Cyanamides as π-Hole Donor Components of Structure-Directing (Cyanamide)···Arene Noncovalent Interactions

Abstract

Crystallization of newly prepared copper­(II) clusters [Cu4X6O­(NCNMe2)4] (X = Cl 1 or Br 2) from toluene and styrene solutions afforded crystalline adducts 1·4PhMe, 1·4PhCHCH2, 2·4PhMe, and 2·4PhCHCH2, which were characterized by physicochemical methods including single-crystal X-ray diffraction. Inspection of the X-ray structures of (1–2)·4­(arene) and the appropriate Hirshfeld molecular surface analysis allowed the recognition of the previously unreported π-hole···arene interactions involving the cyanamide ligands. The presence of these interactions and their structure-directing character was confirmed theoretically by density functional theory calculations including molecular electrostatic potential, energy decomposition, and atoms-in-molecules analyses. The observed π-hole···π interaction between coordinated cyanamide and arene moieties in the adducts exhibits a contribution of π-hole···σ­(C–Haryl) interaction. Analysis of the Cambridge Structure Database revealed that the cyanamide···arene separations in the [Cu4X6O­(NCNMe2)4]­·4­(arene) systems are among the shortest found for all reported cyanamide structures.

Nature and Strength of the π‐Hole Chalcogen Bonded Complexes between Substituted Pyridines and SO3 Molecule

“…The significance of this σ‐hole bonding has been established in the broad domain of rational drug design, anion recognition, synthesis of new material, biochemistry, and other fields [9–12] . With the rapid increase in studies concerned with σ‐hole, it was realized that the depletion of electron density lies not only along the extensions of the covalent bonds, but can also be present above a planar molecule (SO 3 ) or planar groups (of a molecule) such as −NO 2 , phenyl and carbonyl [13–17] . Generally, this positive electrostatic potential lies in an area perpendicular to an atom or group (from a molecule) or on the centroid of aromatic ring.…”

“…Both experimental and theoretical works concerning the presence of π‐hole and their ability to interact with different Lewis bases have been studied with acyl carbons, the SO 2 and SO 3 molecules, RNO 2 molecules, XCN, XZO 2 (X=halogen, Z=pnicogen), and several other molecules [13–22] . Moreover, a wide variety of chalcogen and tetrel bonded complexes resulting from the interaction of π‐hole present in different molecules with a variety of electron donors have also been reported [17,18,23–25] .…”

Copper(II) Prevents the Saccarine-Dialkylcyanamide Coupling by Forming Mononuclear (Saccharinate)(Dialkylcyanamide)copper(II) Complexes

“…2240 cm -1 ) [20] and the mixed-ligand copper(I) complexes [Cu(tpm)(NCNR2)](BF4) (R = Me, Et; ca. 2250 cm -1 ) [21] and the clusters [Cu4X6O(NCNMe2)4] (2255-2261 cm -1 ) [22]. In the IR spectra of all complexes, the two strong bands in the ranges 1306-1330 and 1165-1177 cm -1 were attributed to νsym(SO2) and νasym(SO2) of the saccharinate ligands, respectively.…”

“…In both structures, the copper(II) centers are surrounded by two saccharinate, two water, and one dimethylcyanamide ligands, thus forming the complexes exhibiting a distorted square-pyramidal geometry, where the NCNMe 2 ligand occupies the apical position. The degree of the geometry distortion is greater for the dihydrate (geometry index [23] [22] allyl [27]) and the solvates Cu 4 X 6 O(NCNMe 2 ) 4 •4(arene) [22] (X = Cl, Br; arene = PhMe, PhCH=CH 2 ; 1.903( 10)-1.952(6) Å) as a consequence of different geometry and composition of the complexes. The C≡N and C-N bond lengths of the NCNMe 2 ligands (1.153(5) and 1.312(5) Å for 1 and 1.156( 7) and 1.306(7) Å for 1•2H 2 O, respectively) was quite similar.…”

“…In both structures, the copper(II) centers are surrounded by two saccharinate, two water, and one dimethylcyanamide ligands, thus forming the complexes exhibiting a distorted square-pyramidal geometry, where the NCNMe2 ligand occupies the apical position. The degree of the geometry distortion is greater for the dihydrate (geometry index [23] [22,27,30], and the solvates Cu4X6O(NCNMe2)4•4(arene) (X = Cl, Br; arene = PhMe, PhCH=CH2) [22], and no single example of mononuclear (NCNR2)Cu II was known. For copper(I), there are several known structures of mononuclear complexes [Cu(NCNR2)4](BF4) [20], [Cu(tpm)(NCNR2)](BF4) (tpm = tris-(1,3-dimethylpyrazolyl)methane) [21], and [Cu(NCNMe2)2(DPEphos)](BF4) [32], and polymeric [CuX(NCNAllyl2)] (X = Cl, Br, NO3) species [33].…”