Hydrogen-Bonding Assembly of Coordination Polymers Showing Reversible Dynamic Solid-State Structural Transformations

We herein report the synthesis, single-crystal structures of coordination polymers, and structural transformations of complexes employing 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile (tdpd2−) and pyrazine (pyz) as bridging ligands. {[M(H2O)4(pyz)][M(tdpd)2(pyz)]·6(H2O)}n, [1·10H2O and 2·10H2O where M = Co (1) and Zn (2)], consists of two types of crystallographically independent one-dimensional (1D) structures packed together. One motif, [M(tdpd)2(pyz)] (A), is an anionic infinite pyz bridged 1D array with chelating tdpd2− ligands, and the other motif is a cationic chain, [M(H2O)4(pyz)] (B), which is decorated with four terminal water molecules. The 1D arrays (A) and (B) are arranged in parallel by multi-point hydrogen-bonding interactions in an alternate (A)(B)(A)(B) sequence extending along the c-axis. Both compounds exhibit structural transformations driven by thermal dehydration processes around 350 K to give partially dehydrated forms, 1·2H2O and 2·2H2O. The structural determination of the partially dehydrated form, 2·2H2O, reveals a solid-state structural transformation from a 1D chain structure to a two-dimensional (2D) coordination sheet structure, [Zn2(tdpd)2(H2O)2(pyz)]n (2·2H2O). Further heating to 500 K yields the anhydrous form 2. While the virgin samples of 1·10H2O and 2·10H2O crystallize in different crystal systems, powder X-ray diffraction (PXRD) measurements of the dehydrated forms, 1·2H2O and 2·2H2O, are indicative of the same structure. The structural transformation is irreversible for 1·10H2O at ambient conditions. On the other hand, compound 2·10H2O shows a reversible structural change. The solid-state structural transformation for 1·10H2O was also confirmed by monitoring in-situ magnetic susceptibility, which is consistent with other thermally-induced measurements.


Introduction
Coordination polymers containing guest molecules are very attractive research subjects due to their flexibilities and tunable functional applications, which provide an opportunity to develop advanced functional materials [1][2][3][4][5].To design coordination polymers with excellent performance, the synergistic effects between the metal ions, ligands, and guest molecules are essential factors [6][7][8][9].Weak but significant supramolecular interactions between coordination frameworks and guest molecules, as well as reversible metal-ligand covalent bonds which generate notable flexibility of structural topologies and enhance functionalities, are quite important in supramolecular compounds [10].
Flexible frameworks with bistable phases exhibit solid-state structural transformations involving the rearrangement of bonds driven by external stimuli such as heat, light, and pressure [11][12][13][14][15][16][17].Structural transformations are generally accompanied by removal or exchange of coordinated and/or uncoordinated solvents or guests, changes in coordination number of metal ions, and conformational changes in ligands.Such structural transformations sometimes cause specific sorption behavior related to a breathing effect [1,2,6,18,19].However, reports on the effects in bistable and flexible assemblies are limited, especially in supramolecular frameworks generated from low-dimensional assemblies or discrete molecules.Generally, such structural changes in response to external stimuli are facilitated by weak bonding interactions.These structural transformations induced by chemical and/or physical processes are much more complicated than those encountered in rigid frameworks.Therefore, investigations of solid-state structural transformations between bistable phases in flexible frameworks, such as HOFs (hydrogen-bonded organic frameworks) [20,21] and correlation with their properties, are crucial to design smart, functional materials.
The tdpd 2− (H 2 tdpd = 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile) anion attracted our interest as a potential bifunctional ligand with hydrogen-bonding characteristics.This dianion has both multiple metal-binding and multiple hydrogen bonding sites.Previously, we established that the use of anions containing two AAA sets from [M(tdpd) 2 (H 2 O) 2 ] 2− together with melaminium cations containing one DDD set (A = hydrogen bond acceptor, D = hydrogen bond donor) [22,23] leads to the formation of complementary, triply hydrogen bonded modules in the solid state, even when the products are crystallized from a competitive solvent such as water.In all cases, the building module is further extended by additional hydrogen-bonding interactions to produce tapes, and tapes are then assembled into sheets.We have also reported (II) ion/tdpd 2− /exo-bidentate ligands such as pyz and 4,4 -bipyridine (4,4 -bpy) [24].The pyz and 4,4 -bpy molecules have been utilized as bridging ligands to form two-dimensional (2D) metal-organic frameworks.In this contribution, we extend the chemistry of the metal-tdpd assembly by capitalizing on the competitive and facilitative hydrogen and/or coordination bonding interactions in the assemblies.We aim to control the structural transformations triggered by sorption of coordinated and interstitial solvents.In addition to the crystal structures, sorption and thermal properties are also described.

