Synthesis and properties of red emitter Ru(II) complexes based on 6,6′-disubstituted-4,4′-bipyrimidine

Heteroleptic complexes [Ru(bpy)₂(R₂bpm)]²⁺, where bpy = 2,2′-bipyridine and R₂bpm = 6,6′-diaryl-4,4′-bipyrimidine, have been synthesized and characterized, together with the homoleptic complex [Ru(R₂bpm)₃]²⁺, in which R₂bpm = 6,6′-diphenyl-4,4′-bipyrimidine. The substituent aryl on the bipyrimidine has significant effects on the properties of these complexes as compared to the parent [Ru(bpy)₂(bpm)]²⁺ complex. The complexes exhibit Ru-to-bpm charge transfer (CT) absorptions centered at about 540 nm and Ru-to-bpy CT absorptions centered at about 435 nm. The assignment of the low energy absorptions is supported by the relative ease of the reduction of the new complexes as compared to [Ru(bpy)₃]²⁺. The new complexes exhibit a relatively intense emission at room temperature, with lifetimes in the 10-50 ns range, with the homoleptic species exhibiting the higher-energy (maximum at 724 nm) and the longest-lived (τ = 48 ns) emission among the complexes. Luminescence lifetimes and quantum yields are governed by the energy gap law, indicating that direct deactivation to the ground state is the dominant relaxation pathway for 1-6, while thermally activated processes are inefficient.     

4,4′-Bis(tert-butyl)-2,2′-bipyridinedichlorometal(II) - Synthesis, structure and EPR spectroscopy

Due to the better solubility of the 4,4′-substituted bipyridine ligand a series of 4,4′-bis(tert-butyl)-2,2′-bipyridinedichlorometal(II) complexes, [M(tbbpy)Cl₂], with M = Cu, Ni, Zn, Pd, Pt was synthesised and characterised. The blue copper complex 4,4′-bis(tert-butyl)-2,2′-bipyridinedichlorocopper(II) was isolated in two different polymorphic forms, as prisms 1 with a solvent inclusion and solvent-free as needles 2. Both structures were determined by X-ray structure analysis. They crystallise in the monoclinic space group P2₁/c with four molecules in the unit cell, but with different unit cells and packing motifs. Whereas in the prisms 1, with the unit cell parameters a = 12.1613(12), b = 10.6363(7), c = 16.3074(15) Å, β = 94.446(8)°, the packing is dominated by intra- and intermolecular hydrogen bonds, in the needles 2, with a = 7.738(1), b = 18. 333(2), c = 13.291(3) Å, β = 97.512(15)°, only intramolecular hydrogen bonds appear and the complex molecules are arranged in columns which are stabilised by π-π-stacking interactions. In both complexes the copper has a tetrahedrally distorted coordination sphere. These copper complexes were also studied by EPR spectroscopy in solution, as frozen glass and diamagnetically diluted powder with the analogue [Pd(tbbpy)Cl₂] as host lattice.     

Synthesis and characterization of Os(II)(dpop′) (dpop′ = dipyrido(2,3-a;3′,2′-j)phenazine) complexes with 2,2′-bipyridine(bpy); 2,2′-bipyrimidine(bpm) and 2,3-bis(2-pyridyl)pyrazine(dpp)

