- Email: [email protected]
The geometric and electronic structures of small metal clusters of group 1B metals
A307 Surface Science 156 (1985) 201-205 North-Holland, Amsterdam
201
IR EVIDENCE FOR T H E F O R M A T I O N OF CO 2 T R A N S I T I O N - M E T A L A T O M C O M P L E X E S IN L O W - T E M P E R A T U R E M A T R I C E S Jo~lle MASCETTI and Michel TRANQUILLE Laboratoire de Spectroscopic Infrarouge, LA 124, Universitb de Bordeaux L 351 Cours de la Libbration, F-33405 Talence Cbdex, France Received 20 July 1984 The interactions of C O 2 with several first-row transition-metal atoms in low-temperature matrices (15 K) have been investigated by infrared spectroscopy, In pure CO 2 matrices, Ti, V, Cr, Fe, Co, Ni and Cu form complexes with CO 2 in a bent arrangement, as shown by the new absorptions arising after deposition and isotopic substitutions with 13CO2 and C1SO2. These complexes are stable only at very low temperatures. In the case of Ni, annealing above 80 K leads to the reduction of carbon dioxide into carbon monoxide with simultaneous formation of nickel carbonyl complexes.
206
Surface Science 156 (1985) 206-213 North-Holland, Amsterdam
A S T R U C T U R A L INVESTIGATION O N S M A L L G O L D C L U S T E R S BY EXAFS A. B A L E R N A , E. BERNIERI, P. PICOZZI, A. REALE and S. SANTUCCI Istituto di Fisica, Universita" dell'Acluila, L'Acluila, Italy
and E. B U R A T T I N I and S. MOBILIO INFN, Laboratori Nazionali Frascati, 1-00044 Frascati, Italy Received 13 July 1984; accepted for publication 24 September 1984 A structural investigation using extended X-ray absorption fine structure (EXAFS) spectra, recorded on Au metal clusters whose average dimension ranges from 11 to 50 A, is reported. Data analysis performed on the first and second coordination shells, showed the presence of interatomic distance contractions, a lowering of the mean coordination number and an increasing EXAFS Debye-Waller factor at decreasing mean diameter of the clusters. No structural changes to icosahedra have been observed.
214
Surface Science 156 (1985) 214-227 North-Holland, Amsterdam
T H E GEOMETRIC A N D ELECTRONIC S T R U C T U R E S OF S M A L L METAL C L U S T E R S OF G R O U P IB METALS * J.A. H O W A R D and R. SUTCLIFFE Division of Chemistry, National Research Council of Canada, Ottawa, Ontario, Canada KIA OR9
and
A308 B. M I L E
Department of Chemist(); and Bioehemtstrv. Lit~erpool Polvteehmc, Bvrom Street, Li~,erpool L3 3A £~ UK Received 13 July 1984; accepted for publication 1 September 1984
Small clusters of the coinage metals have been prepared in inert organic matrices m a rotating cryostat at 77 K by a combination of low-temperature quench techniques with metal vapourisation and photoaggregation methods. The ESR spectra of the homonuclear and heteronuclear trimer and pentamer clusters allow their geometric and electronic structures to be determined experimentally for the first time and allow a choice to be made between the various theoretical calculations which predict either linear chains containing up to 30 atoms or a change from linear to three-dimensional structures between 4 and 5 atoms. The trimer clusters Cu 3, Ag~, Au~ and CuAgCu are slightly bent with 2B2 electronic ground state in C=,. symmetry with the unpaired electron located mainly on the terminal atoms. The s orbital contribution in Cu3 is 60% while in Aga, Au 3 and CuAgCu it is 80-90%; this indicates considerable d orbital contribution in Cu 3 which is probably due to the much closer proximity of the energies of the d and s levels in copper. Interestingly it appears that insertion of a single silver atom between the two copper atoms is sufficient to "'insulate" the copper d levels from each other. The homonuclear pentamers Cu 5 and Ags are Jahn Teller distorted trigonal pyramids with a 2B2 in C2~ ground electronic state. The unpaired electron is located mainly on two of the equatorial metal atoms with a small spin population on the third equatorial atom and an even smaller population on the two axial atoms. There is a 40% contribution from the d orbitals of even the silver atoms in the tightly packed pentamer. The heteronuclear pentamers CuAg 4 and CuzAg 3 have a trigonal bipyramidal array of metal atoms and 2A I in C3~ and 2A'~ in D3h electronic ground states, respectively. The reaction of ('u 3 and Cu 5 with molecular oxygen at 77 K results in an almost complete transfer of an electron into the lv~ orbitals of the oxygen with the formation of the tight ion pairs Cu,,+ O2 in which all the copper nuclei have equivalent hyperfine interactions and have an equilateral triangular and regular trigonal bipyramida~ configuration, respectively.
