Crystal Packing in Planar Platinum(II) and Palladium(II) Complexes

Feb 25, 2009 - Emily M. Gussenhoven, Martyn Jevric, Marilyn M. Olmstead*, James C. Fettinger, Mark Mascal* and Alan L. Balch*. Department of Chemistry...
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CRYSTAL GROWTH & DESIGN

Crystal Packing in Planar Platinum(II) and Palladium(II) Complexes. Hydrogen-Bond-Mediated Supramolecular Assembly of Ten Wedge-Shaped Molecules into a Cyclic Array

2009 VOL. 9, NO. 4 1786–1792

Emily M. Gussenhoven, Martyn Jevric, Marilyn M. Olmstead,* James C. Fettinger, Mark Mascal,* and Alan L. Balch* Department of Chemistry, UniVersity of California, DaVis, California 95616 ReceiVed August 19, 2008; ReVised Manuscript ReceiVed January 9, 2009

ABSTRACT: The molecular packing arrangements for the unsolvated compounds, PtCl2(ATQ-CH2NH2) (1a) and PdCl2(ATQCH2NH2) (2) (ATQ ) azatriquinane), and two solvates of the platinum complex, 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b) and 3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2) (1c), are reported. These planar, d8 complexes have a wedgelike shape due to the presence of the bulky azatriquinane unit coordinated directly to the metal. All of the crystals exhibit hydrogen bonding between the N-H groups of one molecule and the chloride ligands on another. Despite the similar sizes and shapes of the complexes, the unsolvated compounds, PtCl2(ATQ-CH2NH2) (1a) and PdCl2(ATQ-CH2NH2) (2), pack in entirely different fashions, with metallophilic interactions between pairs of cofacial complexes in the palladium complex. The platinum complex lacks the metallophillic interactions. The structure of 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b) is noteworthy for two features. First, these crystals contain an ordered cyclic assembly of 10 molecules of the complex with all the Pt-Cl groups directed toward the inside of the ring. The formation of this supramolecular macrocyclic array is facilitated by extensive hydrogen bonding between the NH groups of one molecule and the chloride ligands of another. Second, these crystals also contain a poorly organized region where one PtCl2(ATQ-CH2NH2) molecule is disordered over several orientations. 3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2) (1c) crystallizes with three molecules of the platinum complex in a crescent-shaped array that shows some similarity with the cyclic structure found in 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b). Introduction Molecular packing in planar, d8 transition metal complexes frequently involves the formation of columnar materials in which the planar units are stacked. Usually, this stacking is accompanied by attractive metallophillic interactions between the metal ions. These metal-metal interactions can induce specific physical properties (e.g., conductivity, luminescence) that make them candidates for functional materials. One of the earliest examples was the formation of Magnus’ green salt, [(NH3)4Pt][PtCl4], whose green color differed markedly from that of the component ions-colorless [(NH3)4Pt]2+ and orange [PtCl4]2--and whose one-dimensional properties are under continuing investigation.1-3 Crystals of [(NH3)4Pt][PtCl4] contain stacks of alternating cations and anions with a Pt · · · Pt separation of 3.25 Å. The interactions between the platinum ions are responsible for the green color of this compound. The tetracyano complexes, Mx[PtII(CN)4] · nH2O, where M may be an alkali or alkaline earth ion, are known to stack into one-dimensional extended chains and with a wide range of Pt · · · Pt separations in the crystalline state. Such metal-metal distances can range from 3.09 Å for the violet-red Sr2+ salt to 3.75 Å for the colorless Na+ salt.4 The tunable nature of the metal-metal contacts gives these compounds potential utility as functional materials. Additionally, the [PtII(CN)4]2- ion can form partially oxidized materials, in which the stacking is retained, but the Pt · · · Pt separations are much shorter. For example in Krogmann’s salt, K2[Pt(CN)4Br0.3], the Pt · · · Pt separation is 2.880 Å. Such partially oxidized complexes are one-dimensional conductors along the stacking direction. The chains of planar platinum(II) complexes in salts such as [(RNC)4Pt][Pt(CN)4] (R ) alkyl or aryl) show novel vapochro* To whom correspondence should be addressed. E-mail: [email protected] (A.L.B.); [email protected] (M.M.O.); [email protected] (M.M.). Fax: 530-752-2820.

