Retro-Crystal Engineering Analysis of Two N-Methylethylenediammonium Cadmium Halide Salts Obtained by Dimensional Reduction and Recombination of the Hexagonal CdX2 Lattice
CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 2 673-679
Adrienne Thorn and Roger D. Willett* Department of Chemistry, Washington State University, Pullman, Washington 99164
Brendan Twamley University Research Office, University of Idaho, Moscow, Idaho 83844 Received June 10, 2004
ABSTRACT: The reaction of the N-methylethylenediammonium dication (MEDA2+) with cadmium halides in acid solutions leads to the formation of the compounds (MEDA‚H2O)2Cd4Cl12‚2H2O and (MEDA‚H2O)Cd3Br8‚xH2O. Crystal structure determinations were carried out on both salts, and retro-crystal engineering analyses were made on the structures. The inorganic framework in both structures contain networks of edge-shared octahedra. The chloride complex has the appearance of slices cut from the hexagonal CdCl2 lattice by the MEDA2+ dications. The dications sheath the ribbons with one set of cations lying on the faces of the ribbons and with the second set capping the edges. N-H‚‚‚Cl, O-H‚‚‚Cl, N-H‚‚‚O as well as C-H‚‚‚Cl hydrogen bonds provide three-dimensional stability to the lattice. The bromide salt contains a microporous, stepped layer structure. This structure is derived from the parent hexagonal CdBr2 lattice by dimensional reduction to serrated (Cd3Br93-)∞ ribbons of edge-shared CdBr6 octahedra. Recombination via formation of edge-shared linkages between these ribbons leads to the development of a stepped layer structure. These layers are perforated due to the excision of Cd2Br22+ units at the step-edges in the layers. The MEDA2+ dications sit above and below these holes, providing charge compensation for the excised fragments. Thermal analyses of both compounds show the loss of water molecules in the temperature range of 80120 °C with subsequent decomposition of the organic cations occurring above 300° C. Structural phase transitions were observed near 230 °C in both compounds. Introduction Hybrid organic/inorganic systems provide the opportunity to design new types of materials with unusual structures and properties. Most of the strategies follow a “building block” approach in which structures are built up from smaller oligomeric species. An alternative strategy that has been used to rationalize the structures of many low dimension inorganic AlMmXn materials has been the concept of dimensional reduction. Here the interaction of an AX species with a parent MXn lattice results in the replacement of M-X-M bridges by pairs of terminal M-X bonds, resulting in a structure with lower dimensionality. Tulsky and Long have recently applied this approach to a wide variety of inorganic salts.1 This concept can be readily expanded in two aspects. First, the parent structures can be extended to AMXn structures, such as the three-dimensional AMX3 perovskites.2 Second, it is logical to extend the concept to hybrid organic/inorganic salts of the same AlMmXn type where A(+) is now an organic cation. The most notable success of this approach to hybrid systems has undoubtedly been with the layered perovskite materials. In these systems, monoammonium cations may be used to slice the parent cubic AMX3 perovskite structure into (RNH3)2MX4 layers.3 These contain sheets of MX6 octahedra sheathed by the RNH3+ cations. When M(II) is a paramagnetic transition metal ion, these have played an important role in the development of low dimensional magnets.4 The semiconductive properties
of the Sn(II) and Pb(II) ions make them attractive for device applications because of their low-temperature processibility.5 The structure of another series of hybrid organic/ inorganic compounds can be rationalized in terms of an augmented dimensional reduction process based on the parent CuX2 structure.6 This structure can be envisioned as a stack of infinite planar bibridged CuX2 chains linked into layers via semi-coordinate Cu‚‚‚X bonds.7 This is a ferrodistortive version of the CdX2 lattice.8 Reaction with AX salts leads to the formation of planar bibridged CunX2n+22- oligomers, with n ) 1, 2, ..., 7.9 Simple dimensional reduction leads to the formation of (CunX2n+22-)∞ ribbons. Further dimensional reduction into individual oligomers and recombination of the structures via formation of the semi-coordinate Cu‚‚‚X bonds leads to a wide variety of stacking polytypes of the ribbons structures. In addition, perforated CuX2 layers have been observed where Cu2+ or Cu2X22+ moieties have been excised from the layers by the presence of the A(+) cations.10 Parent structures for the application of the concept of dimensional reduction to M(II) halide compounds with octahedral coordination include those based on the CsNiCl3 structure (chains of face-shared octahedra),11 the hexagonal MX2 structure (layers of edge-shared octahedra),8 and the AMX3 perovskite structure (threedimensional array of corner-shared octahedra).2 Unfortunately, only a few examples of low-dimensional lattices obtained by dimensional reduction of the hexagonal
