Three-Dimensional Cadmium ( II ) Cyanide Coordination Polymers with Ethoxy-, Butoxy-and Hexyloxy-ethanol

The three novel cadmium(II) cyanide coordination polymers with alkoxyethanols, [Cd(CN)2(C2H5OCH2CH2OH)]n (I), [{Cd(CN)2(C4H9OCH2CH2OH)}3{Cd(CN)2}]n (II) and [{Cd(CN)2(H2O)2}{Cd(CN)2}3·2(C6H13OCH2CH2OH)]n (III), were synthesized and charcterized by structural determination. Three complexes have three-dimensional Cd(CN)2 frameworks; I has distorted tridymite-like structure, and, II and III have zeolite-like structures. The cavities of Cd(CN)2 frameworks of the complexes are occupied by the alkoxyethanol molecules. In I and II, hydroxyl oxygen atoms of alkoxyethanol molecules coordinate to the Cd(II) ions, and the Cd(II) ions exhibit slightly distort trigonal-bipyramidal coordination geometry. In II, there is also tetrahedral Cd(II) ion which is coordinated by only the four cyanides. The hydroxyl oxygen atoms of alkoxyethanol connects etheric oxygen atoms of the neighboring alkoxyethanol by hydrogen bond in I and II. In III, hexyloxyethanol molecules do not coordinate to the Cd(II) ions, and two water molecules coordnate to the octahedral Cd(II) ions. The framework in III contains octahedral Cd(II) and tetrahedral Cd(II) in a 1:3 ratio. The Cd(CN)2 framework structures depended on the difference of alkyl chain for alkoxyethanol molecules.


Crystal Structure
Single crystals of the complexes I-III were prepared by a method similar to the literature procedure [1].Crystal data for I-III are listed in Table 1.In the three complexes, all cyanides bridge between two Cd(II) ions, and Cd(CN)2 consists of a three-dimensional framework with large cavities (Figures 1-3).From IR spectra, the peaks of C≡N stretching (νCN) were observed at 2185-2190 cm −1 .The νCN values showed a blue shift from that which was observed for terminal C≡N of K2[Cd(CN)2] (2145 cm −1 ), supporting a view that the C≡N bridged between two Cd(II) ions.The exact arrangements of cyanides (Cd-NC-Cd or Cd-CN-Cd) cannot be determined by single X-ray diffraction because these arrangements are disordered.Nishikiori et al. [6,12,13] show that arrangements of cyanides in Cd(CN)2 host are disordered by 113 Cd-CP/MAS NMR.

