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 Co2+/Ni2+ (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. Besides the flexible QiuSuo design, this CP system is suited for doping (e.g., with μ2-OH2 units to effect charge balance by transforming into μ2-OH-), in order to fine-tune the electron-hole balance, and to achieve high-temperature superconductivity.
In order to highlight the importance of exposure/doping in inducing the superconductivity properties: 1) we have now added magnetic and conductivity data on the longer-exposed samples of Co-DMBD in the revised Figure 4. 2) We have also added Figure S8 for the temperature dependence of magnetic susceptibility for the fresh samples (0 hour exposure to air). In this connection, a new (i.e., the second last) paragraph is inserted, and the last paragraph is expanded for discussions. We have also added Figure S7 for the temperature dependence of magnetic susceptibility for the solid samples measured at 10 Oe, as a supplement to the 5 Oe data presented in Figure 3.
ChemRxiv Telltale Diamagnetic Transition at 50 K of a Coordination Polymer System_SI