Cooperative catalysis of a trinuclear ruthenium(II) complex in transfer hydrogenation of ketones by formic acid

A novel TPA derivative (TPA = tris(2-pyridylmethyl)amine) having two 1,10-phenanthroline (phen) moieties via amide linkage was synthesized and this ligand reacted with [Ru(hmb)Cl₂]₂ (hmb: hexamethylbenzene) to give a trinuclear Ru(II) complex, [RuCl(TPA-{phenRuCl(hmb)}₂-H⁺)](PF₆)₂ (1-Cl), in a moderate yield. The complex involves a deprotonated and oxygen-coordinated amide linkage, which exhibits reversible protonation-deprotonation equilibrium. The chlorido complex was converted to be an aqua complex, [Ru(H₂O)(TPA-{phenRu(H₂O)₂(hmb)}₂-H⁺)](SO₄)_5/2 (1-H₂O), by the reaction of 1-Cl with Ag₂SO₄ in H₂O. Transfer hydrogenation of ketones was examined by using 1-Cl as a catalyst and HCOONa as a hydride source in H₂O/CH₃OH (1:1 v/v) at 50 °C under Ar. The time-course of the transfer hydrogenation of cyclohexanone to give cyclohexanol revealed that 1-Cl showed a cooperative effect on the catalytic reactivity as compared with that of mononuclear [RuCl(hmb)(phen)] (3-Cl) and [RuCl((1-Naph)₂-TPA)]PF₆ in H₂O/CH₃OH (1:2 v/v) under the same conditions. The detailed kinetic study has revealed that the catalytic transfer hydrogenation proceeds via the formato complex, which interacts with a substrate rather than via the hydrido complex. The two Ru centers placed at close proximity in 1-H₂O enhanced the interaction of the formato complex with a substrate, resulting in an increase in the catalytic reactivity as compared with the mononuclear complex.     

Ruthenium(II) carbonyl chloride complexes containing pyridine-functionalised bidentate N-heterocyclic carbenes: Synthesis, structures, and impact of the carbene ligands on catalytic activities

A series of new ruthenium(II) carbonyl chloride complexes with pyridine-functionalised N-heterocyclic carbenes [Ru(Py-NHC)(CO)₂Cl₂], [Py-NHC = 3-methyl-1-(2-pyridyl)imidazol-2-ylidene, 1 (1a and 1b); 3-methyl-1-(2-picoyl)imidazol-2-ylidene, 2 (2a and 2b); 3-methyl-1-(2-pyridyl)benzimidazolin-2-ylidene, 3 (3b); 3-methyl-1-(2-picoyl)benzimidazolin-2-ylidene, 4 (4a and 4b); 1-methyl-4-(2-pyridyl)-1,2,4-triazoline-5-ylidene, 5 (5a and 5b)] have been prepared by transmetallation from the corresponding silver carbene complexes and characterized by NMR, IR spectroscopy and elemental analysis. In these complexes with bidentate Py-NHC ligands, one CO ligand is trans to the Py ligand. In 1a, 2a, 4a, and 5a, the NHC ligand is trans to the other CO ligand, thus leaving the two Cl⁻ ligands trans to each other. In 1b, 2b, 3b, 4b, and 5b, the NHC ligands are trans to one Cl⁻ ligand, and the two Cl⁻ ligands are cis to each other. The structures for 1b, 2b, 3b and 4b have been determined by single-crystal X-ray diffraction. These complexes are efficient catalysts in the transfer hydrogenation of acetophenone and their catalytic activities are found to be influenced by electronic effect of the N-heterocyclic carbene ligands.     

Preparation, characterization, and catalytic properties of (triphenylphosphine)ruthenium complexes bearing N,O,N′-tridentate ligands

Preparation and characterization of (triphenylphosphine)ruthenium complexes bearing N,O,N′-tridentate ligands, [(L₁)RuCl(PPh₃)₂](BF₄) (L₁ = 2-[(2-pyridylmethoxy)methyl]pyridine), 1), [(L₂)RuCl(PPh₃)₂](BF₄) (L₂ = 8-(2-pyridylmethoxy)quinoline, 2) and [(L₃)RuCl₂(PPh₃)] (L₃ = 2-[(2-pyridylmethoxy)methyl]quinoline, 3) are described. Complexes 1-3 have been characterized by NMR and elemental analyses. Molecular structures of 2 and 3 have been determined by X-ray crystallography. Both compounds exhibit the octahedral geometry. L₂ adopts the facial configuration in 2 while L₃ is in a mer-arrangement in 3. Complexes 1-3 have proven to be able to catalyze the transfer hydrogenation of several ketones to alcohols in the presence of KOH and 2-propanol at refluxing, among which complex 3 was found to be the most active.     

