Crystal structure and chemical oxidation of the palladium(II) cyclam complex within the cavity of cucurbit[8]uril

Inclusion compound of a macrocyclic cavitand cucurbit[8]uril (C₄₈H₄₈N₃₂O₁₆, CB[8]) with a square-planar palladium(II) complex of a polyamine ligand cyclam, {[Pd(cyclam)]@CB[8]}Cl₂·16?H₂O (1), was synthesized and characterized by X-ray crystallography, elemental analysis, IR, and electrospray ionization (ESI) mass spectrometry. The complex [Pd(cyclam)]²⁺ undergoes chemical oxidation within the CB[8] cavity leading to the formation of the palladium(IV) inclusion compound {trans-[Pd(cyclam)Cl₂]@CB[8]}Cl₂·14H₂O (2). The Pd(II) and Pd(IV) complexes are completely encapsulated within the CB[8] cavity. The cyclam ring in 1 and 2 adopts the most stable configuration (trans-III (S,S,R,R)).     

Crystal structure and spectroscopic properties of trans-bis(nicotinato)(1,4,8,11-tetraazacyclotetradecane)chromium(III) perchlorate

The trans-[Cr(cyclam)(nic-O)₂]ClO₄ (cyclam = 1,4,8,11-tetraazacyclotetradecane; nic-O = O-coordinated nicotinate) has been prepared and structurally characterized by single-crystal X-ray diffraction at 150 K. The chromium atom is in a tetragonally compressed octahedral environment with four N atoms of the macrocyclic ligand in equatorial positions and two O-bonded nicotinates in trans axial positions. The macrocyclic cyclam adopts the centrosymmetric trans-III configuration with six- and five-membered chelate rings in chair and gauche conformation, respectively. The IR and visible spectral properties are consistent with the result of X-ray crystallography. The resolved band maxima of the electronic d-d spectrum are fitted with secular determinant for quartet state energy of d³ configuration in tetragonal field including configurational interaction. It is found that the nitrogen atoms of the cyclam ligand are a strong σ-donors and that O-bonded nicotinato group has strong σ- and π-donor characteristics toward the chromium(III) ion.     

Side-on binding of p-sulphonatocalix[4]arene to the dinuclear platinum complex trans-[{PtCl(NH3)2}2μ-dpzm] and its implications for anticancer drug delivery

The utility of p-sulphonatocalix[4]arene (s-CX[4]) as a drug delivery vehicle for multinuclear platinum anticancer agents, using trans-[{PtCl(NH₃)₂}₂μ-dpzm]²⁺ (di-Pt; where dpzm = 4,4′-dipyrazolylmethane) as a model complex, has been examined using ¹H nuclear magnetic resonance, electrospray ionisation mass spectrometry, molecular modelling and in vitro growth inhibition assays. s-CX[4] binds di-Pt in a side-on fashion in a ratio of 1:1, with the dpzm ligand of the metal complex located within the s-CX[4] cavity with binding further stabilised by ion-ion interactions and hydrogen bonding between the metal complex am(m)ine groups and the s-CX[4] sulphate groups. Partial encapsulation of di-Pt within the cavity does not prevent binding of 5′-guanosine monophosphate to the metal complex. When bound to two individual guanosine molecules, di-Pt also remains partially bound by s-CX[4]. The cytotoxicity of free di-Pt and s-CX[4] and their host guest complex was examined using in vitro growth inhibition assays in the A2780 and A2780cis human ovarian cancer cell lines. Free di-Pt has an IC₅₀ of 100 and 60 μM, respectively, in the cell lines, which is significantly less active than cisplatin (1.9 and 8.1 μM, respectively). s-CX[4] displays no cytotoxicity at concentrations up to 1.5 mM and does not affect the cytotoxicity of di-Pt, probably because its low binding constant to the metal complex (6.8 × 10⁴ M⁻¹) means the host-guest complex is mostly disassociated at biologically relevant concentrations.     

