding to the HOMO → LUMO+1 transition can be associated with the “cis-peak”.
Solvent photosubstitution occurs with high efficiency in ruthenium(II) bis-bipyridine complexes containing acetonitrile and succinonitrile as ligands.
The electrochemical and photophysical properties ...of two bis-nitrilo ruthenium(II) complexes formulated as Ru(bpy)
2(L)
2(PF
6)
2, where bpy is 2,2′-bipyridine and L is AN
=
CH
3CN and sn
=
NC–CH
2CH
2–CN, have been investigated. Electrochemical data are typical of Ru-bpy complexes with two reversible reduction peaks located near −1.3 and −1.6
V assigned to each bipyridine ligand and one Ru
II/Ru
III oxidation wave centered at approximately +1.5
V. The sn derivative is both IR and Raman active with its coordinated CN stretch appearing at 2277
cm
−1 and 2273
cm
−1, respectively. The UV/Vis absorption spectrum of the sn derivative is dominated by an intense (
ε
max
∼
58700
M
−1
cm
−1) absorption band at 287
nm assigned as a LC (π
→
π∗) transition. The peak observed at 418
nm (
ε
∼
10
400
M
−1
cm
−1) is an MLCT band while the one at 244
nm (
ε
∼
23
600
M
−1
cm
−1) is of LMLCT character. The AN derivative behaves similarly. Both complexes show low-temperature emission at around 537
nm with a lifetime near 10.0
μs.
1H and
13C assignments are consistent with the formulation of the complexes. The complexes undergo photosubstitution of solvent with quantum efficiencies near one. Calculated and experimental results support replacement of the nitrile ligands by solvent. Based on DFT calculations, the electron density of the HOMO lies on the metal center, the bipyridine ligands and the nitrile ligands and electron density of the LUMO resides primarily on the bipyridine ligands. The electronic spectra obtained from TDDFT calculations closely match the experimental ones.
Hydrolysis of 1,10-phenanthrolinopyrrole ethyl ester leads to the acid derivative which is unstable at room-temperature releasing CO2 and forming 1,10-phenanthrolinopyrrole (php). The ligand reacts ...with ruthenium(II) to form a series of complexes of the general formula Ru(php) n (bpy)3 - n 2+, where bpy = 2,2‘-bipyridine and n = 1−3. The photochemical properties reveal that the complexes have longer-lived excited states than the standard complex, Ru(bpy)32+. Their emission lifetimes range from 9.04 μs (n = 1) to 35.5 μs (n = 3) at 77 K compared to 7.57 μs for the standard. Similarly, at room-temperature, emission lifetimes range from 1.20 μs (n = 1) to 1.70 μs (n = 3) relative to the standard (0.56 μs). The emission quantum yields also have higher values than the standard Ru(bpy)32+ under similar conditions. The temperature-dependent studies for the complexes establish the distribution among the radiative, nonradiative, and 3MLCT to 3d−d decay channels and are in agreement with the energy gap law.
The ligand 2,6-dimethylphenylisocyanide (CNx) forms six complexes of the formula Re(CO)3(CNx)(L)+, where L = 1,10-phenanthroline (1), 5-chloro-1,10-phenanthroline (2), 5-nitro-1,10-phenanthroline ...(3), 5-methyl-1,10-phenanthroline (4), 5,6-dimethyl-1,10-phenanthroline (5), and 1,10-phenanthrolinopyrrole (6). The lowest-energy absorption peaks of the complexes red-shift in the order 1 < 2 < 3 < 4 < 5 < 6. The time-dependent density functional theory (TDDFT) and conductor-like polarizable continuum model (CPCM) computed singlet excited states in ethanol deviate by 1000 cm-1 or less from the experimental UV−vis peaks. The complexes undergo reversible reductions and irreversible oxidations. The electronic energy gap increases in the order 3 < 2 < 1 < 4 < 5 < 6, which is the order of increasing electron-donating power of the phen substituents. The reduction potentials linearly correlate with the B3LYP calculated LUMO energies for 1 − 6. The complexes emit at room temperature and at 77 K except 3, which emits only at 77 K. The calculated 3MLLCT energies are within 1100 cm-1 from the experimental emission energies at 77 K. The 77 K emission curve-fitting analysis results agree with the computational assignment of the emitting state as 3MLLCT for 1 − 5 and 3LC for 6. The experimental 77 K emission energies and the calculated 3MLLCT state energies increase in the order 6 < 5, 3 < 2 < 4, 1. The 77 K emission lifetimes increase upon addition of substituents from 65 μs for 1 to 171 μs for 2, to 230 μs for 4 and 5, and to 322 μs for 3. The emission quantum yields at room temperature in solution are 0.77, 0.78, 0.83, 0.56, and 0.11 for complexes 1, 2, 4, 5, and 6, respectively.
A series of compounds of the type (bpy)
2Ru(3,3′-XX-2,2′-bpy)
2+ or (dmb)
2Ru(3,3′-XX-2,2′-bpy)
2+, where X is CH
2OH, COOH, COOCH
3, COOC
2H
5, and COOCH
2C
6H
5 and bpy and dmb are 2,2′-bipyridine ...and 4,4′-dimethyl-2,2′-bipyridine, respectively, have been synthesized. Ru(bpy)
2((COOCH
3)
2bpy)(PF
6)
2·2CH
3CN crystallized in the monoclinic space group
P2
1/
c with
a=15.347 (3),
b=22.767 (4),
c=12.971 (3) Å, and
Z=4.
1H-NMR spectra were assigned. The proton on the carbon atom neighboring the nitrogen coordination site shifts upfield upon coordination to ruthenium(II). Electronic absorptions occur over the visible region from 550 to 400 nm, which are attributed to metal-to-ligand charge transfer and in the UV region from 250 to 350 nm, which are associated with intraligand processes. The absorbance in the visible region of the spectrum displays two components, Ru(dπ)→π*(bpy) and Ru(dπ)→π*((COOR)
2bpy) for R=CH
3, C
2H
5 and CH
2C
6H
5, in the other cases the Ru(dπ)→π* transitions to the three bipyridine ligands overlap. Reduction potentials attributed to the Ru(III/II) couple range from 1.22 V for the CH
2OH derivative to 1.40 V versus SSCE for the COOC
2H
5 derivative. Reductions attributed to the first reduction of the coordinated (3,3′-XX-2,2′-bpy) ligand occur over the range −0.88 to −1.36 V versus SSCE. Emission maxima at room temperature in acetonitrile range from 614 nm for the CH
2OH derivative to 711 nm for the ester derivatives; their emission lifetimes at room temperature in acetonitrile vary from 940 to 258 ns, respectively.