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MX2 layer lattices have been reported. Tulsky and Long cite single and double chains of edge-shared octahedra in their review of inorganic materials, as well as a perforated layer in which individual M2+ ions have been removed. Corradi and co-workers have reviewed the known hybrid organic/inorganic low-dimensional structures found in the cadmium halide system.12 Their review, which includes examples based on each of the three parent structures listed above, documents a variety of ribbon structures that can be described in terms of the dimensional reduction of the hexagonal MX2 structure. In a recent paper, we cited five examples from the literature of hybrid organic/inorganic systems that contain simple ribbons derived for the MX2 layer structure as well as a perforated layer that features the excision of M2X22- species.13 In that paper, we reported the structures of several salts that contain recombined columnar stacks that are polytypes of the simple ribbons that could be cut from the hexagonal layer MX2 lattice. These represented the first examples of hybrid organic/ inorganic polytypic structures based on edge-shared octahedra. In this paper, we report the structures of two cadmium(II) halide structures obtained by the reaction of CdX2 with (N-methylethylenediammonium)X2 (this Nmethyl substituted ethylenediammonium dication is henceforth denoted as MEDA2+). The first structure, that of (MEDA‚H2O)2Cd4Cl12‚2H2O, is derived from the parent CdX2 structure by simple dimensional reduction into ribbons and represents an additional member of this family of ribbons derived from the hexagonal MX2 type lattices. The visualization of the complex structure of (MEDA‚H2O)Cd3Br8‚xH2O involves both dimensional reduction of the parent structure into serrated ribbons followed by fusion into a stepped microporous layer structure, which represents a new variation of the combined concepts of dimensional reduction and recombination. Results Structure Description. Both salts contain extended halometalate frameworks that are interleaved by the diammonium cations and loosely bound water molecules. The (MEDA‚H2O)2Cd4Cl12‚2H2O structure consists of cadmium chloride ribbons separated by (MEDA2+)‚H2O cationic units and waters of hydration. Two disordered and crystallographically independent (MEDA2+)‚H2O cationic units are located at centers of inversion in the triclinic unit cell. One cation unit of each disordered pair is shown in the top portion of Figure 1. Additional lattice water molecules are also present. The lower part of Figure 1 shows the local environment of the cadmium ions in the structure. In this figure, four additional symmetry-generated halide ions (labeled ClnA or ClnB, shown with open ellipsoids in Figure 1b) have been added to complete the octahedral coordination of each Cd atom. A wide variation is observed in the Cd-Cl bond distances, with distances ranging from 2.514(1) to 2.838(1) Å, along with significant angular distortions of the Cd octahedra as well. The Cd and Cl atoms aggregate into (Cd4Cl124-)∞ ribbons of edge-shared octahedra as shown in the balland-stick diagram as well as the polyhedral representation in Figure 2. These may be viewed as slices from
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Figure 1. (top) Illustration of the two independent MEDA‚ H2O2+ pairs, neglecting the disorder imposed by the centers of inversion in (MEDA‚H2O)2Cd4Cl12‚2H2O. (bottom). Illustration of the coordination of the two independent Cd(II) ions. The unique atoms in the asymmetric unit have been augmented with additional symmetry-generated chloride ions (open ellipsoids) to complete the Cd octahedra. The Cd and Cl thermal ellipsoids are shown at the 50% probability level.
Figure 2. Ball-and-stack (top) and polyhedra (bottom) illustrations of the [Cd4Cl124-]∞ ribbons in (MEDA‚H2O)2Cd4Cl12‚2H2O.
Scheme 1
the parent CdCl2 hexagonal edge-shared layer structure. The Cd4Cl124- repeat unit can be described as planar bibridged tetrameric units decorated with additional chloride ions in trans positions at each end of the tetramer. The ribbons are then built up by stacking these tetrameric units in a pattern shown diagrammatically in Scheme 1.14 In this schematic representation, planar bibridged tetrameric units are represented by the linear sequence of four squares, where a Cd atom is at the center of each square and the Cl atoms are located at the corners. (The lines denoting the Cd-Cl bonds are only shown for the uppermost oligomer.) Adjacent tetrameric units are displaced so that linking Cd-Cl bonds are formed between them. The open circles represent the decorative chloride ions needed to complete the octahedral coordination of the terminal Cd ion in each tetrameric unit. This has the augmented Geiser
Retro-Crystal Engineering Analysis
Figure 3. Packing of ribbons in (MEDA‚H2O)2Cd4Cl12‚2H2O, showing disorder of the MEDA‚H2O2+ cationic species, as viewed parallel to the a axis. Short N-H‚‚‚Cl, O-H‚‚‚Cl, and N-H‚‚‚O contacts are shown by the dashed lines.