Chart 1. ATQ Derivatives

mic behavior.5-7 These materials function by reversibly absorbing organic vapors. The vapor absorption causes alterations in the Pt · · · Pt separations within the stacks of planar molecules or ions and changes the colors of the crystals. Bulky ligands are able to inhibit the sort of columnar packing noted above and many planar platinum(II) complexes do not participate in such stacking. Here we consider the molecular packing of a planar platinum(II) complex, PtCl2(ATQ-CH2NH2) whose structure is shown in Chart 1. This complex has a wedgelike shape due to the presence of a convex, tricyclic appendage in the chleating ligand, aminomethylazatriquinane (ATQ-CH2NH2). The parent amine (ATQ) has been reported to be the most basic simple amine in existence.8 The acute pyramidalization of the apical nitrogen caused by the trefoil fusion of three 5-membered rings is responsible for the high basicity of this amine. Results Structures and Molecular Packing for PtCl2(ATQ-CH2NH2) (1a) and PdCl2(ATQ-CH2NH2) (2). Both of these chelated complexes, whose preparations are documented in the Supporting Information, crystallize in solvate-free form. The platinum complex also crystallizes in two solvated forms (vide infra). Yellow plates of PtCl2(ATQ-CH2NH2) (1a) were obtained when a saturated acetonitrile solution of the complex was prepared

10.1021/cg800906x CCC: $40.75  2009 American Chemical Society Published on Web 02/25/2009

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Table 1. Crystallographic Data for MCl2(ATQ-CH2NH2)

emp formula FW color and habit cryst syst space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z T (K) Fcalcd (g cm-3) Mo KR, λ (Å) µ (mm-1) unique data obsd data (I > 2σ(I)) restraints params refined R1a (obsd data) wR2b (all data) a

PtCl2(ATQ-CH2NH2)

6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN)

3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2)

PdCl2(ATQ-CH2NH2)

1a C10H18Cl2N2Pt 432.25 yellow plate orthorhombic Pna21 19.524(3) 7.5482(12) 7.9651(13) 90 90 90 1173.8(3) 4 90(2) 2.446 0.71073 12.377 2435 2112 7 137 0.028 0.069

1b (C60H108Cl12N12Pt6)(C4H6N2) 2675.63 yellow parallelepiped monoclinic P21/n 13.205(5) 31.572(12) 22.652(9) 90 92.293(7) 90 9436(6) 4 90(2) 1.883 0.71073 9.242 21629 17804 509 489 0.1375 0.3391

1c (C30H54Cl6N6Pt3)(C2H4Cl4) 1466.61 yellow needle monoclinic P21/n 14.2780(19) 12.3927(16) 24.519(3) 90 95.554(2) 90 4318.1(10) 4 90(2) 2.256 0.71073 10.347 9905 7496 16 469 0.0287 0.0704

2 C10H18Cl2N2Pd 343.56 orange plate monoclinic P21/c 12.6237(6) 11.0518(5) 8.7066(4) 90 100.0480(10) 90 1196.07(10) 4 90(2) 1.908 0.71073 1.967 3647 3343 0 136 0.0148 0.0371

For data with I > 2σI; R1 )(∑|Fo| - |Fc|)/(∑|Fo|). b For all data. wR2(∑[wFo - Fc])/(∑[w(Fo)]).

