Terpyridyl Units Research Articles

Hourglass-Shaped Nanocages with Concaved Structures Based on Selective Self-Complementary Coordination Ligands and Tunable Hierarchical Self-Assembly.

Three-dimensional (3D) structures constructed via coordination-driven self-assemblies have recently garnered increasing attention due to the challenges in structural design and potential applications. In particular, developing new strategy for the convenient and precise self-assemblies of 3D supramolecular structures is of utmost interest. Introducing the concept of self-coordination ligands, herein the design and synthesis of two meta-modified terpyridyl ligands with selective self-complementary coordination moiety are reported and their capability to assemble into two hourglass-shaped nanocages SA and SB is demonstrated. Within these 3D structures, the meta-modified terpyridyl unit preferably coordinates with itself to serve as concave part. By changing the arm length of the ligands, hexamer (SA) and tetramer (SB) are obtained respectively. In-depth studies on the assembly mechanism of SA and SB indicate that the dimers could be formed first via self-complementary coordination and play crucial roles in controlling the final structures. Moreover, both SA and SB can go through hierarchical self-assemblies in solution as well as on solid-liquid interface, which are characterized by transmission electron microscope (TEM) and scanning tunneling microscopy (STM). It is further demonstrated that various higher-order assembly structures can be achieved by tuning the environmental conditions.

A luminescent europium hairpin for DNA photosensing in the visible, based on trimetallic bis-intercalators

Luminescence monitoring of DNA intercalator complexes is important for assessing their localisation and targeting: We report herein a luminescent hetero-trimetallic complex with europium as a luminescent reporter and two attached platinum acetylide terpyridyl units as the DNA recognition units. The ligand, based on a bisamide derivative of diethylenetriaminepentaacetic acid functionalized with two ethynyl groups, provides a backbone to anchor two platinum terpyridyl units, Pt-tpy, leading to the hairpin-shaped heterometallic complex 1. We also prepared a related mono-nuclear platinum complex 2 to compare its intercalation properties with 1. Linear dichroism, UV–visible and melting experiments show the ability of both complexes to interact with calf thymus DNA, with linear dichroism confirming intercalation and demonstrating the expected greater DNA stiffening by the bis-intercalator 1. Importantly, the tri-metallic complex 1 shows a three-fold enhancement in europium luminescence upon addition of calf thymus DNA; other mono-intercalator lanthanide designs have commonly shown a decrease in emission on binding. The ability of the complex to monitor DNA interactions gives the potential use as a luminescence switch in sensing experiments and highlights the design of heterometallic bis-intercalator complexes as an effective approach for DNA-responsive sensitisation of a lanthanide luminescence signal.

Terpyridyl-based triphenylamine derivatives with aggregation-induced emission characteristics for selective detection of Zn2+, Cd2+ and CN− ions and application in cell imaging

Two terpyridyl triphenylamine derivative luminogens (DTPy-TPA and TPy-TPA) with aggregation-induced emission (AIE) characteristics were designed and synthesized. The number of terpyridyl units of these two compounds has a remarkable effect on the responses towards metal ions. DTPy-TPA with two terpyridyl groups on both sides displayed multi-response to Zn2+ and Cd2+ in THF solution along with distinct absorption and emission spectral changes, and obvious naked-eye color changes. However, TPy-TPA with one terpyridyl phenyl group didn't work. This should be resulted from the formation of supramolecular polymers or oligomers for DTPy-TPA to restrict the intramolecular motions, but dimers for TPy-TPA. Moreover, both of these two compounds in H2O/THF (9:1, v:v) solution could selectively and sensitively detect CN− with distinct fluorescence quenching, which was attributed to the nucleophilic addition of CN− to the α-position of the dicyanovinyl group and thus the free rotation of phenyl groups on TPA. The sensing mechanism of DTPy-TPA or TPy-TPA with CN− was confirmed by 1H NMR titration and Job's plot. Finally, based on their excellent photophysical properties, these two probes were successfully employed to detect CN− in living HEK293 cells using fluorescence bioimaging.

Reversible Self-Assembly of Water-Soluble Gold(I) Complexes.