notation9b n[(t|,t⊥)]Xm ) 4[(3/2,1/2)]Cl2 where n ) number of Cd atoms in the oligomer, t| and t⊥ are the translations (in units of the Cd-Cd repeat distance) parallel and perpendicular to the length of the oligomer, while m and X denote the number and identity of the decoration atoms. This has the result that the two chloride ions at either end of a tetramer are not involved in bridging to an adjacent Cd ion. The packing of the ribbons is shown in Figure 3. The ribbons run parallel to the x-axis and lie roughly on the (0, 3, 3 h ) planes. One set of the MEDA2+‚H2O cationic units caps the edges of the ribbons, while the second set caps the faces of ribbons. The cationic units form hydrogen bonds with the halide ions on the ribbons, with most of the hydrogen bonds directed to nonbridging halide ions. This hydrogen bonding is crucial in providing three-dimensional stability to the structure as the -NH3+ groups (and associated water molecule) hydrogen bond to one ribbon and the -NH2+ groups hydrogen bond to an adjacent ribbon. Numerous other O-H‚‚‚Cl, N-H‚‚‚O as well as C-H‚‚‚Cl interactions also help stabilize the lattice. The structure of (MEDA‚H2O)Cd3Br8‚xH2O is more complex, involving both dimensional reduction of the parent CdX2 edge-shared layer into serrated (Cd3Br92-)∞ ribbons and the recombination of the ribbons back into perforated, kinked layers. The asymmetric unit, again augmented by additional halide ions to complete the Cd octahedra, is shown in Figure 4. The Cd-Br distances again show a range of values, from 2.657(1) to 2.987(1) Å. The cadmium bromide units of the type shown in Figure 4 aggregate to form the serrated (Cd3Br93-)∞ ribbons of the type shown in the ball-and-stick and the polyhedral representations in Figure 5. Prominent in the polyhedral representation are the octahedral tabs protruding from the central portion of the ribbons. Analogous to the Cl salt, these ribbons may be viewed as stacks of planar bibridged oligomers. In this case, the basic repeat unit is composed of the Cd and unique Br atoms in Figure 4. The planar bibridged Cd3Br8 core is augmented by a single Br atom at one end of the trimer. The chain is built up by stacking these units as shown in Scheme 2a. This stacking pattern has the
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Figure 4. Asymmetric unit for (MEDA‚H2O)Cd3Br8‚xH2O, augmented with additional symmetry-generated bromide ions (open ellipsoids) to complete the Cd octahedra. The disorder of the MEDA2+ cation over two principle sites is illustrated (cation 1, solid bond; cation 2, open bonds). The methyl group in cation 1 is disordered over two sites (labeled C5 and C6). The Cd and Br thermal ellipsoids are shown at the 50% probability level.
Figure 5. Ball-and-stick (left) and polyhedral (right) representation of the serrated [Cd3Br82-]∞ ribbons in (MEDA‚H2O)Cd3Br8‚xH2O.
Scheme 2
augmented Geiser notation of 3[(3/2,1/2)(1/2,1/2)]Br. Here the use of two (t|,t⊥) vectors is needed to indicate the alternating translations as one proceeds along the ribbon. In this case, however, the process does not stop with the formation of the ribbons. Instead, edge-sharing of the octahedral tabs on adjacent ribbons occurs, fusing the ribbons back together into the stepped, perforated layers shown in the ball-and-stick and polyhedral representations in Figure 6 as well as being illustrated
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Figure 8. TGA data for (MEDA‚H2O)2Cd4Cl12‚2H2O. Figure 6. Ball-and-stick (left) and polyhedral (right) illustration of the microporous layer in (MEDA‚H2O)Cd3Br8‚xH2O formed by the fusion of the serrated ribbons. Only cation 2 is shown in the ball-and-stick illustration.
Figure 9. TGA data for (MEDA‚H2O)Cd3Br8‚xH2O
Figure 7. Packing diagram of the (MEDA‚H2O)Cd3Br8‚xH2O structure as viewed from the (001) direction. Hydrogen bonding interactions are shown by dashed lines. Only cation 2 is included in the illustration.
