  We create weakly bound bosonic $^{23}\textrm{Na}^{39}\textrm{K}$ molecules in
a mixture of ultracold $^{23}\textrm{Na}$ and $^{39}\textrm{K}$. The creation
is done in the vicinity of a so far undetected Feshbach resonance at about
$196\,\text{G}$ which we identify in this work by atom-loss spectroscopy. We
investigate the involved molecular state by performing destructive radio
frequency binding energy measurements. For the constructive molecule creation
we use radio frequency pulses with which we assemble up to $6000$ molecules. We
analyze the molecule creation efficiency as a function of the radio frequency
pulse duration and the atom number ratio between $^{23}\textrm{Na}$ and
$^{39}\textrm{K}$. We find an overall optimal efficiency of $6\,\%$ referring
to the $^{39}\textrm{K}$ atom number. The measured lifetime of the molecules in
the bath of trapped atoms is about $0.3\,\textrm{ms}$.