at room temperature and allowed to slowly evaporate over a two week period. Crystal data for this and the other complexes are given in Table 1. Figure 1 shows two orthogonal views of PtCl2(ATQ-CH2NH2) (1a). Although the PtN2Cl2 portion of the molecule is planar, the convexity of the ATQ portion gives the molecule an overall wedge shape. Orange plates of PdCl2(ATQCH2NH2) (2) were obtained by cooling an acetonitrile solution of the complex. The molecular structure of this palladium(II) complex is quite similar to that of the platinium(II) analog. Although palladium(II) and platinum(II) have similar sizes and the complexes have similar shapes, PtCl2(ATQ-CH2NH2) (1a) and PdCl2(ATQ-CH2NH2) (2) pack in different fashions. Crystals of PtCl2(ATQ-CH2NH2) (1a) form in the orthorhombic space group Pna21 with one molecule in the asymmetric unit. Figure 2 shows the molecular packing. The closest pair of platinum(II) centers is 5.492(6) Å apart. Thus, no metallophilic interactions exist in this crystal. However, there are intermolecular hydrogen bonding interactions that occur between the primary amine protons on N2 and the Cl2 atoms of an adjacent molecule (Distances: N2 · · · Cl2A, 3.353(7) Å; N2 · · · Cl2B, 3.539(9) Å. Angles: N(2)-H(2A) · · · Cl(2)#1, 119.4; N(2)H(2B) · · · Cl(2)#2, 148.4 °). The solvate-free crystal of PdCl2(ATQ-CH2NH2) (2) contains a single molecule in the asymmetric unit in the space group P21/c. Figure 3 shows how the molecules are arranged in the solid. The structure is dominated by the formation of dimers that result from the packing of a pair of complexes about a center of symmetry. This produces a face-to-face arrangement that is common to the crystal structures of many planar d8 metal complexes. Within a dimer, the Pd · · · Pd separation (3.6161(2) Å) is shorter than the corresponding Pt · · · Pt separation in the platinum analog. Additionally, in this face-to-face arrangement, a chloride ion is situated directly above the palladium ion in the neighboring molecule with a Pd1 · · · Cl1A contact of 3.254 Å. Additionally, strong N-H · · · Cl hydrogen bonding interactions connect the dimeric units into rings of four dimers as seen in Figure 3. The relationship between the packing in PtCl2(ATQ-CH2NH2) (1a) and PdCl2(ATQ-CH2NH2) (2) is somewhat similar to the situation seen in the yellow and red polymorphs of PtII(bpy)Cl2

Figure 1. Orthogonal views of PtCl2(ATQ-CH2NH2) (1a). (a) Looking down onto the PtN2Cl2 plane, (b) looking edge on at the plane.

and PtII(phen)Cl2.9 In the yellow polymorphs, as in PtCl2(ATQCH2NH2) (1a), there are no metallophilic interactions between the complexes, whereas in the red polymorphs, as in PdCl2(ATQ-

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Figure 4. Drawing of the five ordered PtCl2(ATQ-CH2NH2) molecules in 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b) with 50% thermal contours for all atoms. Hydrogen atoms and the sites of the four half-occupied acetonitrile molecules have been omitted for clarity.

Figure 2. Packing of PtCl2(ATQ-CH2NH2) molecules in 1a showing hydrogen-bonding intermolecular interactions between the primary amine and chloride ligands. Hydrogen atoms have been omitted for clarity. Color code: Pt, red; C, gray; N, blue; Cl, green. Symmetry codes: A ) x, y - 1, z; B ) 0.5 - x, y - 0.5, 0.5 + z; C ) 0.5 - x, 0.5 + y, 0.5 + z; D ) 0.5 + x, 1.5 + y, 0.5 + z; E ) -x, 2 - y, 0.5 + z; F ) 0.5 + x, 0.5 - y, z; G ) 1 - x, 1 - y, 0.5 + z.

Figure 3. Packing of PdCl2(ATQ-CH2NH2) molecules in 2 showing weak Pd · · · Pd intermolecular interactions of 3.6161(2) Å and strong hydrogen-bonding contacts that form a ring of dimers. Hydrogen atoms are omitted for clarity; color code: Pd, pink; C, gray; N, blue; Cl, green. Symmetry codes: A ) 1 - x, 1 - y, z; B ) 1 - x, y - 0.5, 0.5 - z; C ) x, 0.5 - y, 0.5 + z; D ) 1 - x, 1 - y, 1 - z; E ) x, y, 1 + z; F ) x, 1.5 - y, 0.5 + z; G ) 1 - x, 0.5 + y, 0.5 - z.

