Synthesis and characterization of novel niccolites [(CH₃)₂NH₂][Fe^IIIM^II(HCOO)₆] (M^II= Zn, Ni, Cu)

Abstract

We report the synthesis, X-ray diffraction, thermal, magnetic, Raman and IR studies of three heterometallic MOFs, [(CH3)2NH2][Fe(III)M(II)(HCOO)6] with M = Zn (DMFeZn), Ni (DMFeNi) and Cu (DMFeCu), crystallizing in the niccolite type structure. DMFeZn and DMFeNi crystallize in the trigonal structure (space group P3[combining macron]1c) while DMFeCu crystallizes in the monoclinic structure (space group C2/c). Magnetic investigation shows that DMFeZn remains paramagnetic down to the lowest temperature obtained in our experiment while DMFeNi and DMFeCu exhibit ferromagnetic order below 42 and 28.5 K, respectively. IR and Raman data confirm the structural model of the monoclinic DMFeCu and show evidence for stronger hydrogen bonds when compared to trigonal DMFeZn and DMFeNi. A different hydrogen bond network in the monoclinic DMFeCu when compared to trigonal DMFeZn and DMFeNi is responsible for the different behavior of these compounds upon cooling, that is, DMFeCu exhibits a sign of short range ordering of dimethylammonium cations at low temperatures while the trigonal analogues show evolution of dynamic disorder into static disorder.

Calculation of the infrared frequency and the damping constant (full width at half maximum) for metal organic frameworks

“…[12] DMFeFe crystallizes in the niccolite type structure (space group P31c) with the disordered dimethylammonium (DMA + ) cations in the cages of the network [14] and it undergoes antiferroelectric phase (space group R3c) at 155 K, [15] as also pointed out previously. [13] DMFeFe shows a sharp heat anomaly at 155.2 K upon warming and 151.8 K upon cooling, characteristic for a first order phase transition, whereas DMFeMg does not undergo any phase transition down to 125 K. [13] Regarding vibrational properties of these niccolite compounds, the observed Raman and IR bands have been assigned to internal vibrations and librations of the DMA + and formate ions as well as translational motions of these ions and metal cations for DMFeNi, DMFeZn, DMFeCu, [12] DMFeFe, and DMFeMg. [13] In the case of DMA + , the internal modes can be stretching υ(NH 2 ), scissoring δ (NH 2 ), rocking ρ(NH 2 ), wagging ω(NH 2 ), and torsion or twisting τ(NH 2 ) modes of the NH 2 group with the internal modes of the CNC and CH 3 groups.…”

“…MOFs By calculating the order parameter S (Eqs. (6a) and (6b)) below T c and fitting S to the observed frequencies (ν data) [12,13] according to Eq. (8) with the parameters a, b, and c (as listed in Table 1), we are able to obtain the IR frequencies of the ρ(NH 2 ) mode (T < T c ) for DMFeM (M = Ni, Zn, Cu, Fe, and Mg).…”

“…We then calculate the damping constant as a function of temperature according to Eqs. (4) and (5), which are fitted to the observed FWHM data [12,13] for the ρ(NH 2 ) IR mode with the values of Γ 0 (Γ 0 ) and A (A ) as determined (as listed in Table 3). Table 3.…”

A Series of Bimetallic Ammonium AlNa Formates

“…The reported Cr 3+ /Fe 3+ –Na + compounds showed similar band shifts but the shifts are somewhat smaller ,. The increased broadness or splits of the IR bands of the AlNa compounds indicate the lowered symmetry of the structures, compared with the Mn compounds, except 1 am and amMn (see caption of Figure ).…”

Giant ferrimagnetism and polarization in a mixed metal perovskite metal-organic framework

“…The doubleperovskites thus formed, with TM ions of differing d-orbital configurations, can not only result in larger magnetization but can also enhance the strength of the exchange coupling interactions pushing the transition temperature higher. However, only a few studies have so far appeared that explore this strategy [20][21][22][23]. In particular, B-site doping in perovskite MOFs aimed at improving ferroic properties is nascent [24][25][26].…”