X-Ray Structures
The crystallographic data appear in Table 1, and selections of the relevant bond distances and angles are given in Table 2.The crystals belong to the triclinic system, P-1, a = 7.0728( 9 , where n is the number of reflections and p is the total number of parameters refined.O consists of two crystallographically-independent and distinct polymeric structures packed together with interstitial water molecules.Figure 1 shows the crystal structure of 1•10H 2 O.Both of the polymeric structures consist of chains of octahedral cobalt (II) ions bridged by pyzs and interstitial waters.The key feature of the structure is the presence of two types of charged one-dimensional (1D) chains and lattice water molecules within the crystal.One of the motifs with the composition of [Co(tdpd) 2 (pyz)] 2− (A) is an anionic infinite pyz bridged 1D array that is decorated with two chelating tdpd 2− ligands.The other motif with the composition of [Co(H 2 O) 4 (pyz)] 2+ (B) is a cationic infinite pyz bridged 1D array that is decorated with four terminal water molecules.In total, 1•10H 2 O can be formulated as {[(A)(B)]•6(H 2 O)} n , and the oxidation states of all independent cobalt centers in the chain are +2.In the 1D array (A), the Co(1) center lies on a crystallographic special position, and displays a six-coordinate elongated octahedral geometry, consisting of two nitrogen atoms of pyz in the trans position, and four oxygen atoms of chelating tdpd 2−

Structure of 2•2H2O
The crystal belonged to the monoclinic system, C2/m, a = 21.0743(11) Å , b = 7.1528(3) Å , c = 8.0963(5) Å , β = 98.7773(2)°,V = 1206.17(11)Å 3 , Z = 2 for 2•2H2O (Figure S1 and Tables 1 and 2).X-ray structure analysis of 2•2H2O revealed the formation of a 2D sheet structure.Figure 3 shows the 2D sheet structure of 2•2H2O.The sheet consists of anionic 1D arrays of [Zn(tdpd)2(pyz)] 2− (A) and cationic 1D arrays of [Zn(H2O)2(pyz)] 2+ (B'), in which two coordinated water molecules are lost from 1D array (B).1D arrays (A) and (B') are inter-connected by coordination bonding between oxygen atoms of tdpd 2− ligands and zinc(II) ions of 1D array (B') to give a neutral sheet structure.1 and 2).X-ray structure analysis of 2•2H 2 O revealed the formation of a 2D sheet structure.Figure 3           These observations are consistent with the TG findings of a first dehydration step to form partially dehydrated samples, followed by a second step to form the anhydrous phases.After anhydrous phases 1 and 2 were cooled to room temperature and exposed to air for 1 week, PXRD measurements were performed.Bragg angles of 1 remain unchanged from that of the anhydrous phase over a period of 1 week.The anhydrous phase 1 appears to be stable in air.The anhydrous 1 could be converted back to the virgin 1•10H 2 O by soaking in water for a sufficient amount of time, but showed somewhat low crystallinity (Figure 5d).On the other hand, with rehydration in air for 2, the reverse process is observed.The PXRD pattern of the rehydrated form of 2 is almost identical to that of the virgin sample, 2•10H 2 O, and the diffraction peaks sharpen considerably, indicating an increased long-range ordering of the structure.

