The response of the nickel chemical bonds to the tensile deformation in the nickel pyridindicarboxamide

We have carried out a theoretic research of plasticity for the coordination and noncovalent bonds modelling uniaxial mechanical deformation of the crystal cell of bis (2-N,6-N-dibutylpyridin-2,6-dicarboxamide)-nickel (II) dichloride. For this purpose, we have modeled stretching deformation of the crystal structure along its crystallographic axes using the 3-corrected Hartree-Fock method with the following semi-empirical corrections for the weak interactions (the Grimme correction of dispersion interactions, D3, basis set superposition error removal by the atom-pair wise geometrical counterpoise correction, gCP, and correction of short-ranged basis set incompleteness effects, SRB) with the use of periodic boundary conditions. We have concluded that the geometry of bis (2-N,6-N-dibutylpyridin-2,6-dicarboxamide complex has high stability to the increased deformations. We have carried out the analysis of the bond lengths and dihedral angels within the metal complex, which has shown insignificant changes of bond lengths, in particular, the bond length change is equal to 4.3 % for N…Ni…N and 5.4 % for Ni…O. The conformation straightening effects of one of the N-butylamine chain has been found under the high stretching deformation of the crystal cell (7-8 Å) due to analysis of dihedral angles and the distance between specific atoms of N-butylamine chain that proves the hypothesis about a forced and twisted conformation state of bis (2-N,6-N-dibutylpyridin-2,6-dicarboxamide. In addition, we have found the appearance of a cavity and a crack at the last deformation steps (8-10 Å), which is caused by shifts of neighbouring metal complexes in relation to each other; it influences the location of chloride ions. It is noteworthy that cavities and cracks are formed regardless of the axis choice along which the tensile deformation is modeled. This fact indicates that the crystal should not exhibit elasticity, but rather brittleness. Keywords: Ni-pyridindicarboxamide, virtual tensile test, coordination bonds, noncovalent bonds, ab initio calculations