DFT Modeling of\nPolyethylene Chains Cross-linked by\nSelected <i>n</i>s<sup>1</sup> and <i>n</i>s<sup>2</sup> Metal Atoms

We\nanalyze the structures, stabilities, and thermochemical properties\nof polyethylene (PE) oligomer chains cross-linked by metal (M) atoms\nthrough C–M–C bonds. Representative PE<sub><i>n</i></sub>–M<i><sub>m</sub></i>–PE<sub><i>n</i></sub> complexes contain between 7 and 15 carbon atoms\nin each oligomer and one to three Li, Be, Mg, Zn, Ag, or Au cross-linking\nmetal elements. PE<sub><i>n</i></sub>–M<i><sub>m</sub></i>–PE<sub><i>n</i></sub> complexes\nare quasiplanar with nearly parallel PE chains. Their stability is\ndetermined by covalent C–M–C bonds accompanied by noncovalent\ndispersion interactions between PE<sub><i>n</i></sub> chains.\nUsing the CAM-B3LYP+D3BJ+ABC functional, the binding energies of PE<sub>15</sub>–M–PE<sub>15</sub> with respect to two PE<sub>15</sub> radicals and metal fragments are −225, −230,\n−322, −551, −289, and −303 kJ/mol for\nLi, Ag, Au, Be, Mg, and Zn atoms, respectively. Entropy contributions\n(109 to 121 kJ/mol at 298.15 K) destabilize all complexes significantly.\nWith two cross-linking metal elements in PE<sub>15</sub>–M<sub>2</sub>–PE<sub>15</sub> complexes, binding energies are about\ndouble. Complexes with several open-shell Li, Ag, or Au doublet atoms\nhave spins located on separated C–M–C bonds. High-spin\nPE<sub>15</sub>–M<sub><i>m</i>1</sub>–PE<sub>15</sub>–M<sub><i>m</i>2</sub>–PE<sub>15</sub> complexes of three PE oligomers cross-linked by up to five doublet\nmetal atoms create parallel PE tubes, which are suggested as elementary\ncells for modeling magnetic polymer tubes.