The variable temperature magnetic susceptibility, X-ray crystallography, and IR and Raman spectra of a new dinuclear complex [{Fe(II)(NCBH(3))(4-phpy)}(2) mu-bpypz)(2)] demonstrated the first two-step spin-crossover associated with a 1 : 1 mixture of high-spin pair [HS-HS] and low-spin pair [LS-LS] at the plateau.