Synthesis and characterisation of a series of mononuclear ruthenium(II) carbonyl complexes of heterocycle-based asymmetric bidentate ligands

In this contribution, the synthesis and characterisation of a series of complexes of the type [Ru(L-L′)(CO)₂Cl₂] are reported, where L-L′ are the chelating ligands L1-L8, 2-(4H-[1,2,4]triazol-3′-yl)-pyridine (L1); 2-(4H-[1,2,4]triazol-3′-yl)-pyrazine; (L2); 2-(1-methyl-4H-[1,2,4]-triazol-3-yl)pyridine (L3); 2-(5-pyridin-2-yl-4H-[1,2,4]-triazole-3-yl)phenol (L4); 3-(5-methylphenyl)-pyridin-2-yl-1,2,4-triazole (L5); 3-(4-methylphenyl)-pyridin-2-yl-1,2,4-triazole (L6); 3-(4-methoxyphenyl)-pyridin-2-yl-1,2,4-triazole (L7); 3,6-bis[(4-methoxyphenyl)iminomethyl]pyridazine (L8). L1-L7 are triazole-based ligands, which provide two distinct bidentate coordinate modes (via N2 or N4 of the triazole) whereas L8 is pyridazine-based and contains two identical bidentate binding pockets. The products obtained are analysed using infrared and NMR spectroscopy. The X-ray and molecular structures of the complexes with the ligands L2, L6, L7 and L8 are reported. These structures are the first to be reported for triazole based ruthenium chloro and ruthenium pyridazine imine complexes. The data show that the triazole ring in L2, L6 and L7 is coordinated via the N2 atom, and that the pyridazine-based ligand L8 uses only one binding pocket hence accommodating only one ruthenium(II) centre. For all compounds the cis(CO)transCl conformation is obtained. The results obtained are compared with those obtained for other similar compounds.     

Synthesis and characterization of ruthenium(II) complexes based on diphenyl-2-pyridylphosphine and their applications in transfer hydrogenation of ketones

Synthesis and characterization of the ruthenium complexes [RuH(CO)Cl(κ¹-P-PPh₂Py)₂(PPh₃)] (1) and [Ru(CO)Cl₂(κ¹-P-PPh₂Py)(κ²-P-N-PPh₂Py)] (2) containing diphenyl-2-pyridylphosphine (PPh₂Py) are described. Spectral and structural data suggested linkage of the PPh₂Py in κ¹-P bonding mode in 1 and both the κ¹-P and κ²-P-N bonding modes in 2. The complex 1 reacted with N,N-donor bases viz., ethylenediamine (en), N,N′-dimethyl-(ethylenediamine) (dimen), 1,3-diaminopropane (diap), 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) and di-2-pyridylaminomethylbenzene (dpa) to afford cationic complexes of formulation [RuH(CO)(κ¹-P-PPh₂Py)₂(N-N)]⁺ (3-8) [N-N = en, 3; dimen, 4; diap, 5; bipy, 6; phen, 7; and dpa, 8], which have been isolated as their tetrafluoroborate salts. The complexes under investigation have been characterized by elemental analyses, spectroscopic and electrochemical studies. Molecular structures of 2, 3, 6, and 8 have been determined by single crystal X-ray diffraction analyses. Further, the complexes 1-8 act as effective precursor catalyst in transfer hydrogenation of acetophenone/ketones in basic 2-propanol.     

