We present a systematic theoretical study on the structural, electronic, and magnetic properties of the novel tetragonal transition-metal-based 7,7,8,8-tetracyanoquinodimethane molecule coordination single sheets (referred to as TM@TCNQ, TM = Cr-Co). Our results unveil that, in TM@TCNQ, two valence electrons would transfer from one TM atom to TCNQ molecules, making them more stable. Among these structures, Cr@TCNQ, Mn@TCNQ, and Fe@TCNQ exhibit long-range antiferromagnetic coupling while Co@TCNQ is paramagnetic; this dictates these sheets being ideal candidates for spintronic devices. Such long-range magnetic coupling in the studied systems is related to the modulation via the TCNQ ligands. Besides, to explain the magnetic moment qualitatively, we propose a model on d splitting named "4 + 1 splitting". The possible underlying physical mechanisms are discussed in detail. In addition, TM@TCNQ may conceal promising performance for hydrogen storage according to our results. These predications strongly revive these new synthesized systems as viable candidates for spintronics and hydrogen storage.