  Spin-state ordering - a periodic pattern of ions with different spin-state
configurations along a crystal lattice - is a rare phenomenon, and its possible
interrelation with other electronic degrees of freedom remains little explored.
Here we perform a structural investigation of the mixed-valence Co homometallic
ludwigite Co$_2^{2+}$Co$^{3+}$O$_2$BO$_3$. A superstructure consistent with a
long-range Co$^{3+}$ spin-state ordering is observed between $T_{4}=580$ K and
$T_{3}=510$ K. Intermediate states with mesoscopic correlations are detected
below $T_{3}$ down to $T_{1}=480$ K with a change of dimensionality at
$T_{2}=495$ K. The spin-state correlations are connected to the charge sector
as revealed by the abrupt changes in the electrical resistance at $T_1$ and
$T_2$. The evolution of the structural parameters below $T_{1}$ indicate that
the spin crossover is ignited by a moderate degree of thermally-induced
Co$^{2+}$/Co$^{3+}$ charge disorder. Charge and spin-state degrees of freedom
can be interrelated in mixed-valence spin-crossover materials, leading to sharp
transitions involving intermediate spin-state/charge correlated states at the
mesoscale.
