We report on a combined nuclear inelastic scattering and metal isotope substitution based Raman spectroscopic investigation of lattice dynamics changes associated with the spin transition in the ferrous complex [Fe(H2B(pz)(2))(2)(phen)] (pz = pyrazolyl, phen = 1,10-phenantroline). These techniques allowed us to identify Raman active metal - ligand stretching vibrations in the high spin (v(HS) = 232 cm(-1)) and low spin (v(LS) = 390 cm(-1)) states as well as to calculate associated changes of the Debye temperature (Theta(HS)(D) = 140 K, Theta(LS)(D) = 146 K), Debye sound velocity (v(HS) = 1282 m/s, v(LS) = 1300 m/s) and Young's modulus (E-HS = 4.7 GPa, E-LS = 5.2 GPa). (C) 2016 Elsevier B.V. All rights reserved.