228
Surface Science 156 (1985) 228 233 North-Holland, Amsterdam
X-RAY A B S O R P T I O N FINE S T R U C T U R E STUDY OF SMALL METAL C L U S T E R S ISOLATED IN RARE-GAS S O L I D S P.A. MONTANO
and H. PURDUM
Department of Physics, West Virginia Unt~ersio, , Mor ffantown. ~'est b'irffima 26506, USA G.K. SHENOY
and T.I. MORRISON
Argonne National Laborato(v. Ar~onne, Illinois, USA and W. SCHULZE
Fritz- Haber- Institute der Max- Planck -Gesellschajt, Faradaywe~ 4 t3, D- l O00 Berhn _¢3, t:ed. Rep. of Germany Received 13 July 1984 The use of extended X-ray absorption fine structure (EXAFS) to determine the interatomic distances in small metal clusters is of considerable scientific as well as technical importance, we have used synchrotron radiation to study the near edge structure as well as the EXAFS spectra of
201
IR EVIDENCE FOR T H E F O R M A T I O N OF CO 2 T R A N S I T I O N - M E T A L A T O M C O M P L E X E S IN L O W - T E M P E R A T U R E M A T R I C E S Jo~lle MASCETTI and Michel TRANQUILLE Laboratoire de Spectroscopic Infrarouge, LA 124, Universitb de Bordeaux L 351 Cours de la Libbration, F-33405 Talence Cbdex, France Received 20 July 1984 The interactions of C O 2 with several first-row transition-metal atoms in low-temperature matrices (15 K) have been investigated by infrared spectroscopy, In pure CO 2 matrices, Ti, V, Cr, Fe, Co, Ni and Cu form complexes with CO 2 in a bent arrangement, as shown by the new absorptions arising after deposition and isotopic substitutions with 13CO2 and C1SO2. These complexes are stable only at very low temperatures. In the case of Ni, annealing above 80 K leads to the reduction of carbon dioxide into carbon monoxide with simultaneous formation of nickel carbonyl complexes.
206
Surface Science 156 (1985) 206-213 North-Holland, Amsterdam
A S T R U C T U R A L INVESTIGATION O N S M A L L G O L D C L U S T E R S BY EXAFS A. B A L E R N A , E. BERNIERI, P. PICOZZI, A. REALE and S. SANTUCCI Istituto di Fisica, Universita" dell'Acluila, L'Acluila, Italy
and E. B U R A T T I N I and S. MOBILIO INFN, Laboratori Nazionali Frascati, 1-00044 Frascati, Italy Received 13 July 1984; accepted for publication 24 September 1984 A structural investigation using extended X-ray absorption fine structure (EXAFS) spectra, recorded on Au metal clusters whose average dimension ranges from 11 to 50 A, is reported. Data analysis performed on the first and second coordination shells, showed the presence of interatomic distance contractions, a lowering of the mean coordination number and an increasing EXAFS Debye-Waller factor at decreasing mean diameter of the clusters. No structural changes to icosahedra have been observed.
214
Surface Science 156 (1985) 214-227 North-Holland, Amsterdam
T H E GEOMETRIC A N D ELECTRONIC S T R U C T U R E S OF S M A L L METAL C L U S T E R S OF G R O U P IB METALS * J.A. H O W A R D and R. SUTCLIFFE Division of Chemistry, National Research Council of Canada, Ottawa, Ontario, Canada KIA OR9
and
A308 B. M I L E
Department of Chemist(); and Bioehemtstrv. Lit~erpool Polvteehmc, Bvrom Street, Li~,erpool L3 3A £~ UK Received 13 July 1984; accepted for publication 1 September 1984
Small clusters of the coinage metals have been prepared in inert organic matrices m a rotating cryostat at 77 K by a combination of low-temperature quench techniques with metal vapourisation and photoaggregation methods. The ESR spectra of the homonuclear and heteronuclear trimer and pentamer clusters allow their geometric and electronic structures to be determined experimentally for the first time and allow a choice to be made between the various theoretical calculations which predict either linear chains containing up to 30 atoms or a change from linear to three-dimensional structures between 4 and 5 atoms. The trimer clusters Cu 3, Ag~, Au~ and CuAgCu are slightly bent with 2B2 electronic ground state in C=,. symmetry with the unpaired electron located mainly on the terminal atoms. The s orbital contribution in Cu3 is 60% while in Aga, Au 3 and CuAgCu it is 80-90%; this indicates considerable d orbital contribution in Cu 3 which is probably due to the much closer proximity of the energies of the d and s levels in copper. Interestingly it appears that insertion of a single silver atom between the two copper atoms is sufficient to "'insulate" the copper d levels from each other. The homonuclear pentamers Cu 5 and Ags are Jahn Teller distorted trigonal pyramids with a 2B2 in C2~ ground electronic state. The unpaired electron is located mainly on two of the equatorial metal atoms with a small spin population on the third equatorial atom and an even smaller population on the two axial atoms. There is a 40% contribution from the d orbitals of even the silver atoms in the tightly packed pentamer. The heteronuclear pentamers CuAg 4 and CuzAg 3 have a trigonal bipyramidal array of metal atoms and 2A I in C3~ and 2A'~ in D3h electronic ground states, respectively. The reaction of ('u 3 and Cu 5 with molecular oxygen at 77 K results in an almost complete transfer of an electron into the lv~ orbitals of the oxygen with the formation of the tight ion pairs Cu,,+ O2 in which all the copper nuclei have equivalent hyperfine interactions and have an equilateral triangular and regular trigonal bipyramida~ configuration, respectively.
228
Surface Science 156 (1985) 228 233 North-Holland, Amsterdam
X-RAY A B S O R P T I O N FINE S T R U C T U R E STUDY OF SMALL METAL C L U S T E R S ISOLATED IN RARE-GAS S O L I D S P.A. MONTANO
and H. PURDUM
Department of Physics, West Virginia Unt~ersio, , Mor ffantown. ~'est b'irffima 26506, USA G.K. SHENOY
and T.I. MORRISON
Argonne National Laborato(v. Ar~onne, Illinois, USA and W. SCHULZE
Fritz- Haber- Institute der Max- Planck -Gesellschajt, Faradaywe~ 4 t3, D- l O00 Berhn _¢3, t:ed. Rep. of Germany Received 13 July 1984 The use of extended X-ray absorption fine structure (EXAFS) to determine the interatomic distances in small metal clusters is of considerable scientific as well as technical importance, we have used synchrotron radiation to study the near edge structure as well as the EXAFS spectra of