Reversible Dehydration-Rehydration and Structural Transformation
Figure 6 shows the results of water adsorption-desorption isotherm measurements for 1 and 2, respectively.The samples were dehydrated at 493 K for 3 h to give the anhydrous forms before measurements, and water adsorption-desorption isotherm measurements were carried out at 298 K.The same measurements were performed using the same sample without further dehydration processes.For the anhydrous form, 1, the adsorbed amount of water gradually increased with increasing pressure up to P/P0 = 0.6, followed by an abrupt water uptake from P/P0 = 0.6-0.9(Figure 6 [1 st (Co)]).The numbers of water molecules per molecular unit are 2 and 8, corresponding to the

Reversible Dehydration-Rehydration and Structural Transformation
Figure 6 shows the results of water adsorption-desorption isotherm measurements for 1 and 2, respectively.The samples were dehydrated at 493 K for 3 h to give the anhydrous forms before measurements, and water adsorption-desorption isotherm measurements were carried out at 298 K.The same measurements were performed using the same sample without further dehydration processes.For the anhydrous form, 1, the adsorbed amount of water gradually increased with increasing pressure up to P/P 0 = 0.6, followed by an abrupt water uptake from P/P 0 = 0.6-0.9(Figure 6 [1 st (Co)]).The numbers of water molecules per molecular unit are 2 and 8, corresponding to the partially dehydrated form and the virgin sample of 1, respectively.This result is in good agreement with the PXRD measurements.When the relative pressure was decreased, the amount of water gradually decreased.An abrupt decrease of the water molecules was observed at P/P 0 = 0.1 and the number of the remaining water molecules per molecular unit was 4. Subsequently, a second adsorption measurement was performed using the same sample (Figure 6 [2 nd (Co)]).The amount of water uptake increased gradually with small steps to P/P 0 = 0.7 and reached a maximum at P/P 0 = 0.9.The number of water molecules per molecular unit was 10, corresponding to the virgin sample of 1•10H 2 O, and the number of water molecules decreased with decreasing pressure.Again, the number of remaining water molecules per molecular unit was 4. This water adsorption-desorption process is reproducible, as shown in Figure 6 [3 rd (Co)].These results suggest that 6 water molecules are labile and can be removed at 298 K simply by decreasing the relative pressure, suggesting that uncoordinated water molecules are released first, and then coordinated water molecules are lost due to the higher stability of the coordination bonding to the metal ions.Thus, the release of the 6 water molecules gives a chain compound,

Magnetic Property
To further probe the structural change during the dehydration process, the magnetic susceptibility (χM) of 1•10H2O was monitored in situ as a function of temperature, where the cobalt(II) ion in 1•10H2O is paramagnetic.The temperature dependence of χM of 1•10H2O was measured over temperature ranges of 2-400 K (heating mode) and 400 K-2 K (cooling mode) in an applied field of  On the other hand, the water adsorption isotherm for the anhydrous form 2 displayed distinct steps at P/P 0 = 0.1 and 0.7, with a large hysteresis loop, as shown in Figure 6 [1 st (Zn)].The numbers of adsorbed water molecules were 2 and 8, respectively.These values are similar to those of anhydrous 1 and correspond to the partially dehydrated form, 2•2H 2 O, and the hydrated form, 2•10H 2 O, respectively.The pressure at the second step is higher than that of 1, indicating the higher stability of the partially dehydrated form, 2•2H 2 O.The desorption isotherm was similar to that of 1; however, the number of remaining water molecules per molecular unit was 2, which is indicative of a structural transformation from the 1D chain compound, 2•10H 2 O, to the 2D layer compound, 2•2H 2 O. Subsequently, a second adsorption measurement was performed using the same sample (Figure 6 [2 nd (Zn)]).The adsorption isotherm of 2•2H 2 O exhibited an abrupt increase, and reached a plateau up to P/P 0 = 0.7, indicative of the structural stability of 2•2H 2 O, while the adsorption isotherm of 1•4H 2 O exhibited a gradual increase with increasing P/P 0 .The number of water molecules decreased with decreasing pressure in the desorption isotherm.An abrupt decrease of the water molecules was observed at P/P 0 = 0.2.This water adsorption-desorption process was reproducible, as shown in Figure 6 [3 rd (Zn)].The large hysteresis of the adsorption-desorption curve is indicative of strong interactions between water molecules and zinc(II) ions.