Crystal Structure
Single crystals of the complexes I-III were prepared by a method similar to the literature procedure [1].Crystal data for I-III are listed in Table 1.In the three complexes, all cyanides bridge between two Cd(II) ions, and Cd(CN) 2 consists of a three-dimensional framework with large cavities (Figures 1-3).From IR spectra, the peaks of C≡N stretching (ν CN ) were observed at 2185-2190 cm −1 .The ν CN values showed a blue shift from that which was observed for terminal C≡N of K 2 [Cd(CN) 2 ] (2145 cm −1 ), supporting a view that the C≡N bridged between two Cd(II) ions.The exact arrangements of cyanides (Cd-NC-Cd or Cd-CN-Cd) cannot be determined by single X-ray diffraction because these arrangements are disordered.Nishikiori et al. [6,12,13] show that arrangements of cyanides in Cd(CN) 2 host are disordered by 113 Cd-CP/MAS NMR.For complex I, crystal structure is shown in Figure 1 and selected parameters are listed in Table 2.The complex I consists of one crystallographically independent Cd(II) ion; the Cd(II) is labeled Cd1.Cd1 exhibits five-coordination (Figure 1a).Five-coordination geometry is estimated by a simple distortion parameter τ.The τ parameter was proposed by Addison et al. [15,16].The τ value is simply defined by τ = (θ 1 − θ 2 )/60, where θ 1 is the largest and θ 2 is second largest basal angle, a perfect square pyramid is characterized by τ = 0, while τ = 1 means a perfect trigonal bipyramid [15,16].For the Cd1, τ is 0.82 from selected bond angles in Table 2. Therefore, Cd1 is slightly distorted Cd TB .Around the Cd1, one hydroxyl oxygen atom O1 of Etcel ligand is located at one of the axial positions and four cyanides are located at the remaining positions, namely, another axial position (denoted as ax ) and three equatorial positions ( eq ).Cd1 is located in the general position.Atoms labeled C2/N2 or C3/N3 are hybrid due to the disorder of arrangement of cyanide (Figure 1a), and due to the midpoints of C≡N bonds on the symmetry of the lattice [1][2][3][4][5][6]12].The values of bond lengths around Cd(II) ions decrease in the order Cd TB -O > Cd TB -(CN) ax > Cd TB -(CN) eq (Table 2).Cd(CN) 2 framework is distorted-tridymite-like structure, and the cavities' shape is distorted [6 5 ] t-afi tile [17,18].The cavities of Cd(CN) 2 network are occupied by the Etcel ligands (Figure 1b,c).Etcel ligand dose not protrude from one cavity.The Etcel ligand is connected with the neighboring Etcel by hydrogen bonds between one ligand's hydroxyl oxygen atom O1 and the other's etheric oxygen atom O2 (Figure 1c and Table 2).In thermogravimetric analysis (TGA) for I (Figure S1), thermogravimetric (TG) and differential thermogravimetric (DTG) curves showed one-step weight loss in the range from about 100 • C to 155 • C.This supported the proposition that the Etcel ligand is crystallographically independent as shown in Figure 1a, and that the Cd(CN) 2 cavity is uniformity as shown in Figure 1b.The absolute values of torsion angles of ethyleneglycol fragment (O-CH 2 -CH 2 -O) are values close to 60 • (Table 2). Tus, the conformation of the ethyleneglycol fragment in Etcel ligand is gauche form.As a result, (O-CH 2 -CH 2 -O) 2 eight-membered ring is constructed by the two ethyleneglycol fragments.The carbon atom (C11 or C11') binding with hydroxyl oxygen atom is disordered (Figure 1a).For complex I, crystal structure is shown in Figure 1 and selected parameters are listed in Table 2.The complex I consists of one crystallographically independent Cd(II) ion; the Cd(II) is labeled Cd1.Cd1 exhibits five-coordination (Figure 1a).Five-coordination geometry is estimated by a simple distortion parameter τ.The τ parameter was proposed by Addison et al. [15,16].The τ value is simply defined by τ = (θ1 − θ2)/60, where θ1 is the largest and θ2 is second largest basal angle, a perfect square pyramid is characterized by τ = 0, while τ = 1 means a perfect trigonal bipyramid [15,16].For the Cd1, τ is 0.82 from selected bond angles in Table 2. Therefore, Cd1 is slightly distorted CdTB.Around the Cd1, one hydroxyl oxygen atom O1 of Etcel ligand is located at one of the axial positions and four cyanides are located at the remaining positions, namely, another axial position (denoted as ax) and three equatorial positions (eq).Cd1 is located in the general position.Atoms labeled C2/N2 or C3/N3 are hybrid due to the disorder of arrangement of cyanide (Figure 1a), and due to the midpoints of C≡N bonds on the symmetry of the lattice [1][2][3][4][5][6]12].The values of bond lengths around Cd(II) ions decrease in the order CdTB-O > CdTB-(CN)ax > CdTB-(CN)eq (Table 2).Cd(CN)2 framework is distorted-tridymite-like structure, and the cavities' shape is distorted [6 5 ] t-afi tile [17,18].The cavities of Cd(CN)2 network are occupied by the Etcel ligands (Figure 1b,c).Etcel ligand dose not protrude from one cavity.The Etcel ligand is connected with the neighboring Etcel by hydrogen bonds between one ligand's hydroxyl oxygen atom O1 and the other's etheric oxygen atom O2 (Figure 1c and Table 2).In thermogravimetric analysis (TGA) for I (Figure S1), thermogravimetric (TG) and differential thermogravimetric (DTG) curves showed one-step weight loss in the range from about 100 °C to 155 °C.This supported the proposition that the Etcel ligand is crystallographically independent as shown in Figure 1a, and that the Cd(CN)2 cavity is uniformity as shown in Figure 1b.The absolute values of torsion angles of ethyleneglycol fragment (O-CH2-CH2-O) are values close to 60° (Table 2).Thus, the conformation of the ethyleneglycol fragment in Etcel ligand is gauche form.As a result, (O-CH2-CH2-O)2 eight-membered ring is constructed by the two ethyleneglycol fragments.The carbon atom (C11 or C11') binding with hydroxyl oxygen atom is disordered (Figure 1a).For complex II, crystal structure is shown in Figure 2 and selected parameters are listed in Table 3.The complex II contains two distinct coordination geometric Cd(II) ions; the one slightly distorted Cd TB (Cd1 (τ = 0.76), Cd2 (τ = 0.87) and Cd3 (τ = 0.82) (from Table 3)) [15,16] and the other Cd T (Cd4) in a ratio of 3:1 (Figure 2a).Around the Cd TB , one hydroxyl oxygen atom of Bucel ligand is located at one of the axial positions and four cyanides are located at the remaining positions.Cd T is coordinated by only four cyanides.All Cd(II) ions are located on the general positions.The values of bond lengths around Cd(II) ions decrease in the order Cd TB -O > Cd TB -(CN) ax > Cd TB -(CN) eq ≈ Cd T -(CN) (Table 3).This tendency is similar to I and Cd 5 (CN) 10 (H 2 O) 4 •4C 6 H 11 OH [6].The Cd(CN) 2 framework forms zeolite-like structure and three kinds of cavities.These cavities' shapes are distorted [6 5 ] t-afi, distorted [6 2 .8 2 ] t-kaa and distorted [4 2 .6 4 ] t-lau tiles [17,18], respectively (Figure 2b-d).To our knowledge, zeolite constructed by the three tiles are not reported and the framework topology is new [17,18].The all cavities of Cd(CN) 2 network are occupied by the Bucel ligands, but the terminals of the butyl groups protrude from one cavity (Figure 2d).This is suggested below; Bucel does not coordinate to one of four Cd(II) ions because total volume of Bucel coordinating to four of four Cd(II) ions exceeds the capacity of the total cavity of the Cd(CN) 2 network.In the t-afi and t-kaa cavities, the Bucel ligand is connected with the neighboring Bucel by hydrogen bonds between one ligand's hydroxyl oxygen atom and the other's etheric oxygen atom (Figure 2d and Table 3) as case of I. Conformations of ethyleneglycol fragments of Bucel ligands are gauche form (Table 3).In TGA for II (Figure S2), TG and DTG curves showed three-steps weight loss in the range of about 100 • C to 180 • C.This suggests that one Bucel ligand was removed from the complex II having three kind of cavities (Figure 2b-d) per one-step.In Bucel ligands, part of butyl groups and of the ethylene groups are disordered.In contrast, because etheric oxygen atoms (O2, O4 and O6) of the Bucel ligand connect hydroxyl oxygen atoms (O3, O1 and O5) of the neighboring Bucel by hydrogen bond, etheric oxygen atoms are in a more strongly fixed position than the butyl groups' atoms and have small anisotropic parameters.
Crystals 2016, 6, 103 5 of 11 bonds between one ligand's hydroxyl oxygen atom and the other's etheric oxygen atom (Figure 2d and Table 3) as case of I. Conformations of ethyleneglycol fragments of Bucel ligands are gauche form (Table 3).In TGA for II (Figure S2), TG and DTG curves showed three-steps weight loss in the range of about 100 °C to 180 °C.This suggests that one Bucel ligand was removed from the complex II having three kind of cavities (Figure 2b-d) per one-step.In Bucel ligands, part of butyl groups and of the ethylene groups are disordered.In contrast, because etheric oxygen atoms (O2, O4 and O6) of the Bucel ligand connect hydroxyl oxygen atoms (O3, O1 and O5) of the neighboring Bucel by hydrogen bond, etheric oxygen atoms are in a more strongly fixed position than the butyl groups' atoms and have small anisotropic parameters.
For complex III, the crystal structure is shown in Figure 3 and selected parameters are listed in Table 4.The complex III contains two distinct coordination geometry Cd(II) ions; the one Cd OC (Cd1) and the other Cd T (Cd2, Cd3 and Cd4) in a ratio of 1:3 (Figure 3a).All Cd(II) ions lie on mirror plane in the cell.Around the Cd OC , two oxygen atoms of water molecules are located at the cis-positions (Figure 3d) and four cyanides are located at the remaining positions.The water molecule (O1 or O11) is disordered (Figure 3a,d).The difference between the bond lengths of Cd1-O1 and Cd1-O11 (Table 4) indicates that the water molecule's position is not constant.Cd T is coordinated by four cyanides.The values of bond lengths around Cd(II) ions decrease in the order Cd OC -O ≈ Cd OC -(CN) ≈ Cd T -(CN) (Table 4).The Cd OC -O bond of III (Table 4) is shorter than Cd TB -O bonds of I and II (Tables 2 and 3).The Cd(CN) 2 framework forms zeolite-like structure and two kind of cavities.These cavities' shape are distorted [6 4 ] t-hes and distorted [4 2 .6 2 .8 2 ] t-kdq tiles 17 , respectively (Figure 3b,c).The fragment of distorted t-kdq tile is similar to Cd(CN) 2 framework for Cd(CN) 2 (H 2 O)•dmf [8].JBW [17,18] zeolite constructed by the above two tiles are reported.However, the III contains more t-hes tile than JBW.To our knowledge, the framework topology is new [17,18].The Hexcel molecule does not coordinate to Cd(II) ion, and the hydroxyl oxygen atom connects the water molecule through weak hydrogen bond in the t-kdq cavity (Figure 3 and Table 4).In the Hexcel molecule, Weak C-H•••O interaction is observed (Table 4).Two crystallographically independent Hexcel molecules exist in the crystal.TG and DTG curves (Figure S3) were observed in three steps of weight loss ranging from about 40 • C to 75 • C, from 80 • C to 205 • C, and from 205 • C to 230 • C. The first weight loss seems to trigger desorption of Hexcel molecules at the second weight loss [19].The third weight loss seems to involve elimination of water ligands.The Hexcel molecules' atoms are disordered.In addition, because Hexcel molecules lie on the mirror plane for the cell (Figure 3a,d), the atoms are almost disordered to symmetrically mirror themselves.

