Cocrystallization of the nitrosoguanidinate complexes [Ni{NHC(NR 2 )NN(O)} 2 ] (R 2 = Me 2 (1), Me/Ph (2), C 5 H 10 and 2•2C 2 I 4 ; all of these solids were studied by single-crystal X-ray diffraction. Each structure exhibits the asymmetric bifurcated halogen bond μ 2 -I•••(N,O) as a characteristic feature and a structure-directing contact. DFT calculations were used to evaluate the energetic features of the bifurcated halogen bonds that range from −6.7 to −8.3 kcal/mol; in general, the I•••O contact is stronger that the I•••N contact. Molecular electrostatic potential (MEP) surfaces along with the quantum theory of "atoms in molecules" (QTAIM) and the noncovalent interaction plot index (NCIPlot) computational tools were used to characterize the bifurcated halogen bonds in the cocrystals of 1−3. Various types of bifurcated halogen bonds involving nonmetal atoms as halogen-bond-accepting centers were systematized and categorized.

Reinvestigation of (o-benzoquinonedioximate)2Ni/I2 systems demonstrated that the reaction itself and also the crystallization conditions dramatically affect the identity of generated species. Crystallization (CHCl3, 20–25 °C) of the nickel­(II) dioximate complex [Ni­(bqoxH)2] (bqoxH2 = o-benzoquinonedioxime) with I2 in the 1:(1–10) molar ratios of the reactants led to several (o-benzoquinonedioximate)2Ni derivatives and/or iodine adducts [Ni­(I)­(bqoxH)­(bqoxH2)]·3/2I2, [Ni­(I3)­(bqoxH)­(bqoxH2)]·[Ni­(bqoxH)2], and [Ni­(I3)­(bqox•–)­(bqoxH2)]·I2; the latter one, featuring the anion-radical bqox•– ligand, is derived from the formal (−2H+/1e –)-oxidation of bqoxH2. In these three adducts, various types of noncovalent interactions were identified experimentally and their existence was supported theoretically. The [Ni­(I3)­(bqox•–)­(bqoxH2)]·I2 adduct exhibits simultaneous semicoordination and coordination patterns of the triiodide ligand; this is the first recognition of the semicoordination of any polyiodide ligand to a metal center. The semicoordination noncovalent contact Ni···I3 (3.7011(10) Å) is substantially longer that the Ni–I3 coordination bond (2.8476(9) Å), and the difference in energies between these two types of linkages is 8–12 kcal/mol.

The 3-Iodo-1-nitrosonaphthalene-2-ol (I-NON) was obtained by the copper(II)-mediated iodination of 1-nitroso-2-naphthol (NON). The suitable reactants and optimized reaction conditions, providing 94% NMR yield of I-NON, included the usage of Cu(OAc)2·H2O and 1:2:8 CuII/NON/I2 molar ratio between the reactants. The obtained I-NON was characterized by elemental analyses (C, H, N), high-resolution ESI+-MS, 1H and 13C{1H} NMR, FTIR, UV-vis spectroscopy, TGA, and X-ray crystallography (XRD). The copper(II) complexes bearing deprotonated I-NON were prepared as follows: cis-[Cu(I-NON–H)(I-NON)](I3) (1) was obtained by the reaction between Cu(NON-H)2 and I2 in CHCl3/MeOH, while trans-[Cu(I-NON–H)2] (2) was synthesized from I-NON and Cu(OAc)2 in MeOH. Crystals of trans-[Cu(I-NON–H)2(THF)2] (3) and trans-[Cu(I-NON–H)2(Py)2] (4) were precipitated from solutions of 2 in CHCl3/THF and Py/CHCl3/MeOH mixtures, respectively. The structures of 1 and 3–4 were additionally verified by X-ray crystallography. The characteristic feature of the structures of 1 and 3 is the presence of intermolecular halogen bonds with the involvement of the iodine center of the metal-bound deprotonated I-NON. The nature of the I···I and I···O contacts in the structures of 1 and 3, correspondingly, were studied theoretically at the DFT (PBE0-D3BJ) level using the QTAIM, ESP, ELF, NBO, and IGM methods.

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