Photochemical Molecular Devices Research Articles

A Direct Z‐Scheme Quasi‐2D/2D Heterojunction Constructed by Loading Photosensitive Metal–Organic Nanorings with Pd Single Atoms on Graphitic–C3N4for Superior Visible Light‐Driven H2Production

Rational design of Z‐scheme composite photocatalysts with 2D/2D heterojunction is a promising method to convert solar energy into chemical fuels. Herein, a Pd2L2‐type metal–organic nanoring (MAC‐1), which can serve as a photochemical molecular device (PMD), is assembled by catalytic Pd2+centers and photosensitive ligands (M‐7). Then MAC‐1 is combined with graphite‐phase carbon nitride (g‐C3N4) to construct a direct Z‐scheme quasi‐2D/2D composite material MAC‐1/g‐C3N4with Pd single atoms. The optimized 3.5% MAC‐1/g‐C3N4single‐atom catalyst (SAC) shows better photocatalytic performance than g‐C3N4, MAC‐1, Pd/g‐C3N4, M‐7/Pd/g‐C3N4, and 3.5% MAC‐1/g‐C3N4‐mixed and also displays good durability for H2production. The H2yield rate of 22.3 mmol g−1 h−1and the corresponding turnover number based on Pd or MAC‐1 amount (TONPd/TONMAC‐1) of 119 172/238 344 within 50 h are achieved for 3.5% MAC‐1/g‐C3N4, which is one of the highest records of all visible light‐driven g‐C3N4‐based photocatalysts reported. Such remarkably enhanced activity can result from the enhanced charge carrier mobility, improved light absorption ability, enlarged heterojunction contact interface, and highly monodispersed Pd active sites. The Z‐scheme SAC composed of metal–organic nanorings and g‐C3N4nanosheets therefore has great potential as an efficient and sustainable photocatalyst for solar‐driven H2production.

Direct Z-scheme photochemical hybrid systems: Loading porphyrin-based metal-organic cages on graphitic-C3N4 to dramatically enhance photocatalytic hydrogen evolution

The rational design of photochemical molecular device (PMD) and its hybrid system has great potential in improving the activity of photocatalytic hydrogen production. A series of Pd6L3 type metal-organic cages, denoted as MOC-Py-M (M = H, Cu, and Zn), are designed for PMDs by combining metalloporphyrin-based ligands with catalytically active Pd2+ centers. These metal-organic cages (MOCs) are first successfully hybridized with graphitic carbon nitride (g-C3N4) to form direct Z-scheme heterogeneous MOC-Py-M/g-C3N4 (M = H, Cu, and Zn) photocatalysts via π–π interactions. Benefiting from its better light absorption ability, the MOC-Py-Zn/g-C3N4 catalyst exhibits high H2 production activity under visible light (10348 μmol g−1 h−1), far superior to MOC-Py-H/g-C3N4 and MOC-Py-Cu/g-C3N4. Moreover, the MOC-Py-Zn/g-C3N4 system obtains an enhanced turn over number (TON) value of 32616 within 100 h, outperforming the homogenous MOC-Py-Zn (TON of 507 within 100 h), which is one of the highest photochemical hybrid systems based on MOC for visible-light-driven hydrogen generation. This confirms the direct Z-scheme heterostructure can promote effective charge transfer, expand the visible light absorption region, and protect the cages from decomposition in MOC-Py-Zn/g-C3N4. This work presents a creative example that direct Z-scheme PMD-based systems for effective and persistent hydrogen generation from water under visible light are obtained by heterogenization approach using homogeneous porphyrin-based MOCs and g-C3N4 semiconductors.

Robust Heterogeneous Photocatalyst for Visible-Light-Driven Hydrogen Evolution Promotion: Immobilization of a Fluorescein Dye-Encapsulated Metal-Organic Cage on TiO2.

