10.1021/ja3040762.s001 Kiplangat Sutter Kiplangat Sutter Jochen Autschbach Jochen Autschbach Computational Study and Molecular Orbital Analysis of NMR Shielding, Spin–Spin Coupling, and Electric Field Gradients of Azido Platinum Complexes American Chemical Society 2012 Molecular Orbital Analysis azide σ bonds 2 p character Electric Field Gradients 14 N NMR signals 15 N NMR data N chemical shifts azido 14 N NMR signals EFG N α nuclei N β signals delocalized π system DFT chemical shifts N γ N β chemical shifts N β nuclei Azido Platinum Complexes 195Pt 14 N N α 2012-08-15 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Computational_Study_and_Molecular_Orbital_Analysis_of_NMR_Shielding_Spin_Spin_Coupling_and_Electric_Field_Gradients_of_Azido_Platinum_Complexes/2496190 <sup>195</sup>Pt, <sup>14</sup>N, and <sup>15</sup>N NMR data for five azido (N<sub>3</sub><sup>–</sup>) complexes are studied using relativistic density functional theory (DFT). Good agreement with experiment is obtained for Pt and N chemical shifts as well as Pt–N <i>J</i>-coupling constants. Calculated <sup>14</sup>N electric field gradients (EFGs) reflect experimentally observed trends for the line broadening of azido <sup>14</sup>N NMR signals. A localized molecular orbital analysis of the nitrogen EFGs and chemical shifts is performed to explain some interesting trends seen experimentally and in the first-principles calculations: (i) <sup>14</sup>N NMR signals for the Pt-coordinating (N<sub>α</sub>) nuclei in the azido ligands are much broader than for the central (N<sub>β</sub>) or terminal (N<sub>γ</sub>) atoms. The N<sub>β</sub> signals are particularly narrow; (ii) compared to N<sub>γ</sub>, the N<sub>α</sub> nuclei are particularly strongly shielded; (iii) N<sub>β</sub> nuclei have much larger chemical shifts than N<sub>α</sub> and N<sub>γ</sub> ; and (iv) The Pt–N<sub>α</sub> <i>J</i>-coupling constants are small in magnitude when considering the formal sp hybridization of N<sub>α</sub> . It is found that for N<sub>α</sub> a significant shielding reduction due to formation of the dative N<sub>α</sub>–Pt bond is counterbalanced by an increased shielding from spin–orbit (SO) coupling originating at Pt. Upon coordination, the strongly delocalized π system of free azide localizes somewhat on N<sub>β</sub> and N<sub>γ</sub> . This effect, along with rehybridization at N<sub>α</sub> upon bond formation with Pt, is shown to cause a deshielding of N<sub>γ</sub> relative to N<sub>α</sub> and a strong increase of the EFG at N<sub>α</sub> . The large 2p character of the azide σ bonds is responsible for the particularly high N<sub>β</sub> chemical shifts. The nitrogen s-character of the Pt–N<sub>α</sub> bond is low, which is the reason for the small <i>J</i>-coupling. Similar bonding situations are likely to be found in azide complexes with other transition metals.