diagrammatically in Scheme 2b. In this manner, holes corresponding to the excision of Cd2Br22- moieties are introduced, producing microporous layers. In addition, the stepped nature of this fusion process leaves a nonbridging Br- ion on each side of the fused tabs (Figure 7). As seen in Figure 6, each micropore is sheathed by pairs of MEDA2+ cations to replace the charge of the excised Cd2Br22+ moieties. In addition, the -NH3+ groups of the dications, which sit between pairs of the nonbridging Br- anions on one layer, also hydrogen bond to the nonbridging Br- anions on adjacent layers to help provide three-dimensional stability to the lattice. The MEDA2+ cation is more severely disordered in this structure. The refinement of the structural model for the cations is complicated by the fact that partial dehydration of the sample had occurred prior to the initiation of the data collection (see thermal analysis discussion below). Thus, several sites for the water molecules were only partially occupied. The two principal disordered sites for the cations are shown in Figure 4, along with the oxygen atom of the water molecule. For this structure also, it is convenient to discuss this portion of the structure in terms of hydrated MEDA2+ cations along with additional lattice water molecules. A monohydrated dication, (MEDA2+)‚H2O, again can be identified, but now with the water molecule hydrogen bonded to the -NH2+ group rather than to the -NH3+ group as in the chloride salt. The cation in site 2 (primed labels in Figure 4) has an additional, partially occupied
water molecule hydrogen bonded to the -NH3+ group. Finally, a lattice water molecule with partial occupancy is also present. (See discussion in the experimental section.) Thermal Analysis. The TGA studies show that both compounds become fully dehydrated in the 80-120 °C region and that decomposition of the organic cation occurs at higher temperatures, leading eventually to the formation of CdX2 in both cases. The studies confirm that both compounds lose water when exposed to room environment (Pullman has very low humidity). However, details of the thermal behavior are quite different for the two compounds. For the chloride salt, weight loss in the 100 °C region was typically 3.5-6.2%, corresponding to the loss of 2.0-3.4 water molecules per formula unit (as compared to 4.0 water molecules theoretically). The percent weight loss decreased the longer the samples were exposed to dry air. Thoroughly air-dried samples showed a weight loss of 3.5% (Figure 8), corresponding to two water molecules. These remaining two water molecules would seem to correlate with the two water molecules hydrogen bonded to the dications. DSC studies of these samples showed anomalies characteristic of phase transitions near 85 and 95 °C, indicating that the loss of water from the two crystallographically different (MEDA2+)‚H2O groups occurs independently. In the higher temperature regime, the DSC results show the presence of another phase transition at approximately 235 °C. This is well before the onset of decomposition of the MEDA2+ cations at approximately 260 °C (Figure 8). The decomposition to CdCl2 is complete by 415 °C with the onset of vaporization of the CdCl2 setting in at temperatures above 450 °C. The observed weight loss (27.7%) corresponds well with that predicted for the loss of 2 moles of (MEDA)Cl2 per formula unit (28.6%). For the bromide salt, the situation is in one way simpler, and in another more complex. Air dried samples show no weight loss in the 100 °C region (see Figure 9), indicating that all of the water molecules are rather
Retro-Crystal Engineering Analysis Scheme 3
Crystal Growth & Design, Vol. 5, No. 2, 2005 677 Table 1. Crystal Data and Structure Refinement for (MEDA‚H2O)2Cd4Cl12‚2H2O and (MEDA‚H2O)Cd3Br8‚xH2O (MEDA‚H2O)2Cd4Cl12 ‚2H2O
loosely held in the crystal structure and were lost from the crystal prior to the thermal analysis. As a consequence, no DSC anomaly corresponding to a phase transition is observed in that temperature regime. Rather, a single phase transition is observed at 235 °C. Again, this probably is primarily associated with a rearrangement of the organic cations. However, as the sample is heated above 100 °C, a gradual weight loss is observed of approximately 3.4%, followed by a major loss of 17.0% initiating at 355 °C. The total loss agrees well with the prediction for one (MEDA)Br2 mole per formula unit (20.2%) to yield CdBr2. The weight loss is complete by 470 °C, at which point the onset of vaporization of CdBr2 begins. These results indicate that the MEDA2+ cations are more stable thermally in the bromide lattice than in the chloride lattice, since decomposition occurs nearly 100 °C higher in the former. This is undoubtedly associated with the layer structure in the bromide lattice, which limits migration of the decomposition products to the surface of the crystallites. The small initial loss in the 150-350 °C region is likely due to the decomposition of cations near the surface. Discussion These two examples again show the potential of hybrid organic/inorganic systems to produce novel and unusual structures in rather simple metal halide compounds. Even though the octahedral coordination geometry of the Cd2+ ion provides strong directional motifs to the structures, the subtle interplay of halide-halide interactions N-H‚‚‚X- and C-H‚‚‚X- hydrogen bonding as well as van der Waals interactions can lead to very different motifs for the lattices. The structural diversity that can be obtained is highlighted by our recent report of the structure of the (Et2NH2)3Pb3X9‚xH2O (X ) Br, I)13 series. Here the recombination of the lattice occurs within the ribbon, rather than between the ribbons as observed here for the bromide compound. The basic repeat unit in the chains is identical to that used to describe the serrated ribbon intermediates in (MEDA‚ H2O)Cd3Br8‚xH2O. However, the stacking pattern in the (Pb3X93-)∞ stacks (Scheme 3) does not lead to a simple ribbon cut from the parent PbX2 edge-shared layer. Rather, the reconstruction leads to a columnar structure that is a polytype of the serrated (Cd3Br92-)∞ ribbons. This columnar arrangement has the extended Geiser notation of 3[(3/2,1/2)(-1/2,1/2)]X. Here, the t⊥ ) -1/2 translation represents a recombinatorial form of the ribbon. Finally, it should be noted that the ethylethylenediammonium cadmium chloride salt15 contains (Cd4Cl124-)n ribbons as in the MEDA salt reported here. However, in this case, neighboring ribbons are rotated by approximately 90°, in contrast to the packing shown in Figure 3. While the concepts of dimensional reduction and recombination are useful tools in the analysis of crystal
emp form form wt temp (K) wavelength (Å) cryst syst space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Z Fcalc (mg/m3) µ (mm-1) F(000) reflx ind reflx Ra indices [I>2σ(I)] R indices (all data) a
(MEDA‚H2O)Cd3Br8 ‚xH2O
C6H32Cd4Cl12N4O4 1099.36 295(2) 0.71073
C3H12Br8Cd3N2(H2O)1.59 1079.07 295(2) 0.71073
triclinic P1 h 6.7129(8) 9.662(1) 13.455(2) 106.402(2) 97.426(2) 107.732(2) 775.0(2) 1 2.355
triclinic P1 h 8.0197(8) 10.391(1) 13.477(1) 76.223(2) 81.478(2) 67.596(2) 1006.4(2) 2 3.561
3.762 524 7007 2639 [R(int) ) 0.0342] R1 ) 0.0307, wR2 ) 0.0662 R1 ) 0.0499, wR2 ) 0.0782
19.01 964 9347 3551 [R(int) ) 0.0387] R1 ) 0.0370, wR2 ) 0.0837 R1 ) 0.0684, wR2 ) 0.0961
R1 ) Σ||Fo| - |Fc||/ Σ|Fo|. wR2 ) [(Σw||Fo|2 - |Fc|2|)/ Σw|Fo|2]1/2.
