Chlorido{2-[(dimethyl­amino)­methyl]phenyl-κ2C1,N}(1-methyl-1H-imidazole-κN3)palladium(II)

Clements, J.W.; Stojanovic, M.; Hoffman, N.W.; Sykora, R.E.

doi:10.1107/S1600536810047367

metal-organic compounds

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 66| Part 12| December 2010| Pages m1639-m1640

https://doi.org/10.1107/S1600536810047367

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Chlorido{2-[(dimethylamino)methyl]phenyl-κ²C¹,N}(1-methyl-1H-imidazole-κN³)palladium(II)

Jason W. Clements,^a Milorad Stojanovic,^a Norris W. Hoffman ^a and Richard E. Sykora ^a ^*

^aDepartment of Chemistry, University of South Alabama, Mobile, AL 36688-0002, USA
^*Correspondence e-mail: rsykora@jaguar1.usouthal.edu

(Received 12 November 2010; accepted 15 November 2010; online 24 November 2010)

In the title compound, [Pd(C₉H₁₂N)Cl(C₄H₆N₂)], which was synthesized from the reaction of 1-methylimidazole with dimeric dichloridobis[2-(dimethylamino)benzyl]palladium(II), the ring-deprotonated N,N-dimethylbenzylamine ligand acts in a C,N-bidentate fashion. The dihedral angle between the ring of the 1-methylimidazole ligand and the palladacycle plane is 57.88 (16)°. The two N atoms from the N,N-dimethylbenzylamine and 1-methylimidazole ligands are trans coordinated to the Pd^II atom.

Related literature

For an overview of the application of palladacycles in organic synthesis, see: DuPont & Flores (2009 ); Bedford et al. (2003 ); Fors & Buchwald (2010 ). For detoxification of phosphorothionate pesticides, see: Lu et al. (2010 ). For studies converting the dimeric precursor (Cope & Friedrich, 1968 ) of the title compound into monomeric square-planar palladacycles, see: Mentes & Büyükgüngör (2004 ); Mentes et al. (2004 ); Deeming et al. (1978 ); Bose & Saha (1987 ). For crystal structures of neutral pyridine-palladacycles, see: Lu et al. (2005 ); Fun et al. (2006 ). For an approach to the study of the relative binding affinities of unidentate ligands for organopalladium(II) species, see: Hoffman et al. (2009 ).

Experimental

Crystal data

[Pd(C₉H₁₂N)Cl(C₄H₆N₂)]
M_r = 358.15
Orthorhombic, P n a 2₁
a = 25.5485 (15) Å
b = 10.0057 (6) Å
c = 5.6733 (4) Å
V = 1450.27 (16) Å³
Z = 4
Mo Kα radiation
μ = 1.45 mm⁻¹
T = 290 K
0.43 × 0.15 × 0.09 mm

Data collection

Oxford Diffraction Xcalibur E diffractometer
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2010 $[Oxford Diffraction (2010). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, England.]$ ) T_min = 0.788, T_max = 1.00
6592 measured reflections
2373 independent reflections
2057 reflections with I > 2σ(I)
R_int = 0.028

Refinement

R[F² > 2σ(F²)] = 0.022
wR(F²) = 0.044
S = 0.96
2373 reflections
167 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.31 e Å⁻³
Δρ_min = −0.38 e Å⁻³
Absolute structure: Flack (1983 ), 852 Friedel pairs
Flack parameter: −0.04 (3)

Data collection: CrysAlis PRO (Oxford Diffraction, 2010 $[Oxford Diffraction (2010). CrysAlis PRO. Oxford Diffraction Ltd, Yarnton, England.]$ ); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536810047367/ng5067sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810047367/ng5067Isup2.hkl

checkCIF report

Comment top

Palladacycles are an important class of catalysts for organic reactions (DuPont & Flores, 2009; Bedford et al., 2003; Fors & Buchwald, 2010), including methanolysis of phosphorothionate pesticides (Lu et al., 2005; Lu et al., 2010). One of the most commonly used, and now commercially available, palladacyclic dimers, di-µ-chlorobis[2-(dimethylamino)benzyl-κ²C¹,N]palladium(II), or [(κ²-dmba)PdCl]₂ for short, was first prepared by Cope & Friedrich (1968), with its structure solved by Mentes, Kemmitt, et al. (2004). Many compounds of the general formula (κ²-dmba)Pd(L)Cl are easily prepared by treating this dimer with two molar equivalents of neutral unidentate ligand, L. The great majority of these products contain pnictogen ligands, primarily phosphines; crystal structures have been published for L = PPh₃ (Mentes, Kemmitt, et al., 2004) and SbPh₃ (Mentes & Büyükgüngör, 2004). Combining four molar equivalents of these triphenylpnictogens with the dimer affords dechelation of the dmba moiety and formation of the square-planar trans-(EPh₃)₂Pd(2-dmba-κC¹)Cl. Relatively few examples of (κ²-dmba)Pd(N-ligand)Cl have been reported, and those are almost exclusively in the pyridine family (Deeming et al., 1978; Bose & Saha, 1987), with crystal structures reported for the pyridine (Lu et al., 2005) and 4-dimethylaminopyridine (Fun et al., 2006) complexes.