Magnetic Property
To further probe the structural change during the dehydration process, the magnetic susceptibility (χ M ) of 1•10H 2 O was monitored in situ as a function of temperature, where the cobalt(II) ion in 1•10H 2 O is paramagnetic.The temperature dependence of χ M of 1•10H 2 O was measured over temperature ranges of 2-400 K (heating mode) and 400 K-2 K (cooling mode) in an applied field of 0.5 T (Figure 7).Upon heating, the χ M T value increased with increasing temperature, indicative of the existence of an antiferromagnetic interaction in the chains.A discontinuity of the χ M T value was observed around 350 K due to the loss of eight molecules of water, changing to a partially dehydrated form of 1•2H 2 O. Plots of χ M −1 versus T were linear between 300 and 50 K for heating mode, and 400 and 50 K for cooling;

Materials and Methods
All chemicals were obtained from Tokyo Chemical Industry (TCI) Co., Ltd.(Tokyo, Japan), Wako Pure Chemical Industries, Ltd. (Osaka, Japan), and Sigma-Aldrich Japan (Tokyo, Japan), and used without further purification.Reactions and subsequent manipulations were performed under aerobic conditions at room temperature.

Materials and Methods
All chemicals were obtained from Tokyo Chemical Industry (TCI) Co., Ltd.(Tokyo, Japan), Wako Pure Chemical Industries, Ltd. (Osaka, Japan), and Sigma-Aldrich Japan (Tokyo, Japan), and used without further purification.Reactions and subsequent manipulations were performed under aerobic conditions at room temperature.

