X-ray Crystallography Research Articles

The Development of Organotin(IV) N-Ethyl-N-Benzyldithiocarbamate Complexes: A Study on Their Synthesis, Characterization, and Cytocidal Effects on A549 Cell Line

Background: Organotin(IV) complexes of dithiocarbamate are vital in medicinal chemistry, exhibiting potential in targeting cancer cells due to their unique properties that enhance targeted delivery. This study aimed to synthesize and characterize organotin(IV) N-ethyl-N-benzyldithiocarbamate complexes (ONBDCs) and evaluate their cytotoxicity against A549 cells, which are commonly used as a model for human lung cancer research. Method: The two ONBDC derivatives – ONBDC 1 (dimethyltin(IV) N-ethyl-N-benzyldithiocarbamate) and ONBDC 2 (triphenyltin(IV) N-ethyl-N-benzyldithiocarbamate) – were synthesized via the reaction of tin(IV) chloride with N-ethylbenzylamine in the presence of carbon disulfide. A range of analytical techniques, including elemental analysis, IR spectroscopy, NMR spectroscopy, UV-Vis spectrometry, TGA/DTA analysis, and X-ray crystallography, was conducted to characterize these compounds comprehensively. The cytotoxic effects of ONBDCs against A549 cells were evaluated using MTT assay. Results: Both compounds were synthesized and characterized successfully via elemental and spectroscopies analysis. MTT assay revealed that ONBDC 2 demonstrated remarkable cytotoxicity towards A549 cells, with an IC50 value of 0.52 μM. Additionally, ONBDC 2 displayed significantly higher cytotoxic activity against the A549 cell line when compared to the commercially available chemotherapeutic agent cisplatin (IC50: 32 μM). Conclusion: Thus, it was shown that ONBDC 2 could have important anticancer properties and should be further explored as a top contender for creating improved and specialized cancer treatments.

Unusually Short H⋅⋅⋅H Contacts in Intramolecularly Cyclized Helically Fused Anthracenes.

The intramolecular coupling of dichloro-substituted helically fused anthracenes using the Yamamoto coupling yielded cyclized products with sterically congested molecular structures. The X-ray analysis and DFT calculations showed that the aromatic framework adopted a nonplanar structure with a twisted conformation about the newly formed single bond, which acts as a chiral axis. Interestingly, the X-ray structure obtained through the Hirshfeld atom refinement revealed short interatomic distances between the inner hydrogen atoms (1.648-1.692 Å), much shorter than the sum of their van der Waals radii. Owing to these unusually short contacts, the 1H NMR spectrum exhibited a significant deshielding (12.5 ppm) and a large nuclear Overhauser effect (44 %). Additionally, the IR spectrum displayed a high-frequency shift of the C-H stretching vibration. These observations, along with the noncovalent interaction plot indicative of a characteristic steric environment, strongly support the presence of steric hindrance. Moreover, dynamic NMR measurement of the mesityl-substituted derivative yielded a barrier to helical inversion of 84 kJ mol-1. The optical properties and crystal packing of the cyclized products are also reported.

Protecting Group-Free Total Synthesis of (-)-Boscartin H.

Herein, we report the first protecting group-free total synthesis of (-)-boscartin H, which features a 5-12-5-fused tricyclic structure. The key steps, which include a diastereoselective THF-ring-forming/aldol reaction sequence and ring-closing metathesis, afforded high stereoselectivity with (-)-boscartin H obtained in 3.6% overall yield using a 11-step long linear sequence. In addition, X-ray crystallography clearly confirmed the stereochemistry of boscartin H.

Automated multiconformer model building for X-ray crystallography and cryo-EM.

In their folded state, biomolecules exchange between multiple conformational states that are crucial for their function. Traditional structural biology methods, such as X-ray crystallography and cryogenic electron microscopy (cryo-EM), produce density maps that are ensemble averages, reflecting molecules in various conformations. Yet, most models derived from these maps explicitly represent only a single conformation, overlooking the complexity of biomolecular structures. To accurately reflect the diversity of biomolecular forms, there is a pressing need to shift toward modeling structural ensembles that mirror the experimental data. However, the challenge of distinguishing signal from noise complicates manual efforts to create these models. In response, we introduce the latest enhancements to qFit, an automated computational strategy designed to incorporate protein conformational heterogeneity into models built into density maps. These algorithmic improvements in qFit are substantiated by superior Rfree and geometry metrics across a wide range of proteins. Importantly, unlike more complex multicopy ensemble models, the multiconformer models produced by qFit can be manually modified in most major model building software (e.g., Coot) and fit can be further improved by refinement using standard pipelines (e.g., Phenix, Refmac, Buster). By reducing the barrier of creating multiconformer models, qFit can foster the development of new hypotheses about the relationship between macromolecular conformational dynamics and function.