The design of artificial photocatalytic devices that simulates the ingenious and efficient photosynthetic systems in nature is promising. Herein, a metal-organic cage [Pd6(NPyCzPF)12]12+ (MOC-PC6) integrating 12 organic ligands NPyCzBP and 6 Pd2+ catalytic centers is designed, which is well defined to include organic dye fluorescein (FL) for constructing a supramolecular photochemical molecular device (SPMD) FL@MOC-PC6. Photoinduced electron transfer (PET) between MOC-PC6 and the encapsulated FL has been observed by steady-state and time-resolved emission spectroscopy. FL@MOC-PC6 is successfully heterogenized with TiO2 by a facile sol-gel method to achieve a robust heterogeneous FL@MOC-PC6-TiO2. The close proximity between the Pd2+ catalytic site and FL included in the cage enables PET from the photoexcited FL to Pd2+ sites through a powerful intramolecular pathway. The photocatalytic hydrogen production assessments of the optimized 4 wt % FL@MOC-PC6-TiO2 demonstrate an initial H2 production rate of 2402 μmol g-1 h-1 and a turnover number of 4356 within 40 h, enhanced by 15-fold over that of a homogeneous FL@MOC-PC6. The effect of the MOC content on photocatalytic H2 evolution (PHE) is investigated and the inefficient comparison systems, such as MOC-PC6, MOC-PC6-TiO2, FL-sensitized MOC-PC6/FL-TiO2, and analogue FL/MOC-PC6-TiO2 with free FL, are evaluated. This study provides a creative and distinctive approach for the design and preparation of novel heterogeneous SPMD catalysts based on MOCs.

A Robust Photocatalytic Hybrid Material Composed of Metal-Organic Cages and TiO2 for Efficient Visible-Light-Driven Hydrogen Evolution.

The design of photochemical molecular devices (PMDs) for photocatalytic H2 production from water is a meaningful but challenging subject currently. Herein, a Pd2 L4 type metal-organic cage (denoted as MOC-Q2) is designed as a PMD, which consists of two catalytic centers (Pd2+ ) and four photosensitive ligands (L-2) with four pyridine anchoring groups. Subsequently, the MOC-Q2 is combined with TiO2 to form TiO2 -MOC-Q2 hybrid materials with different MOC-Q2 contents by a facile sol-gel method, which have micro/mesoporous structures and large surface areas. The optimized TiO2 -MOC-Q2 (6.5 wt%) exhibits high H2 production activity (7.9 mmol g-1 h-1 within 5 h) and excellent durability, giving a TON value of 23477 or 11739 (based on MOC-Q2 or Pd moles) after recycling for 7 rounds. By contrast, the pure MOC-Q2 only shows an ordinary photocatalytic H2 production rate (0.84 mmol g-1 h-1 within 5 h) in the homogeneous system. It can be deduced that TiO2 drives the photocatalysis and simultaneously acts as the structure promoter. This study presents a meaningful and distinctive attempt of a new approach for the design and development of MOC-based heterogeneous photocatalysts.

Constructing Heterogeneous Direct Z-Scheme Photocatalysts Based on Metal-Organic Cages and Graphitic-C3N4 for High-Efficiency Photocatalytic Water Splitting.

The development of artificial devices that mimic the highly efficient and ingenious photosystems in nature is worthy of in-depth study. A metal-organic cage (MOC) Pd2(M-4)4(BF4)4, denoted as MOC-Q1, integrating four organic photosensitized ligands M-4 and two Pd2+ catalytic centers is designed for a photochemical molecular device (PMD). MOC-Q1 is successfully immobilized on graphitic carbon nitride (g-C3N4) by hydrogen bonds to obtain a robust heterogeneous direct Z-scheme g-C3N4/MOC-Q1 photocatalyst for H2 generation under visible light. The optimized g-C3N4/MOC-Q1 (2 wt %) system shows high hydrogen evolution activity (4495 μmol g-1 h-1 based on the catalyst mass) and exhibits stable performances for 25 h (a turnover number of 19,268 based on MOC-Q1), significantly outperforming pure MOC-Q1, g-C3N4, and comparsion materials Pd/g-C3N4/M-4, which is the highest one of all reported heterogeneous MOC-based photocatalysts under visible irradiation. This enhancement can be ascribed to the synergistic effects of high-efficient electron transfer, extended visible-light response region, and good protective environment for MOC-Q1 arising from an efficient direct Z-scheme heterostructure of g-C3N4/MOC-Q1. This rationally designed and synthesized MOC/g-C3N4-based heterogeneous PMD is expected to have great potential in photocatalytic water splitting.

Molecular Scylla and Charybdis: Maneuvering between pH Sensitivity and Excited-State Localization in Ruthenium Bi(benz)imidazole Complexes.

