Niobium and Tantalum Halocyanide Clusters: The Complete Family

Synthetic procedures providing straightforward access to the whole family of Nb and Ta halide clusters with terminal cyanide ligands have been developed. Corresponding [M6X12(CN)12]4– (M = Nb, Ta; X = Cl, Br) can be accessed by ligand-exchange procedures from K4Nb6X18 (X = Cl, Br) and Bu4NCN, (Et4N)2[Ta6Cl18] and Bu4NCN and from [Ta6Br12(H2O)4Br2]·4H2O and KCN in moderate to high yields (50–80%). The products were isolated as Bu4N salts. The compounds were investigated both experimentally and by quantum chemistry, revealing correlations between structural, electrochemical, electrostatic, electronic, and topological features as a function of type of metal, halide, and charge

Influence of the Ligand Alkyl Chain Length on the Solubility, Aqueous Speciation, and Kinetics of Substitution Reactions of Water-Soluble M₃S₄ (M = Mo, W) Clusters Bearing Hydroxyalkyl Diphosphines

Water-soluble [M₃S₄X₃(dhbupe)₃]⁺ diphosphino complexes (dhbupe = 1,2-bis­(bis­(hydroxybutyl)­phosphino)­ethane), <b>1</b>⁺ (M = Mo, X = Cl) and <b>2</b>⁺ (M = W; X = Br), have been synthesized by extending the procedure used for the preparation of their hydroxypropyl analogues by reaction of the M₃S₄(PPh₃)₃X₄(solvent)_<i>x</i> molecular clusters with the corresponding 1,2-bis­(bishydroxyalkyl)­diphosphine. The solid state structure of the [M₃S₄X₃(dhbupe)₃]⁺ cation possesses a <i>C</i>₃ symmetry with a cuboidal M₃S₄ unit, and the outer positions are occupied by one halogen and two phosphorus atoms of the diphosphine ligand. At a basic pH, the halide ligands are substituted by hydroxo groups to afford the corresponding [Mo₃S₄(OH)₃(dhbupe)₃]⁺ (<b>1</b>_<b>OH</b>⁺) and [W₃S₄(OH)₃(dhbupe)₃]⁺ (<b>2</b>_<b>OH</b>⁺) complexes. This behavior is similar to that found in 1,2-bis­(bis­(hydroxymethyl)­phosphino)­ethane (dhmpe) complexes and differs from that observed for 1,2-bis­(bis­(hydroxypropyl)­phosphino)­ethane (dhprpe) derivatives. In the latter case, an alkylhydroxo group of the functionalized diphosphine replaces the chlorine ligands to afford Mo₃S₄ complexes in which the deprotonated dhprpe acts in a tridentate fashion. Detailed studies based on stopped-flow, ³¹P­{¹H} NMR, and electrospray ionization mass spectrometry techniques have been carried out in order to understand the solution behavior and kinetics of interconversion between the different species formed in solution: <b>1</b> and <b>1</b>_<b>OH</b>⁺ or <b>2</b> and <b>2</b>_<b>OH</b>⁺. On the basis of the kinetic results, a mechanism with two parallel reaction pathways involving water and OH^– attacks is proposed for the formal substitution of halides by hydroxo ligands. On the other hand, reaction of the hydroxo clusters with HX acids occurs with protonation of the OH^– ligands followed by substitution of coordinated water by X^–

Water-Soluble Mo₃S₄ Clusters Bearing Hydroxypropyl Diphosphine Ligands: Synthesis, Crystal Structure, Aqueous Speciation, and Kinetics of Substitution Reactions

