Assignment of photoelectron spectra of silatranes: first ionization energies and the nature of the dative Si←N contact

Abstract

The problematic experimental photoelectron spectra of fluoro- and ethoxy-silatranes, XSi[OCH2CH2]3N (X = F and OEt), were assigned using theoretical spectra obtained by combining the OVGF//CCSD vertical ionization energies with the vibrational widths of the electronic transitions (linear vibronic coupling formalism, LVC). Taking into account the overlapping of the silatrane bands with the bands of probable impurities, bicyclic amines, (OH)XSi(OCH2CH2)2NCH2CH2OH, allowed us to reliably determine the position of the low-energy bands (at ∼9.7 eV for F- and at ∼9.2 eV for EtO-silatrane) associated with the ionization from a nitrogen lone pair level. For XSi[OCH2CH2]3N (X = F, H, OEt, Me), the correlation between the first vertical ionization energies, VIEs1, and the geometrical, electronic and orbital characteristics of the Si←N bonding was found. Its analysis suggests that the Si←N coordination in silatranes is orbital-controlled rather than charge-controlled.

Dipole-Bound Anions of Intramolecular Complexes

“…Silatranes, XSi­(OCH 2 CH 2 ) 3 N (see Figure ), are highly polar (∼6–9 D) molecular cages with labile, internal Si ← N dative bonds. These bonds are strongly sensitive to the nature of their axial substituents, X, and to external factors. − An attractive interaction Si ← N in silatranes predetermines the peculiarity of their structure, unusual spectral characteristics, and reactivity as well as a wide spectrum of biological activity. , …”

“…Here we present results from our combined experimental–theoretical study of 1-hydro-silatrane ( HS ) and 1-fluoro-silatrane ( FS ) and their anions. These two were initially selected because they do not have low-lying vacant orbitals (primarily of π-type) − and therefore are candidates for forming dipole-bound anions, HS – and FS – . It is also important to note that HS and FS differ in their Si ← N bond strengths , and that their geometries are known from electron diffraction studies. , …”

Electrochemical Oxidation and Radical Cations of Structurally Non‐rigid Hypervalent Silatranes: Theoretical and Experimental Studies

“…Theoretical considerations suggest the shift of E 0 of a proper oxidized silatrane with respect to a model NR 3 to be dependent on the intensity of N→Si coordination when varying X. This intensity can be described using the interatomic N⋅⋅⋅Si distance ( d SiN ), the Mulliken ( P SiN ) and Wiberg ( W SiN ) populations of the N→Si contact, the NBO energy of the bonding interaction between the N s lone pair (LP), and the antibonding orbital of the Si‐X bond obtained as a second‐order perturbation energy ( E (2)[n n ,σ* SiX ]), the AIM energy of the N→Si interaction ( E SiN ), the degree of the electron density transfer from the nitrogen LP orbital (Δ N [n n ]) to an acceptor moiety XSiO 3 during the formation of the N→Si bond, and others . All these strength characteristics of the N→Si bond, as a rule, vary in a consistent manner with the variation of X .…”

“…This intensity can be described using the interatomic N⋅⋅⋅Si distance ( d SiN ), the Mulliken ( P SiN ) and Wiberg ( W SiN ) populations of the N→Si contact, the NBO energy of the bonding interaction between the N s lone pair (LP), and the antibonding orbital of the Si‐X bond obtained as a second‐order perturbation energy ( E (2)[n n ,σ* SiX ]), the AIM energy of the N→Si interaction ( E SiN ), the degree of the electron density transfer from the nitrogen LP orbital (Δ N [n n ]) to an acceptor moiety XSiO 3 during the formation of the N→Si bond, and others . All these strength characteristics of the N→Si bond, as a rule, vary in a consistent manner with the variation of X . Therefore it could be expected that the potentials of the proper oxidation of 1 to be closely related to the geometrical, energetic, electronic, and orbital parameters of the N→Si attractive interaction in the parent neutral molecule.…”

“…The geometries of 1 were optimized in the restricted variants of the MP2/6–311G(2d,p) and B3PW91/6–311G(d,p) methods and the unrestricted variants of these methods were applied for geometry optimizations for species 1 .+ , according to previously reported data …”