Single Crystal X-ray Diffraction
The structural characterization for I and III were determined by the single crystal X-ray diffraction using a BRUKER APEXII SMART CCD area-detector diffractometer (Bruker, Madison, WI, USA) with monochromated Mo-Kα (λ = 0.71073 Å) under the temperature controlled N 2 gas flow.The structural characterization for the II was determined by the single crystal X-ray diffraction using a BRUKER SMART CCD area-detector diffractometer (Bruker, Madison, WI, USA) with monochromated Mo-Kα under the temperature controlled N 2 gas flow.The diffraction data were treated using APEX2 [20] and SAINT ver.7.23A [21] for I and III, and using SMART [22] and SAINT ver.6.22 [23] for II.Absorption data were performed using SADABS [24].Their structures were solved by direct method, expanded using Fourier techniques, and refined by full-matrix least-square refinement.
For I and II, H atoms for hydroxyl group were located in difference syntheses and refined isotropically.The remaining H atoms were placed at calculated positions, and allowed to ride on the parent atom.For II, the (0 0 2) reflection affected by the beamstop was omitted from the final refinement.
For III, H atoms for water molecules were mixed that were located in difference syntheses, and that were placed at calculated positions.The remaining H atoms were placed at calculated positions.All H atoms were allowed to ride on the parent atom.The (2 0 0) reflection affected by the beamstop was omitted from the final refinement.
Cadmium(II) cyanide clathrates with dialkyl-ether guests are reported that the host with short dialkyl-ether guest are Cd 8 (CN) 16 (H 2 O) 6 (Guest: Et 2 O or i-Pro 2 O) or Cd 3 (CN) 6 (H 2 O) 2 (Guest: Pro 2 O), [9] and that the host with Bu 2 O guest is Cd(CN) 2 [3].This work reveals that Etcel and Bucel molecules coordinate to Cd(II) ion, and that Hexcel molecule does not coordinate to Cd(II) ion.However, the Hexcel molecule may cause water molecules to coordinate to Cd(II) ion.Thus, the polar group of guest molecule may support the proposition that water molecule coordinates to Cd(II) ion in Cd(CN) 2 network, or that the molecule itself coordinates to Cd(II) ion in the network.However, the lipophilic group of the guest molecule may decrease the coordination effects.From the above, it is guessed that short-alkyl alcohol molecules such as propanol coordinate to Cd(II) ion of