The reaction of the gold polymers containing bipyridyl and terpyridyl units, [Au(C≡CC15H10N3)]n and [Au(C≡CC10H7N2)]n, with the water-soluble phosphines 1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane gives rise to the formation of four gold(I) alkynyl complexes that self-assemble in water (H2O) and dimethyl sulfoxide (DMSO), through different intermolecular interactions, with an impact on the observed luminescence displayed by the supramolecular assemblies. A detailed analysis carried out by NMR studies performed in different DMSO/deuterated H2O mixtures indicates the presence of two different assembly modes in the aggregates: (i) chain assemblies, which are based mainly on aurophilic interactions, and (ii) stacked assemblies, which are based on Au···π and π···π interactions. These different supramolecular environments can also be detected by their intrinsic optical properties (differences in absorption and emission spectra) and are predicted by the changes in the relative binding energy from density functional theory calculations carried out in DMSO and H2O. Small-angle X-ray scattering (SAXS) experiments performed in the same mixture of solvents are in agreement with the formation of aggregates in all cases. The aromatic units chosen, bipyridine and terpyridine, allow the use of external stimuli to reversibly change the aggregation state of the supramolecular assemblies. Interaction with the Zn2+ cation is observed to disassemble the aggregates, while encapsulating agents competing for Zn2+ complexation revert the process to the aggregation stage, as verified by SAXS and NMR. The adaptive nature of the supramolecular assemblies to the metal-ion content is accompanied by significant changes in the absorption and emission spectra, signaling the aggregation state and also the content on Zn2+.

Syntheses and Structural Characterizations of Mononuclear and Dinuclear Platinum(II) Terpyridyl Acetylide Complexes

Six mononuclear and dinuclear platinum(II) terpyridyl acetylide complexes were synthesized and structurally characterized by using single crystal X-ray diffraction. They are [(tpy)Pt−C≡C-SiMe3]PF6 (1, tpy=terpyridine), [(tpy)Pt−C≡CH]PF6 (2), [(tpy)Pt−C≡C–C10H7]PF6 (3, C10H7=1-naphthyl), [(tpy)Pt−C≡C–C14H9]PF6 (4, C14H9=9-anthryl), [(tpy)Pt−C≡C–C10H6-C≡C−Pt(tpy)](CuICl2I) (5, C10H6=1,8-naphthyl), and [(tpy)Pt−C≡C–C14H8-C≡C−Pt(tpy)](PF6)2 (6, C14H8=1,8-anthryl). As catalyzed by copper(I) iodide, reactions of Pt(II) terpyridyl complex [Pt(tpy)Cl]PF6 and corresponding alkynes gave mononuclear complexes 1 (with trimethylsilylacetylene), 3 (with 1-ethynylnaphthalene), 4 (with 9-ethynylanthracene), and gave dinuclear complexes 5 (with 1,8-diethynylnaphthalene) and 6 (with 1,8-diethynylanthracene), respectively. Complex 2, which contains the simplest −C≡CH acetylide ligand, was obtained by removing the trimethylsilyl group in complex 1 through deprotection with tetrabutylammonium fluoride. In all these complexes, the Pt(II) centers are coordinated by a tpy ligand through three N atoms and by an acetylide ligand through a C atom to give a distorted square-planar geometry. In mononuclear complexes 1–4, with Pt⋅⋅⋅Pt and π–π interactions, these square-planar Pt(II) terpyridyl molecules stack with a head-to-tail arrangement to give one-dimensional chains in the solid state. Structural analysis showed that the packing of these Pt(II) terpyridyl molecules in the solid state is largely controlled by the acetylide group through steric effects and π–π interactions. In dinuclear complexes 5–6, the two square-planar Pt(II) terpyridyl units in the same molecule have a face-to-face arrangement, although molecules of 5–6 also stack with a head-to-tail arrangement to give one-dimensional chains in the solid state. The rarely observed face-to-face arrangement of two square-planar Pt(II) terpyridyl units is realized by using pre-organized and rigid dinucleating ligands 1,8-diethynylnaphthalene and 1,8-diethynylanthracene.