Bi(benz)imidazoles (b(b)im) acting as N,N-chelates in ruthenium complexes represent a unique class of ligands. They do not harbor metal-to-ligand charge-transfer (MLCT) excited states in ruthenium polypyridyl complexes upon visible-light excitation provided that no substitution is introduced at the N atoms. Hence, they can be used to steer light-driven electron-transfer pathways in a desired direction. Nonetheless, the free N atoms are susceptible to protonation and, hence, introduce highly pH-dependent properties into the complexes. Previous results for ruthenium complexes containing R2bbim ligands with alkylic or arylic N,N'-substitution indicated that, although pH insensitivity was accomplished, unexpected losses of spectator ligand features incurred simultaneously. Here, we report the synthesis and photophysical characterization of a series of differently N,N'-alkylated b(b)im ligands along with their corresponding [(tbbpy)2Ru(R2b(b)im)](PF6)2 complexes (tbbpy = 4,4'-tert-butyl-2,2'-bipyridine). The data reveal that elongation of a rigid ethylene bridge by just one methylene group drastically increases the emission quantum yield, emission lifetime, and photostability of the resultant complexes. Quantum-chemical calculations support these findings and allow us to rationalize the observed effects based on the energetic positions of the respective excited states. We suggest that N,N'-propylene-protected 1H,1'H-2,2'-biimidazole (prbim) is a suitable spectator ligand because it stabilizes sufficiently long-lived MLCT excited states exclusively localized at auxiliary bipyridine ligands. This ligand represents, therefore, a vital building block for next-generation photochemical molecular devices in artificial photosynthesis.

Synthesis and fluorescence properties of dansyl labeled triazine dendrons

A series of fluorescent dendrons with dansulfonyl group as a fluorophore attached at the focal point were synthesized by a convergent method. There was no need for tedious and lengthy protection/deprotection or chromatographic separation. The method provided simple operation and high yield. Their fluorescence characteristic in dichloromethane was investigated. The results indicated that the dendritic modification had positive effect on the emission of fluorescence, and the emission maximum of dansylated dendrons was enhanced up to 20-fold. Meanwhile, the fluorescent intensity of dansylated dendrons could be remarkably improved with the increase of dendron generation. These findings can contribute significantly to the general understanding of the dendron systems and also for potential applications in photochemical molecular devices and organic electroluminescent devices.

Synthesis and hydrogen evolving catalysis of a panchromatic photochemical molecular device

The photocatalytic activity of a new broad absorbing osmium–platinum photocatalyst is determined by the choice of excitation wavelength.

Heterogenization of Photochemical Molecular Devices: Embedding a Metal-Organic Cage into a ZIF-8-Derived Matrix To Promote Proton and Electron Transfer.

Application of a molecular catalyst in artificial photosynthesis is confronted with challenges such as rapid deactivation due to photodegradation or detrimental aggregation in harsh conditions. In this work, a metal-organic cage [Pd6(RuL3)8]28+ (MOC-16), characteristic of a photochemical molecular device (PMD) concurrently integrating eight Ru2+ light-harvesting centers and six Pd2+ catalytic centers for efficient homogeneous H2 production, is successfully heterogenized through incorporation into a metal-organic framework (MOF) of ZIF-8 and then transformed into a carbonate matrix of Znx(MeIm)x(CO3)x (CZIF), leading to hybridized MOC-16@CZIF. This MOC@MOF integrated photocatalyst inherits a highly efficient and directional electron transfer in the picosecond domain of MOC-16 and possesses one order increased microsecond magnitude of the triplet excited-state electron in comparison to that of the primitive MOC-16. The carbonate CZIF matrix endows MOC-16@CZIF with water wettability, serving as a proton relay to facilitate proton delivery by virtue of H2O as proton carriers. Electron transfer during the photocatalytic process is also enhanced by infiltration of a sacrificial agent of BIH into the CZIF matrix to promote conductivity, owing to its strong reducing ability to induce free charge carriers. These synergistic effects contribute to the extra high activity for H2 generation, making the turnover frequency of this heterogeneous MOC-16@CZIF photocatalyst maintain a level of ∼0.4 H2·s-1, increased by 50-fold over that of a homogeneous PMD. Meanwhile, it is robust enough to tolerate harsh reaction conditions, presenting an unprecedented heterogenization example of homogeneous PMD with a MOF-derived matrix to mimic catalytic features of a natural photosystem, which may shed light on the design of multifunctional PMD@MOF materials to expand the number of molecular catalysts for practical application in artificial photosynthesis.

A metal-organic cage incorporating multiple light harvesting and catalytic centres for photochemical hydrogen production.