Scheme 1 .
Scheme 1. Structural formulae of alkoxyethanol compounds used in this work.

Figure 1 .
Figure 1.Crystal structure of I. H atoms except OH hydrogens are omitted for clarity: (a) Asymmetric unit.Displacement ellipsoids are drawn at the 30% probability level.Because arrangements of cyanides (Cd-NC-Cd or Cd-CN-Cd) are disordered, the atoms of cyanide are labeled less clearly; (b) The Cd(CN)2 network structure view along the a axis; (c) Hydrogen bonds between neighboring Etcel ligands in cavities of distorted-tridymite-like cadmium cyanide network of I. Displacement ellipsoids are drawn at the 30% probability level.The disorder part is omitted for clarity.(Symmetry codes: iv = −x + 1, y, −z + 3/2).

Figure 1 .
Figure 1.Crystal structure of I. H atoms except OH hydrogens are omitted for clarity: (a) Asymmetric unit.Displacement ellipsoids are drawn at the 30% probability level.Because arrangements of cyanides (Cd-NC-Cd or Cd-CN-Cd) are disordered, the atoms of cyanide are labeled less clearly; (b) The Cd(CN) 2 network structure view along the a axis; (c) Hydrogen bonds between neighboring Etcel ligands in cavities of distorted-tridymite-like cadmium cyanide network of I. Displacement ellipsoids are drawn at the 30% probability level.The disorder part is omitted for clarity.(Symmetry codes: iv = −x + 1, y, −z + 3/2).

Table 1 .
Crystal Data for I, II and III.
Scheme 1. Structural formulae of alkoxyethanol compounds used in this work.

Table 2 .
Selected Parameters for I.

Table 3 .
Selected Parameters for II.

Table 4 .
Selected Parameters for III.