Electrochemical and photovoltaic studies on water soluble triads: Metallosupramolecular self-assembly of ditopic bis(imidazole)perylene diimide with platinum(II)-, and palladium(II)-2,2′:6′,2″-terpyridyl complex ions

1,6,7,12-tetrakis-(4-methoxyphenoxy)perylene-3,4,9,10-tetracarboxylic dianhydride was functionalized to possess imidazole ligating sites at the imide positions, namely N,N′-bis(3-propylimidazole)-1,6,7,12-tetrakis-(4-methoxyphenoxy)perylene diimide (PDI-1). By using metal ion-ligand coordination approach, self-assembly of newly synthesized ditopic ligand (PDI-1) with 2,2′:6′,2″-terpyridyl-platinum(II) and/or -palladium(II) complex ions produced novel water soluble triads [(terpy)M(II)-(PDI-1)-M(II)(terpy)](NO3)4, M(II) = Pt(II) (PDI-2), and Pd(II) (PDI-3), respectively. The isolated triads were characterized by FT-IR, 1D-NMR (1H NMR and 13C DEPT NMR), 2D-NMR (1H-1H COSY, 1H-13C HSQC, 1H-13C HMBC), MALDI TOF mass and UV/Vis spectroscopy. Redox and electrochromic properties of the compounds have been identified by electrochemical, in situ spectroelectrochemical, and in situ electrocolorimetric measurements. The measurements showed that the novel chromophores display both a reduction and oxidation process, with considerably narrow electrochemical HOMO-LUMO band gaps in suitable solvents. The reduction of the novel compounds at modest potentials especially, makes these novel chromophores good electron acceptors. Net spectral changes between the blue, red or pink and green colours suggested that the novel compounds are suitable for application in electrochromic devices. Furthermore, the introduction of the square-planar Pt(II) and/or Pd(II)-terpyridyl units to the PDI core by coordination to the imidazole ends of the PDI moiety strongly influenced the performance of the photovoltaic devices.

4′-(3,4-Dimethoxyphenyl)-2,2′:6′,2′′-terpyridine

In the title compound, C23H19N3O2, the terpyridine unit has a dimethoxyphenyl substituent at the 4-position of the central pyridyl ring. The three pyridyl rings are in atransoidconformation with respect to the interannular C—C bonds. In addition, the pendant dimethoxyphenyl substituent is almost coplanar with the terpyridyl unit; the dihedral angle between the central pyridyl ring and the benzene ring is 7.14 (11)°, which is much smaller than that found in the structural isomer with a 2,5-dimethoxyphenyl substituent. The C—C and C—N bond lengths within the aromatic rings are normal. One of the terminal pyridyl rings is disordered over two sets of sites with an occupancy ratio of 0.744 (7):0.256 (7). The orientation of the two methoxy groups at the 3- and 4-positions is such that the methyl groups point away from each other in opposite directions. In the crystal structure, C–H...N hydrogen bonds form chains alongbwhile C—H...O contacts form inversion dimers, creating double chains. These combine with C—H...π contacts and π...π interactions, with a centroid-centroid distance of 3.858 (4) Å, to stack molecules along theb-axis direction.

Nanopatterning of Surfaces with Monometallic and Heterobimetallic 1D Coordination Polymers: A Molecular Tectonics Approach at the Solid/Liquid Interface.

The self-assembly of multiple molecular components into complex supramolecular architectures is ubiquitous in nature and constitutes one of the most powerful strategies to fabricate multifunctional nanomaterials making use of the bottom-up approach. When spatial confinement in two dimensions on a solid substrate is employed, this approach can be exploited to generate periodically ordered structures from suitably designed molecular tectons. In this study we demonstrate that physisorbed directional periodic arrays of monometallic or heterobimetallic coordination polymers can be generated on a highly oriented pyrolitic graphite surface by combinations of a suitably designed directional organic tecton or metallatecton based on a porphyrin or nickel(II) metalloporphyrin backbone bearing both a pyridyl unit and a terpyridyl unit acting as coordinating sites for CoCl2. The periodic architectures were visualized at the solid/liquid interface with a submolecular resolution by scanning tunneling microscopy and corroborated by combined density functional and time-dependent density functional theory calculations. The capacity to nanopattern the surface for the first time with two distinct metallic centers exhibiting different electronic and optical properties is a key step toward the bottom-up construction of robust multicomponent and, thus, multifunctional molecular nanostructures and nanodevices.

Self-assembled vesicles from amphiphilic platinum(II) terpyridyl complex in water

A new cationic amphiphile (1) functionalised with platinum(II) terpyridyl unit was designed and synthesised to realize self-assembly in water. Using UV–vis and emission spectroscopy, scanning electron microscopy, cryogenic transmission electron microscopy, dynamic light scattering and time-correlated single-photon counting technique, we have demonstrated that amphiphile 1 can self-assemble into stable vesicular aggregates upon direct dissolution in water, which is rarely observed in the literature.