A Triply Linked Copper(III) Dicarbacorrole Dimer.

A triply linked dicarbacorrole dimer (7) was synthesized from a new meso-meso singly linked dicarbacorrole dimer precursor (6) via an oxidative fusion reaction by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in the presence of trifluoromethanesulfonic acid (TfOH). Single crystal X-ray structure of 7 adopts a flat conformation with a length as ca. 15.946 Å and a width as 6.903 Å, which can be regarded as a short carbaporphyrinoid tape. Two coordinated Cu ions keeps the +3 oxidation state in 7, as confirmed by NMR spectroscopy, single crystal X-ray diffraction and X-ray photoelectron spectroscopy (XPS). This is in sharp contrast to the Osuka's triply linked tetrapyrrolic corrole dimers, where the inner 3NH form is not stable and thus can only act as a divalent ligand. Due to the non-aromatic nature of dicarbacorrole macrocycle, the largely decreased HOMO-LUMO gap and red-shifted absorption of 7 are best ascribed to the strong electronic interaction between two dipyrromethene-type chromophores. To our knowledge, this is the first fully fused carbaporphyrinoid dimer with β-β, meso-meso, β-β triply linkages prepared to date.

Coinage Metal Complexes of a Sterically Encumbered Anionic Pyridylborate.

Sterically loaded, anionic pyridine has been synthesized and utilized successfully in the stabilization of a isoleptic series of coinage metal complexes. The treatment of [4-(Ph3B)-2,6-Trip2Py]K (Trip=2,4,6-iPr3C6H2) with CuBr(PPh3), AgCl(PPh3) or AuCl(PPh3) (Py=pyridine) afforded the corresponding [4-(Ph3B)-2,6-Trip2Py]M(PPh3) (M=Au, Ag, Cu) complexes, via salt metathesis, as isolable, crystalline solids. Notably, these reactions avoid the facile single electron transfer chemistry reported with the less bulky ligand systems. The X-ray structures revealed that they are two-coordinate metal adducts. The M-N and M-P bond distances are longest in the silver and shortest in the copper adduct among the three group 11 family members. Computational analysis revealed an interesting stability dependence on steric bulk of the anionic pyridine (i. e., pyridyl borate) ligand. A comparison of structures and bonding of [4-(Ph3B)-2,6-Trip2Py]Au(PPh3) to pyridine and m-terphenyl complexes, {[2,6-Trip2Py]Au(PPh3)}[SbF6] and [2,6-Trip2Ph]Au(PPh3) are also provided. The Au(I) isocyanide complex, [4-(Ph3B)-2,6-Trip2Py]Au(CNBut) has been stabilized using the same anionic pyridylborate illustrating that it can support other gold-ligand moieties as well.

Integrated Experimental and Theoretical Investigation of Copper Active Site Properties of a Lytic Polysaccharide Monooxygenase from Serratia marcescens.

In this paper, we employed a multidisciplinary approach, combining experimental techniques and density functional theory (DFT) calculations to elucidate key features of the copper coordination environment of the bacterial lytic polysaccharide monooxygenase (LPMO) from Serratia marcescens (SmAA10). The structure of the holo-enzyme was successfully obtained by X-ray crystallography. We then determined the copper(II) binding affinity using competing ligands and observed that the affinity of the histidine brace ligands for copper is significantly higher than previously described. UV-vis, advanced electron paramagnetic resonance (EPR), and X-ray absorption spectroscopy (XAS) techniques, including high-energy resolution fluorescence detected (HERFD) XAS, were further used to gain insight into the copper environment in both the Cu(II) and Cu(I) redox states. The experimental data were successfully rationalized by DFT models, offering valuable information on the electronic structure and coordination geometry of the copper center. Finally, the Cu(II)/Cu(I) redox potential was determined using two different methods at ca. 350 mV vs NHE and rationalized by DFT calculations. This integrated approach not only advances our knowledge of the active site properties of SmAA10 but also establishes a robust framework for future studies of similar enzymatic systems.