The [Mo₃S₄Cl₃(dhprpe)₃]⁺ (<b>1</b>⁺) cluster cation has been prepared by reaction between Mo₃S₄Cl₄(PPh₃)₃ (solvent)₂ and the water-soluble 1,2-bis­(bis­(hydroxypropyl)­phosphino)­ethane (dhprpe, L) ligand. The crystal structure of [<b>1</b>]₂[Mo₆Cl₁₄] has been determined by X-ray diffraction methods and shows the typical incomplete cuboidal structure with a capping and three bridging sulfides. The octahedral coordination around each metal center is completed with a chlorine and two phosphorus atoms of the diphosphine ligand. Depending on the pH, the hydroxo group of the functionalized diphosphine can substitute the chloride ligands and coordinate to the cluster core to give new clusters with tridentate deprotonated dhprpe ligands of formula [Mo₃S₄(dhprpe-H)₃]⁺ (<b>2</b>⁺). A detailed study based on stopped-flow, ³¹P­{¹H} NMR, and electrospray ionization mass spectrometry techniques has been carried out to understand the behavior of acid–base equilibria and the kinetics of interconversion between the <b>1</b>⁺ and the <b>2</b>⁺ forms. Both conversion of <b>1</b>⁺ to <b>2</b>⁺ and its reverse process occur in a single kinetic step, so that reactions proceed at the three metal centers with statistically controlled kinetics. The values of the rate constants under different conditions are used to discuss on the mechanisms of opening and closing of the chelate rings with coordination or dissociation of chloride

Water-Soluble Mo₃S₄ Clusters Bearing Hydroxypropyl Diphosphine Ligands: Synthesis, Crystal Structure, Aqueous Speciation, and Kinetics of Substitution Reactions

The [Mo₃S₄Cl₃(dhprpe)₃]⁺ (<b>1</b>⁺) cluster cation has been prepared by reaction between Mo₃S₄Cl₄(PPh₃)₃ (solvent)₂ and the water-soluble 1,2-bis­(bis­(hydroxypropyl)­phosphino)­ethane (dhprpe, L) ligand. The crystal structure of [<b>1</b>]₂[Mo₆Cl₁₄] has been determined by X-ray diffraction methods and shows the typical incomplete cuboidal structure with a capping and three bridging sulfides. The octahedral coordination around each metal center is completed with a chlorine and two phosphorus atoms of the diphosphine ligand. Depending on the pH, the hydroxo group of the functionalized diphosphine can substitute the chloride ligands and coordinate to the cluster core to give new clusters with tridentate deprotonated dhprpe ligands of formula [Mo₃S₄(dhprpe-H)₃]⁺ (<b>2</b>⁺). A detailed study based on stopped-flow, ³¹P­{¹H} NMR, and electrospray ionization mass spectrometry techniques has been carried out to understand the behavior of acid–base equilibria and the kinetics of interconversion between the <b>1</b>⁺ and the <b>2</b>⁺ forms. Both conversion of <b>1</b>⁺ to <b>2</b>⁺ and its reverse process occur in a single kinetic step, so that reactions proceed at the three metal centers with statistically controlled kinetics. The values of the rate constants under different conditions are used to discuss on the mechanisms of opening and closing of the chelate rings with coordination or dissociation of chloride

Water-Soluble Mo₃S₄ Clusters Bearing Hydroxypropyl Diphosphine Ligands: Synthesis, Crystal Structure, Aqueous Speciation, and Kinetics of Substitution Reactions

The [Mo₃S₄Cl₃(dhprpe)₃]⁺ (<b>1</b>⁺) cluster cation has been prepared by reaction between Mo₃S₄Cl₄(PPh₃)₃ (solvent)₂ and the water-soluble 1,2-bis­(bis­(hydroxypropyl)­phosphino)­ethane (dhprpe, L) ligand. The crystal structure of [<b>1</b>]₂[Mo₆Cl₁₄] has been determined by X-ray diffraction methods and shows the typical incomplete cuboidal structure with a capping and three bridging sulfides. The octahedral coordination around each metal center is completed with a chlorine and two phosphorus atoms of the diphosphine ligand. Depending on the pH, the hydroxo group of the functionalized diphosphine can substitute the chloride ligands and coordinate to the cluster core to give new clusters with tridentate deprotonated dhprpe ligands of formula [Mo₃S₄(dhprpe-H)₃]⁺ (<b>2</b>⁺). A detailed study based on stopped-flow, ³¹P­{¹H} NMR, and electrospray ionization mass spectrometry techniques has been carried out to understand the behavior of acid–base equilibria and the kinetics of interconversion between the <b>1</b>⁺ and the <b>2</b>⁺ forms. Both conversion of <b>1</b>⁺ to <b>2</b>⁺ and its reverse process occur in a single kinetic step, so that reactions proceed at the three metal centers with statistically controlled kinetics. The values of the rate constants under different conditions are used to discuss on the mechanisms of opening and closing of the chelate rings with coordination or dissociation of chloride