Photocatalytic water splitting is a natural but challenging chemical way of harnessing renewable solar power to generate clean hydrogen energy. Here we report a potential hydrogen-evolving photochemical molecular device based on a self-assembled ruthenium–palladium heterometallic coordination cage, incorporating multiple photo- and catalytic metal centres. The photophysical properties are investigated by absorption/emission spectroscopy, electrochemical measurements and preliminary DFT calculations and the stepwise electron transfer processes from ruthenium-photocentres to catalytic palladium-centres is probed by ultrafast transient absorption spectroscopy. The photocatalytic hydrogen production assessments reveal an initial reaction rate of 380 μmol h−1 and a turnover number of 635 after 48 h. The efficient hydrogen production may derive from the directional electron transfers through multiple channels owing to proper organization of the photo- and catalytic multi-units within the octahedral cage, which may open a new door to design photochemical molecular devices with well-organized metallosupramolecules for homogenous photocatalytic applications.

Making Use of Obstacles: Alternative Synthetic Approaches towards Osmium(II)‐Based Photochemical Molecular Devices

Two synthetic approaches towards the mononuclear complex [(tbbpy)2OsII(tpphz)]2+ (tbbpy = 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine; tpphz = tetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐h:2′′′,3′′′‐j]phenazine) based on the precursor [(tbbpy)2OsIICl2] and its oxidized side product [(tbbpy)2OsIIICl2]+ are presented. The first route is analogous to that for the isostructural ruthenium complex, whereas the second strategy efficiently uses the oxidized OsIII complex under reducing conditions to obtain so‐called virtual dilution, which avoids the formation of the dinuclear complex [(tbbpy)2OsII(tpphz)OsII(tbbpy)2]. Concentration‐dependent NMR investigations were performed, and a dimerization constant (KD = 400) could be calculated due to π–π interactions of the tpphz moiety. Solid‐state structures of all synthesized complexes show comparable bond lengths and angles with respect to each other and their ruthenium analogues. Photophysical investigations show the expected absorption in the UV/Vis region and a single emission at 758 nm for [(tbbpy)2OsII(tpphz)]2+. Electrochemical measurements show comparable behavior to the structurally similar complexes [(bpy)2M(tpphz)]2+ (M = Os, Ru).

ChemInform Abstract: Synthesis and Photophysical Application of Functionalized 2,2′:6′,2“‐Terpyridine Metal Complexes

AbstractReview: 37 refs.

Optimization of hydrogen-evolving photochemical molecular devices.

A molecular photocatalyst consisting of a Ru(II) photocenter, a tetrapyridophenazine bridging ligand, and a PtX2 (X=Cl or I) moiety as the catalytic center functions as a stable system for light-driven hydrogen production. The catalytic activity of this photochemical molecular device (PMD) is significantly enhanced by exchanging the terminal chlorides at the Pt center for iodide ligands. Ultrafast transient absorption spectroscopy shows that the intramolecular photophysics are not affected by this change. Additionally, the general catalytic behavior, that is, instant hydrogen formation, a constant turnover frequency, and stability are maintained. Unlike as observed for the Pd analogue, the presence of excess halide does not affect the hydrogen generation capacity of the PMD. The highly improved catalytic efficiency is explained by an increased electron density at the Pt catalytic center, this is confirmed by DFT studies.

Synthesis and characterization of an immobilizable photochemical molecular device for H2-generation.

With [Ru(II)(bpyMeP)2tpphzPtCl2](2+) (4) a molecular photocatalyst has been synthesized for visible-light-driven H2-evolution. It contains the ligand bpyMeP (4,4'-bis(diethyl-(methylene)-phosphonate)-2,2'-bipyridine) with phosphate ester groups as precursors for the highly potent phosphonate anchoring groups, which can be utilized for immobilization of the catalyst on metal-oxide semiconductor surfaces. The synthesis was optimized with regard to high yields, bpyMeP was fully characterized and a solid-state structure could be obtained. Photophysical studies showed that the photophysical properties and the localization of the excited states are not altered compared to similar Ru-complexes without anchoring group precursors. (4) was even more active in homogenous catalysis experiments than [Ru(II)(tbbpy)2tpphzPtCl2](2+) (6) with tbbpy (4,4'-bis(tbutyl)-2,2'-bipyridine) as peripheral ligands. After hydrolysis (4) was successfully immobilized on NiO, suggesting that an application in photoelectrosynthesis cells is feasible.

