Consecutive Irreversible Single-Crystal to Single-Crystal and Reversible Single-Crystal to Glass Transformations and Associated Magnetism of the Coordination Polymer, [Mn^II(<i>rac</i>-pnH)(H₂O)Cr^III(CN)₆]·H₂O

The achiral coordination polymer [MnII(rac-pnH)(H2O)CrIII(CN)6]·H2O, (rac-pn = racemic 1,2-diaminopropane), 1·2H2O, has been prepared, and its crystal structures, optical and magnetic properties have been studied before and after dehydration followed by rehydration. The in situ X-ray diffraction, performed on one selected single crystal, shows an unusual irreversibility from the as-prepared 1·2H2O to the dehydrated [Mn(rac-pnH)Cr(CN)6], 1, and reversibility from 1 to rehydrated [Mn(rac-pnH)(H2O)Cr(CN)6]·H2O 1-HP. Virgin 1·2H2O crystallizes in the monoclinic achiral P21/m space-group having a two-dimensional (2D) square-network of Mn−Cr with bridging cyanide, and behaves as a soft ferrimagnet (TC = 36 K). Dehydrated 1 has a three-dimensional (3D) network with an additional cyanide bridge between layers and adopts the orthorhombic achiral Pmnb space-group exhibiting a ferrimagnetic behavior (TC = 70 K). Rehydrated 1-HP (TC = 36 K) is poorly crystallized having the same unit-cell as 1·2H2O and reversibly transforms to the crystalline 1 (TC = 70 K). The dehydration is associated to a change in the coordination of the amine from one layer to its neighboring one involving a proton transfer, going from {Mn-NH2CH(CH3)CH2N′H3+·····(H2O)Mn′} for 1·2H2O to {Mn-NC·····NH3+CH(CH3)CH2H2N′−Mn′} for 1. The irreversible transformation of virgin single crystal 1·2H2O to single-crystal 1 is promoted by the availability of only one Mn in the vicinity of the cyanide while during the rehydration process the reversible single-crystal 1 to a glassy 1-HP is due to the presence of two equidistant Mn atoms, which is the cause of the disorder. The change in magnetism, that is, the increase of the Curie temperature and coercive field, is associated to the structural transformation from 2D to 3D

Consecutive Irreversible Single-Crystal to Single-Crystal and Reversible Single-Crystal to Glass Transformations and Associated Magnetism of the Coordination Polymer, [Mn^II(<i>rac</i>-pnH)(H₂O)Cr^III(CN)₆]·H₂O

The achiral coordination polymer [MnII(rac-pnH)(H2O)CrIII(CN)6]·H2O, (rac-pn = racemic 1,2-diaminopropane), 1·2H2O, has been prepared, and its crystal structures, optical and magnetic properties have been studied before and after dehydration followed by rehydration. The in situ X-ray diffraction, performed on one selected single crystal, shows an unusual irreversibility from the as-prepared 1·2H2O to the dehydrated [Mn(rac-pnH)Cr(CN)6], 1, and reversibility from 1 to rehydrated [Mn(rac-pnH)(H2O)Cr(CN)6]·H2O 1-HP. Virgin 1·2H2O crystallizes in the monoclinic achiral P21/m space-group having a two-dimensional (2D) square-network of Mn−Cr with bridging cyanide, and behaves as a soft ferrimagnet (TC = 36 K). Dehydrated 1 has a three-dimensional (3D) network with an additional cyanide bridge between layers and adopts the orthorhombic achiral Pmnb space-group exhibiting a ferrimagnetic behavior (TC = 70 K). Rehydrated 1-HP (TC = 36 K) is poorly crystallized having the same unit-cell as 1·2H2O and reversibly transforms to the crystalline 1 (TC = 70 K). The dehydration is associated to a change in the coordination of the amine from one layer to its neighboring one involving a proton transfer, going from {Mn-NH2CH(CH3)CH2N′H3+·····(H2O)Mn′} for 1·2H2O to {Mn-NC·····NH3+CH(CH3)CH2H2N′−Mn′} for 1. The irreversible transformation of virgin single crystal 1·2H2O to single-crystal 1 is promoted by the availability of only one Mn in the vicinity of the cyanide while during the rehydration process the reversible single-crystal 1 to a glassy 1-HP is due to the presence of two equidistant Mn atoms, which is the cause of the disorder. The change in magnetism, that is, the increase of the Curie temperature and coercive field, is associated to the structural transformation from 2D to 3D

