where G(ω) is the generalized phonon density of states defined elsewhere, 48 M = l M l /N, n is the thermalequilibrium occupation number of the vibrational state and < n + 1 >= exp exp(ℏωβ)-1 with β = 1 K B T . The exponential term is the Debye-Waller factor for neutron attenuation by thermal motion and ω the phonon frequencies obtained by employing the ph.x package in Quantum Espresso. Q corresponds to kinematical range of IN1-LAGRANGE. A convolution with a Gaussian function is also applied to account for the resolution of the monochromators with a standard deviation of 3.0 cm -1 for the range [0 -478] cm -1 and around 0.01ω for [478 -4033] cm -1 , close to the experimental resolution of IN1-LAGRANGE which is 0.02-0.03ω. Orientation of the pyrazines. The orientational configuration of the pyrazine rings depends on the nature and amount of the guest molecules incorporated in the material. Recently, the present authors reported an ordered structure for the empty Hofmann clathrate Fe(pz)[Pt(CN)4] with the pyrazine ligands oriented in a perpendicular configuration. The ordered structure is found below the spin-transition temperature (ca. 285 K), whereas at higher temperature the Fe(II) atoms switch to HS and the pyrazines display a dynamic disorder. In presence of adsorbed molecules, the orientation of the pyrazines can remain perpendicular or change to a parallel configuration as reported for water, depending on the type and amount of adsorbed gas. To study this, we have collected diffraction data on the deuterated homologue, taking advantage of the sensitivity of this technique to the deuterium position and consequently to the pyrazine orientation. The different configurations where explored also by DFT calculations by studying an increasing number of adsorbed CO and CO2 molecules: 1, 1.5, and 2 molecules per formula unit (f.u.) both in the parallel and the perpendicular configuration of the pyrazines. To accomodate the perpendicular configuration, a supercell with lattice parameters a ′ = √ 2a and b ′ = √ 2b is used, where a and b are the lattice parameters of the primitive cell. The PBE+D2 lattice parameters of the bare MOF are a = 10.096 Å, b = 10.097 Å, and c = 6.711 Å.