Electrophilic–Nucleophilic Dualism of Nickel(II) toward Ni···I Noncovalent Interactions: Semicoordination of Iodine Centers via Electron Belt and Halogen Bonding via σ-Hole

Abstract

The nitrosoguanidinate complex [Ni{NH═C(NMe₂)NN(O)}₂] (1) was cocrystallized with I₂ and sym-trifluorotriiodobenzene (FIB) to give associates 1·2I₂ and 1·2FIB. Structures of these solid species were studied by XRD followed by topological analysis of the electron density distribution within the framework of Bader's approach (QTAIM) at the M06/DZP-DKH level of theory and Hirshfeld surface analysis. Our results along with inspection of XRD (CCDC) data, accompanied by the theoretical calculations, allowed the identification of three types of Ni···I contacts. The Ni···I semicoordination of the electrophilic nickel(II) center with electron belt of I₂ was observed in 1·2I₂, the metal-involving halogen bonding between the nucleophilic nickel(II)-d_z² center and σ-hole of iodine center was recognized and confirmed theoretically in the structure of [FeNi(CN)₄(IPz)(H₂O)]_n (IPz = 4-N-coordinated 2-I-pyrazine), whereas the arrangement of FIB in 1·2FIB provides a boundary case between the semicoordination and the halogen Ni···I bondings. In 1·2I₂ and 1·2FIB, noncovalent interactions were studied by variable temperature XRD detecting the expansion of noncovalent contacts with preservation of covalent bond lengths upon the temperature increase from 100 to 300 K. The nature and energies of all identified types of the Ni···I noncovalent interactions in the obtained (1·2I₂ and 1·2FIB) and in the previously reported ([FeNi(CN)₄(IPz)(H₂O)]_n, [NiL₂](I₃)₂·2I₂ (L = o-phenylene-bis(dimethylphosphine), [NiL]I₂ (L = 1,4,8,11-tetra-azacyclotetradecane), Ni(en)₂]_n[AgI₂]_2n (en = ethylenediamine), and [NiL](ClO₄) (L = 4-iodo-2-((2-(2-(2-pyridyl)ethylsulfanyl)ethylimino)methyl)-phenolate)) structures were studied theoretically. The estimated strengths of these Ni···I noncovalent contacts vary from 1.6 to 4.1 kcal/mol and, as expected, become weaker on heating. This work is the first emphasizing electrophilic-nucleophilic dualism of any metal center toward noncovalent interactions.