CH2NH2) (2), there are metallophilic interactions. According to the conclusions of Grzesiak and Matzger, the Pt · · · Pt interactions in the red forms interfered with close packing; the yellow forms had more densely packed molecular units, yet had

no metallophilic interactions. The calculated density of PtCl2(ATQCH2NH2) (1a) is 2.446 g cm-3, whereas the hypothetical density of PtCl2(ATQ-CH2NH2), if it crystallized as PdCl2(ATQCH2NH2) (2) does, would be 2.400 g cm-3. Likewise, the packing index value for the percentage of filled space occupied by PdCl2(ATQ-CH2NH2) (2) is 74.6%, whereas it is greater, 77.2%, for PtCl2(ATQ-CH2NH2) (1a). Remarkable Cyclic Molecular Packing in 6{PtCl2(ATQCH2NH2)}·2(CH3CN)(1b).Yellowparallelepipedsof6{PtCl2(ATQCH2NH2)} · 2(CH3CN) (1b) were obtained by dissolving the complex in boiling acetonitirile, filtering the hot solution, and allowing it to cool overnight. Under these conditions, crystals of solvate-free PtCl2(ATQ-CH2NH2) (1a) did not form. The asymmetric unit contains five ordered PtCl2(ATQ-CH2NH2) molecules, one disordered PtCl2(ATQ-CH2NH2) molecule, and four half-occupied sites for acetonitrile molecules. Figure 4 shows the relative orientations of the five ordered molecules of the complex. These five molecules pack about a center of symmetry to produce the remarkable, self-assembled cycle of 10 complexes shown in Figure 5. The polar PtCl2 portions of this cyclic array point toward the center of the ring, while the organic ATQ ligands occupy the perimeter. This arrangement is reminiscent of that in reversed micelles. The assembly is mediated by 20 NH · · · Cl hydrogen bonds, with N · · · Cl distances ranging from 3.28(2) to 3.37(2) Å and N-H · · · Cl angles ranging from 149 to 166°. The lower part of Figure 5 shows some of the distances between platinum atoms. Across the ring the average distance between opposing platinum atoms is 13.465 Å. The closest contacts between neighboring platinum atoms range from 4.1310(2) to 4.295(2) Å, so any metallophillic interactions between these molecules are clearly very subtle. Although this supramolecular cyclic array is well-ordered, there is a second, highly disordered region in the crystal. This region contained a single PtCl2(ATQ-CH2NH2) molecule that was partially modeled with four orientations of cis-PtCl2 moieties, but we were unable to model the locations of the chelating ATQ-CH2NH2 ligands. The resulting set of partially occupied platinum portions {Pt6 (0.30), Pt7 (0.25), Pt8 (0.20), and Pt9 (0.25)} comprises one PtCl2(ATQ-CH2NH2) unit in the overall formula. Figure 6 shows that the disordered regions lie immediately above and below the ring of ten molecules. Additionally, disordered acetonitrile molecules are situated near this region. The presence of acetonitrile in the crystal has been verified by 1H NMR spectroscopy in dichloromethane-d2 solution. The spectrum showed a singlet at 1.94 ppm due to acetonitrile in addition to the resonances of the platinum

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Figure 6. View of 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b) showing the orientation of the cyclic assembly of 10 complexes and the disordered PtCl2(ATQ-CH2NH2) molecules that occupy multiple positions above and below the ring. Hydrogen atoms and acetonitrile solvent molecules have been omitted; color code: Pt, red; C, gray; N, blue; Cl, green.

Figure 7. View of the crescent-shaped packing of three PtCl2(ATQCH2NH2) molecules in 3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2) (1c). Hydrogen atoms and dichloromethane solvent molecules have been omitted for clarity. Color code: Pt, red; C, gray; N, blue; Cl, green. Symmetry codes: A ) 1.5 - x, 0.5 + y, 1.5 - z; B ) 1 - x, 1 - y, 1 - z; C ) x - 0.5, 0.5 - y, 0.5 - z. Figure 5. View of the 10-membered ring in 6{PtCl2(ATQCH2NH2)} · 2(CH3CN) (1b) with N-H · · · Cl hydrogen bonds and weak Pt · · · Pt intermolecular interactions. Symmetry codes: A ) 1 - x, 1 y, 1 - z. The lower drawing shows the distances between platinum atoms.