Preparation of {[Co
An aqueous solution of cobalt acetate dihydrate (20 mmol) and H 2 tdpd (40 mmol) was transferred to a glass tube, then a methanol solution of pyz (40 mmol) was poured into the glass tube without mixing the two solutions.Orange crystals began to form at the ambient temperature in 1 week.One of these crystals was used for X-ray crystallography.Physical measurements were conducted on a polycrystalline powder that was synthesized as follows: An aqueous solution (30 mL) of cobalt acetate dihydrate (30 mmol) was added to an aqueous solution (30 mL) of H 2 tdpd (60 mmol).After stirring the mixture, a methanol solution of pyz (60 mmol) was added.Upon stirring the mixture, orange powders were obtained.The powders were washed with water and methanol and dried in air (yield 70%).An aqueous solution of zinc acetate dihydrate (20 mmol) and H 2 tdpd (40 mmol) was transferred to a glass tube, then an ethanol solution of pyz (40 mmol) was poured into the glass tube without mixing the two solutions.Colorless crystals began to form at the ambient temperature in 1 week.One of these crystals was used for X-ray crystallography.Physical measurements were conducted on a polycrystalline powder that was synthesized as follows: An aqueous solution (30 mL) of zinc acetate dihydrate (30 mmol) was added to an aqueous solution (30 mL) of H 2 tdpd (60 mmol).After stirring the mixture, a methanol solution of pyz (60 mmol) was added.Upon stirring the mixture, white powders were obtained.The powders were washed with water and methanol and dried in air (yield 70%).Calcd
ligands in the basal plane.The octahedrons are distorted with O-Co(1)-O bond angles [79.89(13) • ] and the Co(1)-N bond distances [2.102(5) Å] are longer than the Co-O bond distances [2.080(3) and 2.092(3) Å], thus the elongation axis is N-Co-N, which runs in the chain direction.The bond angle of N-Co(1)-N [180.0 • ] is linear, thus Co(1)-pyz-Co(1) sequences make a straight chain.The Co•••Co distance within 1D array (A) is 7.07 Å with Co-pyz-Co connectivity.In the 1D array (B), the Co(2) center also lies on a crystallographic special position and displays a six-coordinate distorted {CoN 2 O 4 } octahedral geometry, consisting of two nitrogen atoms of pyz in the trans position, and four oxygen atoms of coordinated water molecules.The water molecules form the basal plane.Co(2)-N bond distances are 2.096(5) Å, and Co(2)-O bond distances are 2.094(5) and 2.059(4) Å.The N-Co(2)-N bond angle [180.0 • ] is similar to that of the 1D array (A), and indicates a linear chain structure of the 1D array (B).The Co•••Co distance of 7.07 Å within the 1D array (B) is similar to that found in the 1D array (A) with Co-pyz-Co connectivity.While the bond distances of Co(2) are similar to those found in Co(1), the O-Co(2)-O bond angles are larger (ranging from 88.58(15) • -91.42(15) • ) than those found in 1D array (A).This is due to the chelating tdpd 2− ligand found in the 1D array (A).axis is N-Co-N, which runs in the chain direction.The bond angle of N-Co(1)-N [180.0°] is linear, thus Co(1)-pyz-Co(1) sequences make a straight chain.The Co•••Co distance within 1D array (A) is 7.07 Å with Co-pyz-Co connectivity.In the 1D array (B), the Co(2) center also lies on a crystallographic special position and displays a six-coordinate distorted {CoN2O4} octahedral geometry, consisting of two nitrogen atoms of pyz in the trans position, and four oxygen atoms of coordinated water molecules.The water molecules form the basal plane.Co(2)-N bond distances are 2.096(5) Å , and Co(2)-O bond distances are 2.094(5) and 2.059(4) Å .The N-Co(2)-N bond angle [180.0°] is similar to that of the 1D array (A), and indicates a linear chain structure of the 1D array (B).The Co•••Co distance of 7.07 Å within the 1D array (B) is similar to that found in the 1D array (A) with Co-pyz-Co connectivity.While the bond distances of Co(2) are similar to those found in Co(1), the O-Co(2)-O bond angles are larger (ranging from 88.58(15)°-91.42(15)°)than those found in 1D array (A).This is due to the chelating tdpd 2-ligand found in the 1D array (A).

Figure 2
Figure 2 shows the hydrogen-bonding interactions between the 1D arrays (A) and (B) and the water molecules.The 1D arrays (A) and (B) are involved in an AA-DD (A = hydrogen-bond acceptor, D = hydrogen-bond donor) arrangement.The nearest neighbor inter-chain Co•••Co distance is 6.03 Å .Four coordinated water molecules of 1D array (B) act as hydrogen-bonding donors and the chelating tdpd 2− ligand acts as a hydrogen-bonding acceptor.The coordinated water molecules of 1D array (B) strongly interact with an oxygen atom and a nitrogen atom of 1D array (A) with an O-H•••O distance of 2.673(5) Å and an OH•••N distance of 2.789(7) Å .The inter-chain hydrogen-bond distances are very similar to that of a 1D chain compound in which a structural transformation from a 1D chain into a 3D framework was observed [25].The basal planes of 1D arrays (A) and (B) are arranged in parallel

Figure 2
Figure 2 shows the hydrogen-bonding interactions between the 1D arrays (A) and (B) and the water molecules.The 1D arrays (A) and (B) are involved in an AA-DD (A = hydrogen-bond acceptor, D = hydrogen-bond donor) arrangement.The nearest neighbor inter-chain Co•••Co distance is 6.03 Å.Four coordinated water molecules of 1D array (B) act as hydrogen-bonding donors and the chelating tdpd 2− ligand acts as a hydrogen-bonding acceptor.The coordinated water molecules of 1D array (B) strongly interact with an oxygen atom and a nitrogen atom of 1D array (A) with an O-H•••O distance of 2.673(5) Å and an OH•••N distance of 2.789(7) Å.The inter-chain hydrogen-bond distances are very similar to that of a 1D chain compound in which a structural transformation from a 1D chain into a 3D framework was observed [25].The basal planes of 1D arrays (A) and (B) are arranged in parallel by multi-point hydrogen-bonding interactions in an alternate (A)(B)(A)(B) sequence extending along

Figure 2 .
Figure 2. Hydrogen-bonding interactions between the 1D arrays (A) and (B) and the water molecules.Dashed lines indicate hydrogen-bonding interactions.