Triphenylamine-based linear conjugated polyfluorenes with various pendant groups: Synthesis, characterization, and ion responsive properties

This study describes the synthesis of three triphenylamine-based linear conjugated polyfluorenes, differing in the proton (PFH), aldehyde (PFCHO), and 4′-(4-vinylphenyl)-2,2′:6′,2″-terpyridine (PFTPY) pendant groups that attach to the para position relative to 4,4′-dibromotriphenylamine monomer, by using Suzuki coupling polymerization. The structural effect on optical properties and the effect of the terpyridine unit on sensory characteristics of fluorescent chemosensors were investigated. The molecular structures, as well as the thermal, optical, and electrochemical properties of the polymers, were characterized by using 1H NMR, elemental analysis, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analyzer, absorption, photoluminescence spectroscopies, and cyclic voltammetry. These polymers were soluble in common organic solvents and exhibited favorable thermal stability with a thermal decomposition temperature above 393.3 °C. The ionization potentials of the polyfluorene derivatives (PFH, PFCHO and PFTPY) were decreased after introducing the triphenylamine segments, as confirmed by the highest occupied molecular orbital level (5.22–5.42 eV) below vacuum relative to PF without a triphenylamine segment (5.65 eV). PFTPY with a pendant terpyridyl unit showed higher sensitivities to Fe3+ and Ni2+, as compared with other metal ions. Adding a Zn2+ ion not only caused partial fluorescence quenching but also induced a broad emission peak in the range of 525–700 nm. PFTPY revealed higher fluorescence quantum yields (ΦPL = 0.44), suggesting that it is a promising material for PLED and chemosensor candidates.

Syntheses and structures of Mn(II), Co(II), and Zn(II) complexes of 1,3-diterpyridyl-substituted p-tert-butylcalix[4]arene

The calix[4]arene-based podand which incorporates two terpyridine functions in 1,3-alternate positions with flexible propylene spacers at lower rim has been prepared and subjected to complexation studies with some transition metal ions. Single-crystal structures of Mn(II), Co(II), and Zn(II) complexes were determined by X-ray diffraction. These metal complexes are formed with a 2 : 1 ratio of metal and ligand. Coordination of each metal is five-coordinate distorted trigonal-bipyramidal geometry by three nitrogen atoms from a terpyridyl unit and two chloride atoms.

1,4-Bis[(2,2':6',2''-terpyridin-4'-yl)-oxy]butane.

The title compound, C34H28N6O2, has an inversion centre located at the mid-point of the central C—C bond of the diether bridging unit. The central pyridine rings of the terpyridyl units and the diether chain are co-planar: the maximum deviation from the 18-atom mean plane defined by the bridging unit and the central pyridyl ring is for the pyridyl N atom which sits 0.055 (1) Å above the plane. The dihedral angles between the terminal pyridine rings with this plane are 10.3 (1) and 37.6 (1)°, repectively. In the crystal, weak C—H⋯N inter­actions link the mol­ecules into infinite chains parallel to the a axis.

(2,2′-Bipyridine-κ2N,N′)chlorido[4′-(2,5-dimethoxyphenyl)-2,2′:6′,2′′-terpyridine-κ3N,N′,N′′]ruthenium(II) hexafluoridophosphate acetonitrile monosolvate

In the title compound, [RuCl(C10H8N2)(C23H19N3O2)]PF6·CH3CN, the ligand environment about the RuII atom is distorted octa­hedral, with the substituted terpyridyl ligand coordinated in a meridional fashion, the bipyridyl ligand coordinated in a cis fashion and the Cl atom trans to one of the bipyridyl N atoms. The Ru—N distances are in the range 2.036 (2)–2.084 (2) Å with the exception of the central Ru—N bond from the terpyridyl ligand, which is shorter [1.9503 (19) Å], as expected. The pendant dimethoxy­phenyl substituent is not coplanar with the terpyridyl unit; the dihedral angle between the central pyridyl ring and the benzene ring is 46.72 (11)°. The anion is disordered equally over two positions around an F—P—F bond axis.