New Os(II) complexes including [Os(dpop′)₂](PF₆)₂ (dpop′= dipyrido(2,3-a;3′,2′-j)phenazine) and a series of mixed ligand [Os(dpop′)(N-N)Cl]PF₆ (N-N = 2,2′-bipyridine(bpy); 2,2′-bipyrimidine(bpm) and 2,3-bis(2-pyridyl)pyrazine(dpp)) were synthesized. The Os dπ → dpop′ π^∗ MLCT transitions for [Os(dpop′)₂]²⁺ are observed at lower energy than for Os dπ → tpy π^∗ (tpy = 2,2′:6′,2″-terpyridine) and Os dπ → tppz π^∗ (tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) (The ligand abbreviations tpd, tpp and tpypz have also appeared in the literature for 2,3,5,6- tetrakis(2-pyridyl)pyrazine in addition to tppz.) MLCT transitions in the comparative [Os(tpy)₂]²⁺ and [Os(tppz)₂]²⁺ complexes. The Os dπ → dpop′ π^∗ MLCT transitions are observed at lower energy in mixed bidentate ligand N-N systems compared with [Os(dpop′)₂]²⁺. Cyclic voltammetry shows more positive osmium oxidation, and less negative ligand reduction potentials for [Os(dpop′)₂]²⁺ as compared to [Os(tpy)₂]²⁺ and [Os(tppz)₂]²⁺ complexes. The osmium oxidation potentials in mixed ligand [Os(dpop′)(N-N)Cl]⁺ complexes are at less positive potential than for the [Os(dpop′)₂]²⁺ ion. NMR results show different chemical shifts for ring protons either trans or cis to dpop′ in mixed ligand systems, and also show two geometrical isomers for the [Os(dpop′)(dpp)Cl]⁺ complex. The [Os(dpop′)(dpp)Cl]⁺ geometric isomer with the pyrazine ring of dpp trans to dpop′ is found more predominate by 1.0/0.7 over the isomer with the pyrazine ring of dpp cis to dpop′ and that inter-conversion of geometric isomers does not occur in room temperature solution on the NMR timescale.     

Preparation and photophysical studies of copper(I) and ruthenium(II) complexes of 4,4′-bis(3,5-dimethoxyphenyl)-6,6′-dimethyl-2,2′-bipyridine

We report the synthesis of a new ligand, 4,4′-bis(3,5-dimethoxyphenyl)-6,6′-dimethyl-2,2′-bipyridine, optimised for binding to copper(I) and with pendant functionality that can eventually be developed into metallodendritic structures. The synthesis and photophysical properties of complexes with copper(I) and ruthenium(II) are reported. The solid state structure of the complex [Cu(1)₂][PF₆] · MeCN (1 = 4,4′-bis(3,5-dimethoxyphenyl)-6,6′-dimethyl-2,2′-bipyridine) is also described.     

On the elusive, non-emissive yet reactive, upper excited states of [(4,4′-bpy)Re(CO)3(dppz)]PF6 (dppz = dipyridil[3,2-a:2′3′-c]phenazine)

Gradual solvation of [(4,4′-bpy)Re^I(CO)₃(dppz)]⁺ (dppz = dipyridil[3,2-a:2′3′-c]phenazine) by water molecules causes a quenching of the emission in accordance with Perrin’s model of spheres. The calculated radius of the sphere, r = 2.6 ± 0.2 ?, is therefore very close to the distance from the Re center to the oxygen atom of the CO ligands, i.e., l = 2.73 ?. In addition, excited state reactions with TEA produce [(4,4′-bpy⁻)Re^I(CO)₃(dppz)] and [(4,4′-bpy)Re^I(CO)₃(dppz⁻)]. This experimental observation is inconsistent with the formation of the products in the lowest lying and emissive dppz-centered ³ππ* excited state. Jablonski schemes based on the participation of excited states other than the lowest ³ππ* excited state are proposed.     

Synthesis, structure and DNA cleavage activity of two 4,4′-dimethyl-2,2′-bipyridyl manganese(II) complexes

Two new mononuclear Mn(II) complexes, Mn(dmbpy)₂(OCN)₂ (1) and Mn(dmbpy)₂(dca)₂ (2) (dmbpy = 4,4′-dimethyl-2,2′-bipyridine, dca = dicyanamide), have been synthesized and characterized by IR, elemental analysis, and single crystal X-ray analysis. Both complexes have similar molecular structures. The coordination sphere of the Mn(II) ion in 1 or 2 is a seriously distorted octahedron formed by two dmbpy ligands and two OCN⁻ or dca anions in cis positions. For both complexes, the most striking feature is that the mononuclear molecules are linked together by plentiful weak C-H?N hydrogen bonds into a compact 3D supramolecular structure. DNA cleavage studies show that the complexes can promote plasmid DNA cleavage in the presence of H₂O₂ under physiological conditions, and their cleavage activities are obviously both pH value and complex concentration-dependent. The cleavage mechanism between the complexes and plasmid DNA is likely to involve hydroxyl radicals as reactive oxygen species.     