Interfacial electron transfer on TiO2 sensitized with an axially anchored trans tetradentate Ru(II) compound

The ruthenium complexes, trans-[Ru(phen-NH-phen)(eina)₂](PF₆)₂ and trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ where phen-NH-phen = N,N-bis(1,10-phenanthroline-2-yl)amine, ina = isonicotinic acid and eina = ethyl isonicotinate, have been synthesized and characterized by ¹H NMR, elemental analysis, and IR spectroscopy. The compounds were non-emissive at room temperature, but displayed intense photoluminescence in 4:1 ethanol/methanol glasses at 77 K with corrected emission maximum at 570-580 nm. A quasi-reversible wave observed in cyclic voltammetry experiments was assigned to the Ru^III/II couple, E° (trans-[Ru(phen-NH-phen)(eina)₂)^3+/2+ = +1.22 V versus Ag/AgCl. The trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ compound was found to bind to nanocrystalline TiO₂ thin films from acetonitrile solution. Pulsed 532 nm excitation of trans-[Ru(phen-NH-phen)(ina)₂](PF₆)₂ anchored to mesoporous nanocrystalline TiO₂ thin films resulted in an absorption difference spectra consistent with the formation of an interfacial charge separated state trans-[Ru^III (phen-NH-phen)(ina)₂]⁺/TiO₂ (e⁻). The formation of this state could not be time resolved, consistent with rapid excited state injection into the TiO₂, k_inj > 10⁸ s⁻¹. Comparative measurements with a thin film actinometer yielded an injection quantum yield (?_inj) of 0.8. Charge recombination required milliseconds for completion and followed a bi-second-order equal concentration kinetic model with k₁ = 1.0 × 10⁸ s⁻¹, and k₂ = 3.0 × 10⁵ s⁻¹. In regenerative solar cells with 0.5 M LiI and 0.005 M I₂ in acetonitrile, incident photon-to-current efficiencies were typically less than 10%.     

Generation of trans-dioxoruthenium(VI) porphyrins: A photochemical approach

trans-Dioxoruthenium(VI) porphyrin complexes have been developed as one of the best-characterized model systems for heme-containing enzymes. Traditionally, this type of compounds can be prepared by oxidation of ruthenium(II) precursors with peroxyacids and other terminal oxidants under different conditions, depending on the porphyrin ligands. In this work, a new photochemical generation of trans-dioxoruthenium(VI) porphyrins has been developed by extension of the known photo-induced ligand cleavage reactions. Refluxing ruthenium(II) carbonyl porphyrins [Ru^II(Por)(CO)] in carbon tetrachloride afforded dichlororuthenium(IV) complexes [Ru^IV(Por)Cl₂]. Facile exchange of the counterions in [Ru^IV(Por)Cl₂] with Ag(ClO₃) or Ag(BrO₃) gave the corresponding dichlorate [Ru^IV(Por)(ClO₃)₂] or dibromate [Ru^IV(Por)(BrO₃)₂] salts. Visible-light photolysis of the photo-labile porphyrin-ruthenium(IV) dichlorates or dibromates resulted in homolytic cleavage of the two O-Cl or O-Br bonds in the axial ligands to produce trans-dioxoruthenium(IV) species [Ru^VI(Por)O₂] bearing different porphyrin ligands.     