Synthesis, characterization, photophysics and intramolecular energy transfer process in bimetallic rhenium(I)-ruthenium(II) complexes

Two new heterobimetallic complexes of rhenium(I) and ruthenium(II) [(CO)₃(NN)Re(4,4′-bpy)Ru(NN)₂Cl](PF₆)₂ and already known monometallic complexes [Cl(NN)₂Ru(4,4′-bpy)](PF₆) and [(CO)₃(NN)Re(4,4′-bpy)](PF₆) and bimetallic complexes [Cl(NN)₂Ru(4,4′-bpy)Ru(NN)₂Cl](PF₆)₂, [(CO)₃(NN)Re(4,4′-bpy)Re(NN)(CO)₃](PF₆)₂ (NN = 2,2′-bipyridine, 1,10-phenanthroline; 4,4′-bpy = 4,4′-bipyridine) are synthesized and characterized by spectral techniques. The photophysical properties of all the complexes are studied. It is found that attachment of rhenium(I) altered the photophysical characteristics of ruthenium(II). Excited state energy transfer from the rhenium(I) chromophore to the ruthenium(II) is observed upon excitation at 355 nm.     

Synthesis and anti-cancer activity of bis-amino-phosphine ligand and its ruthenium(II) complexes

The development of both chemotherapeutic drug resistance as well as adverse side effects suggest that the current chemotherapeutic drugs remain ineffective in treating the various types of cancers. The development of new metallodrugs presenting anti-cancer activity is therefore needed. Ruthenium complexes have gained a great deal of interest due to their promising anti-tumour properties and reduced toxicity in vivo. This study highlighted the effective induction of cell death in a malignant melanoma cell by two novel bis-amino-phosphine ruthenium(II) complexes referred to as GA105 and GA113. The IC₅₀ concentrations were determined for both the complexes, the ligand and cisplatin, for comparison. Both complexes GA105 and GA113 displayed a high anti-cancer selectivity profile as they exhibited low IC₅₀ values of 6.72 µM and 8.76 µM respectively, with low toxicity towards a non-malignant human cell line. The IC₅₀ values obtained for both complexes were lower than that of cisplatin. The new complexes were more effective compared to the free ligand, GA103 (IC₅₀ = >20 µM). Morphological studies on treated cells induced apoptotic features, which with further studies could indicate an intrinsic cell death pathway. Additionally, flow cytometric analysis revealed that the mode of cell death of complex GA113 was apoptosis. The outcomes herein give further insight into the potential use of selected Ru(II) complexes as alternative chemotherapeutic drugs in the future.     

trans- and cis-Ru(II) aminophosphine complexes: Syntheses, X-ray structures and catalytic activity in transfer hydrogenation of acetophenone derivatives

The ability of transition metal catalysts to add or remove hydrogen from organic substrates by transfer hydrogenation process is a valuable synthetic tool. For this aim, a novel Ru(II) complex with the P-N ligand [(Ph₂P)₂NCH₂-C₄H₃S] derived from thiophene-2-methylamine was synthesized starting with the complex [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂ and isolated in two isomeric forms: trans- and cis-[Ru((PPh₂)₂NCH₂-C₄H₃S)₂Cl₂], 2 and 3, respectively. The structures of both isomers were also determined by single crystal X-ray diffraction. The cis-isomer 3 can be isolated from the solution of major trans-isomer 2 as yellow crystals. However, upon dissolution 3 is rapidly converted to the trans-isomer 2. The new ruthenium(II) complex provides high catalytic activity in the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of 2-propanol as the hydrogen source. This transfer hydrogenation is characterized by low reversibility under the experimental conditions.     

Diether functionalized rhodium(I)-N-heterocyclic carbene complexes and their catalytic application for transfer hydrogenation reactions

N-heterocyclic carbene (NHC) complexes of rhodium(I) (3 and 4) bearing one diether (MeOCH₂CH₂OCH₂CH₂-NHC) functionality on N¹ and bulky benzyl groups (CH₂-C₆H₂(CH₃)₃-2,4,6 and CH₂-C₆(CH₃)₅) on N³ of (5,6-dimethyl)benzimidazole were synthesized by deprotonation of the corresponding benzimidazolium salt with [Rh(μ-OMe)(1,5-cod)]₂ in dichloromethane at ambient temperature. All compounds have been fully characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy. X-ray diffraction studies on single crystals of 3a and 3b confirm the cis square planar geometry. All of the new benzimidazol-2-ylidene rhodium(I) complexes were found to be effective catalysts for the transfer hydrogenation reaction.     

