Magnetism and charge order in the ladder compound <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Co</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>BO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>

There are two known ludwigites containing a single transition metal element, ${\text{Fe}}_{3}{\text{O}}_{2}{\text{BO}}_{3}$ and ${\text{Co}}_{3}{\text{O}}_{2}{\text{BO}}_{3}$. The structure of these materials has low-dimensional units in the form of three-legged ladders (3LL) that confer to each of them unique magnetic and electronic properties. ${\text{Fe}}_{3}{\text{O}}_{2}{\text{BO}}_{3}$ presents a staggered charge density wave (CDW) transition in the ladders near room temperature and two magnetic transitions. It has remained a mystery why the other compound ${\text{Co}}_{3}{\text{O}}_{2}{\text{BO}}_{3}$ behaves so conventionally, with a single magnetic transition and no CDW in spite of similar structural and electronic configurations. Neutron diffraction results presented here in this system finally unravel these differences. Far from a trivial explanation, we uncover a coexistence of low and high spin Co ions in well-defined octahedral sites. Our results allow one to solve the contrasting behavior of the Fe and Co ludwigites in terms of a subtle and unique charge ordering mechanism occurring at the microscopic level of the rungs of the 3LL.