Computational study on the mechanisms of action of the potential anticancer drug trans-isopropylaminedimethylaminedichloroplatinum (trans-IPADMADP) and its cis isomer with DNA purine bases

The monofunctional and bifunctional bindings of the potential anticancer drug trans-isopropylaminedimethylaminedichloroplatinum (trans-IPADMADP) and its cis isomer to purine base in DNA are explored by using density functional theory and IEF-PCM solvation models. The computed lowest free energy barrier in the aqueous solution is 14.0/11.6 kcal/mol (from trans-Pt-chloroaqua complex to trans-/cis-monoadduct) for guanine(G), and 11.7/13.3 kcal/mol (from trans-Pt-chloroaqua complex to trans-/cis-monoadduct) for adenine(A). Our calculations demonstrate that the trans reactant complexes (or isolated reactants) can generate trans- or cis-monoadducts via similar trigonal bipyramidal transition state structures, suggesting that the monoadducts can subsequently close to form the bifunctional intrastrand Pt-DNA adducts and simultaneously distort DNA in the similar way as cisplatin. Our calculations show that Pt(isopropylamine)(dimethylamine)G₂²⁺ head-to-head path has the lowest free energy of activation at 17.6 kcal/mol, closely followed by the Pt(isopropylamine)(dimethylamine)GA²⁺ head-to-head path at 19.6 kcal/mol when the monofunctional cis-Pt-G complex serves as the reactant; while the Pt(isopropylamine)(dimethylamine)G₂²⁺ head-to-tail adduct has the lowest barrier of 20.5 kcal/mol, closely followed by the Pt(isopropylamine)(dimethylamine)GA²⁺ head-to-tail adduct at 23.0 kcal/mol if the monofunctional trans-Pt-G complex is the reactant.The calculated relatively lower activation energy barrier than that of cisplatin theoretically confirm that trans-[PtCl₂(isopropylamine)(dimethylamine)] is a potential anticancer drug as described by experiment.     

Identification of cis/trans isomers of bis(acetylacetonato)nickel(II) complexes in solution based on electronic spectra

Electronic spectra of Ni(acac)₂ were studied in acetone, DMF, and some other solvents for the purpose of identifying the cis/trans isomers from the spectra (acac⁻ = acetylacetonate anion). The spectral components were investigated in the spin-allowed transition bands, and a relationship was found between the spectral pattern and the cis/trans isomers. According to this relationship, it was concluded that the cis isomer was formed in DMF and in N-methylformadide, whereas the trans isomer was formed in acetone and in pyridine. Based on the DFT computation, the cis-[Ni(acac)₂(DMF)₂] was found to be stabilized by intramolecular hydrogen bonds between acetylacetonate and DMF.     

Quantification of cis and trans influences in [PtX(PPh3)3] complexes. A P NMR study

In [PtX(PPh₃)₃]⁺ complexes (X = F, Cl, Br, I, AcO, NO₃, NO₂, H, Me) the mutual cis and trans influences of the PPh₃ groups can be considered constants in the first place, therefore the one bond Pt-P coupling constants of P_(cis) and P_(trans) reflect the cis and trans influences of X. The compounds [PtBr(PPh₃)₃](BF₄) (2), [PtI(PPh₃)₃](BF₄) (3), [Pt(AcO)(PPh₃)₃](BF₄) (4), [Pt(NO₃)(PPh₃)₃](BF₄) (5), and the two isomers [Pt(NO₂-O)(PPh₃)₃](BF₄) (6a) and [Pt(NO₂-N)(PPh₃)₃](BF₄) (6b) have been newly synthesised and the crystal structures of 2 and 4·CH₂Cl₂·0.25C₃H₆O have been determined. From the ¹J_PtP values of all compounds we have deduced the series: I > Br > Cl > NO₃ > ONO > F > AcO > NO₂ > H > Me (cis influence) and Me > H > NO₂ > AcO > I > ONO > Br > Cl > F > NO₃ (trans influence). These sequences are like those obtained for the (neutral) cis- and trans-[PtClX(PPh₃)₂] derivatives, showing that there is no dependence on the charge of the complexes. On the contrary, the weights of both influences, relative to those of X = Cl, were found to depend on the charge and nature of the complex.     