Synthesis, structure and magnetic studies of two-dimensional network of Cu(II) polymer using malonate and 4,4′-azobispyridine ligands

The malonato-bridged copper(II) complex [Cu(mal)(H₂O)(azpy)_1/2] · H₂O (1) (mal = malonate, azpy = 4,4′-azobispyridine) has been synthesized and characterized by X-ray diffraction. The structure of 1 consists of malonato-bridged uniform copper(II) chains which are covalent connected through azpy to form two-dimensional wavelike network. The magnetic pathway of complex 1 is through a single syn-anti carboxylate bridge connecting equatorial and equatorial positions of adjacent copper(II) atoms, and have the value of the intrachain ferromagnetic coupling (J = 8.73(3) cm⁻¹) and interchain antiferromagnetic coupling (zJ′ = − 1.31(1) cm⁻¹) through a numerical expression for a ferromagnetic uniform chain.     

Three new multidimensional organic-inorganic hybrids based on polyoxometalates and copper coordination polymers with 4,4′-bipyridine ligands

Three new organic-inorganic hybrid materials with 4,4′-bipy ligands and copper cations as linkers, [Cu^II(H₂O)(4,4′-bipy)₂][Cu^II(H₂O)(4,4′-bpy)₂]₂H[Cu^IIP₈Mo₁₂O₆₂H₁₂] · 5H₂O (1), [Cu^I(4,4′-bipy)][Cu^II(4,4′-bipy)]₂ (BW₁₂O₄₀) · (4,4′-bipy) · 2H₂O (2) and [Cu^I (4,4′-bipy)]₃ (PMo₁₂O₄₀) · (pip) · 2H₂O (3) (pip = piperazine; 4,4′-bipy = 4,4′-bipyridine), have been hydrothermally synthesized. The single X-ray structural analysis reveals that the structure of 1 is constructed from [Cu(H₂O)(4,4′-bipy)₂] complexes into a novel, three-dimensional supermolecular network with 1-D channels in which Cu[P₄Mo₆]₂ dimer clusters reside. To the best of our knowledge, compound 1 is the first complex in which the [P₄Mo₆] clusters have been used as a non-coordinating anionic template for the construction of a novel, three-dimensional supermolecular network. Compound 2 is constructed from the six-supported [BW₁₂O₄₀]⁵⁻ polyoxoanions and [Cu^I(4,4′-bipy)] and [Cu^II(4,4′-bipy)] groups into a novel, 3-D network. Compound 3 exhibits unusual 3-D supramolecular frameworks, which are constructed from tetrasupporting [PMo₁₂O₄₀]³⁻ clusters and [Cu^I (4,4′-bipy)_n] coordination polymer chains. The electrochemical properties of 2 and 3 have been investigated in detail.     

Syntheses, characterization, and DFT investigation of new mononuclear acetonitrile- and chloro-ruthenium(II) terpyridine complexes

A series of mononuclear acetonitrile complexes of the type [Ru(CH₃CN)(L)(terpy)]²⁺ {L = phen (1), dpbpy (3), and bpm (5)}, and their reference complexes [RuCl(L)(terpy)]⁺ {L = phen (2), dpbpy (4), and dpphen (6)} were prepared and characterized by electrospray ionization mass spectrometry, UV-vis spectroscopy, and cyclic voltammograms (CV). Abbreviations of the ligands (Ls) are phen = 1,10-phenanthroline, dpbpy = 4,4′-diphenyl-2,2′-bipyridine, bpm = 2,2′-bipyrimidine, dpphen = 4,7-diphenyl-1,10-phenanthroline, bpy = 2,2′-bipyridine, and terpy = 2,2′:6′,2″-terpyridine. The X-ray structures of the two complexes 2 and 3 were newly obtained. The metal-to-ligand charge transfer (MLCT) bands in the visible region for 1, 3, and 5 in acetonitrile were blue shifted relative to those of the reference complexes [RuCl(L)(terpy)]⁺. CV for all the [Ru(CH₃CN)(L)(terpy)]²⁺ complexes showed the first oxidation wave at around 0.95 V, being more positive than those of [RuCl(L)(terpy)]⁺. The time-dependent-density-functional-theory approach (TDDFT) was used to interpret the absorption spectra of 1 and 2. Good agreement between computed and experimental absorption spectra was obtained. The DFT approach also revealed the orbital interactions between Ru(phen)(terpy) and CH₃CN or Cl⁻. It is demonstrated that the HOMO-LUMO energy gap of the acetonitrile ligand is larger than that of the Cl⁻ one.     