Acyclic Cucurbit[n]uril Receptors Function as Solid State Sequestrants for Organic Micropollutants.

The accumulation of organic micropollutants (OMP) in aquatic systems is a major societal problem that can be addressed by approaches including nanofiltration, flocculation, reverse osmosis and adsorptive methods using insoluble materials (e.g. activated carbon, MOFs, nanocomposites). More recently, polymeric versions of supramolecular hosts (e.g. cyclodextrins, calixarenes, pillararenes) have been investigated as OMP sequestrants. Herein, we report our study of the use of water insoluble dimethylcatechol walled acyclic cucurbit[n]uril (CB[n]) hosts as solid state sequestrants for a panel of five OMPs. A series of hosts (H1 - H4) were synthesized by reaction of glycoluril oligomer (monomer - tetramer) with 3,6-dimethylcatechol and fully characterized by spectroscopic means and x-ray crystallography. The solid hosts sequester OMPs from water with removal efficiencies exceeding 90% in some cases. The removal efficiencies of the new hosts parallel the known molecular recognition properties of analogous water soluble acyclic CB[n]. OMP uptake by solid host occurs rapidly (≈120 seconds). Head-to-head comparison with CB[6] in batch-mode separation and DARCO activated carbon in flow-through separation mode show that tetramer derived host (H4) performs very well under identical conditions. The work establishes insoluble acyclic CB[n]-type receptors as a promising new platform for OMP sequestration.

Interactions of Phenylalanine Derivatives with Human Tyrosinase: Lessons from Experimental and Theoretical tudies.

The pigmentation of the skin, modulated by different actors in melanogenesis, is mainly due to the melanins (protective pigments). In humans, these pigments' precursors are synthetized by an enzyme known as tyrosinase (TyH). The regulation of the enzyme activity by specific modulators (inhibitors or activators) can offer a means to fight hypo- and hyper-pigmentations responsible for medical, psychological and societal handicaps. Herein, we report the investigation of phenylalanine derivatives as TyH modulators. Interacting with the binuclear copper active site of the enzyme, phenylalanine derivatives combine effects induced by combination with known resorcinol inhibitors and natural substrate/intermediate (amino acid part). Computational studies including docking, molecular dynamics and free energy calculations combined with biological activity assays on isolated TyH and in human melanoma MNT-1 cells, and X-ray crystallography analyses with the TyH analogue Tyrp1, provide conclusive evidence of the interactions of phenylalanine derivatives with human tyrosinase. In particular, our findings indicate that an analogue of L-DOPA, namely (S)-3-amino-tyrosine, stands out as an amino phenol derivative with inhibitory properties against TyH.

Non-Covalent and Covalent Binding of New Mixed-Valence Cage-like Polyoxidovanadate Clusters toLysozyme.

Thehigh-resolution X-ray structures of the model protein lysozyme in the presence of the potential drug [VIVO(acetylacetonato)2] from crystals grown in 1.1 M NaCl, 0.1 M sodium acetate at pH 4.0 reveal the binding to the protein of different and unexpected mixed-valence cage-like polyoxidovanadates (POVs): [V15O36(OH2)]5-, which non-covalently interacts with the lysozyme surface, [V15O33(OH2)]+ and [V20O51(OH2)]n- (this latter based on an unusual {V18O43} cage) which covalently bind the protein. EPR spectroscopy confirms the partial oxidation of VIV to VV and the formation of mixed-valence species. The results indicate that the interaction with proteins can stabilize the structure of unexpected - both for dimension and architecture - POVs, not observed in aqueous solution.

Global profiling of functional histidines in live cells using small-molecule photosensitizer and chemical probe relay labelling.

Recent advances in chemical proteomics have focused on developing chemical probes that react with nucleophilic amino acid residues. Although histidine is an attractive candidate due to its importance in enzymatic catalysis, metal binding and protein-protein interaction, its moderate nucleophilicity poses challenges. Its modification is frequently influenced by cysteine and lysine, which results in poor selectivity and narrow proteome coverage. Here we report a singlet oxygen and chemical probe relay labelling method that achieves high selectivity towards histidine. Libraries of small-molecule photosensitizers and chemical probes were screened to optimize histidine labelling, enabling histidine profiling in live cells with around 7,200 unique sites. Using NMR spectroscopy and X-ray crystallography, we characterized the reaction mechanism and the structures of the resulting products. We then applied this method to discover unannotated histidine sites key to enzymatic activity and metal binding in select metalloproteins. This method also revealed the accessibility change of histidine mediated by protein-protein interaction that influences select protein subcellular localization, underscoring its capability in discovering functional histidines.