Synthesis,characterization and DNA binding and cleavage properties of ruthenium(II) complexes with various polypyridyls

Polypyridyl chlororuthenium(II) complexes have been synthesized and characterized. The binding mode of the complexes to DNA has been evaluated from the combined results of electronic absorption spectroscopy and viscosity measurement study. The results suggest that complexes 1, 2 and 3 bind to DNA via classical intercalation, electrostatic interaction and partial intercalation mode, respectively. Complex 2 shows less affinity for DNA. Cleavage of pUC19 DNA by complexes has been checked using gel electrophoresis. The data disclose that complex 1 has the highest cleaving ability.     

Synthesis, characterization and reactivity of polypyridyl ruthenium(II) carbonyl complexes with phosphine derivatives: Ruthenium-carbon bond labilization based on steric and electronic effects

Ruthenium phosphine complexes with a CO ligand [Ru(tpy)(PR₃)(CO)Cl]⁺ (tpy = 2,2′:6′,2″-terpyridine, R = Ph or p-tolyl), were prepared by introduction of CO gas to the corresponding dichloro complexes at room temperature. New carbonyl complexes were characterized by various methods including structural analyses. They were shown to release CO following the addition of several N-donors to form the corresponding substituted complexes. The kinetic data and structural results observed in this study indicated that the CO release reactions proceeded in an interchange mechanism. The molecular structures of [Ru(tpy)(PPh₃)(CO)Cl]PF₆, [Ru(tpy)(P(p-tolyl)₃)(CO)Cl]PF₆ and [Ru(tpy)(PPh₃)(CH₃CN)Cl]PF₆ were determined by X-ray crystallography.     

Supported organometallic complexes part 39: cationic diamine(ether-phosphine)ruthenium(II) complexes as precursors for the hydrogenation of trans-4-phenyl-3-butene-2-one

Treatment of RuCl₂(η¹-Ph₂PCH₂CH₂OCH₃)₂(diamine) (1L₁-1L₇) with one equivalent of AgX (X=OTf, BF₄) in CH₂Cl₂ results in the formation of the monocationic ruthenium(II) complexes [RuCl(η¹-Ph₂PCH₂CH₂OCH₃)(η²-Ph₂PCH₂CH₂OCH₃)(diamine)]⁺X⁻ (2L₁-2L₇). These complexes were characterized by NMR, and mass spectroscopy as well as by elemental analyses, 2L₁ additionally by an X-ray structural analysis. Complex 2L₁ crystallizes in the monoclinic space group C2/c with Z=8. The monocationic and neutral complexes were applied as catalysts in the selective hydrogenation of trans-4-phenyl-3-butene-2-one. With the exception of 1L₃/1L₇ and 2L₃/2L₇ all catalysts showed high activities and selectivities toward the hydrogenation of the carbonyl group under mild conditions. However, the activity of the cationic catalysts is only half of that of their neutral congeners.     

Reactivity of cationic carbonyl/phosphine ruthenium(II) compounds

Cis(or trans)-[RuCl₂(CO)₂(PPh₃)₂] react with two and one equivalents of AgBF₄ to give the recently reported [Ru(CO)₂(PPh₃)₂][BF₄]₂·CH₂Cl₂ (1) and novel [RuCl(CO)₂(PPh₃)₂][BF₄] · 1/2 CH₂Cl₂ (2), respectively. Cis-[RuCl₂(CO)₂(PPh₃)₂] also reacts with two equivalents of AgBF₄ in the presence of CO to give [Ru(CO)₃(PPh₃)₂][BF₄]₂ (3). Reactions of 1 and 2 with NaOMe and CO at 1 atm produce the carbomethoxy species [Ru(COOMe)₂(CO)₂(PPh₃)₂] (4) and [RuCl(COOMe)(CO)₂(PPh₃)₂] (5), respectively. Complex 4 can also be formed from the reaction of 3 with NaOMe and CO. Alternatively, 4 is formed from cis-[RuCl₂(CO)₂(PPh₃)₂] with NaOMe and CO at elevated pressure (10 atm); if these reactants are refluxed under 1 atm of CO, [Ru(CO)₃(PPh₃)₂] is the product. The reaction of [RuCl(CO)₃(PPh₃)₂][AlCl₄] with NaOMe provides an alternative route to the preparation of 5, but the product is contaminated with [RuCl₂(CO)₂(PPh₃)₂]. Compounds 1. 2, 4 and 5 have been characterised by IR, ¹H NMR and analysis, whilst the formulation of 3 is proposed from spectroscopic data only. This account also examines the reactivity of [Ru(CO)₂(PPh₃)₂][BF₄]₂ · CH₂Cl₂ with NaBH₄, conc. HCl, KI and, finally, MeCOONa in the presence of CO. The products of these reactions, namely cis-[RuH₂(CO)₂(PPh₃)₂], cis-[RuCl₂(CO)₂(PPh₃)₂], cis-[RuI₂(CO)₂(PPh₃)₂] and [Ru(OOCMe)₂(CO)₂(PPh₃)₂], have been identified by comparison of their spectra with previous literature.     