The synthesis and characterization of mixed ligand Ru(II) complexes with dipyrido(2,3-a:3′,2′-j)phenazine (dpop′) and 2,3,5,6-tetra(2-pyridyl)-pyrazine (tppz)

The synthesis of the mixed ligand mono metallic [Ru(dpop′)(tppz)]²⁺ and bimetallic [(dpop′)Ru(tppz)Ru(dpop′)]⁴⁺ (dpop′ = dipyrido(2,3-a:3′,2′-j)phenazine; tppz = 2,3,5,6 tetra-(2-pyridyl)pyrazine) complexes is described. The [Ru(dpop′)(tppz)]²⁺ complex display an intense absorption at 518 nm which is assigned to a Ru(dπ) → dpop′ (π∗) MLCT transition, and at 447 nm which is assigned to a Ru(dπ) → tppz(π∗) MLCT transition. It undergoes emission at RT in CH₃CN with λ_em = 722 nm. The bimetallic [(dpop′)Ru(tppz)Ru(dpop′)]⁴⁺ complex shows a low energy absorption shoulder near 635 nm assigned to a Ru(dπ) → tppz(π∗) MLCT transition and an intense peak at 542 nm due to Ru(dπ) → dpop′ (π∗) MLCT transition. The bimetallic complex also emits at RT in CH₃CN with λ_em = 785 nm. Cyclic voltammetry shows reversible Ru^+2/+3 oxidations at 1.68 V for the monometallic complex and Ru^+2/+3 oxidation couples at +1.94 and +1.70 V for the bimetallic complex.     

Aminocarboxylate complexes of vanadium(III): Electronic structure investigation by high-frequency and -field electron paramagnetic resonance spectroscopy

Aminocarboxylate complexes of vanadium(III) are of interest as models for biologically and medicinally relevant forms of this interesting and somewhat neglected ion. The V(III) ion is paramagnetic, but not readily suited to conventional EPR, due to its integer-spin ground state (S = 1) and associated large zero-field splitting (zfs). High-frequency and -field EPR (HFEPR), however, has the ability to study such systems effectively. Three complexes, all previously structurally characterized: Na[V(trdta)] · 3H₂O, Na[V(edta)(H₂O)] · 3H₂O, and [V(nta)(H₂O)₃] · 4H₂O (where trdta stands for trimethylenediamine-N,N,N′,N′-tetraacetate and nta stands for nitrilotriacetate) were studied by HFEPR. All the investigated complexes produced HFEPR responses both in the solid state, and in aqueous solution, but those of [V(nta)(H₂O)₃] · 4H₂O were poorly interpretable. Analysis of multi-frequency HFEPR spectra yielded a set of spin Hamiltonian parameters (including axial and rhombic zfs parameters: D and E, respectively) for these first two complexes as solids: Na[V(trdta)] · 3H₂O: D = 5.60 cm⁻¹, E = 0.85 cm⁻¹, g = 1.95; Na[V(edta)(H₂O)] · 3H₂O: D = 1.4 cm⁻¹, E = 0.14 cm⁻¹, g = 1.97. Spectra in frozen solution yielded similar parameters and showed multiple species in the case of the trdta complex, which are the consequence of the flexibility of this ligand. The EPR spectra obtained in frozen aqueous solution are the first, to our knowledge, of V(III) in solution in general and show the applicability of HFEPR to these systems. In combination with very insightful previous studies of the electronic absorption of these complexes which provided ligand-field parameters, it has been possible to describe the electronic structure of V(III) in [V(trdta)]⁻ and [V(edta)(H₂O)]⁻; the quality of data for [V(nta)(H₂O)₃] does not permit analysis. Qualitatively, six-coordinate V(III) complexes with O,N donor atoms show no electronic absorption band in the NIR region, and exhibit relatively large magnitude zfs (D ? 5 cm⁻¹), while analogous seven-coordinate complexes do have a NIR absorption band and show relatively small magnitude zfs (D < 2 cm⁻¹).     