Our interest in studying relative binding affinities of soft metal centers for ligands of moderate and weak donor power using ¹⁹F and ³¹P NMR spectroscopy (Hoffman et al., 2009) to monitor ligand-substitution equilibria led us to prepare the title complex (I), whose structure is shown in Figure 1. Suitable single crystals were grown from vapor diffusion of heptane into a solution of the 1-methylimidazole complex at room temperature. All four Pd-ligand bond lengths were similar to those reported for other (κ²-dmba)Pd(L)Cl structures, especially those for the two pyridine-family complexes (Lu et al., 2005; Fun et al., 2006). The angle between the imidazole ring and the palladacycle plane (Pd1–N2–C1–C2–C7) in I is 57.88 (16)°, on par with the 49.2° angle between the pyridine and palladacycle rings in (κ²-dmba)Pd(py)Cl (Lu et al., 2005). However, both these angles are quite smaller than the comparable dihedral angles in (κ²-dmba)Pd(dmap)Cl (dmap = 4-(dimethylamino)pyridine) (Fun et al., 2006) for which three crystallographically independent molecules yielded values of 76.80 (14)°, 81.85 (14)°, and 83.74 (14)°.

Related literature top

For an overview of the application of palladacycles in organic synthesis, see: DuPont & Flores (2009); Bedford et al. (2003); Fors & Buchwald (2010). For detoxification of phosphorothionate pesticides, see: Lu et al. (2010). For studies converting the dimeric precursor (Cope & Friedrich, 1968) of the title compound into monomeric square-planar palladacycles, see: Mentes & Büyükgüngör (2004); Mentes et al. (2004); Deeming et al. (1978); Bose & Saha (1987). For crystal structures of neutral pyridine-palladacycles, see: Lu et al. (2005); Fun et al. (2006). For an approach to the study of the relative binding affinities of unidentate ligands for organopalladium(II) species, see: Hoffman et al. (2009).

Experimental top

To a solution of 0.100 mmol [(κ²-C₉H₁₂N)PdCl]₂ (Sigma-Aldrich) in 2.0 ml e thanol-free reagent chloroform (Fisher) in a 10-ml glass vial was added with stirring 0.200 mmol neat 1-methylimidazole (Sigma-Aldrich). The resulting pale-yellow solution was subjected to vapor diffusion with 30 ml heptane (Fisher reagent) at room temperature for 3 days. The small amount of liquid remaining was removed by disposable glass pipet from the resulting off-white needles, and the crystals were washed twice with 5.0 ml of hexanes (Fisher reagent). All reagents and solvents were used as received. The desired needles were removed from the vial and air-dried overnight in the dark (94% yield).

Structure description top

For an overview of the application of palladacycles in organic synthesis, see: DuPont & Flores (2009); Bedford et al. (2003); Fors & Buchwald (2010). For detoxification of phosphorothionate pesticides, see: Lu et al. (2010). For studies converting the dimeric precursor (Cope & Friedrich, 1968) of the title compound into monomeric square-planar palladacycles, see: Mentes & Büyükgüngör (2004); Mentes et al. (2004); Deeming et al. (1978); Bose & Saha (1987). For crystal structures of neutral pyridine-palladacycles, see: Lu et al. (2005); Fun et al. (2006). For an approach to the study of the relative binding affinities of unidentate ligands for organopalladium(II) species, see: Hoffman et al. (2009).

Computing details top

Data collection: CrysAlis PRO (Oxford Diffraction, 2010); cell refinement: CrysAlis PRO (Oxford Diffraction, 2010); data reduction: CrysAlis PRO (Oxford Diffraction, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

Fig. 1. A thermal ellipsoid plot (50%) of I showing the labeling scheme.

