Spectroscopic Studies of Mixed Amine Carbonyl Complexes of d6 Structure. I. Visible and Ultraviolet Absorption Spectra of Diamine-tetracarbonyl Complexes of Chromium(0), Molybdenum(0) and Tungsten(0)

Abstract

Chromium(0), molybdenum(0) and tungsten(0) complexes of [M.(CO)4AA]° type (AA= ethylenediamine (en), l-propylenediamine (l-pn), trimethylenediamine (tn), bipyridyl (bp), and phenanthroline (phen) ; l-pn and to derivatives are new compounds) have been synthesized and their absorption spectra, rotatory dispersion (RD) and circular dichroism (CD) measured in methanol at room temperature. The nature of the absorption bands has been discussed by comparing them with one another and with those of hexacarbonyl-and piperidinepentacarbonyl complexes of these elements. The peaks in the region 23000 to 25000 cm -1 seem to be due to spinallowed d-d transition. The bands at 30000 to 33000 cm-1 appears to correspond to the metal to carbonyl charge transfer band of hexacarbonyls at ca. 36000 cm-1. Besides them, complexes of aromatic amines (bp and phen) show broad and strong bands at 21000 to 22000 cm -I which seem to owe to metal to amine charge transfer.

Wavelength-Dependent Photochemistry of W(CO)4(en) (en = Ethylenediamine): Evidence for Distinct Chemical Reactivities from Singlet and Triplet Ligand Field Excited States

“…The electronic absorption spectrum of W(CO) 4 (en) in acetonitrile at room temperature is shown in Figure . The complex exhibits a band maximum at 397 nm which has been previously assigned to the lowest lying spin-allowed LF transition. , A low-energy shoulder is also observed at 450 nm; this feature is only revealed by the tungsten derivative and has been attributed to the lowest lying spin-forbidden LF transition. , In accordance with the LF assignment, these absorption bands are not significantly solvent dependent. Higher energy LF and W → π*(CO) charge transfer transitions are associated with the region immediately below 320 nm.…”

“…Purity of W(CO) 4 (en) was confirmed by comparison with literature UV−vis and infrared data. UV−vis, W(CO) 4 (en) in CH 3 CN: 397 nm (ε = 1400 M -1 cm -1 ), 450 (sh) nm (ε = 400 M -1 cm -1 ) [lit . in CH 3 OH: 397 nm (ε = 1400 M -1 cm -1 ), 450 (sh) nm (ε = 400 M -1 cm -1 )].…”

Photochemistry of metal carbonyls

“…37 The data for amine complexes In Table II strongly support the notion that the first band in c/'s-M(CO)4(X)2 and M(CO)sX should occur at similar energies, and the lowest bands have been assigned as LF. 21,22 Only the W complexes exhibit the familiar shoulder associated with the lowest singlet -* triplet absorption. Like the M(CO)e11 and many M(CO)s(X) complexes, the bands for c/'s-M(CO)4(X)2 exhibit only a very modest solvent dependence.22 For the M(CO)4(phenanthrollne) complexes though, a very large solvent effect on the first transition Is observed.…”

Electronic Structure of the Lowest Excited States of Cr(CO)4(2,2‘-bipyridine): A CASSCF/CASPT2 Analysis

“…Another maximum at 30 000 cm -1 (ε = 6650 M -1 cm -1 ) superimposed on a strong broad absorption was observed 6 in C 6 H 6 . Both UV absorptions for the second unoccupied π* bpy,a 2 and for π* CO orbitals, as well as bpy-localized intraligand transitions, are expected in this spectral region. ,, On excitation at 25 000 cm -1 , Cr(CO) 4 (bpy) shows in benzene solution , two weak emission bands at 16 000 and 12 850 cm -1 , respectively. They were assigned to emissions from two different MLCT states which, presumably, are in thermal equilibrium.…”

“…CrCO) 4 (bpy) Absorption/Emission Spectra. Cr(CO) 4 (bpy) exhibits ,,,,, an intense absorption band in the visible region and even stronger absorption in the UV region, at energies above ca. 22 000 cm -1 .…”