structure results that allow one to trace the genesis of a particular crystal structure, the application of these principles in the actual design of specific hybrid organic/ inorganic structures is still in its infancy. Although the octahedral stereochemistry of the metal halide provides strong directional character in the assembly of the metal halide framework, other factors involved, such as steric interactions, hydrogen bonding, and other electrostatic effects, make it difficult to predict and control the actual crystalline structure that is obtained. This implies that the analyses of the observed structures in terms of their relationship to a particular parent structure is usually an a posterior proposition, and thus should properly be termed retro-crystal engineering. Experimental Section Synthesis. The diammonium halide salts, (MEDA)X2, X ) Cl-, Br-, were prepared as follows: 3 mL of N-methylethylenediamine was combined with 3 mL of H2O. Excess 1.0 M HX (60-80 mL) was added with stirring. The resultant solutions were slowly evaporated over low heat until the salts crystallized. The salts were isolated by filtration and washing with cold 1-butanol. The cadmium salts were prepared as follows: (MEDA‚H2O)2Cd4Cl12‚2H2O: 0.2929 g of (MEDA)Cl2 and 0.7317 g of CdCl2 were dissolved in 10 mL of H2O that contained 5 drops of 4 M HCl. Rod-shaped colorless crystals were grown by slow evaporation in a desiccator. (MEDA‚H2O)Cd3Br8‚xH2O: 0.2399 g of (MEDA)Br2 and 0.5468 g of CdBr2 were dissolved in 10 mL of H2O that contained 5 drops of 4 M HBr. Flat platelike crystals were grown by slow evaporation in a desiccator. Crystals removed from solution slowly became cloudy during microscopic examination, indicating the possible loss of solvent molecules from the crystal. Thermal Analysis. TGA and DSC analyses of samples of freshly harvested and of air-dried crystals of (MEDA‚H2O)2Cd4Cl12‚2H2O and (MEDA‚H2O)Cd3Br8‚xH2O were carried out with a Perkin-Elmer TGA-7 Thermogravimetric analyzer and a Perkin-Elmer DSC 7 Differential Scanning calorimeter, respectively. TGA scans were carried out with a scan rate of 15 °C/min over the temperature range 30-800 °C. The DSC
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Table 2. Metal-Halide Bond Lengths [Å] and Angles [°] for (MEDA‚H2O)2Cd4Cl12‚2H2Oa atoms
distance
atoms
angle
atoms
angle
Cd(1)-Cl(6) Cd(1)-Cl(1) Cd(1)-Cl(3) Cd(1)-Cl(2) Cd(1)-Cl(4) Cd(1)-Cl(5)#1 Cd(2)-Cl(3) Cd(2)-Cl(2)#2 Cd(2)-Cl(5)#3 Cd(2)-Cl(4) Cd(2)-Cl(5) Cd(2)-Cl(4)#4
2.513 (2) 2.518(1) 2.630(1) 2.642(1) 2.755(1) 2.837 (1) 2.539(1) 2.558(1) 2.635(1) 2.660(1) 2.694(1) 2.713(1)
Cl(6)-Cd(1)-Cl(1) Cl(6)-Cd(1)-Cl(3) Cl(1)-Cd(1)-Cl(3) Cl(6)-Cd(1)-Cl(2) Cl(1)-Cd(1)-Cl(2) Cl(3)-Cd(1)-Cl(2) Cl(6)-Cd(1)-Cl(4) Cl(1)-Cd(1)-Cl(4) Cl(3)-Cd(1)-Cl(4) Cl(2)-Cd(1)-Cl(4) Cl(6)-Cd(1)-Cl(5)#1 Cl(1)-Cd(1)-Cl(5)#1 Cl(3)-Cd(1)-Cl(5)#1 Cl(2)-Cd(1)-Cl(5)#1 Cl(4)-Cd(1)-Cl(5)#1 Cl(3)-Cd(2)-Cl(2)#2 Cl(3)-Cd(2)-Cl(5)#3 Cl(2)#2-Cd(2)-Cl(5)#3 Cl(3)-Cd(2)-Cl(4) Cl(2)#2-Cd(2)-Cl(4)
101.16(5) 96.48(5) 90.92(4) 90.65(5) 97.80(4) 167.48(4) 93.55(5) 164.53(5) 82.63(4) 86.60(4) 170.85(5) 86.13(4) 88.86(4) 82.82(4) 79.72(3) 94.10(4) 174.92(4) 90.90(4) 86.30(4) 98.55(4)
Cl(5)#3-Cd(2)-Cl(4) Cl(3)-Cd(2)-Cl(5) Cl(2)#2-Cd(2)-Cl(5) Cl(5)#3-Cd(2)-Cl(5) Cl(4)-Cd(2)-Cl(5) Cl(3)-Cd(2)-Cl(4)#4 Cl(2)#2-Cd(2)-Cl(4)#4 Cl(5)#3-Cd(2)-Cl(4)#4 Cl(4)-Cd(2)-Cl(4)#4 Cl(5)-Cd(2)-Cl(4)#4 Cd(2)#1-Cl(2)-Cd(1) Cd(2)-Cl(3)-Cd(1) Cd(2)-Cl(4)-Cd(2)#4 Cd(2)-Cl(4)-Cd(1) Cd(2)#4-Cl(4)-Cd(1) Cd(2)#3-Cl(5)-Cd(2) Cd(2)#3-Cl(5)-Cd(1)#2 Cd(2)-Cl(5)-Cd(1)#2