Observation of a Picosecond Light-Induced Spin Transition in Polymeric Nanorods.

Spin transition (ST) materials are attractive for developing photoswitchable devices, but their slow material transformations limit device applications. Size reduction could enable faster switching, but the photoinduced dynamics at the nanoscale remains poorly understood. Here, we report a femtosecond optical pump multimodal X-ray probe study of polymeric nanorods. Simultaneously tracking the ST order parameter with X-ray emission spectroscopy and structure with X-ray diffraction, we observe photodoping of the low-spin-lattice within ∼150 fs. Above a ∼16% photodoping threshold, the transition to the high-spin phase occurs following an incubation period assigned to vibrational energy redistribution within the nanorods activating the molecular spin switching. Above ∼60% photodoping, the incubation period disappears, and the transition completes within ∼50 ps, preceded by the elastic nanorod expansion in response to the photodoping. These results support the feasibility of ST material-based GHz optical switching applications.

De novo design of proteins housing excitonically coupled chlorophyll special pairs.

Natural photosystems couple light harvesting to charge separation using a 'special pair' of chlorophyll molecules that accepts excitation energy from the antenna and initiates an electron-transfer cascade. To investigate the photophysics of special pairs independently of the complexities of native photosynthetic proteins, and as a first step toward creating synthetic photosystems for new energy conversion technologies, we designed C2-symmetric proteins that hold two chlorophyll molecules in closely juxtaposed arrangements. X-ray crystallography confirmed that one designed protein binds two chlorophylls in the same orientation as native special pairs, whereas a second designed protein positions them in a previously unseen geometry. Spectroscopy revealed that the chlorophylls are excitonically coupled, and fluorescence lifetime imaging demonstrated energy transfer. The cryo-electron microscopy structure of a designed 24-chlorophyll octahedral nanocage with a special pair on each edge closely matched the design model. The results suggest that the de novo design of artificial photosynthetic systems is within reach of current computational methods.

Controlling Redox Potential of a Manganese(III)-Bis(hydroxo) Complex through Protonation and the Hydrogen-Atom Transfer Reactivity.

A series of mononuclear manganese(III)-hydroxo and -aqua complexes, [MnIII(TBDAP)(OH)2]+ (1), [MnIII(TBDAP)(OH)(OH2)]2+ (2) and [MnIII(TBDAP)(OH2)2]3+ (3), were prepared from a manganese(II) precursor and confirmed using various methods including X-ray crystallography. Thermodynamic analysis showed that protonation from hydroxo to aqua species resulted in increased redox potentials (E1/2) in the order of 1 (-0.15 V) < 2 (0.56 V) < 3 (1.11 V), while pKa values exhibited a reverse trend in the order of 3 (3.87) < 2 (11.84). Employing the Bordwell Equation, the O-H bond dissociation free energies (BDFE) of [MnII(TBDAP)(OH)(OH2)]+ and [MnII(TBDAP)(OH2)2]2+, related to the driving force of 1 and 2 in hydrogen atom transfer (HAT), were determined as 75.3 and 77.3 kcal mol-1, respectively. It was found that the thermodynamic driving force of 2 in HAT becomes greater than that of 1 as the redox potential of 2 increases through protonation from 1 to 2. Kinetic studies on electrophilic reactions using a variety of substrates revealed that 1 is only weakly reactive with O-H bonds, whereas 2 can activate aliphatic C-H bonds in addition to O-H bonds. The reaction rates increased by 1.4 × 104-fold for the O-H bonds by 2 over 1, which was explained by the difference in BDFE and the tunneling effect. Furthermore, 3, possessing the highest redox potential value, was found to undergo an aromatic C-H bond activation reaction under mild conditions. These results provide valuable insights into enhancing electrophilic reactivity by modulating the redox potential of manganese(III)-hydroxo and -aqua complexes through protonation.

The Importance of Structured Water in HDAC8 for Correct Binding Pose Applied for Drug Design of Anticancer Molecules.

