Why Is BCl₃ a Stronger Lewis Acid with Respect to Strong Bases than BF₃?^,

Abstract

Geometries and bond dissociation energies of the complexes Cl(3)B[bond]NH(3) and F(3)B[bond]NH(3) have been calculated using DFT (PW91) and ab initio methods at the MP2 and CCSD(T) levels using large basis sets. The calculations give a larger bond dissociation energy for Cl(3)B[bond]NH(3) than for F(3)B[bond]NH(3). Calculations of the deformation energy of the bonded fragments reveal that the distortion of BCl(3) and BF(3) from the equilibrium geometry to the pyramidal form in the complexes requires nearly the same energy. The higher Lewis acid strength of BCl(3) in X(3)B[bond]H(3) compared with BF(3) is an intrinsic property of the molecule. The energy partitioning analysis of Cl(3)B[bond]NH(3) and F(3)B[bond]NH(3) shows that the stronger bond in the former complex comes from enhanced covalent interactions between the Lewis acid and the Lewis base which can be explained with the energetically lower lying LUMO of BCl(3).

Coordination chemistry of the main group elements with phosphine, arsine and stibine ligands

“…The detailed and somewhat subtle conclusions show considerable dependence on the level and model of calculations employed, and have often proved controversial in detail. These are well summarised in [10,107] and some key contributions are in [108][109][110][111][112] and refs therein. Much of this work deals with 4+ redrawn from Ref.…”

Some Interesting Features of Non-Covalent Interactions

“…A paradigmatic example is that of the complexes between ammonia and BF 3 and BCl 3 , where the dissociation energy of the complex into NH 3 + BX 3 (X = F, Cl) is larger for the BCl 3 complex than for the BF 3 . 24 Why BCl 3 behaves apparently as a stronger Lewis acid than BF 3 is not a trivial question, that certainly cannot be explained in terms of the deformation energies, because the deformation energies of BF 3 and BCl 3 are practically identical. The origin of the larger acidity of BCl 3 can be traced using the frontier orbital energy, which shows that the LUMO of BCl 3 lies lower in energy than that of BF 3 , and therefore one should expect the former to be a better electron acceptor, and as a consequence a better Lewis acid than the latter.…”

“…The origin of the larger acidity of BCl 3 can be traced using the frontier orbital energy, which shows that the LUMO of BCl 3 lies lower in energy than that of BF 3 , and therefore one should expect the former to be a better electron acceptor, and as a consequence a better Lewis acid than the latter. 24 However, even this model may be incomplete if the effect of the deformations on the properties of the interacting units is not taken into account. Naively, one would expect the Lewis acidity to increase by successive substitution by F atoms as BH 3 < BH 2 F < BHF 2 < BF 3 .…”

An efficient method for computing the binding energy of an adsorbed molecule within a periodic approach. The application to vinyl fluoride at rutile TiO2(1 1 0) surface

“…In studies of inter-molecular interactions, BE is variously referred to as the stabilisation [2][3][4][5], total interaction [6][7][8], total bond [9][10][11][12] or bond dissociation [13][14][15][16] energy. BE can be separated into two contributions: the distortion energy, E dis , and the interaction energy, E int [17][18][19][20][21][22];…”

“…E dis is variously referred to as the deformation [2,3,6,9,17,[23][24][25][26][27], relaxation [4,5,8,28] or preparation [10][11][12][13][14][15][16]29], energy.…”