93.56(4) 95.19(4) 87.31(4) 84.43(4) 173.84(4) 90.73(4) 174.55(4) 84.21(4) 84.25(4) 89.75(4) 98.35(5) 97.97(4) 95.75(4) 92.16(4) 98.09(4) 95.57(4) 97.96(4) 90.66(4)
a
Symmetry transformations used to generate equivalent atoms: #1 x + 1, y, z; #2 x - 1, y, z; #3 -x, -y, -z; #4 -x + 1, -y, -z. Table 3. Metal-Halide Bond Lengths [Å] and Angles [°] for (MEDA‚H2O)Cd3Br8‚xH2Oa atoms
distance
atoms
angle
atoms
angle
Cd(1)-Br(2) Cd(1)-Br(1) Cd(1)-Br(1)#1 Cd(1)-Br(4) Cd(1)-Br(7)#2 Cd(1)-Br(3) Cd(2)-Br(4) Cd(2)-Br(8)#3 Cd(2)-Br(3) Cd(2)-Br(5) Cd(2)-Br(5)#2 Cd(2)-Br(6) Cd(3)-Br(7) Cd(3)-Br(8) Cd(3)-Br(3)#2 Cd(3)-Br(6) Cd(3)-Br(5) Cd(3)-Br(6)#3
2.657(1) 2.758(1) 2.760(1) 2.789(1) 2.798(1) 2.988(1) 2.684(1) 2.686(1) 2.769(1) 2.818(1) 2.831(1) 2.836(1) 2.683(1) 2.693(1) 2.778(1) 2.797(1) 2.842(1) 2.852(1)
Br(2)-Cd(1)-Br(1) Br(2)-Cd(1)-Br(1)#1 Br(1)-Cd(1)-Br(1)#1 Br(2)-Cd(1)-Br(4) Br(1)-Cd(1)-Br(4) Br(1)#1-Cd(1)-Br(4) Br(2)-Cd(1)-Br(7)#2 Br(1)-Cd(1)-Br(7)#2 Br(1)#1-Cd(1)-Br(7)#2 Br(4)-Cd(1)-Br(7)#2 Br(2)-Cd(1)-Br(3) Br(1)-Cd(1)-Br(3) Br(1)#1-Cd(1)-Br(3) Br(4)-Cd(1)-Br(3) Br(7)#2-Cd(1)-Br(3) Br(4)-Cd(2)-Br(8)#3 Br(4)-Cd(2)-Br(3) Br(8)#3-Cd(2)-Br(3) Br(4)-Cd(2)-Br(5) Br(8)#3-Cd(2)-Br(5) Br(3)-Cd(2)-Br(5) Br(4)-Cd(2)-Br(5)#2 Br(8)#3-Cd(2)-Br(5)#2 Br(3)-Cd(2)-Br(5)#2 Br(5)-Cd(2)-Br(5)#2 Br(4)-Cd(2)-Br(6) Br(8)#3-Cd(2)-Br(6) Br(3)-Cd(2)-Br(6) Br(5)-Cd(2)-Br(6)
96.72(3) 97.07(3) 87.50(3) 90.29(3) 172.96(4) 91.05(3) 89.92(3) 91.65(3) 173.01(4) 88.96(3) 171.13(4) 89.34(3) 89.64(3) 83.76(3) 83.42(3) 94.42(3) 90.10(3) 94.48(3) 174.05(4) 90.75(3) 92.42(3) 90.29(3) 174.67(3) 87.99(3) 84.42(3) 91.98(3) 87.99(3) 176.64(3) 85.27(3)
Br(5)#2-Cd(2)-Br(6) Br(7)-Cd(3)-Br(8) Br(7)-Cd(3)-Br(3)#2 Br(8)-Cd(3)-Br(3)#2 Br(7)-Cd(3)-Br(6) Br(8)-Cd(3)-Br(6) Br(3)#2-Cd(3)-Br(6) Br(7)-Cd(3)-Br(5) Br(8)-Cd(3)-Br(5) Br(3)#2-Cd(3)-Br(5) Br(6)-Cd(3)-Br(5) Br(7)-Cd(3)-Br(6)#3 Br(8)-Cd(3)-Br(6)#3 Br(3)#2-Cd(3)-Br(6)#3 Br(6)-Cd(3)-Br(6)#3 Br(5)-Cd(3)-Br(6)#3 Cd(1)-Br(1)-Cd(1)#1 Cd(2)-Br(3)-Cd(3)#2 Cd(2)-Br(3)-Cd(1) Cd(3)#2-Br(3)-Cd(1) Cd(2)-Br(4)-Cd(1) Cd(2)-Br(5)-Cd(2)#2 Cd(2)-Br(5)-Cd(3) Cd(2)#2-Br(5)-Cd(3) Cd(3)-Br(6)-Cd(2) Cd(3)-Br(6)-Cd(3)#3 Cd(2)-Br(6)-Cd(3)#3 Cd(3)-Br(7)-Cd(1)#2 Cd(2)#3-Br(8)-Cd(3)
89.36(3) 94.13(3) 89.71(3) 94.55(3) 174.64(3) 90.69(3) 92.25(3) 89.55(3) 175.76(3) 87.58(3) 85.56(3) 91.36(3) 87.54(3) 177.58(3) 86.50(3) 90.26(3) 92.50(3) 93.52(3) 89.96(3) 90.29(3) 96.12(3) 95.58(3) 94.27(3) 90.85(3) 94.87(3) 93.50(3) 88.77(3) 96.50(3) 95.41(3)
a Symmetry transformations used to generate equivalent atoms: #1 -x + 1, -y + 1, -z - 1; #2 -x + 1, -y + 1, -z; #3 -x + 2, -y + 1, -z.
scans were carried out at 5 °C/min for both samples with a temperature range of 30-290 °C for the chloride salt and 80500 °C for the bromide salt. Crystallography. Data for both compounds were collected on a Bruker 3-circle platform diffractometer equipped with a SMART 1K CCD detector. X-ray examination of fresh Br salt crystals yielded lattice constants that gradually changed with time over a several day period, with slowly decreasing unit cell volumes. This is consistent with a gradual loss of solvent. Data were collected on a crystal that had been removed from solution for several weeks. The frame data were acquired with the SMART16 software at 295 K using MoKR radiation (λ ) 0.71073 Å). The frames were then processed using the SAINT software17 to give the hkl file corrected for Lp/decay. The absorption correction was performed using the SADABS18 program. The structures were solved by Patterson techniques using the SHELX-9019 program and refined by the least-