Syntheses, structures and magnetic properties of two copper(II) tricyanomethanide complexes with 2,2′-bipyrimidine as bridging ligands

Two copper(II) tricyanomethanide (tcm) complexes with 2,2′-bipyrimidine (bpym) as co-ligands Cu₄(bpym)₅(tcm)₈ · 2H₂O (1) and [Cu₂(bpym)₂(tcm)₄ · H₂O]_n (2) have been synthesized, and structurally and magnetically characterized. Compound 1 displays a tetranuclear structure, in which each middle copper(II) atom is coordinated by two bridging bpym molecules and two terminal tcm ligands to form a tetragonal bipyramidal geometry, while each side copper(II) atom is surrounded by one bridging bpym, one terminal bpym, one terminal bonded tcm and one terminal weakly coordinated tcm ligands to give a square bipyramidal geometry. In 1 the four neighbouring copper(II) atoms are joined to each other by the bpym molecules, which leads to the formation of a tetranuclear structure. Compound 2 features an infinite chain structure, in which two slightly different chains exist. In each chain the copper(II) atom is bonded to two bridging bpym molecules and two terminal tcm ligands to form a tetragonal bipyramidal geometry, the adjacent copper(II) atoms are linked each other by the bpym ligands to define an infinite chain structure. In 2 the distances between two neighbouring copper(II) atoms in one chain are different. Moreover these distances in one chain are also different from those of the other chain. Magnetic susceptibility measurements for the two complexes in the temperature range 2-300 K reveal the occurrence of significant antiferromagnetic interactions for 1 (J₁ = −20.42 cm⁻¹, J₂ = −5.29 cm⁻¹ and g = 2.22) and 2 (T > 50 K, θ = −20.00 K, C = 0.86 cm³ mol⁻¹ K), respectively.     

Hybrid organic-inorganic assemblies built up from saturated heteropolyoxoanions and copper coordination polymers with mixed 4,4′-bipyridine and 2,2′-bipyridine ligands

Three new organic-inorganic hybrid compounds [Cu^I(2,2′-bipy)(4,4′-bipy)_0.5]₂[Cu^I(2,2′-bipy)(4,4′-Hbipy)][Cu^I(4,4′-bipy)]₂[P₂W₁₈O₆₂] · 3H₂O (1), [Cu^I(2,2′-bipy)(4,4′-bipy)_0.5]₂[Cu^I(4,4′-bipy)]₂[PW₁₂O₄₀] · 0.25H₂O (2), and[Cu^I(4,4′-bipy)]₃[PMo₁₂O₄₀] · en · 3H₂O (3) (2,2′- bipy = 2,2′-bipyridine, 4,4′-bipy = 4,4′-bipyridine), have been hydrothermally synthesized. Compound 1 represents the first 1D ladderlike structure formed by Dawson-type polyoxoanion [P₂W₁₈O₆₂]⁶⁻ and coordination polymer with mixed 4,4′-bipy and 2,2′-bipy ligands. The novel structure of 2 is composed of 1D hybrid zigzag chains linked by chains into a 3D framework. In compound 3, the [PMo₁₂O₄₀]³⁻ clusters are hung on chains to form a new 1D chain.     

Carboxy-derived (tpy)2Ru complexes as sub-units in supramolecular architectures: The solubilized ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy and its homoleptic Ru(II) complex

We herein describe the synthesis and characterization of a series of homoleptic, Ru(II) complexes bearing peripheral carboxylic acid functionality based upon the novel ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy (L₁), as well as 4′-(4-carboxyphenyl)tpy (L₂) and 4′-(carboxy)tpy (L₃) (where tpy = 2,2′: 6′,2″-terpyridine). Inspection of the metal-based oxidations (E_1/2 = 1.22-1.42 V) indicates an anodic shift (∼0.2 V) for (L₃)₂Ru²⁺ (3b) (E_1/2 = 1.40 V) relative to (L₂)₂Ru²⁺ (2b) (E_1/2 = 1.22 V). The metal-based oxidation (E_1/2 = 1.22 V) and ligand-based reductions (E_1/2 = −1.25 to −1.52 V) of (L₁)₂Ru²⁺ (1) are essentially invariant relative to those of the structural analogue 2b (PF₆)₂, which suggests no significant electronic effect caused by the tert-butyl groups. This is supported by invariance in the metal-to-ligand charge transfer bands in both the electronic absorption (494-489 nm) and emission spectra (654-652 nm). However, contrary to 2b, complex 1 is both very soluble and exhibits a highly porous solid-state structure with internal cavity dimensions of 15 Å × 14 Å due to the preclusion of inter-annular interactions by the bulky tert-butyl substituents.     

