One of the most spectacular examples of bistability is the spin crossover (SCO) phenomenon in molecular coordination compounds. [1] SCO materials are increasingly investigated for their potential technological applications in molecular electronics [2] and memory devices, [3] and as contrast agents for magnetic resonance imaging. [4] Their bistable behavior results from a switching between the high-spin (HS) state and the low-spin (LS) state leading to distinctive changes in color, structure, and magnetism, which may be triggered by an external stimulus, such as temperature, pressure, magnetic field, or light irradiation. [1,5] Although SCO occurs in transition-metal ions with 3d n (n = 4-7) electronic configuration, it is most common for iron complexes, especially those containing nitrogen donor atoms. Among the N ligands used, the versatile classes of anionic tris(pyrazolyl)borates [6] and their neutral isoelectronic tris(pyrazolyl)methane analogues [7] provide useful platforms for investigating electronic spinstate crossover properties of iron(II) in nitrogen-rich coordination environments. [8] In the solid state, the prototypical purple bis[hydrotris(pyrazolyl)borato]iron(II) derivative, [Fe{HB(pz) 3 } 2 ] (pz = 1-pyrazolyl; Scheme 1, A), is LS at room temperature and undergoes a SCO transition to the colorless HS state above approximately 420 K. [9] In contrast, its colorless counterpart, bearing a methyl group at the 3position of the pyrazolyl ring, [Fe{HB(3-Mepz) 3 } 2 ] (Scheme 1, B), is HS at room temperature and undergoes a spin conversion into the purple LS state on cooling to 4.2 K. [10,11] This behavior is also detected in iron(II) species having a fourth substituent placed on the central boron, [Fe-{R'B(pz) 3 } 2 ] (Scheme 1, C), [12, 13a,b] which are purple LS complexes, whereas the 3-methylated analogues, [Fe{R'B(3-Mepz) 3 } 2 ] (Scheme 1, D), [13,14] are colorless HS species at