complex. The latter observation is significant because it assures us that PtCl2(ATQ-CH2NH2) was the only complex that could occupy the disordered region in the structure. No other platinum complex was present as an impurity that could have contributed to the disorder. Molecular Packing for 3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2) (1c). Yellow needles of 3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2) (1c) were obtained by crystallizing the platinum(II) complex from a mixture of acetonitrile and dichloromethane and allowing the solution to evaporate over a period of 4 days. This solvate crystallizes with three ordered PtCl2(ATQ-CH2NH2) molecules and two dichloromethane molecules in the asymmetric unit. Figure 7 shows the relative orientations of the three molecules in the asymmetric unit, and Figure 8 shows an expanded view of the molecular packing. The three molecules in the asymmetric

unit form a crescentlike shape that resembles the curvature of the cyclic assembly in the acetonitrile solvate (1b). Again, the polar Pt-Cl units pack together and the chelating ligands are positioned on the periphery of the crescent. As seen in Figure 8, there are four N-H · · · Cl hydrogen bonds that connect these three molecules. The three molecules in the asymmetric unit pack about a crystallographic center of symmetry and form a wavelike arrangement as seen in Figure 8. There are no significant metal-metal contacts here. The Pt · · · Pt distances (4.2366(6) and 4.2629(5) Å) are longer than twice the van der Waals radius (2.05, 2.09 Å) of platinum(II).10,11 Similar packing of three planar, d8 complexes was observed in the crystal structure of [PdCl2{N1-Me2-(S)-pn}] · 1/2H2O (pn ) 1,2-propanediamine), where three molecules are connected by strong hydrogen bonds between the chloride and nitrogen atoms in a zigzag fashion.12 Absorption (UV/vis) and Emission (Luminescence) Spectroscopy.TheelectronicabsorptionspectraforthePtCl2(ATQCH2NH2) (1a) and PdCl2(ATQ-CH2NH2) (2) in dichloromethane

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Figure 8. View of the wavelike packing between sets of three PtCl2(ATQ-CH2NH2) molecules in 3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2) (1c), revealing hydrogen-bonding interactions. Hydrogen atoms and dichloromethane solvent molecules have been omitted for clarity. Color code: Pt, red; C, gray; N, blue; Cl, green. Symmetry codes: A ) 1.5 x, 0.5 + y, 1.5 - z; B ) 1 - x, 1 - y, 1 - z; C ) x - 0.5, 0.5 - y, 0.5 - z.

solutions are shown in Figure 9a. PtCl2(ATQ-CH2NH2) (1a) absorbs strongly in the ultraviolet region with four maximum absorbance features at 220, 281 (377 M-1 cm-1), 310 (390 M-1 cm-1), and 370 nm (84 M-1 cm-1), which are similar to the absorption spectral features of cis-PtCl2(NH3)2.13,14 The absorption spectrum for PdCl2(ATQ-CH2NH2) (2) exhibits a shoulder at 279 nm (1560 M-1 cm-1) and a maximum at 394 nm (518 M-1 cm-1). It is known that simple platinum ammine complexes are luminescent. For example, cis-PtCl2(NH3)2 is emissive at 590 nm in a frozen dimethylsulfoxide solution.12,15 Consequently, the luminescence behaviors of PtCl2(ATQ-CH2NH2) and PdCl2(ATQ-CH2NH2) were examined in order to determine whether crystal packing influenced the emission. Neither the free ligand, ATQ-CH2NH2, nor PdCl2(ATQ-CH2NH2) were emissive. However, PtCl2(ATQ-CH2NH2) (1a) produces a yellow-orange luminescence. Figure 9b compares the luminescence of a frozen ethanol solution of PtCl2(ATQ-CH2NH2) with the emission of crystals of PtCl2(ATQ-CH2NH2) (1a) and 6{PtCl2(ATQCH2NH2)} · 2(CH3CN) (1b) at 77 K. The emission and excitation maxima are: PtCl2(ATQ-CH2NH2) (1a), frozen ethanol solution, λEm ) 634, λEx ) 367 nm, crystalline λEm ) 644 nm, λEx ) 373 nm; 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b), λEm ) 662 nm, λEx ) 375 nm. The excitation profiles are consistent with the absorption spectrum reported for PtCl2(ATQ-CH2NH2) (1a) in Figure 9a. The similarity of the emission and excitation for PtCl2(ATQ-CH2NH2) (1a) in the crystalline state and in ethanol glass indicates that the molecule is intrinsically emissive. The differences in emission and excitation between PtCl2(ATQCH2NH2) (1a) and 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b) are small. Thus, it appears that the unusual solid-state packing in