Synthesis, structure, sorption and magnetic properties of Ni(II) and Cu(II) complexes with thiosemicarbazone of 2-hydroxybenzaldehyde, bridged by 4,4′-bipyridine

(ML)₂(bipy) complexes (LH₂ = thiosemicarbazone of 2-hydroxybenzaldehyde, bipy = 4,4′-bipyridine, M = Ni(II), 1, or Cu(II), 2) were synthesized and characterized by X-ray crystallography. Compound 1 possessed porous structure due to peculiarities of crystal packing, whereas 2 formed infinite zig-zag chains with dense non-porous packing. It was shown that 1 absorbed 0.013 cm³/g of methanol vapor in two steps. Complex 1 was diamagnetic; for 2, the dependency of χ versus T could be interpreted by Bleaney-Bowers expression in 20-300 K temperature range (J = −6.8 cm⁻¹, g = 2.07).     

Syntheses and electrochemical properties of ruthenium(II) complexes with 4,4-bipyrimidine and 4,4-bipyrimidinium ligands

The syntheses and electrochemical properties of novel ruthenium(II) polypyridyl complexes with 4,4^′-bipyrimidine, [Ru(trpy)(bpm)Cl](X) ([1](X; X=PF₆⁻, BF₄⁻)) and with a quaternized 4,4^′-bipyrimidinium ligand, [Ru(trpy)(Me₂bpm)Cl](BF₄)₃ ([2](BF₄)₃) (trpy=2,2^′:6^′,2″-terpyridine, bpm=4,4^′-bipyrimidine, Me₂bpm=1,1^′-dimethyl-4,4^′-bipyrimidinium) are presented. The bpm complex [1]⁺ was prepared by the reaction of Ru(trpy)Cl₃ with 4,4^′-bipyrimidine in EtOH/H₂O. The structural characterization of [1]⁺ revealed, that the bpm ligand coordinated to the ruthenium atom with the bidentate fashion. Diquaternization of the non-coordinating nitrogen atoms on bpm of [1]⁺ by (CH₃)₃OBF₄ in CH₃CN gave [2](BF₄)₃. The electrochemical and spectroelectrochemical properties of the complexes are described.     

Meso-[{Ru(phen)2}2(μ-bpm)]: A high-affinity DNA bulge probe {bpm = 2,2′-bipyrimidine; phen = 1,10-phenanthroline}

The binding of the stereoisomers of [{Ru(Me₂bpy)₂}₂(μ-bpm)]⁴⁺, [{Ru(phen)₂}₂(μ-bpm)]⁴⁺ and [{Ru(Me₂phen)₂}₂(μ-bpm)]⁴⁺ (Me₂bpy = 4,4′-dimethyl-2,2′-bipyridine; bpm = 2,2′-bipyrimidine; phen = 1,10-phenanthroline; Me₂phen = 4,7-dimethyl-1,10-phenanthroline) to a tridecanucleotide d(CCGAGAATTCCGG)₂ which contains a single adenine bulge site, and four control dodecanucleotides, have been studied using a fluorescence intercalator displacement (FID) assay. The meso isomer of [{Ru(phen)₂}₂(μ-bpm)]⁴⁺ showed the strongest binding to the bulge-containing tridecanucleotide. In order to gain a greater understanding of the basis of the higher affinity exhibited by the meso isomer towards the bulge sequence, a ¹H NMR study of the binding of the two enantiomers (ΔΔ and ΛΛ) of rac-[{Ru(phen)₂}₂(μ-bpm)]⁴⁺, and the, meso (ΔΛ) diastereoisomer, to the tridecanucleotide d(CCGAGAATTCCGG)₂ was carried out. The NMR results suggest that the meso isomer binds selectively at the bulge site in the tridecanucleotide minor groove, but closer to the 3′-direction and with less structural perturbations of the groove than the ΔΔ and ΛΛ isomers. The results of this study confirm that dinuclear ruthenium complexes have excellent potential as DNA bulge probes, and meso-[{Ru(phen)₂}₂(μ-bpm)]⁴⁺ in particular has a high affinity (1 × 10⁶ M⁻¹) and selectivity for a single adenine bulge site.     