Cytotoxic trans-oriented iminoether platinum complexes - Kinetics of binding to DNA oligonucleotides determined by N NMR spectroscopy

The kinetics of reactions between cytotoxic trans-oriented iminoether platinum complexes and DNA oligonucleotides have been studied by 1D and 2D [¹H, ¹⁵N] HMQC NMR spectroscopy. The results for the two isomers of the mono-iminoether compound trans-[PtCl₂(NH₃){E/Z-HNC(OMe)Me}] (trans-E and trans-Z) are compared with those of the bis-iminoether derivative trans-[PtCl₂{E-HNC(OMe)Me}₂] (trans-EE). Earlier we have shown that quite unexpectedly, trans-EE is practically inert towards a central GG residue in a 12-mer double-helical duplex. We now show that the less bulky trans-E and trans-Z compounds do bind to the interior of the duplex [5′-d(G₁G₂T₃A₄C₅C₆G₇G₈ T₉A₁₀C₁₁C₁₂)]₂ which contains terminal and central “hot” GG site. The platination by trans-E and trans-Z is as expected most pronounced for the solvent exposed, terminal GG-step but significantly, competitive binding is also observed for the central GG-step. The rate of platination of the terminal G-sites is almost an order of magnitude larger for the oligomer than for the monomer GMP which was studied for comparison. The role of trans-platinum carrier ligands in influencing the type and rate of formation of adducts with DNA and other relevant biomolecules is discussed.     

Coordination diversity of N-phosphoryl-N′-phenylthiourea (LH) towards Co, Ni and Pd cations: Crystal structure of ML2-N,S and ML2-O,S chelates

Thiourea, PhNHC(S)NHP(O)(OPrⁱ)₂ (LH) chelates of Co^II, Ni^II, and Pd^II ions have been obtained and investigated by single-crystal X-ray diffraction, UV, IR, NMR spectroscopy, and EI mass-spectrometry. The unusual 1,3-N,S-coordination via sulfur and NP(O) nitrogen atoms has been found in the trans-square-planar NiL₂ and PdL₂ complexes, whereas the 1,5-O,S-coordination is realized in the tetrahedral CoL₂ complex. DFT calculations have revealed significant stabilization of the 1,3-N,S-structures due to stronger crystal field and the NH-OP hydrogen bonds.     

Effect of solvent environment on the CO band position in the infrared spectrum of trans-[Fe(CN)4(CO)2]

Density functional theory (DFT) is used to understand the effect of hydrogen bonding solvents on the CO band position in the infrared (IR) spectrum of a mono-iron complex, trans-[Fe^II(CN)₄(CO)₂]²⁻. This mono-iron complex has received much attention recently due its potential relation to the biosynthesis of Fe-only hydrogenase enzymes. Our calculations show that the polar solvent molecules preferentially hydrogen bond to the cyano ligands in this complex. The effect of such hydrogen bonding on the electron density distribution is analyzed in terms of the population in natural bond orbitals (NBO). Our results show that the presence of hydrogen bonding to the cyano ligands decreases the extent of back bonding from the metal to the carbonyl ligand. This results in decreased electron density in the π^∗ orbitals of the carbonyl bond leading to a strengthening of the CO bond and a consequent blue shift in the IR band position of the carbonyl group. We also show that the extent of blue shift correlates with the number of nearest neighbor solvent molecules.     

Heteroligand copper(I) complexes of N-thiophosphorylated thioureas and phosphanes: Versatile structures and luminescence