Mechanistic Insight into the Electronic Influences Imposed by Substituent Variation in Polyazine‐Bridged Ruthenium(II)/Rhodium(III) Supramolecules

AbstractInvited for the cover of this issue are researchers from the Department of Chemistry at Virginia Tech featuring work on electrochemical properties of photochemical molecular devices for solar hydrogen production. The image highlights the complexity of the redox chemistry of the studied supramolecules, detailing speciation following reduction. Mr. Skye King assisted in the development of the molecular models for the cover. Read the full text of the article at 10.1002/chem.201402564.

Light-powered molecular devices and machines

One century ago Giacomo Ciamician predicted that photochemistry would have had a wealth of useful applications, starting from the conversion of solar energy into fuels. Most of Ciamician's predictions have not yet been achieved, but in the last decade outstanding progress concerning the interaction between light and molecules has led to the creation of artificial photochemical molecular devices and machines capable of using light as an energy supply (to sustain energy-expensive functions) or as an input signal (to be processed and/or stored). This paper illustrates (i) the principles of photochemical molecular devices for information processing, with a few examples of memories, logic functions, and encoding/decoding systems; (ii) the operational mechanisms of light-powered molecular machines, with some examples of rotary motors, shuttles, valves, and switchable boxes; and (iii) the recent progress made in the design and construction of the components of artificial photosynthetic systems. The use of photons to convert abundant low energy molecules into high energy valuable compounds, and to read, write, and erase smart molecular and supramolecular systems for information processing is likely to play a fundamental role for the progress of mankind.

From the periodic table to photochemical molecular devices and machines

It is well known that the position of an element in the periodic table is related to its electronic structure and that elements belonging to the same column exhibit similar properties because they have the same outer-shell electronic configurations. The similarity between two elements, as predicted by the periodic table, extends to the chemical properties of their metal complexes, but fades and may also completely vanish in going from chemistry to photochemistry, a new dimension of chemistry that follows its own rules. For example, [Ru(bpy)3]2+ and [Fe(bpy)3]2+ (bpy = 2,2′-bipyridine) exhibit completely different photochemical behavior, with the first, but not the second one, being a fundamental component of several molecular devices and machines. After a brief recall of the important ideas advanced one century ago by Giacomo Ciamician, the father of photochemistry and the prophet of solar energy utilization, this paper illustrates examples of light-powered molecular devices and machines: wires, switches, extension cables, antennas, and nanomotors.

Design Considerations for a System for Photocatalytic Hydrogen Production from Water Employing Mixed-Metal Photochemical Molecular Devices for Photoinitiated Electron Collection

Supramolecular complexes coupling Ru(II) or Os(II) polyazine light absorbers through bridging ligands to Rh(III) or Ir(III) allow the study of factors impacting photoinitiated electron collection and multielectron water reduction to produce hydrogen. The [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5) system represents the first photoinitiated electron collector in a molecular system (bpy = 2,2'-bipyridine, dpb = 2,3-bis(2-pyridyl)benzoquinoxaline). The [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) system represents the first photoinitiated electron collector that affords photochemical hydrogen production from water in the presence of an electron donor, N,N-dimethylaniline (dpp = 2,3-bis(2-pyridyl)pyrazine). The complexes [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5), [{(bpy)(2)Ru(dpp)}(2)RhBr(2)](PF(6))(5), [{(phen)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5), [{(bpy)(2)Os(dpp)}(2)RhCl(2)](PF(6))(5), [{(tpy)RuCl(dpp)}(2)RhCl(2)](PF(6))(3), [{(tpy)OsCl(dpp)}(2)RhCl(2)](PF(6))(3), and [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5) are herein evaluated with respect to their functioning as hydrogen photocatalysts (tpy = 2,2':6',2''-terpyridine, phen = 1,10-phenanthroline). With the exceptions of [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5) and [{(tpy)OsCl(dpp)}(2)RhCl(2)](PF(6))(3), all other complexes demonstrate photocatalytic activity. The functioning systems possess a rhodium localized lowest unoccupied molecular orbital that serves as the site of electron collection and a metal-to-ligand charge-transfer ((3)MLCT) and/or metal-to-metal charge-transfer ((3)MMCT) excited-state with sufficient driving force for excited-state reduction by the electron donor. The lack of photocatalytic activity by [{(bpy)(2)Ru(dpb)}(2)IrCl(2)](PF(6))(5), although photoinitiated electron collection occurs, establishes the significance of the rhodium center in the photocatalytic system. The lack of photocatalytic activity of [{(tpy)OsCl(dpp)}(2)RhCl(2)](PF(6))(3) is attributed to the lower-energy (3)MLCT state that does not possess sufficient driving force for excited-state reduction by the electron donor. The variation of electron donor showed the photocatalysis efficiency to decrease in the order N,N-dimethylaniline > triethylamine > triethanolamine. The general design considerations for development of supramolecular assemblies that function as water reduction photocatalysts are discussed.