squares method on F2, SHELXL-97,20 incorporated in SHELXTL V 5.03.21 For the chloride salt, the solution process yielded a metal/ halide ribbon composed of edge-shared octahedra in which there are two crystallographically independent Cd(II) ions. Refinement in the centrosymmetric P1 h space group yielded two crystallographically independent MEDA2+ cations located on two different centers of inversion. This forced a 2-fold disorder of the cations at each site. Additional peaks near the cations were assumed to be water molecules hydrogen bonded to the terminal -NH3+ end of the cations. For the cation containing the N1 atom, the center of the C-C was located essentially coincident with the center of inversion. Hence, N1 and C1 were included with full occupancy and the disorder modeled by assigning half occupancy to the C2 and O2 atoms and all nonhydrogen atoms were assigned anisotropic thermal parameters. For the second cation (the one containing N2),
Retro-Crystal Engineering Analysis the cation was displaced a significant distance from the center of inversion and the disorder was modeled assuming 50% occupancy of the two inversion related sites. Weak geometrical restrictions were placed on the geometry of the cation and isotropic thermal parameters were assigned to all atoms. In addition, a lattice water molecule was apparent. Hydrogen atoms for the cations were placed at calculated positions, but no hydrogen atoms were assigned to the water molecules. All non-hydrogen atoms were refined with anisotropic thermal parameters. The structure solution for the bromide salt in the triclinic space group P1 h yielded a complex two-dimensional metal halide structure of edge-shared octahedra. The difference Fourier syntheses based on this Cd/Br network clearly showed the presence of disorder of the MEDA2+ cation and an associated water molecule in the structure. The main features of the disorder could be accounted by a two-site model with refinement proceeding successfully with a minimum of loose constraints on the C-C and C-N distances. In addition, one of the sites includes an additional water molecule with partial occupancy. The results are shown in Figure 4. However, the difference Fourier maps still showed small residual electron density remote from any other atoms. This was assigned as a partially occupied water molecule site. This is consistent with the microscopic and preliminary X-ray examination. Given the presence of disorder of the cations in the presence of the heavy Cd and Br atoms, the final structure refinement was carried out with isotropic thermal displacement parameters for the N, C, and O atoms. The occupancy factors for the two cation sites refined to 0.55(1) and 0.45(1), while the occupancy factors were 0.21(1) for the additional water molecule associated with the second site and 0.41(2) for the lattice water molecule. Hydrogen atoms were not included for the water molecules, given the disorder and the fractional occupancy of some of those sites. Table 1 gives a summary of crystal data with collection and refinement parameters. Tables 2 and 3 give the Cd-X distances and angles for the Cl and Br salts, respectively.