Synthesis, structural characterization, antiradical and antidiabetic activities of copper(II) and zinc(II) Schiff base complexes derived from salicylaldehyde and beta-alanine

A series of copper(II) and zinc(II) complexes involving a tridentate O,N,O'-donor Schiff base derived from salicylaldehyde and beta-alanine {i.e. N-salicylidene-beta-alanine(2-), (L)}, having the composition [Cu(2)(L)(2)(H(2)O)].H(2)O (1), [Cu(L)(H(2)O)](n) (2), and [Zn(L)(H(2)O)](n) (3), have been prepared and characterized by elemental analyses, UV-visible (UV-VIS), FT-IR and ESI-MS spectra, and thermal analyses. Complexes 1 and 2 have been investigated by single crystal X-ray analysis and also by temperature dependent magnetic susceptibility measurements (294-80K). All prepared complexes have been evaluated by the antiperoxynitrite activity assay and alloxan-induced diabetes model. The significant antioxidant and antidiabetic activities have been found in the case of both copper(II) complexes 1 and 2. In spite of first two complexes, the zinc(II) complex 3, as well as the potassium salt of the ligand (KHL) showed only insignificant protective effect against the tyrosine nitration in vitro.     

Synthesis and characterization of new ruthenium(II) complexes containing coupled di(2-pyridyl) and 1,3-dithiole units

Two new ruthenium (II) complexes containing coupled di(2-pyridyl) and 1,3-dithiole units, cis-[Ru(Medpydt)₂(NCS)₂] (2, Medpydt = dimethyl 2-(di(2-pyridyl)methylene)-1,3-dithiole-4,5-dicarboxylate) and cis-[Ru(H₂dpydt)₂(NCS)₂] (3, H₂dpydt = 2-(di(2-pyridyl)methylene)-1,3-dithiole-4,5-dicarboxylate), have been synthesized and characterized. The structure of complex 2 has been determined by X-ray crystallography. There exist intermolecular H-bonding interactions between carbomethoxy groups on neighboring pyridine rings giving rise to 2D H-bonded arrays. The metal-to-ligand charge-transfer (MLCT) absorptions were observed around 480 nm. Redox properties of ruthenium complexes have been investigated by cyclic voltammetry. Solar cells involving thin films of anatase TiO₂ impregnated with cis-[Ru(H₂dpydt)₂(NCS)₂] were prepared, and the photovoltaic performance was preliminarily investigated.     

Synthesis,characterization, redox behavior,DNA and protein binding and antibacterial activity studies of ruthenium(II) complexes of bidentate schiff bases

Two new ruthenium(II) complexes of Schiff base ligands (L) derived from cinnamaldehyde and ethylenediamine formulated as [Ru(L)(bpy)₂](ClO₄)₂, where L¹ = N,N’-bis(4-nitrocinnamald-ehyde)ethylenediamine and L² = N,N’-bis(2-nitrocinnamaldehyde)-ethylenediamine for complex 1 and 2, respectively, were isolated in pure form. The complexes were characterized by physicochemical and spectroscopic methods. The electrochemical behavior of the complexes showed the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The interaction of the complexes with calf thymus DNA (CT-DNA) using absorption, emission spectral studies and electrochemical techniques have been used to determine the binding constant, K_b and the linear Stern–Volmer quenching constant, K_SV. The results indicate that the ruthenium(II) complexes interact with CT-DNA strongly in a groove binding mode. The interactions of bovine serum albumin (BSA) with the complexes were also investigated with the help of absorption and fluorescence spectroscopy tools. Absorption spectroscopy proved the formation of a ground state BSA-[Ru(L)(bpy)₂](ClO₄)₂ complex. The antibacterial study showed that the Ru(II) complexes (1 and 2) have better activity than the standard antibiotics but weak activity than the ligands.     