Reaction of the potassium salts of (EtO)₂P(O)CH₂C₆H₄-4-(NHC(S)NHP(S)(OiPr)₂) (HL^I), (CH₂NHC(S)NHP(S)(OiPr)₂)₂ (H₂L^II) or cyclam(C(S)NHP(S)(OiPr)₂)₄ (H₄L^III) with [Cu(PPh₃)₃I] or a mixture of CuI and Ph₂P(CH₂)_1-3PPh₂ or Ph₂P(C₅H₄FeC₅H₄)PPh₂ in aqueous EtOH/CH₂Cl₂ leads to [Cu(PPh₃)L^I] (1), [Cu₂(Ph₂PCH₂PPh₂)₂L^II] (2), [Cu{Ph₂P(CH₂)₂PPh₂}L^I] (3), [Cu{Ph₂P(CH₂)₃PPh₂}L^I] (4), [Cu{Ph₂P(C₅H₄FeC₅H₄)PPh₂}L^I] (5), [Cu₂(PPh₃)₂L^II] (6), [Cu₂(Ph₂PCH₂PPh₂)L^II] (7), [Cu₂{Ph₂P(CH₂)₂PPh₂}₂L^II] (8), [Cu₂{Ph₂P(CH₂)₃PPh₂}₂L^II] (9), [Cu₂{Ph₂P(C₅H₄FeC₅H₄)PPh₂}₂L^II] (10), [Cu₈(Ph₂PCH₂PPh₂)₈L^IIII₄] (11), [Cu₄{Ph₂P(CH₂)₂PPh₂}₄L^III] (12), [Cu₄{Ph₂P(CH₂)₃PPh₂}₄L^III] (13) or [Cu₄{Ph₂P(C₅H₄FeC₅H₄)PPh₂}₄L^III] (14) complexes. The structures of these compounds were investigated by IR, ¹H, ³¹P{¹H} NMR spectroscopy; their compositions were examined by microanalysis. The luminescent properties of the complexes 1-14 in the solid state are reported.     

Structure and reactivity of [Ru(2,3-Medpp)2Cl2]

The structure and reactivity of the complex [Ru(2,3-Medpp)₂Cl₂](PF₆)₂ (2,3-Medpp⁺=2-[2-(1-methylpyridiniumyl)]-3-(2-pyridyl)pyrazine) was investigated by X-ray diffraction (XRD), ¹H NMR, redox, and UV-Vis absorption measurements. X-ray analysis shows that crystals obtained from an acetonitrile-toluene solution contain the trans-Cl₂, trans-pyrazine isomeric form, while ¹H NMR and redox measurements on the main product of the synthetic workup indicate the presence of the trans-Cl₂, cis-pyrazine isomer. In the dark at 70 °C, the complex [Ru(2,3-Medpp)₂Cl₂]²⁺ reacts slowly in acetonitrile isomerizing to the cis-[Ru(2,3-Medpp)₂(CH₃CN)Cl]³⁺ species. Under ambient light in the presence of excess AgNO₃ the cis-[Ru(2,3-Medpp)₂(CH₃CN)₂]⁴⁺ species is obtained.     

Mono- and dinuclear (o-thioetherphenolato)-copper(II) complexes. Structural models for galactose oxidase

Three new o-thioetherphenol ligands have been synthesized: 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenylsulfanyl)ethane (H₂bse), 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenylsulfanyl)benzene (H₂bsb), and 4,6-di-tert-butyl-2-phenylsulfanylphenol (Hpsp). Their complexes with copper(II) were prepared and investigated by UV-Vis-, EPR-spectroscopy; their electro- and magnetochemistry have also been studied: [Cu^II(psp)₂] (1), [Cu^II₂(bse)₂] (2), [Cu^II₂(bsb)₂] (3), [Cu^II(bsb)(py)₂] (4). The crystal structures of the ligands H₂bse, H₂bsb, Hpsp and of the complexes 1, 2, 3, 4 have been determined by X-ray crystallography.     

