This work presents that the x-bases and xx-bases can be combined with their counterparts to form stable Watson-Crick ring-expanded base pairs. For double-electron oxidation Watson-Crick ring-expanded base pairs, they possess open-shell broken symmetry singlet states except for [xxGC](2+). Some complexes exhibit a significantly large amount of diradical character and some of diradical base pairs also possess excellent magnetic characteristics. [xGC](2+), [xAT](2+) and [xxAT](2+) show more and more strong AFM with the size expansion of guanine and adenine. The magnetic interactions get relatively weaker and weaker with the size expansion of cytosine and thymin. [xxTA](2+) even manifests a weak FM character. (C) 2018 Elsevier B.V. All rights reserved.