A Copper(II)‐Nitrite Complex Hydrogen‐Bonded to a Protonated Amine in the Second‐Coordination‐Sphere

Nitrous acid (HONO) plays pivotal roles in various metal-free as well metal-mediated routes relevant to biogeochemistry, atmospheric chemistry, and mammalian physiology. While the metastable nature of HONO hinders detailed investigations into its reactivity at a transition metal site, this report herein utilizes heteroditopic copper(II) cryptate [oC]CuII featuring proton-responsive second-coordination-sphere located suitable distance from [CuII](ONO) core, thereby enabling isolation [CuII](κ1-ONO⋅⋅⋅H+) complex (2H-NO2). A set complementary analytical studies (UV-vis, 14N/15N FTIR, 15N NMR, HRMS, EPR, CHN) on 2H-NO2 15N-isotopomer (2H-15NO2) reveals formulation {[oCH]CuII(κ1-ONO)}(ClO4)2. Non-covalent interaction index (NCI) based reduced density gradient (RDG) analysis {[oCH]CuII(κ1-ONO)}2+ discloses H-bonding between apical 3° ammonium site nitrite anion bound site. The FTIR spectra species (2H-NO2) shows shift NH vibrational feature lower wavenumber due with nitrite. profile towards anaerobic nitration substituted phenol (2,4-DTBP) is distinctly different relative that closely related tripodal [CuII]-nitrite complexes (1-NO2/3-NO2/4-NO2).