Interplay of a nitro group and metal ions: from coordinative binding to noncovalent semicoordination

Abstract

The characteristic feature of the solid-state structures of Group 10 iodonium tetracyanidometallates [Ar¹Ar²I]₂[Ni(CN)₄]·CH₂Cl₂ (Ar¹/Ar² = 2,4,6-(MeO)₃C₆H₂/4-NO₂-C₆H₄; 1·CH₂Cl₂), [Ar¹Ar²I]₂[Pd(CN)₄]·MeNO₂ (2·MeNO₂), and [Ar¹Ar²I]₂[Pt(CN)₄]·MeNO₂ (3·MeNO₂) is the presence of M⋯O_NO2 semicoordination between any one of the metal sites and the nitroaryl group. Although there should be a continuum between covalent and noncovalent interactions, both in the geometry and bonding description, we succeeded in identifying the interatomic distances and the corresponding intervals, which are responsible for the covalent (2.0–2.3 Å) and noncovalent (>2.5 Å) bindings of various nitro groups. The geometric parameters of the three structures are in good agreement with the latter range. The noncovalent interactions including M⋯O_NO2 interactions and I⁺⋯NC–M(CN)₃ halogen bonds (HaB) were explored using DFT calculations. Several computational techniques, such as molecular electrostatic potential (MEP) surfaces, QTAIM/NCIplot topological analysis, electron localization function (ELF) analysis, electron density (ED) and electrostatic potential (ESP) profiles analysis (ED/ESP) and energy decomposition analysis (EDA using the Kitaura–Morokuma method) were employed to comprehensively characterize these interactions. Theoretical insights revealed that both M⋯O_NO2 and HaB interactions significantly affect the molecular structures. In-depth examinations using ELF, ED/ESP and EDA methods highlighted the predominant influence of electrostatic effects and confirmed the philicities in the M⋯O interactions. This study is the first that found a place for NO₂-group semicoordination in the entire palette of metal-involving interactions of various nitro groups.