4′-[2-(Trifluoromethyl)phenyl]-2,2′:6′,2′′-terpyridine

The title compound, C22H14F3N3, is a versatile tridentate N-donor ligand consisting of a terpyridyl (terpy) molecule substituted in the 4′-position by a phenyl group, itself substituted in an ortho-position by a bulky trifluoro­methyl group. The phenyl ring is twisted as a result of steric inter­actions involving the bulky trifluoro­methyl substituent. This is reflected in the dihedral angle between the mean plane through the C atoms of the phenyl ring and the terpyridyl unit being 69.2 (1)°. The crystal structure contains no short van der Waals contacts. However, the terpy units stack in a head-to-tail orientation perpendicular to the c axis. The structure is is loosely stabilized by π–π inter­actions between the terminal pyridine rings of adjacent mol­ecules along the stack. The perpendicular distance between the mean planes through the terpy moieties of adjacent mol­ecules is 3.4 (1) Å.

Post-coordination functionalisation of pyrazolyl-based ligands as a route to polynuclear complexes based on an inert RuIIN6core

The simple mononuclear complex [Ru(H2bpp)2][PF6]2 [H2bpp = 2,6-bis(pyrazol-3-yl)pyridine] contains four coordinated pyrazolyl ligands which each have a reactive NH site at the position adjacent to the coordinated N atom. Alkylation of these with either 2-[1-{4-(bromomethyl)benzyl}-1H-pyrazol-3-yl]pyridine or 4′-[(4-bromomethyl)phenyl]terpyridine allows attachment of four additional chelating groups, either bidentate pyrazolyl–pyridine and terdentate terpyridyl units, respectively, which are pendant from the central kinetically inert RuIIN6 complex core. These functionalised mononuclear complexes [Ru(L1)2][PF6]2 (with four pendant pyrazolyl–pyridine bidentate sites) and [Ru(L2)2][PF6]2 (with four pendant terpyridyl sites) can be used as the starting point for polynuclear assemblies by attachment of additional labile metal ions as the secondary sites. As examples of this we prepared and structurally characterised the trinuclear complex [RuAg2(L1)2][ClO4]4, an unusual example of a polynuclear helicate containing a kinetically inert metal centre, and the pentanuclear complex [RuCu4(MeCN)5(H2O)1.5(L2)2](SbF6)6(BF4)4 in which each of the pendant terpyridyl sites of the [Ru(L2)2]2+ core is coordinated to a Cu(II) ion.

Synthesis and characterization of light‐emitting main‐chain metallo‐polymers containing bis‐terpyridyl ligands with various lateral substituents

AbstractA series of conjugated monomers (5a‐5d) with various lateral substituents were symmetrically synthesized by the Sonogashira coupling reaction, in which central aromatic units (i.e. 9,9‐dipropylfluorenes) were linked to 2,2′:6′,2′‐terpyridyl (tpy) units via phenylene/ethynylene fragments. These light‐emitting monomers were further reacted with zinc(II) ions and subsequently anion exchanged to produce supramolecular main‐chain metallo‐polymers (6a‐6d). The formation of polymers 6a‐6d was confirmed by the increased viscosities (up to 1.5–1.83 times) relative to those of their analogous monomers. The results of 1H NMR titration and UV‐Vis spectral titration revealed a detailed complexation process of metallo‐polymers by varying the molar ratios of zinc(II) ions to monomers. After coordination with zinc(II) ions, the luminescent and thermal properties of the polymers were enhanced by the formation of metallo‐supramolecular structures in contrast to their monomer counterparts. PLED devices employing these metallo‐polymers as emitters gave yellow to orange electroluminescence (EL) emissions with turn‐on voltages around 6 V. The maximum power efficiency, external quantum yield, and brightness of the PLED device containing polymer 6c were 0.33 cd A−1 (at 14 V), 1.02%, and 931 cd m−2 (at 14 V), respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3243–3255, 2007

Luminescent 1D chain of platinum(ii) terpyridyl units with p-dithiobenzoquinone organometallic linker: self-aggregation imparted from Pt⋯Pt/π–π interactions

Unlike p-dithiobenzoquinone (), which is extremely reactive and has never been isolated, the metal-stabilised p-dithiobenzoquinone [Cp*Ir(eta4-C6H4S2)] () was prepared and used as an efficient organometallic linker to construct novel supramolecular assemblies. Treatment of with the electrophilic Pt(II)(terpy) building blocks produced the supramolecular assembly {[Pt(terpy){Cp*Ir-p-(eta4-C6H4S2)}Pt(terpy)][OTf]4}n (), which was fully characterised and its molecular structure was determined by X-ray crystallography. The structure of revealed the presence of pi-pi and Pt[dot dot dot]Pt interactions among individual molecules describing a 1D chain. Complex showed unusual UV/Vis absorption and luminescence behaviour at low temperature, imparted from self-aggregation mediated by pi-pi and Pt...Pt interactions.

