Ferromagnetism in Two-Dimensional Carbon Chains Linked by 1,3,5-Benzenetriyl Units

Development of organic materials with novel magnetic properties has been an important and challenging topic in organic chemistry. A useful paradigm in this direction is to have spin containing (SC) components linked by ferromagnetic coupling (FC) units. Compared with the traditional SC components such as poly(1,3-phenylenecarbene)s and poly(1,3-phenylenephenylmethine)s, we show that the atomic carbon chains, due to their inherent magnetism and structural Simplicity, can be promising magnetic building blocks of 2-D magnetic carbon structures. Using calculations based on density functional theory, we show that the structures constructed by the carbon chains with in Odd number of C atoms linked by 1,3,5-benzenetriyl units are ferromagnetic. Independent of the chain length, each structural unit cell has a magnetic moment of 6.0 mu(B) and couples ferromagnetically in the 2-D lattice, although the energy difference between the ferromagnetic and antiferromagnetic coupling decreases with increasing chain length. The dynamic stability of the structures is confirmed by frequency calculations. The middle and high vibrational frequencies corresponding to the A(1g) and E(2g) modes of the structures with odd number carbon chains lie in the range of 950-1470 cm(-1), which are lower than those (980 and 1555 cm(-1)) with even-numbered carbon chain structures. This suggests that Raman spectra can be used to identify the parity of carbon chains.