Figure 9. (a) UV/vis absorption spectra of dichloromethane solutions of PtCl2(ATQ-CH2NH2) (1a) (solid line, 3.75 mM) and PdCl2(ATQCH2NH2) (1) (dashed line, 0.844 mM) at 298 K. (b) Emission (solid lines) and excitation (dashed lines) spectra for solid-state samples of PtCl2(ATQ-CH2NH2) (1a) (red), 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b) (black), and PtCl2(ATQ-CH2NH2) (1a) in an ethanol glass (blue) at 77 K.

the latter does not have a major impact on the luminescence of the platinum complex. Discussion The molecular packing of PtCl2(ATQ-CH2NH2) (1a) and PdCl2(ATQ-CH2NH2) (2) display a number of variations that are atypical for planar d8 complexes. In particular the acetonitrile solvate, 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b), forms an unusual 10-membered array shown in Figures 5 and 6. However, the crystallographic study of 1b is complicated by the existence of an additional region where a disordered PtCl2(ATQ-CH2NH2 molecule and solvate molecules reside. From a simple analytical perspective, this particular crystalline material would not be considered the ideal subject for a crystallographic investigation. However, repeated attempts to obtain ordered crystals of 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b) always led to the formation of the same phase. Thus, the disorder must be considered an intrinsic feature of this interesting material. If the goal is the accurate determination of the molecular structure of PtCl2(ATQ-CH2NH2), the solvate-free PtCl2(ATQ-CH2NH2) (1a) or the dichloromethane solvate 3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2) (1c) give more satisfactory data. However, if the goal is examination of molecular packing, then the structural results

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Table 2. Selected Inter- and Intramolecular Distancesa and Anglesb for MCl2(ATQ-CH2NH2) (M ) Pd or Pt) complex

c

M1 · · · M1A

PtCl2(ATQ-CH2NH2) 1a {5.492(6)}e (4.071(2)-4.295(2))

M1-Cl1

2.3152(17)

M1-Cl2

2.319(2)

M1-N1

2.069(6)

M1-N2

2.036(6)

Cl1-M1-Cl2

91.81(6)

Cl2-M1-N1

93.83(16)

N1-M1-N2

83.2(2)

N2-M1-Cl1

91.20(17)

Cl1-M1-N1

174.3(2)

Cl2-M1-N2

175.9(2)

6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) d 1b

3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2) d 1c {4.250[13]}e

4.19[7] (4.2366(6) 2.318[4] (2.313(6)-2.324(7)) 2.314[2] (2.311(7)-2.317(7)) 2.072[4] (2.064(13)-2.077(13)) 2.030[3] (2.027(14)-2.034(14)) 91.6[2] (91.2(3)-92.0(3)) 93.7[2] (93.4(4)-94.2(5)) 84.5[2] (84.2(6)-84.8(6)) 90.2[3] (89.6(5)-90.8(5)) 173.9[5] (173.2(5)-174.9(5)) 178.1[2] (177.8(6)-178.4(5))

PdCl2(ATQ-CH2NH2) 2 3.6161(2)

4.2629(5)) 2.311[5] (2.3068(15)-2.3188(15)) 2.3216[17] (2.3203(14)-2.3242(15)) 2.067[7] (2.060(5)-2.077(5)) 2.026[7] (2.020(5)-2.036(5)) 91.2[1.1] (89.96(5)-92.84(6)) 93.9[1.3] (91.98(15)-94.91(14)) 84.5[2] (84.28(19)-84.80(2)) 90.4[4] (89.76(13)-91.06(14)) 174.6[4] (173.98(14)-175.03(15)) 178.1[9] (176.74(15)-178.84(14))

2.3068(3) 2.3375(3) 2.0739(10) 2.0146(11) 93.049(12) 94.93(3) 84.94(4) 87.85(3) 168.65(3) 174.83(3)

a Bond lengths in Å. b Angles in deg. c M is Pt or Pd. d Average of similar values with average deviation from mean in [ ]; i.e.m for 2bm average of contacts Pt1 · · · Pt2 and Pt1 · · · Pt3 for “M1 · · · M1A”, or average of bond lengths Pt1-N1, Pt2-N3, and Pt3-N5 for “M1-N1”; range of values given in parentheses. e Too long to be considered as a metallophilic interaction, but included for comparison purposes.