Consecutive Irreversible Single-Crystal to Single-Crystal and Reversible Single-Crystal to Glass Transformations and Associated Magnetism of the Coordination Polymer, [Mn^II(<i>rac</i>-pnH)(H₂O)Cr^III(CN)₆]·H₂O

The achiral coordination polymer [MnII(rac-pnH)(H2O)CrIII(CN)6]·H2O, (rac-pn = racemic 1,2-diaminopropane), 1·2H2O, has been prepared, and its crystal structures, optical and magnetic properties have been studied before and after dehydration followed by rehydration. The in situ X-ray diffraction, performed on one selected single crystal, shows an unusual irreversibility from the as-prepared 1·2H2O to the dehydrated [Mn(rac-pnH)Cr(CN)6], 1, and reversibility from 1 to rehydrated [Mn(rac-pnH)(H2O)Cr(CN)6]·H2O 1-HP. Virgin 1·2H2O crystallizes in the monoclinic achiral P21/m space-group having a two-dimensional (2D) square-network of Mn−Cr with bridging cyanide, and behaves as a soft ferrimagnet (TC = 36 K). Dehydrated 1 has a three-dimensional (3D) network with an additional cyanide bridge between layers and adopts the orthorhombic achiral Pmnb space-group exhibiting a ferrimagnetic behavior (TC = 70 K). Rehydrated 1-HP (TC = 36 K) is poorly crystallized having the same unit-cell as 1·2H2O and reversibly transforms to the crystalline 1 (TC = 70 K). The dehydration is associated to a change in the coordination of the amine from one layer to its neighboring one involving a proton transfer, going from {Mn-NH2CH(CH3)CH2N′H3+·····(H2O)Mn′} for 1·2H2O to {Mn-NC·····NH3+CH(CH3)CH2H2N′−Mn′} for 1. The irreversible transformation of virgin single crystal 1·2H2O to single-crystal 1 is promoted by the availability of only one Mn in the vicinity of the cyanide while during the rehydration process the reversible single-crystal 1 to a glassy 1-HP is due to the presence of two equidistant Mn atoms, which is the cause of the disorder. The change in magnetism, that is, the increase of the Curie temperature and coercive field, is associated to the structural transformation from 2D to 3D

Consecutive Irreversible Single-Crystal to Single-Crystal and Reversible Single-Crystal to Glass Transformations and Associated Magnetism of the Coordination Polymer, [Mn^II(<i>rac</i>-pnH)(H₂O)Cr^III(CN)₆]·H₂O

The achiral coordination polymer [MnII(rac-pnH)(H2O)CrIII(CN)6]·H2O, (rac-pn = racemic 1,2-diaminopropane), 1·2H2O, has been prepared, and its crystal structures, optical and magnetic properties have been studied before and after dehydration followed by rehydration. The in situ X-ray diffraction, performed on one selected single crystal, shows an unusual irreversibility from the as-prepared 1·2H2O to the dehydrated [Mn(rac-pnH)Cr(CN)6], 1, and reversibility from 1 to rehydrated [Mn(rac-pnH)(H2O)Cr(CN)6]·H2O 1-HP. Virgin 1·2H2O crystallizes in the monoclinic achiral P21/m space-group having a two-dimensional (2D) square-network of Mn−Cr with bridging cyanide, and behaves as a soft ferrimagnet (TC = 36 K). Dehydrated 1 has a three-dimensional (3D) network with an additional cyanide bridge between layers and adopts the orthorhombic achiral Pmnb space-group exhibiting a ferrimagnetic behavior (TC = 70 K). Rehydrated 1-HP (TC = 36 K) is poorly crystallized having the same unit-cell as 1·2H2O and reversibly transforms to the crystalline 1 (TC = 70 K). The dehydration is associated to a change in the coordination of the amine from one layer to its neighboring one involving a proton transfer, going from {Mn-NH2CH(CH3)CH2N′H3+·····(H2O)Mn′} for 1·2H2O to {Mn-NC·····NH3+CH(CH3)CH2H2N′−Mn′} for 1. The irreversible transformation of virgin single crystal 1·2H2O to single-crystal 1 is promoted by the availability of only one Mn in the vicinity of the cyanide while during the rehydration process the reversible single-crystal 1 to a glassy 1-HP is due to the presence of two equidistant Mn atoms, which is the cause of the disorder. The change in magnetism, that is, the increase of the Curie temperature and coercive field, is associated to the structural transformation from 2D to 3D

