title: Reversible capture of small molecules on bimetallaborane clusters: synthesis, structural characterization, and photophysical aspects.
abstract: Metallaborane compounds containing two adjacent metal atoms, [(PMe(2)Ph)(4)MM'B(10)H(10)] (where MM' = Pt(2), 1; PtPd, 7; Pd(2), 8), have been synthesized, and their propensity to sequester O(2), CO, and SO(2) and to then release them under pulsed and continuous irradiation are described. Only [(PMe(2)Ph)(4)Pt(2)B(10)H(10)], 1, undergoes reversible binding of O(2) to form [(PMe(2)Ph)(4)(O(2))Pt(2)B(10)H(10)] 3, but solutions of 1, 7, and 8 all quantitatively take up CO across their metal-metal vectors to form [(PMe(2)Ph)(4)(CO)Pt(2)B(10)H(10)] 4, [(PMe(2)Ph)(4)(CO)PtPdB(10)H(10)] 10, and [(PMe(2)Ph)(4)(CO)Pd(2)B(10)H(10)] 11, respectively. Crystallographically determined interatomic M-M distances and infrared CO stretching frequencies show that the CO molecule is bound progressively more weakly in the sequence {PtPt} > {PtPd} > {PdPd}. Similarly, SO(2) forms [(PMe(2)Ph)(4)(SO(2))Pt(2)B(10)H(10)] 5, [(PMe(2)Ph)(4)(SO(2))PtPdB(10)H(10)] 12, and [(PMe(2)Ph)(4)(SO(2))Pd(2)B(10)H(10)] 13 with progressively weaker binding of the SO(2) molecule. The uptake and release of gas molecules are accompanied by changes in their absorption spectra. Nanosecond transient absorption spectroscopy clearly shows that the O(2) and CO molecules are liberated from the bimetallic binding site with high quantum yields of about 0.6. For 3, in addition to dioxygen release in the triplet ground state, singlet oxygen O(2)((1)Δ(g)) was also detected with a quantum yield <0.01. In most cases, the release and rebinding of the gas molecules can be cycled with little photodegradation of the compounds. Femtosecond transient absorption spectroscopy further reveals that the photorelease of the O(2) and CO molecules, from 3 and 4 respectively, is an ultrafast process taking place on a time scale of tens of picoseconds. For SO(2), the release is even faster (<1 ps), but only in the case of mixed metal PtPd adducts, most probably because of the metal-metal bonding asymmetry in the mixed metal clusters; for the corresponding symmetric Pt(2) and Pd(2) adducts, 5 and 13, the release of SO(2) is significantly slower (>1 ns). All these compounds may have potential to serve as light-triggered local and instantaneous sources of the studied gases.
authors.affiliation: Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic, v.v.i., 250 68 Husinec-Řež, Czech Republic. jbould@gmail.com
authors.forename: Jonathan
authors.initials: J
authors.lastname: Bould
authors.forename: Tomáš
authors.initials: T
authors.lastname: Baše
authors.forename: Michael G S
authors.initials: MG
authors.lastname: Londesborough
authors.forename: Luis A
authors.initials: LA
authors.lastname: Oro
authors.forename: Ramón
authors.initials: R
authors.lastname: Macías
authors.forename: John D
authors.initials: JD
authors.lastname: Kennedy
authors.forename: Pavel
authors.initials: P
authors.lastname: Kubát
authors.forename: Marcel
authors.initials: M
authors.lastname: Fuciman
authors.forename: Tomáš
authors.initials: T
authors.lastname: Polívka
authors.forename: Kamil
authors.initials: K
authors.lastname: Lang
mesh_terms: D001880:Boranes / Q000138:chemical synthesis* / Q000737:chemistry; D002248:Carbon Monoxide / Q000737:chemistry*; D018360:Crystallography, X-Ray; D010100:Oxygen / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D010777:Photochemistry; D010984:Platinum / Q000737:chemistry*; D011789:Quantum Theory; D013458:Sulfur Dioxide / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D001880:Boranes; D013458:Sulfur Dioxide; D010984:Platinum; D010165:Palladium; D002248:Carbon Monoxide; D010100:Oxygen