The Diiodine Basicity Scale: Toward a General Halogen‐Bond Basicity Scale

Abstract

The new diiodine basicity scale pK(BI2) is quasi-orthogonal to most known Lewis basicity scales (hydrogen-bond, dative-bond and cation basicity scales). The diiodine basicity falls in the sequence N>P≈Se>S>I≈O>Br>Cl>F for the iodine-bond acceptor atomic site and SbO≈NO≈AsO>SeO>PO>SO>C=O>-O->SO(2) or PS≫-S->C=S≫N=C=S for the functionality of oxygen or sulfur bases. Substituent effects are quantified through linear free energy relationships, which allow the calculation of individual complexation constants for each site of polybases and thus the classification of aromatic ethers as carbon π bases and of aromatic amines, thioethers and selenoethers as N, S and Se bases, respectively. The pK(BI2) values of nBu(3)N(+)-N(-)C≡N, 2-aminopyridine and 1,10-phenanthroline reveal a superbasic nitrile, a hydrogen-bond-assisted iodine bond and a two-centre iodine bond, respectively. The diiodine basicity scale is a general inorganic but family-dependent organic halogen-bond basicity scale because organic halogen-bond donors such as IC≡N and ICF(3) have a stronger electrostatic character than I(2). The family independence can be restored by the addition of an electrostatic parameter, either the experimental pK(BHX) hydrogen-bond basicity scale or the computed minimum electrostatic potential.

Interplay between non-covalent interactions in complexes and crystals with halogen bonds

“…168 In particular, the pK BI2 values of 2-aminopyridine (2.45) and its methylated analogue, (2-N,N-dimethylamino)pyridine (0.95), were compared. 167 The difference between them equal to 1.50 pK BI2 units is partially due to the steric effect. However, the steric effect for 2-methylpyridine (pK BI2 = 2.35) and 2-isopropylpyridine (pK BI2 = 1.65) was estimated as *0.70 pK BI2 units.…”

“…To reveal the nature of this discrepancy, the effect of the N7H_I hydrogen bond on the strengthening of the N_ I halogen bond was studied using the quantum topological characteristics of the electron density (QTAIM method) and NBO analysis. 167 It was found that the electron density values at bond critical points are relatively high, a charge of 0.03 e is transferred from the iodine atom to the antibonding orbital of the N7H bond and that the second-order stabilization energy E (2) is 3.3 kJ mol 71 . The results obtained thus evidence in favour of synergism between these interactions.…”

“…166,167 Recently, the iodine basicity scale became popular because it can be used to assess the strength of interactions with iodine-containing molecules in crystals. 168 In particular, the pK BI2 values of 2-aminopyridine (2.45) and its methylated analogue, (2-N,N-dimethylamino)pyridine (0.95), were compared.…”

Halogen bonding in water results in enhanced anion recognition in acyclic and rotaxane hosts

“…Surprisingly, however, experimental data quantifying this increasingly important interaction remain limited and confined merely to selected measurements in organic solvents 8,[21][22][23][24] . To the best of our knowledge, a quantitative and systematic comparison of XB and hydrogen bonding (HB) interactions in water has yet to be reported, despite the importance of developing functional supramolecular systems for applications in this biologically and environmentally relevant solvent medium.…”

Isomer Dependence of Efficiency and Charge Recombination in Dye‐Sensitized Solar Cells Using Ru Complex Dyes Bearing Halogen Substituents

“…[28] However, if the contribution of resonance or π-effects to the Hammett parameters for these dyes (Br = -0.22, Cl = -0.19, F = -0.39) are considered; an increase in the rate of the recombination correlates to a decrease in donation of the lone pairs of the halogen atom into the bpy ring. It is feasible that increased resonance into the bpy ring will reduce the availability of the lone pairs for binding to iodine; thus explaining the trends observed.…”