Chlorido{2-[(dimethylamino)methyl]phenyl-κ²C¹,N}(1- methyl-1H-imidazole-κN³]palladium(II) top

Crystal data top

[Pd(C₉H₁₂N)Cl(C₄H₆N₂)]	F(000) = 720
M_r = 358.15	D_x = 1.640 Mg m⁻³
Orthorhombic, Pna2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2n	Cell parameters from 3299 reflections
a = 25.5485 (15) Å	θ = 3.1–25.6°
b = 10.0057 (6) Å	µ = 1.45 mm⁻¹
c = 5.6733 (4) Å	T = 290 K
V = 1450.27 (16) Å³	Prism, colorless
Z = 4	0.43 × 0.15 × 0.09 mm

Data collection top

Oxford Diffraction Xcalibur E diffractometer	2373 independent reflections
Radiation source: fine-focus sealed tube	2057 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.028
Detector resolution: 16.0514 pixels mm^-1	θ_max = 25.7°, θ_min = 3.1°
ω scans	h = −31→31
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2010)	k = −12→10
T_min = 0.788, T_max = 1.00	l = −6→6
6592 measured reflections

Refinement top

Refinement on F²	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.022	w = 1/[σ²(F_o²) + (0.0205P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.044	(Δ/σ)_max = 0.003
S = 0.96	Δρ_max = 0.31 e Å⁻³
2373 reflections	Δρ_min = −0.38 e Å⁻³
167 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.0038 (2)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983), 852 Friedel pairs
Secondary atom site location: difference Fourier map	Absolute structure parameter: −0.04 (3)

Crystal data top

[Pd(C₉H₁₂N)Cl(C₄H₆N₂)]	V = 1450.27 (16) Å³
M_r = 358.15	Z = 4
Orthorhombic, Pna2₁	Mo Kα radiation
a = 25.5485 (15) Å	µ = 1.45 mm⁻¹
b = 10.0057 (6) Å	T = 290 K
c = 5.6733 (4) Å	0.43 × 0.15 × 0.09 mm

Data collection top

Oxford Diffraction Xcalibur E diffractometer	2373 independent reflections
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2010)	2057 reflections with I > 2σ(I)
T_min = 0.788, T_max = 1.00	R_int = 0.028
6592 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.022	H-atom parameters constrained
wR(F²) = 0.044	Δρ_max = 0.31 e Å⁻³
S = 0.96	Δρ_min = −0.38 e Å⁻³
2373 reflections	Absolute structure: Flack (1983), 852 Friedel pairs
167 parameters	Absolute structure parameter: −0.04 (3)
1 restraint

Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > 2σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Pd1	0.644535 (8)	0.91814 (2)	0.75150 (8)	0.02903 (8)
Cl1	0.67437 (4)	0.69431 (8)	0.66642 (19)	0.0466 (3)
C1	0.65047 (13)	1.1994 (4)	0.6894 (7)	0.0385 (12)
C2	0.62563 (13)	1.1054 (3)	0.8301 (6)	0.0331 (9)
C3	0.59495 (14)	1.1503 (4)	1.0170 (7)	0.0378 (9)
H3	0.5781	1.0885	1.1131	0.045*
C4	0.58921 (15)	1.2846 (4)	1.0615 (8)	0.0494 (11)
H4	0.5694	1.3131	1.1894	0.059*
C5	0.61300 (17)	1.3768 (4)	0.9156 (9)	0.0560 (13)
H5	0.6084	1.4677	0.9432	0.067*
C6	0.64348 (13)	1.3354 (3)	0.7301 (14)	0.0507 (11)
H6	0.6594	1.3979	0.6322	0.061*
C7	0.68436 (15)	1.1482 (4)	0.4924 (7)	0.0424 (10)
H7A	0.7140	1.2075	0.4690	0.051*
H7B	0.6644	1.1446	0.3470	0.051*
C8	0.71890 (16)	0.9419 (4)	0.3383 (7)	0.0460 (10)
H8A	0.7460	0.9922	0.2615	0.069*
H8B	0.6892	0.9346	0.2354	0.069*
H8C	0.7317	0.8541	0.3754	0.069*
C9	0.74967 (12)	1.0235 (3)	0.7096 (7)	0.0422 (11)
H9A	0.7773	1.0667	0.6236	0.063*
H9B	0.7610	0.9364	0.7585	0.063*
H9C	0.7410	1.0760	0.8458	0.063*
C10	0.53338 (14)	0.8549 (4)	0.9384 (8)	0.0464 (10)
H10	0.5162	0.9102	0.8317	0.056*
C11	0.51014 (15)	0.7778 (4)	1.1018 (7)	0.0475 (11)
H11	0.4744	0.7707	1.1295	0.057*
C12	0.59415 (13)	0.7524 (3)	1.1267 (7)	0.0397 (9)
H12	0.6268	0.7233	1.1774	0.048*
C13	0.54318 (17)	0.6178 (4)	1.4131 (8)	0.0577 (12)
H13A	0.5750	0.5678	1.4306	0.087*
H13B	0.5148	0.5577	1.3805	0.087*
H13C	0.5361	0.6658	1.5561	0.087*
N1	0.58669 (10)	0.8386 (3)	0.9548 (6)	0.0344 (7)
N2	0.70326 (11)	1.0106 (3)	0.5575 (5)	0.0312 (7)
N3	0.54872 (11)	0.7121 (3)	1.2190 (7)	0.0388 (8)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Pd1	0.02726 (11)	0.02814 (13)	0.03167 (13)	−0.00098 (10)	0.0002 (2)	0.0043 (2)
Cl1	0.0495 (5)	0.0321 (5)	0.0582 (7)	0.0077 (4)	0.0119 (5)	0.0049 (4)
C1	0.0352 (19)	0.034 (2)	0.047 (4)	0.0014 (15)	−0.0090 (17)	0.0041 (17)
C2	0.0269 (16)	0.032 (2)	0.041 (3)	0.0007 (15)	−0.0080 (15)	0.0031 (16)
C3	0.034 (2)	0.037 (2)	0.043 (3)	0.0004 (17)	−0.0025 (18)	0.0003 (19)
C4	0.046 (2)	0.044 (3)	0.058 (3)	0.009 (2)	−0.004 (2)	−0.011 (2)
C5	0.048 (2)	0.033 (2)	0.087 (4)	0.0030 (19)	−0.018 (3)	−0.009 (2)
C6	0.0475 (19)	0.033 (2)	0.071 (3)	0.0001 (16)	−0.008 (3)	0.006 (3)
C7	0.044 (2)	0.042 (2)	0.041 (3)	−0.0068 (18)	−0.006 (2)	0.020 (2)
C8	0.051 (2)	0.053 (2)	0.034 (2)	−0.0084 (18)	0.0101 (18)	0.0017 (18)
C9	0.0295 (16)	0.060 (2)	0.037 (3)	−0.0068 (15)	−0.002 (2)	0.006 (2)
C10	0.034 (2)	0.053 (3)	0.052 (3)	0.0031 (18)	0.000 (2)	0.006 (2)
C11	0.031 (2)	0.056 (3)	0.055 (3)	−0.0065 (19)	0.006 (2)	0.002 (2)
C12	0.036 (2)	0.032 (2)	0.051 (2)	−0.0019 (17)	0.0034 (18)	0.000 (2)
C13	0.062 (3)	0.054 (3)	0.057 (3)	−0.007 (2)	0.018 (2)	0.013 (2)
N1	0.0316 (16)	0.0307 (17)	0.0410 (19)	−0.0003 (13)	0.0020 (14)	0.0018 (15)
N2	0.0309 (15)	0.0324 (17)	0.0302 (18)	−0.0020 (13)	−0.0020 (13)	0.0029 (14)
N3	0.0405 (15)	0.0363 (15)	0.039 (2)	−0.0060 (11)	0.0153 (18)	0.0031 (18)

Geometric parameters (Å, º) top

Pd1—C2	1.985 (3)	C8—H8A	0.9600
Pd1—N1	2.037 (3)	C8—H8B	0.9600
Pd1—N2	2.078 (3)	C8—H8C	0.9600
Pd1—Cl1	2.4145 (9)	C9—N2	1.472 (4)
C1—C2	1.388 (5)	C9—H9A	0.9600
C1—C6	1.391 (5)	C9—H9B	0.9600
C1—C7	1.504 (5)	C9—H9C	0.9600
C2—C3	1.393 (5)	C10—C11	1.345 (5)
C3—C4	1.375 (5)	C10—N1	1.375 (4)
C3—H3	0.9300	C10—H10	0.9300
C4—C5	1.381 (6)	C11—N3	1.358 (5)
C4—H4	0.9300	C11—H11	0.9300
C5—C6	1.373 (8)	C12—N1	1.316 (4)
C5—H5	0.9300	C12—N3	1.335 (4)
C6—H6	0.9300	C12—H12	0.9300
C7—N2	1.505 (4)	C13—N3	1.457 (5)
C7—H7A	0.9700	C13—H13A	0.9600
C7—H7B	0.9700	C13—H13B	0.9600
C8—N2	1.476 (4)	C13—H13C	0.9600