pH responsive luminescent switches of ruthenium(II) complexes containing two imidazole groups: Synthesis, spectroscopy, electrochemistry and theoretical calculations

A series of new mononuclear polypyridyl ruthenium(II) complexes containing two imidazole groups have been synthesized and characterized by ¹H NMR, ES-MS, FAB-MS, IR spectra and elemental analysis. Their electrochemistry and spectroscopic properties including UV-Vis absorption, steady-state and time-resolved emission have been studied using both experimental methods and theoretical calculations. These complexes have been found to be sensitive luminescent pH switches, as their absorption and emission spectra respond to the solutions pH disturbances with extraordinary sensitivity, through the protonation and deprotonation of the imidazole groups. DFT calculations have been carried out to reveal the exact protonation and deprotonation route. The ground-state and excited-state ionization constants (pK_a and ) of each acid-base equilibrium have also been calculated according to the absorbance and emission data under different pH.     

DNA interaction and cytotoxicity studies of new ruthenium(II) cyclopentadienyl derivative complexes containing heteroaromatic ligands

Four ruthenium(II) complexes with the formula [Ru(η⁵-C₅H₅)(PP)L][CF₃SO₃], being (PP = two triphenylphosphine molecules), L = 1-benzylimidazole, ; (PP = two triphenylphosphine molecules), L = 2,2′bipyridine, ; (PP = two triphenylphosphine molecules), L = 4-Methylpyridine, ; (PP = 1,2-bis(diphenylphosphine)ethane), L = 4-Methylpyridine, , were prepared, in view to evaluate their potentialities as antitumor agents. The compounds were completely characterized by NMR spectroscopy and their crystal and molecular structures were determined by X-ray diffraction. Electrochemical studies were carried out giving for all the compounds quasi-reversible processes. The images obtained by atomic force microscopy (AFM) suggest interaction with pBR322 plasmid DNA. Measurements of the viscosity of solutions of free DNA and DNA incubated with different concentrations of the compounds confirmed this interaction. The cytotoxicity of compounds 1234 was much higher than that of cisplatin against human leukemia cancer cells (HL-60 cells). IC₅₀ values for all the compounds are in the range of submicromolar amounts. Apoptotic death percentage was also studied resulting similar than that of cisplatin.     

Palladium(II) complexes of a bis-2-aminobiphenyl N-heterocyclic carbene: Synthesis, structural studies and catalytic activity

A new imidazolinium [(SIBiphen)H](BF₄) was synthesized in three steps from 2-aminobiphenyl. The reaction of the salt with Pd(OAc)₂, NaI and t-BuOK gave a dimeric Pd(II) complex [(SIBiphen)PdI₂]₂, which was analyzed by an X-ray diffraction study. The reaction of [Pd(allyl)Cl]₂, the imidazolinium salt and t-BuOK in THF at −78 °C gave the monomeric Pd complex, in which the N-heterocyclic carbene was bound to the metal centre, as confirmed by a single-crystal X-ray diffraction study. A preliminary catalytic study showed that these new systems were moderately active in the Suzuki-Miyaura coupling of aryl halides.     

Diastereoisomerically pure pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2-bipyridine: structural, electrochemical and spectral studies

Pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2^′-bipyridine of composition [(bpy)₂Ru(pzdc)Ru(bpy)₂](ClO₄) · H₂O (1) and [(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2) have been obtained in high yield and have been separated to their homochiral (ΛΛ/ΔΔ) rac (1a, 2a) and heterochiral (ΛΔ/ΔΛ) meso (1b, 2b) diastereoisomers. The distinctive structural features of these diastereoisomers have been characterized by 1-D and 2-D ¹H NMR spectroscopy. The X-ray crystal structure of rac-[(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2a) has been determined. The electrochemical and electronic spectral studies have established that there remain difference in properties and hence difference in intermetallic communication between the diastereoisomeric forms in each case.