Diverse dimensionalities and structures in copper coordination polymers incorporating substituted aliphatic dicarboxylate ligands and 4,4′-bipyridine

Hydrothermal synthesis has afforded a series of divalent copper coordination polymers with substituted glutarate ligands and the rigid rod tether 4,4′-bipyridine (bpy): {[Cu(Hdmg)₂(bpy)]·H₂O}_n (1, dmg = 3,3-dimethylglutarate), {[Cu₂(dmg)(bpy)₂](ClO₄)]_n (2), [Cu₂(emg)₂(bpy)]_n (3, emg = 3-ethyl, 3-methylglutarate) and [Cu₂(cda)₂(bpy)]_n (4, cda = 1,1-cyclopentanediacetate). All materials were characterized by single-crystal X-ray diffraction. Compound 1 manifests μ₂-oxygen bridged [Cu₂(Hdmg)₄] “X”-patterns connected into a ribbon motif by bpy linkers. On the other hand, 2 possesses mixed-valence [Cu^ICu^IICu^IICu^I] tetrameric clusters bridged by dmg ligands and pillared into an 8-connected body-centered cubic (bcu) cationic lattice by bpy linkers. Compounds 3 and 4 are structurally very similar, displaying chain motifs with {Cu₂(CO₂)₄} paddlewheels connected by dicarboxylates, in turn conjoined into (4,4)-grid coordination polymer layers by bpy tethers. Variable temperature magnetic data indicate the presence of very strong antiferromagnetic coupling within the {Cu₂(CO₂)₄} paddlewheels in the latter two complexes, with g = 2.30(2) and J = −352(3) cm⁻¹ for 3 and g = 2.35(2) and J = −352(5) cm⁻¹ for 4. Significant structural contrasts are evident when compared to previously reported divalent copper/4,4′-bipyridine coordination polymers with unsubstituted or 2-methyl substituted glutarate ligands.     

Ruthenium polypyridyl complexes containing the bischelating ligand 2,2′-azobispyridine. Synthesis, characterization and crystal structures

Three ruthenium polypyridyl compounds of structural formula [Ru(apy)(tpy)Lⁿ⁻](ClO₄)_(2−n) (apy = 2,2′-azobispyridine; tpy = 2,2′:6′,2″-terpyridine; L = Cl, H₂O, CH₃CN) (1a-c) were synthesized and crystallized. These complexes were fully characterized by means of 1D and 2D ¹H NMR spectroscopy, as well as mass spectrometry and elemental analysis. Although in theory two isomers are possible, i.e. the one in which the central N atom in tpy is trans to the azo N in apy and the one in which the former is trans to the pyridine N in apy, in all cases only the latter was observed. The molecular structures of the compounds were elucidated by single-crystal X-ray diffraction.     

Probing inter-ligand excited state interaction in homo and heteroleptic ruthenium(II) polypyridyl complexes using selective deuteriation

The effect of deuteriation on the photophysical properties of two series of regioselectively deuteriated Ru(II) complexes ([Ru(bipy)_x(ph₂phen)_3−x]²⁺, where x = 0-3 and ph₂phen is 4,7-diphenyl-1,10-phenanthroline and [Ru(bipy)₂(dcbipy²⁻)], where H₂dcbipy is 4,4′-dicarboxy-2,2′-bipyridyl) is reported. Although overall, deuteriation results in an increase in emission lifetime for all complexes, the effect of substitution of hydrogen for deuterium shows strong regioselectivity both in terms of the ligand and the position on individual ligands that are exchanged.