C2—Pd1—N1	93.72 (13)	H8B—C8—H8C	109.5
C2—Pd1—N2	82.79 (13)	N2—C9—H9A	109.5
N1—Pd1—N2	176.23 (11)	N2—C9—H9B	109.5
C2—Pd1—Cl1	175.52 (10)	H9A—C9—H9B	109.5
N1—Pd1—Cl1	88.84 (8)	N2—C9—H9C	109.5
N2—Pd1—Cl1	94.54 (8)	H9A—C9—H9C	109.5
C2—C1—C6	120.6 (4)	H9B—C9—H9C	109.5
C2—C1—C7	117.4 (3)	C11—C10—N1	108.8 (4)
C6—C1—C7	122.0 (4)	C11—C10—H10	125.6
C1—C2—C3	118.4 (3)	N1—C10—H10	125.6
C1—C2—Pd1	113.5 (3)	C10—C11—N3	107.1 (3)
C3—C2—Pd1	127.8 (3)	C10—C11—H11	126.4
C4—C3—C2	121.0 (4)	N3—C11—H11	126.4
C4—C3—H3	119.5	N1—C12—N3	111.2 (3)
C2—C3—H3	119.5	N1—C12—H12	124.4
C3—C4—C5	119.7 (4)	N3—C12—H12	124.4
C3—C4—H4	120.1	N3—C13—H13A	109.5
C5—C4—H4	120.1	N3—C13—H13B	109.5
C6—C5—C4	120.5 (4)	H13A—C13—H13B	109.5
C6—C5—H5	119.8	N3—C13—H13C	109.5
C4—C5—H5	119.8	H13A—C13—H13C	109.5
C5—C6—C1	119.7 (5)	H13B—C13—H13C	109.5
C5—C6—H6	120.1	C12—N1—C10	105.8 (3)
C1—C6—H6	120.1	C12—N1—Pd1	124.8 (2)
C1—C7—N2	108.3 (3)	C10—N1—Pd1	129.3 (3)
C1—C7—H7A	110.0	C9—N2—C8	108.5 (3)
N2—C7—H7A	110.0	C9—N2—C7	108.8 (3)
C1—C7—H7B	110.0	C8—N2—C7	107.8 (3)
N2—C7—H7B	110.0	C9—N2—Pd1	108.1 (2)
H7A—C7—H7B	108.4	C8—N2—Pd1	115.7 (2)
N2—C8—H8A	109.5	C7—N2—Pd1	107.8 (2)
N2—C8—H8B	109.5	C12—N3—C11	107.0 (3)
H8A—C8—H8B	109.5	C12—N3—C13	125.2 (3)
N2—C8—H8C	109.5	C11—N3—C13	127.8 (3)
H8A—C8—H8C	109.5

Experimental details

Crystal data
Chemical formula	[Pd(C₉H₁₂N)Cl(C₄H₆N₂)]
M_r	358.15
Crystal system, space group	Orthorhombic, Pna2₁
Temperature (K)	290
a, b, c (Å)	25.5485 (15), 10.0057 (6), 5.6733 (4)
V (Å³)	1450.27 (16)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	1.45
Crystal size (mm)	0.43 × 0.15 × 0.09

Data collection
Diffractometer	Oxford Diffraction Xcalibur E
Absorption correction	Multi-scan (CrysAlis PRO; Oxford Diffraction, 2010)
T_min, T_max	0.788, 1.00
No. of measured, independent and observed [I > 2σ(I)] reflections	6592, 2373, 2057
R_int	0.028
(sin θ/λ)_max (Å⁻¹)	0.610

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.022, 0.044, 0.96
No. of reflections	2373
No. of parameters	167
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.31, −0.38
Absolute structure	Flack (1983), 852 Friedel pairs
Absolute structure parameter	−0.04 (3)

Computer programs: CrysAlis PRO (Oxford Diffraction, 2010), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), OLEX2 (Dolomanov et al., 2009), publCIF (Westrip, 2010).

Acknowledgements

The authors gratefully acknowledge the National Science Foundation (NSF-CAREER grant to RES, CHE-0846680), the Department of Chemistry at USA, and the University Committee for Undergraduate Research at USA for their generous support.

References

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