Validating the docking procedure and maintaining the structural water molecules at HDAC8 catalytic site. Molecular docking simulations play a significant role in Computer-Aided Drug Design, contributing to the development of new molecules. To ensure the reliability of these simulations, a validation process called "Re-docking" is employed, focusing on the binding mode of a ligand co-crystallized with the protein of interest. In this study, several molecular docking studies were conducted using five X-ray structures of HDAC8-ligand complexes from the PDB. Ligands initially complexed with HDAC8 were removed and re-docked onto the free protein, revealing a poor reproduction of the expected binding mode. In response to this, we observed that most HDAC8-ligand complexes contained one to two water molecules in the catalytic site, which were crucial for maintaining the cocrystallized ligand. These water molecules enhance the binding mode of the co-crystallized ligand by stabilizing the proteinligand complex through hydrogen bond interactions between ligand and water molecules. Notably, these interactions are lost if water molecules are removed, as is often done in classical docking methodologies. Considering this, molecular docking simulations were repeated, both with and without one or two conserved water molecules near Zn+2 in the catalytic cavity. Simulations indicated that replicating the native binding pose of co-crystallized ligands on free HDAC8 without these water molecules was challenging, showing greater coordinate displacements (RMSD) compared to those including conserved water molecules from crystals. The study highlighted the importance of conserved water molecules within the active site, as their presence significantly influenced the successful reproduction of the ligands' native binding modes. The results suggest an optimal molecular docking procedure for validating methods suitable for filtering new HDAC8 inhibitors for future experimental assays.

High-confidence placement of low-occupancy fragments into electron density using the anomalous signal of sulfur and halogen atoms.

Fragment-based drug design using X-ray crystallography is a powerful technique to enable the development of new lead compounds, or probe molecules, against biological targets. This study addresses the need to determine fragment binding orientations for low-occupancy fragments with incomplete electron density, an essential step before further development of the molecule. Halogen atoms play multiple roles in drug discovery due to their unique combination of electronegativity, steric effects and hydrophobic properties. Fragments incorporating halogen atoms serve as promising starting points in hit-to-lead development as they often establish halogen bonds with target proteins, potentially enhancing binding affinity and selectivity, as well as counteracting drug resistance. Here, the aim was to unambiguously identify the binding orientations of fragment hits for SARS-CoV-2 nonstructural protein 1 (nsp1) which contain a combination of sulfur and/or chlorine, bromine and iodine substituents. The binding orientations of carefully selected nsp1 analogue hits were focused on by employing their anomalous scattering combined with Pan-Dataset Density Analysis (PanDDA). Anomalous difference Fourier maps derived from the diffraction data collected at both standard and long-wavelength X-rays were compared. The discrepancies observed in the maps of iodine-containing fragments collected at different energies were attributed to site-specific radiation-damage stemming from the strong X-ray absorption of I atoms, which is likely to cause cleavage of the C-I bond. A reliable and effective data-collection strategy to unambiguously determine the binding orientations of low-occupancy fragments containing sulfur and/or halogen atoms while mitigating radiation damage is presented.

Synthesis and cytotoxicity of copper(II) semicarbazone complexes with lipophilic counter-anions

A series of (2,4-dihydroxybenzaldehyde dibenzyl semicarbazone) perfluoroalkyl carboxylato copper(II) complexes, [CF3(CF2)nCO2(LH)Cu] (LH2 = 2,4-dihydroxybenzaldehyde dibenzyl semicarbazone; n = 0, 2, 4, 6; 1–4), and (2,4-dihydroxybenzaldehyde dibenzyl semicarbazone) pyridine copper(II) perfluoroalkyl carboxylates, [(LH)(py)Cu]+[CF3(CF2)nCO2]− (5–8) were synthesized. The lipophilicity of these compounds was determined by reverse-phase thin layer chromatography and correlated with their cytotoxicity towards MOLT-4 human leukaemia cells. Cytotoxicity is more strongly correlated with lipophilicity for the non-ionic compounds (1–4) than for the ionic compounds (5–8). Compounds 5–8 (IC50 2.8–3.8 μM) are generally more cytotoxic than compounds 1–4 (IC50 3.6–8.4 μM). They also exhibit slightly higher cytotoxicity than the parent anticancer compound [(LH)(py)Cu]+[NO3]− (IC50 4.15 μM), suggesting that it is possible to enhance the cytotoxicity of [(LH)(py)Cu]+[NO3]− by replacing nitrate with anions of higher lipophilicity. Attempts to synthesize the non-fluorinated analogue [(LH)(py)Cu]+[CH3CO2]− resulted in the formation of the deprotonated complex [L(py)Cu], whose structure was confirmed by X-ray crystallography. The structural parameters indicate that the deprotonation site is the hydrazonic nitrogen of the semicarbazone ligand.