Consecutive Irreversible Single-Crystal to Single-Crystal and Reversible Single-Crystal to Glass Transformations and Associated Magnetism of the Coordination Polymer, [Mn^II(<i>rac</i>-pnH)(H₂O)Cr^III(CN)₆]·H₂O

The achiral coordination polymer [MnII(rac-pnH)(H2O)CrIII(CN)6]·H2O, (rac-pn = racemic 1,2-diaminopropane), 1·2H2O, has been prepared, and its crystal structures, optical and magnetic properties have been studied before and after dehydration followed by rehydration. The in situ X-ray diffraction, performed on one selected single crystal, shows an unusual irreversibility from the as-prepared 1·2H2O to the dehydrated [Mn(rac-pnH)Cr(CN)6], 1, and reversibility from 1 to rehydrated [Mn(rac-pnH)(H2O)Cr(CN)6]·H2O 1-HP. Virgin 1·2H2O crystallizes in the monoclinic achiral P21/m space-group having a two-dimensional (2D) square-network of Mn−Cr with bridging cyanide, and behaves as a soft ferrimagnet (TC = 36 K). Dehydrated 1 has a three-dimensional (3D) network with an additional cyanide bridge between layers and adopts the orthorhombic achiral Pmnb space-group exhibiting a ferrimagnetic behavior (TC = 70 K). Rehydrated 1-HP (TC = 36 K) is poorly crystallized having the same unit-cell as 1·2H2O and reversibly transforms to the crystalline 1 (TC = 70 K). The dehydration is associated to a change in the coordination of the amine from one layer to its neighboring one involving a proton transfer, going from {Mn-NH2CH(CH3)CH2N′H3+·····(H2O)Mn′} for 1·2H2O to {Mn-NC·····NH3+CH(CH3)CH2H2N′−Mn′} for 1. The irreversible transformation of virgin single crystal 1·2H2O to single-crystal 1 is promoted by the availability of only one Mn in the vicinity of the cyanide while during the rehydration process the reversible single-crystal 1 to a glassy 1-HP is due to the presence of two equidistant Mn atoms, which is the cause of the disorder. The change in magnetism, that is, the increase of the Curie temperature and coercive field, is associated to the structural transformation from 2D to 3D

On the Nature of the Reversibility of HydrationDehydration on the Crystal Structure and Magnetism of the Ferrimagnet [Mn^II(enH)(H₂O)][Cr^III(CN)₆]·H₂O

We report the synthesis, crystal structure, and thermal and magnetic properties of the two-dimensional achiral soft ferrimagnet [MnII(enH)(H2O)][CrIII(CN)6]·H2O (1), en = 1,2-diaminoethane, as well as the recyclability of the dehydration and rehydration and their influence on the crystal structure and its magnetic properties. Unlike [Mn(S-pnH)(H2O)][Cr(CN)6]·H2O (2S, pn = 1,2-diaminopropane), which is a chiral (P212121) enantiopure ferrimagnet (TC = 38 K), 1 crystallizes in the achiral orthorhombic Pcmn space group, having a similar two-dimensional square network of Mn−Cr with bridging cyanide, and 1 behaves also as a soft ferrimagnet (TC = 42 K). X-ray diffraction experiments on a single crystal of 1 indicate a transformation from a single crystal to an amorphous phase upon dehydrataion and partial recovery of its crystallinity upon rehydration. The dehydrated phase 1-DP exhibits long-range ordering at 75 K to a ferrimagnetic state and coercive field at 2 K of 100 Oe, which are a higher critical temperature and coercive field than for the virgin sample (HC = 60 Oe). Thermogravimetric analyses indicate that the crystallinity deteriorates upon hydration−dehydration cycling, with persistence toward the amorphous phase, as also seen by magnetization measurements. This effect is associated with an increase of statistical disorder inherent in the dehydration−rehydration process. X-ray powder diffraction suggests that 1-DP may retain order within the layers but loses coherence in the stacking of the layers

