Spectroscopic characterization of heteronuclear iron-chromium carbonyl cluster anions.

Infrared photodissociation spectroscopy has been used to investigate CrFe(CO)n- (n = 4-9) clusters in the gas phase. Comparison of the observed spectra in the carbonyl stretching frequency region with those predicted for low-lying isomers by DFT calculations showed that the observed CrFe(CO)n- (n = 4-8) clusters could be characterized to have Cr-Fe bonded (OC)4Fe-Cr(CO)n-4 structures. The coexistence of isomers with the (OC)Fe-Cr(CO)5 and (OC)3Fe-Cr(CO)4 structures was also observed for CrFe(CO)6- and CrFe(CO)7- anions, respectively. The CrFe(CO)n- (n = 4-8) complexes were strongly bonded systems. The CrFe(CO)8- complex was a coordination-saturated cluster, and the CrFe(CO)9- anion was characterized to contain a CrFe(CO)8- core tagged by one CO molecule. Bonding analysis revealed that the Cr-Fe bonds in the CrFe(CO)n- (n = 4-8) clusters were predominantly σ-type single bonds. The iron center in the Fe(CO)4 moiety and the chromium center in the Cr(CO)5 moiety fulfilled the 18-electron configuration for the CrFe(CO)n- (n = 4-6) clusters. As in the CrFe(CO)n- (n = 7, 8) complexes, the iron center in the Fe(CO)4 moiety exhibited a 17-electron configuration, while the chromium center in the Cr(CO)4 moiety exhibited a 16-electron configuration. These findings provide valuable insights into the structure and bonding mechanism of heterometallic carbonyl clusters.

Infrared photodissociation spectroscopy of heteronuclear group 15 metal-iron carbonyl cluster anions AmFe(CO)n- (A = Sb, Bi; m, n = 2, 3).

Heteronuclear group 15 metal-iron carbonyl cluster complexes of AmFe(CO)n- (A = Sb, Bi; m, n = 2-3) were generated in the gas phase and studied by infrared photodissociation spectroscopy in the carbonyl stretching region. Their structures were determined by comparing the experimental spectra with predicted spectra derived from DFT calculations at the B3LYP and BP86 levels. All of the AmFe(CO)n- cluster anions were determined to have Fe(CO)n- fragments with all of the CO ligands terminally bonded to the iron center, and they can be regarded as being formed via the interactions of the neutral group 15 metal clusters with the Fe(CO)n- fragments. Bonding analyses indicated that each A2Fe(CO)n- (n = 2, 3) cluster anion contained two A-Fe single bonds and one A-A double bond. Each A3Fe(CO)n- (n = 2, 3) cluster anion involved three A-Fe single bonds and three A-A single bonds. There is an isolobal relationship between the Fe(CO)3- group and the group 15 atoms. The substitution of an Fe(CO)3- group in place of one A atom in the tetrahedral A4 molecule resulted in an A3Fe(CO)3- cluster anion with the closed-shell electronic configuration for all the group 15 metals and iron atoms.

Infrared Photodissociation Spectroscopy of Heteronuclear Arsenic-Iron Carbonyl Cluster Anions.

Heteronuclear arsenic-iron carbonyl cluster anions AsmFe(CO)n- (m, n = 2, 3) have been generated in the gas phase and investigated by mass-selected infrared photodissociation spectroscopy and density functional theory calculations at the B3LYP/BP86/TPSS levels. All the AsmFe(CO)n- (m, n = 2, 3) cluster anions are determined to contain Fe(CO)n- fragments, which can be regarded as being formed by replacing one arsenic atom of the arsenic clusters Asm+1 with the Fe(CO)n- group. Bonding analyses indicated that each As2Fe(CO)n- (n = 2, 3) cluster anion involves two Fe-As single bonds and one As-As double bond. Each As3Fe(CO)n- (n = 2, 3) cluster anion has three Fe-As single bonds and three As-As single bonds. The Fe(CO)3- group with a 15-electron configuration is valence isoelectronic to the As atom and can serve as a building block for forming heteronuclear arsenic-iron carbonyl clusters.