Abstract
Two isostructural trans-[MI2(CNXyl)2]·I2 (M = Pd or Pt; CNXyl = 2,6-dimethylphenyl isocyanide) metallopolymeric cocrystals containing uncommon bifurcated iodine···(metal–iodide) contact were obtained. In addition to classical halogen bonding, single-crystal X-ray diffraction analysis revealed a rare type of metal-involved stabilizing contact in both cocrystals. The nature of the noncovalent contact was studied computationally (via DFT, electrostatic surface potential, electron localization function, quantum theory of atoms in molecules, and noncovalent interactions plot methods). Studies confirmed that the I···I halogen bond is the strongest noncovalent interaction in the systems, followed by weaker I···M interaction. The electrophilic and nucleophilic nature of atoms participating in I···M interaction was studied with ED/ESP minima analysis. In trans-[PtI2(CNXyl)2]·I2 cocrystal, Pt atoms act as weak nucleophiles in I···Pt interaction. In the case of trans-[PdI2(CNXyl)2]·I2 cocrystal, electrophilic/nucleophilic roles of Pd and I are not clear, and thus the quasimetallophilic nature of the I···Pd interaction was suggested.
Highlights
Noncovalent interactions (NCIs) are a powerful instrument applied in such fields as synthesis,[1] catalysis,[2,3] design of photoactive materials,[4−6] and biochemistry.[7,8]
In cocrystals of metal complexes, classical XB is represented by donor/acceptor interaction of an electron-deficient area located on a XB donor (XBD) and an electron-rich area located either on a ligand or on the metal center itself
Observed NCIs can be clarified by analysis of anisotropic charge distribution, which is visualized by electrostatic surface potential (ESP).[3,67,72−76] ESP visualizes electron-rich and -deficient areas of the molecule that are likely to participate in electrostatic intermolecular interactions
Summary
Noncovalent interactions (NCIs) are a powerful instrument applied in such fields as synthesis,[1] catalysis,[2,3] design of photoactive materials,[4−6] and biochemistry.[7,8] Halogen bonding (XB), in particular, has been found to be a very useful NCI, for example, in the synthesis of self-assembled polymers,[9,10] due to its high directionality and possibilities for fine-tuning. Examples of PdII···I31,42−47 and PtII···I48−50 semicoordination bonds have been described in the literature Both types of discussed noncovalent interactions between metal centers and halogen atoms can be considered polar NCIs (with clear electrophilic or nucleophilic[51] roles assignable to interacting atoms). Careful analysis of experimental and theoretical data along with a literature search revealed atypical I−I···(I−M) bifurcated noncovalent bonds, in which classical halogen bond is stabilized by an uncommon type of an I···M contact between a metal center and halogen atom In this contact, the halogen atom is neither interacting via a σhole (Figure 1A) nor via an electron belt (Figure 1C), but presumably via a transitional area (Figure 1B).
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