A detailed structural disorder investigation of Prussian blue analogues M 1.5 [Cr(CN) 6 ]·zH 2 O (M = Fe and Co) has been done by carrying out a reverse Monte Carlo (RMC) simulation on the powder neutron diffraction data. Xray diffraction, infrared spectroscopy, Mossbauer spectroscopy, and dc magnetization measurements have also been employed to investigate the structural and magnetic properties of the compounds. The Rietveld refinement of the X-ray and neutron diffraction patterns reveals that both compounds are in a single phase with a face-centered cubic crystal structure (space group Fm3m). The observation of characteristic absorption bands in the range 1900−2200 cm −1 of infrared (IR) spectra, which corresponds to the CN stretching frequency of M II NCCr III sequence, confirms the formation of Prussian blue analogues, M 1.5 [Cr(CN) 6 ]·zH 2 O. The IR study also infers the presence of cyanide flipping in the Fe 1.5 [Cr(CN) 6 ]·zH 2 O compound. The Mossbauer study on the Fe 1.5 [Cr(CN) 6 ]·zH 2 O compound confirms the presence of high as well as low spin Fe II ions due to isomerization of some Cr III CNFe II linkages to the Cr III NCFe II form. The magnetization data show a soft ferromagnetic nature of both compounds with a Curie temperature of ∼17 and ∼22 K for Fe 1.5 [Cr(CN) 6 ]·zH 2 O and Co 1.5 [Cr(CN) 6 ]·zH 2 O, respectively. A large amount of structural disorder is present in both compounds, which is manifested in the form of a diffuse scattering in neutron diffraction patterns. The RMC results, obtained after the modeling, simulation, and analysis of the neutron diffraction data, propose that the water molecules and the [Cr(CN) 6 ] vacancies are mainly responsible for the structural disorder. Moreover, a clustering of the noncoordinated oxygen atoms around the coordinated oxygen atoms is also ascertained by the RMC analysis. The correlation of structural disorder with the water content and [Cr(CN) 6 ] vacancies is also discussed. ■ INTRODUCTIONPeriodic arrangements of atoms in a material decide the crystalline nature, and the local deviation of atoms from their atomic sites leads to the structural disorder in the materials. Structural disorder occurs due to an uncertainty in the spatial arrangements of atoms in a material. The disordered materials display interesting physical properties that are not always seen in their crystalline counterparts. Therefore, the disordered materials have also received great attention and are equally important from the scientific as well as technological point of view when compared to crystalline materials. For example, the disordered semiconductor materials, produced by metal doping, are highly useful in microelectronics technology. 1 Further, the high temperature superconductor can be synthesized with an optimal amount of doping of defects/disorder in the materials. 2,3 The disorder can be introduced in the materials either by using external stimuli, such as temperature, pressure, heat, magnetic field, or light, or intrinsically due to doping of atomic species,...

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Hydrothermally synthesized oxalate and phenanthroline based ferrimagnetic one-dimensional spin chain molecular magnets [{Fe(D)Fe(L)} 1Àx {Cr(D) Cr(L)} x (ox) 2 (phen) 2 ] n (x ¼ 0, 0.1 and 0.5) with giant coercivity of 3.2 Tesla

A one-dimensional single-chain molecular magnet [{Co II (Δ)Co II (Λ)}(ox) 2 (phen) 2 ] n with a cross-linked π−π coordination network has been synthesized hydrothermally and investigated for its structural and magnetic properties. Oxalate (ox) ligands bridge the paramagnetic Co II metal ions, whereas phenanthroline (phen) ligands exhibit π−π coordination networks. The compound has been thoroughly investigated using room-temperature X-ray and neutron diffraction, infrared spectroscopy, dc magnetization, and reverse Monte Carlo (RMC) simulation methods. Rietveld refinement of the powder X-ray and neutron diffraction patterns at room temperature confirms the single-phase formation of the compound in the monoclinic structure with a space group P2 1 . Structural analysis reveals that the compound assembles in the form of a one-dimensional zigzag chainlike structure. Chains consist of two asymmetric Δand Λ-Co II ions and a π−π coordinating network bridged by ox and phen ligands, respectively. The chain lies in the crystallographic ac plane, infinite in length with the absence of interchain π−π overlap. dc magnetization data fitted over the high-temperature regime (T > 5 K) using the Ising chain model reveals the one-dimensional magnetic nature of the compound with alternately spaced magnetic Co II sites with two different Landég factors and exchange coupling constant values. Different Landég factors (2.5 and 2.1) and negative exchange coupling constant values (−108 and −20 K) at two alternating Co II sites indicate a ferrimagnetic behavior of this chain compound. In the low-temperature regime (T < 5 K) the compound exhibits spontaneous magnetization and hysteresis at 1.6 K, due to the occurrence of long-range threedimensional (3-D) magnetic ordering. A prominent clustering of the C atoms around the Co atoms is ascertained by RMC analysis of diffuse scattering in the neutron diffraction pattern. The pair correlations distances between Co−Co, Co−C, Co−N, and Co−O atoms are found to be 5.0, 2.2, 2.5, and 2.4 Å, respectively, for the compound.

We report a detailed structural disorder study of the Ba(x)Mn[Fe(CN)(6)](2(x+1)/3)·zH(2)O (x = 0 and 0.3) molecular magnets by carrying out Reverse Monte Carlo (RMC) simulations of neutron diffraction data. Both samples have also been investigated using X-ray diffraction, infrared spectroscopy and dc magnetization techniques. Rietveld refinement of X-ray and neutron diffraction patterns confirmed the single phase formation for both compounds in a face-centered cubic structure. IR spectral study establishes the presence of cyanide flipping in both compounds, thereby revealing inherent structural disorder in the compounds. A ferrimagnetic coupling of Mn(2+) (S = 5/2) spins and the Fe(3+) (S = 1/2) spins is found for both compounds. Results of RMC simulations of neutron diffraction data for both compounds show that: (i) around the coordinated oxygen atoms (located at the 24e crystallographic sites with [Fe(CN)(6)] vacancies), there are formations of small clusters of non-coordinated oxygen atoms; and (ii) Ba substitution leads to a reduction in this structural disorder. The role of reduced water content as well as vacancies of [Fe(CN)(6)] towards the observed reduction in the structural disorder is discussed.