Synthesis, characterization and kinetic studies of the cis-[RuCl2(cyclen)] complex

We report here the synthesis, characterization and kinetic studies of cis-[RuCl₂(cyclen)]⁺ in aqueous solution, where cyclen is the macrocyclic ligand 1,4,7,10-tetraazacyclododecane. The complex releases one Cl⁻ producing cis-[RuCl(OH)(cyclen)]⁺ in aqueous solution at pH 4.60. The product of this reaction was characterized by Ultraviolet-Visible (UV-Vis) spectrum in comparison to the synthesized cis-[RuCl(OH)(cyclen)](BF₄)·2H₂O. The electrochemical data showed that E_pc of the Ru(III/II) peak increases as the macrocycle ring size decreases and also when the trans conformation is changed to cis. The chloride affinity of Ru(III) depends on the macrocycle ring size since cis-[RuCl₂(cyclam)]⁺ (cyclam=1,4,8,11-tetraazacyclotetradecane) does not release chloride for at least 12 h. The overall effect between cyclam and cyclen reflects the fact that the electron involved in the reduction enters a nonbonding π-d orbital and its energy is affected by the macrocyclic ligand.     

Probing electron transfer reactions between two azurins from Alcaligenes xylosoxidans GIFU 1051 with optically active Ru complexes as molecular recognition probes: Importance of the 43rd residue

Electron transfer reactions between optically-active Ru^II/III complexes incorporating (S)-/(R)-amino acids, and the two azurins, azurin-1 (az-1Cu) and azurin-2 (az-2Cu) isolated from Alcaligenes xylosoxidans GIFU 1051, have been studied to probe molecular recognition sites on the two azurins. The Ru^II/III complexes are K[Ru^II(L)(bpy)] and [Ru^III(L)(bpy)], and have a tripodal ligand (L) derived from the (S)-/(R)-amino acids, which are in turn exchanged for other functional substituent groups, such as (S)-/(R)-phenylalanine, -leucine, -valine, -alanine, and -glutamic acid (L = (S)-/(R)-BCMPA, -BCMLE, -BCMVA, -BCMAL, and -BCMGA). In the oxidation reaction of az-1Cu^I promoted by the Ru^III complexes, the kinetic parameters exhibited enantio- and stereo-selectivities, while the same reaction of az-2Cu^I was less enantio- and stereo-selective. These differences suggest that the processes of formation of the activated states are different for the two azurins. On the other hand, such a difference has not been observed for az-1 and az-2 with respect to the reduction reactions promoted by both azurins Cu^II by the Ru^II complexes within the experimental error. This suggests that the neutrality of the Ru complexes is important for precise molecular recognition of azurins. His117 has been proposed as the electron transfer site. The local structures in the vicinity of the His117 side chain in the two azurins, are essentially identical with the exception of the 43rd residue, Val43 and Ala43 for az-1 and az-2, respectively. Electron transfer reactions between Ru^III complexes and a mutant azurin, V43A-az-1, were also carried out. Interestingly, the activation parameters estimated were very similar to those of az-2, indicating that the 43rd residue acts as the electron transfer site in azurins and provides rationalization for the different mechanisms of az-1 and az-2 in redox reactions.     

A mutational analysis of active site residues in trans-3-chloroacrylic acid dehalogenase

trans-3-Chloroacrylic acid dehalogenase (CaaD) catalyzes the hydrolytic dehalogenation of trans-3-haloacrylates to yield malonate semialdehyde by a mechanism utilizing βPro-1, αArg-8, αArg-11, and αGlu-52. These residues are implicated in a promiscuous hydratase activity where 2-oxo-3-pentynoate is processed to acetopyruvate. The roles of three nearby residues (βAsn-39, αPhe-39, and αPhe-50) are unexplored. Mutants were constructed at these positions (βN39A, αF39A, αF39T, αF50A and αF50Y) and kinetic parameters determined along with those of the αR8K and αR11K mutants. Analysis indicates that αArg-8, αArg-11, and βAsn-39 are critical for dehalogenase activity whereas αArg-11 and αPhe-50 are critical for hydratase activity. Docking studies suggest structural bases for these observations.     