Magnetic Properties and Magnetic Structure of Cu^II₃Mo^VI₂O₉

The magnetic properties and the low-temperature nuclear and magnetic structures of Cu3Mo2O9 are reported. It consists of magnetic chains of oxygen-bridged vertex-shared Cu4 tetrahedra connected into a 3D network by bridging MoO4. Each chain is a segment of the pyrochlore structure. The magnetic properties are dominated by antiferromagnetic coupling and show a low-dimensional behavior with a broad maximum at 20 K. At 9.5 K, long-range antiferromagnetic ordering with a small canting is observed. The magnetic structure determination from neutron diffraction resolves only the orientations and magnitude (1.0(1) μB per Cu) of the moments of two of the three crystallographically independent atoms. The third appears not to contribute to the long-range ordering. Geometric frustration may be responsible for the randomness. It is a unique antiferromagnet with eight sublattices (two sets of four) in the ac plane, leaving the canting to be only possible along the b axis

Construction of Hydrogen-Bonded and Coordination-Bonded Networks of Cobalt(II) with Pyromellitate: Synthesis, Structures, and Magnetic Properties

Synthesis (hydrothermal and metathesis), characterization (UV−vis, IR, TG/DTA), single-crystal X-ray structures, and magnetic properties of three cobalt(II)−pyromellitate complexes, purple [Co2(pm)]n (1), red [Co2(pm)(H2O)4]n·2nH2O (2), and pink [Co(H2O)6](H2pm) (3) (H4pm = pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid)), are described. 1 consists of one-dimensional chains of edge-sharing CoO6 octahedra that are connected into layers via O−C−O bridges. The layers are held together by the pyromellitate (pm4-) backbone to give a three-dimensional structure, each ligand participating in an unprecedented 12 coordination bonds (Co−O) to 10 cobalt atoms. 2 consists of a three-dimensional coordination network possessing cavities in which unbound water molecules reside. This highly symmetric network comprises eight coordinate bonds (Co−O) between oxygen atoms of pm4- to six trans-Co(H2O)2. 3 possesses a hydrogen-bonded sandwich structure associating layers of [Co(H2O)6]2+ and planar H2pm2-. The IR spectra, reflecting the different coordination modes and charges of the pyromellitate, are presented and discussed. The magnetic properties of 1 indicate complex behavior with three ground states (collinear and canted antiferromagnetism and field-induced ferromagnetism). Above the Néel temperature (TN) of 16 K it displays paramagnetism with short-range ferromagnetic interactions (ϑ = +16.4 K, μeff = 4.90 μB per Co). Below TN a weak spontaneous magnetization is observed at 12.8 K in low applied fields (H H > 1000 Oe) metamagnetic behavior is observed. Two types of hysteresis loops are observed; one centered about zero field and the second about the metamagnetic critical field. The critical field and the hysteresis width increase as the temperature is lowered. The heat capacity data suggest that 1 has a 2D or 3D magnetic lattice, and the derived magnetic entropy data confirm an anisotropic seff = 1/2 for the cobalt(II) ion. Magnetic susceptibility data indicate that 2 and 3 are paramagnets

Consecutive Irreversible Single-Crystal to Single-Crystal and Reversible Single-Crystal to Glass Transformations and Associated Magnetism of the Coordination Polymer, [Mn^II(<i>rac</i>-pnH)(H₂O)Cr^III(CN)₆]·H₂O