Figure 4 .
Figure 4. TG curves of (a) 1•10H2O and (b) 2•10H2O.Since the single-crystals of (a) 1•10H2O and (b) 2•10H2O do not survive the dehydration process, the temperature-dependent PXRD patterns were measured up to 550 K in air to monitor the structural changes (Figure 5).Both crystalline powders of (a) 1•10H2O and (b) 2•10H2O were heated to 350 K, the temperature at which the first weight loss steps were finished to form a partially dehydrated form.The PXRD patterns of the virgin samples at room temperature match well with the simulated patterns based on the single-crystal structures.The partially dehydrated forms of the compounds at 350 K exhibit different diffraction peaks from those of the virgin samples.The results are indicative of structural transformations driven by thermal dehydration processes.We note that the virgin samples of 1•10H2O and 2•10H2O crystallize in different crystal systems to give different diffraction patterns.However, the partially dehydrated forms, 1•2H2O and 2•2H2O, show similar PXRD patterns,

Figure 4 .
Figure 4. TG curves of (a) 1•10H O and (b) 2•10H 2 O. Since the single-crystals of (a) 1•10H 2 O and (b) 2•10H 2 O do not survive the dehydration process, the temperature-dependent PXRD patterns were measured up to 550 K in air to monitor the structural changes (Figure 5).Both crystalline powders of (a) 1•10H 2 O and (b) 2•10H 2 O were heated to 350 K,
Figure6shows the results of water adsorption-desorption isotherm measurements for 1 and 2, respectively.The samples were dehydrated at 493 K for 3 h to give the anhydrous forms before measurements, and water adsorption-desorption isotherm measurements were carried out at 298 K.The same measurements were performed using the same sample without further dehydration processes.For the anhydrous form, 1, the adsorbed amount of water gradually increased with increasing pressure up to P/P 0 = 0.6, followed by an abrupt water uptake from P/P 0 = 0.6-0.9(Figure6[1 st (Co)]).The numbers of water molecules per molecular unit are 2 and 8, corresponding to the partially dehydrated form and the virgin sample of 1, respectively.This result is in good agreement with the PXRD measurements.When the relative pressure was decreased, the amount of water gradually decreased.An abrupt decrease of the water molecules was observed at P/P 0 = 0.1 and the number of the remaining water molecules per molecular unit was 4. Subsequently, a second adsorption measurement was performed using the same sample (Figure6[2 nd (Co)]).The amount of water uptake increased gradually with small steps to P/P 0 = 0.7 and reached a maximum at P/P 0 = 0.9.The number of water molecules per molecular unit was 10, corresponding to the virgin sample of 1•10H 2 O, and the number of water molecules decreased with decreasing pressure.Again, the number of remaining water molecules per molecular unit was 4. This water adsorption-desorption process is reproducible, as shown in Figure6[3 rd (Co)].These results suggest that 6 water molecules are labile and can be removed at 298 K simply by decreasing the relative pressure, suggesting that uncoordinated water molecules are released first, and then coordinated water molecules are lost due to the higher stability of the coordination bonding to the metal ions.Thus, the release of the 6 water molecules gives a chain compound, 1•4H 2 O, {[Co(H 2 O) 4 (pyz)][Co(tdpd) 2 (pyz)]} n .Interestingly, the water isotherm at 298 K shows an irreversible water adsorption-desorption, from 1•2H 2 O to 1•10H 2 O, while PXRD measurements indicate a reversible transformation by heating and cooling with high humidity, suggesting higher stability of 1•4H 2 O at 298 K.This means 1•4H 2 O is metastable.Inorganics 2018, 5, x FOR PEER REVIEW 9 of 14 stability of the partially dehydrated form, 2•2H2O.The desorption isotherm was similar to that of 1; however, the number of remaining water molecules per molecular unit was 2, which is indicative of a structural transformation from the 1D chain compound, 2•10H2O, to the 2D layer compound, 2•2H2O.Subsequently, a second adsorption measurement was performed using the same sample (Figure 6 [2 nd (Zn)]).The adsorption isotherm of 2•2H2O exhibited an abrupt increase, and reached a plateau up to P/P0 = 0.7, indicative of the structural stability of 2•2H2O, while the adsorption isotherm of 1•4H2O exhibited a gradual increase with increasing P/P0.The number of water molecules decreased with decreasing pressure in the desorption isotherm.An abrupt decrease of the water molecules was observed at P/P0 = 0.2.This water adsorption-desorption process was reproducible, as shown in Figure 6 [3 rd (Zn)].The large hysteresis of the adsorption-desorption curve is indicative of strong interactions between water molecules and zinc(II) ions.
Curie-Weiss fits (χ M = C/T − θ) for the data gave Curie constants (C) of 6.16 and 5.86 cm 3 K mol −1 .As the C values are higher than those predicted for a spin only value (C = 3.76 cm 3 K mol −1 with g = 2.00), the strong magnetic anisotropy stemming from the unquenched orbital angular momentum must be invoked, whereas Weiss constants (θ) are −20.06 and −33.23 K, indicative of antiferromagnetic interactions between cobalt(II) centers.Interestingly, upon cooling, the magnetic behavior of 1•2H 2 O is different from that of 1•10H 2 O, suggesting the difference on the dimensionality of the compounds, as well as the coordination geometry.Inorganics 2018, 5, x FOR PEER REVIEW 10 of 14 antiferromagnetic interactions between cobalt(II) centers.Interestingly, upon cooling, the magnetic behavior of 1•2H2O is different from that of 1•10H2O, suggesting the difference on the dimensionality of the compounds, as well as the coordination geometry.