Acknowledgment. This work was supported in part by ACS-PRF Grant 34779-AC5. The Bruker (Siemens) SMART CCD diffraction facility was established at the University of Idaho with the assistance of the NSFEPSCoR program and the M. J. Murdock Charitable Trust, Vancouver, WA. Supporting Information Available: Crystal data for both compounds in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.
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Crystal Growth & Design, Vol. 5, No. 2, 2005 679 (3) See Mitzi, D. B. J. Chem. Soc, Dalton 2001, 1 for a good review. (4) de Jongh, L. J.; Miedema, A. R. Adv. Phys. 1974, 23, 1 (5) Mitzi D. B.; Chondroudis, K.; Kagan, C. R., IBM J. Res., Dev. 2001, 45, 29. (6) Willett, R. D. Acta Crystallogr. 1998, B54, 503. (7) Wells, A. F. J. Chem. Soc. 1947, 1670. (8) (a) Pauling, L.; Hoard, J. L. Z. Kristallogr. Kristallgeom. Kristallphys. Kristallchem. 1930, 74, 546. (b) Smirvona, L.; Brager, A.; Zhdanov, H. Acta Physicochim. 1941, 15, 255. (9) (a) Halvorson, K. E.; Grigereit, T.; Willett, R. D. Inorg. Chem. 1987, 26, 1716. (b) Geiser, U.; Willett, R. D.; Lindbeck, M.; Emerson, K. Inorg. Chem. 1986, 25, 1173. (c) Willett, R D.; Geiser, U. Acta Chem. Croat. 1984, 57, 751. (d) Bond, M. R.; Willett, R. D. Inorg. Chem. 1984, 28, 3267. (e) Willett, R.D.; Bond, M. R.; Pon, G. Inorg. Chem. 1990, 29, 4160. (f) Willett, R. D. Acta Crystallogr. 1993, A49, 613. (10) (a) Weiss, S.; Willett, R. D. Acta Crystallogr. 1993, B49, 283. (b) Murray, K.; Willett, R. D. Acta Crystallogr. 1993, C49, 1739. (11) McPherson, G. L.; Wall, J. E. Jr.; Hermann, A. M. Inorg. Chem. 1968, 7, 2629. (12) Bonomartini-Corradi, A.; Ferrari, A. M.; Pellacani, G. C. Inorg. Chim. Acta 1998, 272, 253. (13) Willett, R. D.; Maxcy, K. R.; Twamley, B. Inorg. Chem. 2002, 41, 7024. (14) The stacking diagrams and associated Geiser notation were developed to describe structural types derived from the ferrodistortive CuX2 structure. The Jahn-Teller elongation of the octahedra defines a unique orientation for the stacking diagrams and Geiser notation. In these structures, based on the hexagonal CdX2 structure types, the stacking patterns are now being developed from one of three different possible orientations. Our choice is made so as to give the longest possible base oligomer and the simplest repeat pattern in the stacking pattern. This choice is different than that in ref 12. (15) Bonomartini-Corradi, A.; Cramarossa, M. R.; Pellacani, G. C.; Battaglia, L P.; Giusti, J. Gazz. Chim. Ital. 1994, 124, 481. (16) SMART V4.045 Software for the CCD Detection system, Bruker AXS Inc., Madison, WI, 1996. (17) SAINT V 4.035 Software for the CCD Detector System, Bruker AXS, Inc., Madison, WI, 1996. (18) SADABS Program for Absorption Correction for Area Detectors, Bruker AXS Inc., Madison, WI, 1996. (19) Sheldrick, G. M., SHELXS-90, Program for the Solution of Crystal Structure, University of Go¨ttingen, Germany, 1986. (20) Sheldrick, G. M., SHELXL-97, Program for the Refinement of Crystal Structures, University of Go¨ttingen, Germany, 1997. (21) SHELXTL 5.10 (PC Version), Program Library for Structure Solution and Molecular Graphics, Bruker AXS Inc., Madison, WI, 1997.
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