on the acetonitrile solvate, 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b), must be considered as well, despite the intrinsic disorder found in one region of the solid. In all the structures considered here, there is a significant degree of hydrogen bonding with the N-H group of one complex acting as a donor and the chloride ligand on another complex acting as the acceptor. The M-Cl group has been shown previously to be a better hydrogen bond acceptor than a C-Cl group.16,17 These N-H · · · Cl interactions are also complemented by some degree of metal-metal interaction, although the consequences of the latter are subtle. Experimental Section X-ray Crystallography and Data Collection. The crystals were removed from the vials or glass tubes in which they were grown and immediately coated with hydrocarbon oil on microscope slides. Suitable crystals were mounted on glass fibers with silicone grease and placed in a cold stream of either a Bruker SMART CCD or a Bruker SMART ApexII diffractometer. Dinitrogen (90(2) K) cooling was accomplished by use of CRYO Industries devices. The crystal structures were solved by direct methods, and all data were refined (based on F2) using SHELXTL 5.1 software. A multiscan method utilizing equivalents was employed to correct for the absorption of heavy atoms.18 Hydrogen atoms were located in a difference map, added geometrically, and refined with a riding model. All cif files were checked and crystal packing index percentages (K.P.I.) were determined using PLATON software.19 Crystallographic data and selected bond lengths and angles, together with metallophilic geometry, are collected in Tables 1 and 2. PtCl2(ATQ-CH2NH2) (1a). The data for PtCl2(ATQ-CH2NH2) (1a) were refined as an inversion twin with a twin parameter of 0.318(16). In addition, the atoms N(1) and N(2) were assigned isotropic thermal parameters because they became nonpositive definite; no cause for this was found, but it could result from truncation errors. ADDSYM detected a pseudo center of symmetry (93 PerFi) and a possible pseudo/new space group of Pnma. We tested the space group Pnma; however, the refinement was not satisfactory. 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b). A number of approaches were attempted to try to resolve the disorder, and various twin models were also considered. In the final model, the region encompassing the sixth coordination compound was modeled with four different PtCl2 groups, but without the other ligand atoms. The resulting set, {Pt6,

Pt7, Pt8, Pt9}, comprises one platinum(II) complex in the empirical formula. The occupancies of the platinum and attached chlorine atoms were fixed at 0.30, 0.25, 0.20, and 0.25, respectively. Only the platinum atoms within this disordered set were assigned anisotropic thermal parameters. In the other five complexes, both the platinum and chlorine atoms were refined anisotropically. SAME restraints were applied to atoms of the five complete complexes. All carbon and nitrogen atoms were modeled with isotropic parameters. The difference map contains a large number of peaks that could not be reasonably assigned to a model. The twenty largest peaks range from 7.34 to 2.87 e Å-3. Several crystals were examined from different batches, and all exhibited the same disordered structure. 3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2) (1c). Two of the carbon atoms (C26 and C28) in the complex involving Pt3 were disordered with relative occupancies of 0.811(13)/0.189(13). The minor components (C26B and C28B) were kept isotropic.

Acknowledgment. We thank the Petroleum Research Fund (Grant 37056-AC to A.L.B.) and the National Science Foundation (Grant CHE-0448976 to MM) for support. We also thank the Tyco Electronics Foundation and the UC Davis Fletcher Jones fellowships for E.M.G. The Bruker SMART 1000 diffractometer was funded in part by NSF Instrumentation (Grant CHE-9808259). In addition, we thank Drs. H. Hope and A. J. Blake for their kind crystallography advice, Brandon Mercado and Dr. William Jewell for their assistance with the mass spectral experiments, and Prof. Mark J. Kurth for the use of his IR spectrometer. Supporting Information Available: X-ray crystallographic files, in CIF format, for PtCl2(ATQ-CH2NH2) (1a), 6{PtCl2(ATQ-CH2NH2)} · 2(CH3CN) (1b), 3{PtCl2(ATQ-CH2NH2)} · 2(CH2Cl2) (1c), and PdCl2(ATQ-CH2NH2) (2); experimental preparative methods and additional tables (PDF). This material is available free of charge via the Internet at http://pubs.acs.org.

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