  We detail the optimized synthesis of the Mo$_3$O$_8$-type cluster Mott
insulator (CMI) Na$_3$Sc$_2$(MoO$_4$)$_2$Mo$_3$O$_8$, which has been considered
a candidate for realizing the spin liquid ground state. The optimized
Na$_3$Sc$_2$(MoO$_4$)$_2$Mo$_3$O$_8$, characterized by x-ray diffraction,
energy-dispersive x-ray spectroscopy, and magnetic and heat capacity
measurements, exhibited an effective magnetic moment close to the ideal 1.73
$\mu_{\mathrm B}$ for $S = 1/2$ spin and magnetic ordering at $\sim$ 5 K. These
observations categorize Na$_3$Sc$_2$(MoO$_4$)$_2$Mo$_3$O$_8$ as the second
Mo$_3$O$_8$-type CMI to achieve a magnetic ground state, following
Li$_2$InMo$_3$O$_8$. They highlight the stabilization of the magnetic ground
state over the theoretically anticipated quantum spin liquid state through
precise valence and chemical disorder tuning. Our findings challenge the
existing theory that the magnetic ground state of Mo$_3$O$_8$-type CMIs is
determined by the breathing parameter, instead showing that magnetic order is
suppressed by spin defects. This study underscores the crucial role of chemical
precision in investigating quantum magnetism. It suggests that precise tuning
of valence states could induce magnetic ordering in previously nonmagnetic
Mo$_3$O$_8$-type CMIs. Additionally, the negative findings regarding the
existence of quantum spin liquids highlight the need for applied research and a
reevaluation of our fundamental understanding of electronic states from both
theoretical and experimental aspects.