Solar energy conversion using photochemical molecular devices: photocatalytic hydrogen production from water using mixed-metal supramolecular complexes

Photocatalytic generation of hydrogen from water is an integral part of the next generation clean fuel technologies. The conversion of solar energy into useful chemical energy is of great interest in contemporary investigations. The splitting of water is a multi-electron process involving the breaking and making of chemical bonds which requires multi-component photocatalytic systems. Supramolecular complexes [{(TL)2Ru(BL)}2RhX2](Y)5 (where TL = terminal ligand, BL = bridging ligand, X = Cl− or Br−, and Y = PF6− or Br−) have been synthesized and studied for their light absorbing, electrochemical and photocatalytic properties. The supramolecular complexes in this investigation are multi-component systems comprised of two ruthenium based light absorbers connected through bridging ligands to a central rhodium, which acts as an electron collecting center upon excitation. These complexes absorb light throughout the ultraviolet and visible regions of the solar spectrum. The supramolecular complexes possess ruthenium based highest occupied molecular orbitals (HOMO) and a rhodium based lowest unoccupied molecular orbital (LUMO). These molecular devices have been investigated and shown to function as photoinitiated electron collectors at the reactive rhodium metal center, and explored as photocatalysts to generate hydrogen from water in an aqueous solution in the presence of an electron donor.

Ruthenium polypyridine complexes of tris-(2-pyridyl)-1,3,5-triazine—unusual building blocks for the synthesis of photochemical molecular devices

The mononuclear compounds bis-(2,2'-bipyridine)ruthenium(ii)-(tris(2-pyridyl)triazine) [(bpy)(2)Ru(tpt)](PF(6))(2) and bis-(4,4'-di-tert-butyl-2,2'-bipyridine)ruthenium(ii)-(tris(2-pyridyl)triazine) [(tbbpy)(2)Ru(tpt)](PF(6))(2) have been synthesised and fully characterised. The attempted syntheses of heterodinuclear complexes with the tris(2-pyridyl)triazine (tpt) ligand as bridging ligand and various palladium(ii)- and platinum(ii)-dichloro complexes using the ruthenium complexes as starting materials resulted in a partial hydrolysis of the triazine based bridging ligand in case of and an unselective decomposition in case of . Compound reacts with Pd(DMSO)(2)Cl(2) and Pt(DMSO)(2)Cl(2) substituting three ligands from the metal centres of these precursors with partial hydrolysis of the triazine moiety of the bridging ligand yielding the dinuclear complexes bis-(4,4'-di-tert-butyl-2,2'-bipyridine)ruthenium(ii)-N-((picolinamido)(pyridin-2-yl)methylene)picolinamide)chloro-palladium(ii) [(tbbpy)(2)Ru(tptO)PdCl](PF(6))(2) and bis-(4,4'-di-tert-butyl-2,2'-bipyridine) ruthenium(ii)-N-((picolinamido)(pyridin-2-yl)methylene)picolinamide)chloro-platinum(ii) [(tbbpy)(2)Ru(tptO)PtCl](PF(6))(2). The newly formed bridging ligand coordinates in a bidentate fashion at the ruthenium centre and acts as a tridentate ligand for the second metal centre. The structures of all the complexes have been fully characterised and their photophysical properties are reported. A similar reaction sequence using the (4'-(p-bromophenyl)-2,2':6',2''-terpyridine)ruthenium(ii)-(tris(2-pyridyl)triazine) complex [(BrPhtpy)Ru(tpt)](PF(6))(2) and Pd(CH(3)CN)(2)Cl(2) as starting materials did not yield the hydrolysed bridging ligand but the expected dinuclear complex [(BrPhtpy)Ru(tpt)PdCl(2)](PF(6))(2) suggesting that the coordination of two pyridine rings of the tpt by the ruthenium centre is essential for the stabilisation of the tpt frame work. Preliminary investigations show that the dinuclear ruthenium-palladium and -platinum complexes are not active catalysts in the light-driven hydrogen production.