Manganese (III) cyclam complexes with aqua, iodo, nitrito, perchlorato and acetic acid/acetato axial ligands

The syntheses, structures and magnetic properties of five new manganese (III) cyclam complexes, trans-[Mn(cyclam)(OH₂)₂](CF₃SO₃)₃ · H₂O, trans-[Mn(cyclam)I₂]I, trans-[Mn(cyclam)(ONO)₂]ClO₄, trans-[Mn(cyclam)(OClO₃)₂]ClO₄ and trans-[Mn(cyclam)(CH₃COO)(CH₃COOH)](ClO₄)₂, are reported. Cyclam is the tetradentate amine ligand 1,4,8,11-tetraazacyclotetradecane. The complexes all exhibit pronounced tetragonal elongation of the coordination octahedron with the four cyclam nitrogens occupying the four equatorial positions. The magnetic properties are consistent with the formulation of the complexes as high-spin d⁴ systems. trans-[Mn(cyclam)(OH₂)₂](CF₃SO₃)₃ · H₂O is shown to be a convenient starting material for the syntheses of trans cyclam complexes. [Mn(cyclam)(CH₃COO)(CH₃COOH)](ClO₄)₂ exhibits extremely short intermolecular hydrogen bonds resulting in a pseudo-chain structure. The tilt of the axial ligands with respect to the equatorial plane containing the manganese and the cyclam nitrogen atoms is discussed.     

Photoactivation of trans diamine platinum complexes in aqueous solution and effect on reactivity towards nucleotides

We show that UVA irradiation (365 nm) of the Pt^IV complex trans,trans,trans-[Pt^IVCl₂(OH)₂(dimethylamine)(isopropylamine)] (1), induces reduction to Pt^II photoproducts. For the mixed amine Pt^II complex, trans-[Pt^IICl₂(isopropylamine)(methylamine)] (2), irradiation at 365 nm increases the rate and extent of hydrolysis, triggering the formation of diaqua species. Additionally, irradiation increases the extent of reaction of complex 2 with guanosine-5′-monophosphate and affords mainly the bis-adduct, while reactions with adenosine-5′-monophosphate and cytidine-5′-monophosphate give rise only to mono-nucleotide adducts. Density Functional Theory calculations have been used to obtain insights into the electronic structure of complexes 1 and 2, and their photophysical and photochemical properties. UVA-irradiation can contribute to enhanced cytotoxic effects of diamine platinum drugs with trans geometry.     

Modulation of trans-to-cis photoisomerization and photoluminescence of 1,2-bis(4-pyridyl)ethylene or 4-styrylpyridine coordinated to fac-tricarbonyl(5-chloro-1,10-phenathroline)rhenium(I)

Photochemical and photophysical properties of fac-[Re(CO)₃(Clphen)(trans-L)]⁺ complexes, Clphen = 5-chloro-1,10-phenathroline and L = 1,2-bis(4-pyridyl)ethylene, bpe, or 4-styrylpyridine, stpy, were investigated to complement the understanding of intramolecular energy transfer process in tricarbonyl rhenium(I) complexes having an electron withdrawing group attached to polypyridyl ligands. These new compounds were synthesized, characterized and the photoisomerization quantum yields were accurately determined by ¹H NMR spectroscopy. The true quantum yields for fac-[Re(CO)₃(Clphen)(trans-bpe)]⁺ were constant (Φ = 0.55) at all investigated irradiation wavelengths. However, for fac-[Re(CO)₃(Clphen)(trans-stpy)]⁺, similar true quantum yields were observed only at higher energy irradiation (Φ_{313 nm} = 0.53 and Φ_{365 nm} = 0.57), but it decreased significantly at 404 nm (Φ = 0.41). These results indicated different deactivation pathways for the trans-stpy complex photoisomerization. Quantum yields decreased as the ³IL_trans-L and ³MLCT_Re→NN excited states become closer and the behavior was discussed in terms of the excited state energy gaps. Additionally, luminescence properties of photoproducts, fac-[Re(CO)₃(Clphen)(cis-L)]⁺, were also investigated in different environments to analyze the relative energy of the ³MLCT_Re→Clphen excited state for each compound.