Solid-State Ligand Dynamics in Interpenetrating Mn[N(CN)₂]₂(Pyrazine):  A Neutron Spectroscopy Study

Abstract

We have used quasielastic neutron scattering to probe the solid-state ligand dynamics in the coordination polymer Mn[N(CN)(2)](2)(pyz) [pyz = pyrazine] which has double-interpenetrating 3D lattices. A reversible structural phase transition occurs at 410 K as shown by neutron spectroscopy and differential scanning calorimetry. The origin of this transition is linked to rotational dynamics associated with the bridging pyz ligands. At 425 K, the pyrazine ring motion can be solely regarded as a 180 degrees reorientational jump about the axis defined by the Mn-N coordinative bonds, occurring with a correlation time of approximately 70 ps. This model can be extended to the 200-410 K temperature region using high-resolution backscattering spectroscopy to measure an identical motion on the time scale of nanoseconds with an activation energy of 24 +/- 2 kJ mol(-1). In contrast, no quasielastic scattering is seen for the 2D layered variant beta-Cu[N(CN)(2)](2)(pyz), owing to its more compact layer packing motif. Importantly, this work represents the very first study of solid-state rotational dynamics in an interpenetrating lattice structure.

Crystal structure of bis(di(pyrazin-2-yl)sulfane-κN)tetrakis(μ2-acetato-κ2O:O')dicopper(II), C12H12CuN4O4S

“…Ligands based on the pyrazinyl group have been widely used in coordination chemistry owing to its linear linkage mode in construction metal complexes with different structures [2][3][4][5].The angular-shaped-S-fragment is widelyu sed as ar igid hinge to construct aseries of heterocyclic-based ligand in alarge number of transition metal complexes [6][7]. We recently reported the synthesisand charaterizationofaseriesofAg(I) complexes with di-2-pyrazinylsulfide [8], al igand with an angular-S-hinge group.…”

Neutron Instruments for Research in Coordination Chemistry

“…At low temperatures, the system is antiferromagnetic, but at > 220 K, the framework becomes dynamic while the analogous Cu II compound does not. [141] A further dynamic transition is evident at around 400 K ( Figure 18). The dynamic scans between 250 K and 400 K are used to follow the Q-dependence of the QENS signal.…”

“…An example illustrating the range of capabilities of HFBS is the study of the interpenetrated coordination network Mn[N(CN) 2 ] 2 · pyrazine, which is comprised of layers of almost square planar sheets of Mn–NCNCN‐Mn linkages bridged by pyrazine ligands that are coordinated through nitrogen bonds to the Mn II centers. At low temperatures, the system is antiferromagnetic, but at > 220 K, the framework becomes dynamic while the analogous Cu II compound does not . A further dynamic transition is evident at around 400 K (Figure ).…”

“…The excellent background makes it quite responsive even for very weak scattering systems, such as small moment magnetic fluctuations. For MOFs, it has been used to probe the dynamical response of jump-rotation of pyrazine rings in an inter-penetrated coordination framework, [141] identified the existence of a temperature induced "breathing" for the pores in an MOF (MIL-53) through a change in low energy phonons, [83c] and detailed the orientation potential of the methyl groups in a zeolitic imidazolate framework (ZIF). [142] While DCS-style instruments are excellent at determining diffusional time-scales and length-scales for adsorbed species, [143] there has been relatively few applications of DCS towards this goal in coordination polymer systems.…”

The dynamical properties of the aromatic hydrogen bond in NH4(C6H5)4B from quasielastic neutron scattering

“…In previous QENS studies of other solid compounds [20][21][22] local diffusive reorientational motions of phenyl rings have been observed on a time scale of 10 −11 -10 −9 s at room temperature. Therefore we used the elastic energy resolution of 32 eV that corresponds to a time scale of about 10 −10 s to measure the QENS spectra of ATPB and ATPB-D, in order to study the phenyl ring reorientations.…”