A Systematic Investigation of Coinage Metal Carbonyl Complexes Stabilized by Fluorinated Alkoxy Aluminates

The reaction of CuI, AgI, and AuI salts with carbon monoxide in the presence of weakly coordinating anions led to known and structurally unknown non-classical coinage metal carbonyl complexes [M(CO)n][A] (A=fluorinated alkoxy aluminates). The coinage metal carbonyl complexes [Cu(CO)n(CH2Cl2)m]+[A]− (n=1, 3; m=4−n), [Au2(CO)2Cl]+[A]−, [(OC)nM(A)] (M=Cu: n=2; Ag: n=1, 2) as well as [(OC)3Cu⋅⋅⋅ClAl(ORF)3] and [(OC)Au⋅⋅⋅ClAl(ORF)3] were analyzed with X-ray diffraction and partially IR and Raman spectroscopy. In addition to these structures, crystallographic and spectroscopic evidence for the existence of the tetracarbonyl complex [Cu(CO)4]+[Al(ORF)4]− (RF=C(CF3)3) is presented; its formation was analyzed with the help of theoretical investigations and Born–Fajans–Haber cycles. We discuss the limits of structure determinations by routine X-ray diffraction methods with respect to the CO bond lengths and apply the experimental CO stretching frequencies for the prediction of bond lengths within the carbonyl ligand based on a correlation with calculated data. Moreover, we provide a simple explanation for the reported, partly confusing and scattered CO stretching frequencies of [CuI(CO)n] units.