Conjugated Metallopolymers for Fluorescent Turn-On Detection of Nitric Oxide

A series of eight pi-conjugated polymers (CPs) composed of phenylenevinylene, phenyleneethynylene, fluorene, and thiophene derivatives have been prepared with bipyridyl or terpyridyl substituents within the pi-conjugated backbone or at side-chain positions. These ligand-modified CPs serve as macromolecular scaffolds for conducting metallopolymers. The optical and photoluminescent properties of the polymers and corresponding copper(II) metallopolymers were investigated. Copper(II) is a highly efficient quencher of CP emission (75-100% quenching). CPs featuring bipyridyl units within the CP backbone are quenched more efficiently than those with terpyridyl units. The copper(II) metallopolymer undergoes reduction to the corresponding copper(I) species upon reaction with nitric oxide, with concomitant changes in integrated emission ranging from a 50% decrease to a 320% increase. The positive emission response is largest when Cu(II) was bound to the CP through bipyridyl units within the backbone, making these materials the best candidates for NO sensing by a turn-on emission mechanism.

Near infra-red luminescence from bis-terpyridyl iridium(III) complexes incorporating electron-rich pendants

Iridium(III) bis-terpyridine complexes have been prepared which incorporate aminobenzene or pyrene substituents at the 4′-position of the terpyridine. The homoleptic complexes, [Ir(L 1) 2] 3+ and [Ir(L 2) 2] 3+ {L 1 = 4′-( p-Me 2N-C 6H 4)-2,2′:6′,2″-terpyridine; L 2 = 4′-( p-Ph 2N-C 6H 4)-2,2′:6′,2″-terpyridine} display an intense absorption band in the visible region, which exhibits slight positive solvatochromism, due to an excited state of intra-ligand charge transfer (ILCT) character, in which the aminobenzene unit acts as the electron donor and the metal-bound terpyridyl unit as the acceptor. The complexes are weakly luminescent in the near infra-red ( λ max 750–800 nm); this short-lived, low-energy emission, whose likely origin is an excited state of primarily ILCT character, is in contrast to the long-lived 3π–π* luminescence of previously studied bis-terpyridyl iridium complexes. The corresponding ILCT absorption band in the heteroleptic, pyrene-substituted complex, [Ir(tpy)L 3] 3+ {L 3 = 4′-(1-pyrenyl)-2,2′:6′,2″-terpyridine}, displays negative solvatochromism, owing to the excited state having lower polarity than the ground state. This complex emits weakly at slightly higher energy (710 nm). The switch to ILCT character upon appending the [Ir(tpy) 2] 3+ core with a pyrene substituent may be compared to the influence of the pyrene unit in [PtL 3Cl] +, but contrasts with the triplet–triplet equilibrium that is established in structurally related ruthenium complexes incorporating pyrene pendants. The electrochemical properties of the pyrene-substituted ligand and complex in solution are also described.

Long-Range Electronic Coupling in Bis(cyclometalated) Ruthenium Complexes

Symmetrical and unsymmetrical ligands containing terpyridyl coordinating units (N, N, N) or a cyclometalating equivalent (N, C, N), connected back-to-back either directly or via a p-terphenylene or 1,3-phenylene spacer, have been used to construct new diruthenium complexes. These compounds incorporate various terdentate chelates as capping ligands, to allow a double control of the electronic properties of each subcomplex and of the ensemble: via the terminal ligand or through the bridging fragment. Electronic coupling was studied from the intervalence transitions observed in several bimetallic ruthenium complexes of the bis(cyclometalated) type differing by the substitution of a nitrogen atom by carbon in the terminal terpyridyl unit. The largest metal−metal interaction was found in complexes for which the terminal complexing unit is of the 1,3-di-2-pyridylbenzene type, i.e., with the carbon atom located on the metal−metal C2 axis of the molecule. Investigations of the mechanism of interaction by extende...