Thrombin - A Molecular Dynamics Perspective.

Thrombin is a crucial enzyme involved in blood coagulation, essential for maintaining circulatory system integrity and preventing excessive bleeding. However, thrombin is also implicated in pathological conditions such as thrombosis and cancer. Despite the application of various experimental techniques, including X-ray crystallography, NMR spectroscopy, and HDXMS, none of these methods can precisely detect thrombin's dynamics and conformational ensembles at high spatial and temporal resolution. Fortunately, molecular dynamics (MD) simulation, a computational technique that allows the investigation of molecular functions and dynamics in atomic detail, can be used to explore thrombin behavior. This review summarizes recent MD simulation studies on thrombin and its interactions with other biomolecules. Specifically, the 17 studies discussed here provide insights into thrombin's switch between 'slow' and 'fast' forms, active and inactive forms, the role of Na+ binding, the effects of light chain mutation, and thrombin's interactions with other biomolecules. The findings of these studies have significant implications for developing new therapies for thrombosis and cancer. By understanding thrombin's complex behavior, researchers can design more effective drugs and treatments that target thrombin.

Overcrowded 14,14'-Bidibenzo[a,j]anthracenes: Challenges in Syntheses and Atypical Property of Lacking Symmetry-Breaking Charge Transfer (SBCT).

14,14'-Bidibenzo[a,j]anthracenes (BDBAs) were prepared by iridium-catalyzed annulation of 5,5'-biterphenylene with alkynes. The molecular geometries of overcrowded BDBAs were verified by X-ray crystallography. The two dibenzo[a,j]anthryl moieties are connected through the sterically hindered 14 positions, resulting in highly distorted molecular halves. The conformation with a small twist angle between two molecular halves can minimize steric conflicts between the substituents at 1 and 13 positions and the carbon atoms of the central axis, as well as steric clashes between those substituents. One such example is octafluoro-substituted BDBA, where the interplanar angle between two anthryl moieties is approximately 31° (currently the lowest reported value, cf. 81° in 9,9'-bianthracene). The intramolecular interactions and electronic couplings between two molecular halves resulted in upfield 1H NMR signals, redshifted absorption and emission bands, and a reduced HOMO-LUMO gap. Photodynamic investigations on BDBAs indicated that the formation of the conventional symmetry-breaking charge transfer (SBCT) state was suspended by restricted rocking around the central C-C bond. Such a mechanism associated with this highly constrained conformation was examined for the first time.

Tri and hexaosmium clusters bearing saccharinate and diphosphine ligands: Synthesis, structure and fluxionality

The reactivity of saccharinate-bridged triosmium cluster [Os3(CO)10(μ-H)(μ-sac)] (1) with two diphosphines namely bis(diphenylphosphino)methane (dppm) and 1,1′-bis(diphenylphosphino)ferrocene (dppf) have been investigated. Cluster 1 reacts with dppm in refluxing toluene to yield triosmium [Os3(CO)9(κ1-dppm)(μ-H)(μ-sac)] (2), [Os3(CO)9(κ1-dppm)(μ-H)(μ-sac)] (3) and [Os3(CO)8(µ-dppm)(μ-H)(µ-sac)] (4) along with the hexaosmium [{Os3(CO)9(μ-H)(µ-sac)}2(κ2-dppm)] (5). The dppm ligand acts as a monodentate ligand in 2 and 3 by coordinating to a single osmium, while it bridges an osmium-osmium edge in 4 and connects to triosmium units in 6. A similar reaction with dppf furnishes [Os3(CO)9(κ1-dppf)(μ-H)(μ-sac)] (6), [Os3(CO)8(µ-dppf)(μ-H)(μ-sac)] (7) and [{Os3(CO)9(μ-H)(µ-sac)}2(κ2-dppf)] (8) which are dppf analogues of 3–5, respectively. Control experiments confirms that 3 is the precursor of 4 and 5, while 6 is the precursor of 7 and 8. All the products are formed via substitution of carbonyl by the diphosphine, and have been characterized by analytical and spectroscopic data. The molecular structures of 2 and 4–7 have been determined by X-ray crystallography. Cluster 7 shows fluxional behavior in solution at room temperature, and its fluxionality has been probed by VT NMR experiments.