The synthesis of coordination polymers (e.g. Prussian blue) is as old as modern chemistry itself

but never stops surprising people. We here report superconductivity observed of a designer coordination polymer system sporting the chemically soft mercaptan and hard carboxyl groups. The mercapto-carboxyl (dubbed Mercarb

or QiuSuo in Mandarin Pinyin) synergy hints at Daoism and here carries over from the molecular to the solid state: the soft sulfur donors bond with Co

2+

/Ni

2+

(or other transition metal ions) to afford 2D sheets for charge transport

while the interlayer metal-carboxylate domain is more ionic and mediates the transition into the superconductive state.