Figure 7 .
Figure 7. Temperature dependence of DC magnetic data for 1•10H2O.Red and blue open circles represent heating and cooling modes, respectively.(Left) χMT versus T plot.Inset: An emphasized view of the high-temperature region.(Right) χM versus T plot in the temperature region of 2-100 K. Inset: χM −1 versus T plot with Curie-Weiss fits (solid black lines).

Figure 7 .
Figure 7. Temperature dependence of DC magnetic data for 1•10H 2 O. Red and blue open circles represent heating and cooling modes, respectively.(Left) χ M T versus T plot.Inset: An emphasized view of the high-temperature region.(Right) χ M versus T plot in the temperature region of 2-100 K. Inset: χ M −1 versus T plot with Curie-Weiss fits (solid black lines).
Calcd for 1•10H 2 O: C 20 N 12 O 14 H 28 Co 2 : C, 30.86;H, 3.63; N, 21.59.Found: C, 30.70;H, 3.52; N, 21.45.The identity of the batches for physical measurements and single-crystal data collection was established by comparison of the powder X-ray diffraction patterns.The experimental patterns of the powder samples were in good agreement with simulated patterns reproduced from the Fc values of the calculated crystal structures.

for 2 •
10H 2 O: C 20 N 12 O 14 H 28 Zn 2 : C, 30.36;H, 3.57; N, 21.24.Found: C, 30.60;H, 3.47; N, 21.35.The identities of the batches for physical measurements and single-crystal data collection were established by comparison of the powder X-ray diffraction patterns.The experimental patterns of the powder samples were in good agreement with simulated patterns reproduced from the Fc values of the calculated crystal structures.The powders of 2•10H 2 O were dried under reduced pressure (1.3 × 10 −1 Pa) at 350 K for 3 h, which were efficiently transformed to 2•2H 2 O.