Cu-based metalorganic systems: an ab initio study of the electronic structure

Within a first principles framework, we study the electronic structure of the recently synthesized polymeric coordination compound Cu(II)-2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene (CuCCP), which has been suggested to be a good realization of a Heisenberg spin-1/2 chain with antiferromagnetic coupling. By using a combination of classical with ab initio quantum mechanical methods, we design on the computer reliable modified structures of CuCCP aimed at studying effects of Cu–Cu coupling strength variations on this spin-1/2 system. For this purpose, we performed two types of modifications on CuCCP. In one case, we replaced H in the linker by (i) an electron donating group (NH₂) and (ii) an electron withdrawing group (CN), while the other modification consisted of adding H₂O and NH₃ molecules in the structure which change the local coordination of the Cu(II) ions. With the Nth order muffin tin orbital (NMTO) downfolding method, we provide a quantitative analysis of the modified electronic structure and the nature of the Cu–Cu interaction paths in these new structures and discuss its implications for the underlying microscopic model.