The achiral coordination polymer [MnII(rac-pnH)(H2O)CrIII(CN)6]·H2O, (rac-pn = racemic 1,2-diaminopropane), 1·2H2O, has been prepared, and its crystal structures, optical and magnetic properties have been studied before and after dehydration followed by rehydration. The in situ X-ray diffraction, performed on one selected single crystal, shows an unusual irreversibility from the as-prepared 1·2H2O to the dehydrated [Mn(rac-pnH)Cr(CN)6], 1, and reversibility from 1 to rehydrated [Mn(rac-pnH)(H2O)Cr(CN)6]·H2O 1-HP. Virgin 1·2H2O crystallizes in the monoclinic achiral P21/m space-group having a two-dimensional (2D) square-network of Mn−Cr with bridging cyanide, and behaves as a soft ferrimagnet (TC = 36 K). Dehydrated 1 has a three-dimensional (3D) network with an additional cyanide bridge between layers and adopts the orthorhombic achiral Pmnb space-group exhibiting a ferrimagnetic behavior (TC = 70 K). Rehydrated 1-HP (TC = 36 K) is poorly crystallized having the same unit-cell as 1·2H2O and reversibly transforms to the crystalline 1 (TC = 70 K). The dehydration is associated to a change in the coordination of the amine from one layer to its neighboring one involving a proton transfer, going from {Mn-NH2CH(CH3)CH2N′H3+·····(H2O)Mn′} for 1·2H2O to {Mn-NC·····NH3+CH(CH3)CH2H2N′−Mn′} for 1. The irreversible transformation of virgin single crystal 1·2H2O to single-crystal 1 is promoted by the availability of only one Mn in the vicinity of the cyanide while during the rehydration process the reversible single-crystal 1 to a glassy 1-HP is due to the presence of two equidistant Mn atoms, which is the cause of the disorder. The change in magnetism, that is, the increase of the Curie temperature and coercive field, is associated to the structural transformation from 2D to 3D

Consecutive Irreversible Single-Crystal to Single-Crystal and Reversible Single-Crystal to Glass Transformations and Associated Magnetism of the Coordination Polymer, [Mn^II(<i>rac</i>-pnH)(H₂O)Cr^III(CN)₆]·H₂O

The achiral coordination polymer [MnII(rac-pnH)(H2O)CrIII(CN)6]·H2O, (rac-pn = racemic 1,2-diaminopropane), 1·2H2O, has been prepared, and its crystal structures, optical and magnetic properties have been studied before and after dehydration followed by rehydration. The in situ X-ray diffraction, performed on one selected single crystal, shows an unusual irreversibility from the as-prepared 1·2H2O to the dehydrated [Mn(rac-pnH)Cr(CN)6], 1, and reversibility from 1 to rehydrated [Mn(rac-pnH)(H2O)Cr(CN)6]·H2O 1-HP. Virgin 1·2H2O crystallizes in the monoclinic achiral P21/m space-group having a two-dimensional (2D) square-network of Mn−Cr with bridging cyanide, and behaves as a soft ferrimagnet (TC = 36 K). Dehydrated 1 has a three-dimensional (3D) network with an additional cyanide bridge between layers and adopts the orthorhombic achiral Pmnb space-group exhibiting a ferrimagnetic behavior (TC = 70 K). Rehydrated 1-HP (TC = 36 K) is poorly crystallized having the same unit-cell as 1·2H2O and reversibly transforms to the crystalline 1 (TC = 70 K). The dehydration is associated to a change in the coordination of the amine from one layer to its neighboring one involving a proton transfer, going from {Mn-NH2CH(CH3)CH2N′H3+·····(H2O)Mn′} for 1·2H2O to {Mn-NC·····NH3+CH(CH3)CH2H2N′−Mn′} for 1. The irreversible transformation of virgin single crystal 1·2H2O to single-crystal 1 is promoted by the availability of only one Mn in the vicinity of the cyanide while during the rehydration process the reversible single-crystal 1 to a glassy 1-HP is due to the presence of two equidistant Mn atoms, which is the cause of the disorder. The change in magnetism, that is, the increase of the Curie temperature and coercive field, is associated to the structural transformation from 2D to 3D