Tuning Molecular Structures Using Weak Noncovalent Interactions

ARTICLE pubs.acs.org/crystal

Tuning Molecular Structures Using Weak Noncovalent Interactions: Theoretical Study and Structure of trans-Bis(2-chloropyridine)dihalocopper(II) and trans-Bis(3-chloropyridine)dibromocopper(II) Published as part of the Crystal Growth & Design virtual special issue on Halogen Bonding in Crystal Engineering: Fundamentals and Applications Firas Awwadi,*,† Roger D. Willett,‡ and Brendan Twamley§ †

Department of Chemistry, The University of Jordan, Amman 11 942, Jordan Department of Chemistry, Washington State University, Pullman, Washington 99164, United States § University Research Office, University of Idaho, Moscow, Idaho 83844, United States ‡

bS Supporting Information ABSTRACT: The effect of the weak noncovalent interactions (C
H 3 3 3 X
Cu, C
Y 3 3 3 Cu, and C
Y 3 3 3 H
C) on the molecular structure of Cu(nYP)2X2 (where nYP denotes the n-halopyridine ligand, n = 2 or 3, X = Cl
or Br
, and Y = H, F, Cl, or Br) has been investigated using the DFT/B3LYP method. The molecular structure of Cu(nYP)2X2 was optimized using two different starting geometries; the two Y groups are (a) L-cis arrangement and (b) L-trans arrangement with respect to each other, L for ligand. The optimized molecular structures of the Cu(nYP)2X2 structures indicate that the L-cis isomer is more stable than corresponding L-trans one by avg = 9.45 kJ/mol (range 4.29
13.15 kJ/mol). The analysis of theoretical results indicates the strength of the noncovalent interactions follows the order C
Y 3 3 3 H
C < C
Y 3 3 3 Cu < C
H 3 3 3 X
Cu. The L-cis isomer is stabilized by C
H 3 3 3 X
Cu interactions, in contrast, the L-trans isomer is stabilized by C
Y 3 3 3 H
C and C
Y 3 3 3 Cu. There is no perfect agreement (L-trans and L-cis-isomerism) between the optimized structures and the solidstate molecular structures. This is possibly because the optimization process ignores the effect of intermolecular interactions, and the energy difference between each L-trans and L-cis corresponding isomer is quite small. The structures of Cu(2CP)2X2 and Cu(3CP)2Br2 have been determined. An infinite [Cu(3CP)2Br2]n chain structure forms based on the Cu 3 3 3 Br semicoordinate bond, whereas the semicoordinate bond connects the molecular species of Cu(2CP)2X2 to form a dimer structure. The chains of Cu(3CP)2Br2 are subsequently linked via C
Cl 3 3 3 Br
Cu halogen bonding interactions besides the weak C
H 3 3 3 X
Cu hydrogen bonding interactions in the three-dimensional structure. The C
Cl 3 3 3 X
Cu interactions are absent in Cu(2CP)2X2, and the dimer structures of Cu(2CP)2X2 are linked via C
Cl 3 3 3 Cl
C interactions to form chain structures. This competition would indicate that C
Cl 3 3 3 X
Cu and C
Cl 3 3 3 Cl
C are of comparable strength. Another interesting observation, even though the two Cu(2CP)2X2 structures are isomorphous, is that the symmetrical C
Cl 3 3 3 Cl
C halogen bonding interactions play the dominant role in developing Cu(2CP)2Br2 crystal structures. In contrast, the perpendicular C
Cl 3 3 3 Cl
C halogen bonding interactions play the dominant role in the case of Cu(2CP)2Cl2.

’ INTRODUCTION The arrangement of supramolecular synthons within crystalline lattices is controlled by several factors, for example, intermolecular interactions, shape, and size of crystalline species.1
12 Intermolecular interactions are not only major factors in shaping the internal architecture of crystalline materials but also affect the physical properties of these materials (electrical, magnetic, and nonlinear optical properties).13,14 These intermolecular interactions include the hydrogen bonding, halogen bonding, and many other intermolecular interactions. Halogen bonding interaction can be represented as D
Y 3 3 3 X
A, where D
Y is a halogen donor and X
A is a halogen acceptor.9 The halogen acceptor should have a negative character. r 2011 American Chemical Society

Halogen 3 3 3 halogen interactions are considered as a special type of halogen bonding interaction. The most studied halogen 3 3 3 halogen interactions are C
Y1 3 3 3 Y2
C interactions (Y 6¼ F); these interactions are characterized by the fact that the interhalogen distances are less than the sum of van der Waals radii. There are two preferred arrangements for these supramolecular synthons (Scheme 1).15 The first arrangement occurs when θ1 = θ2 = 150° (type I). The second one occurs when θ1 = 180° and θ2 = 90°; this arrangement is known as type II or the Received: July 14, 2011 Revised: October 4, 2011 Published: October 14, 2011 5316

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Crystal Growth & Design Scheme 1. The Two Preferred Geometries for Halogen 3 3 3 Halogen Contacts and the Interaction of Covalently Bound Halogen Atom with Electrophiles: (a) θ1 = θ2; (b) θ1 = 180°, θ2 = 90°; (c) θ = 90°

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Table 1. Summary of Data Collection and Refinement Parameters for the Cu(nCP)2X2 Complexes crystal formula

perpendicular arrangement. Related halogen 3 3 3 halogen interactions are C
Y 3 3 3 X
M interactions, M = metal; in this case, the halogen acceptor is a halide ligand. These interactions are characterized by an essentially linear C
Y 3 3 3 X
angle and Y 3 3 3 X distances are less than the sum of van der Waals radii of halogen atoms. Special interest has been given to C
Y 3 3 3 X
M interactions due to their crucial role in determining the self-assembly of the crystalline species in mixed organic
inorganic materials. There are two types of C
Y 3 3 3 X
M interactions: (A) the charge assisted one; it occurs when the halogen donor is part of a positively charged species and the halogen acceptor is part of a negatively charge species. (B) The normal one, in this type of interaction, neither the halogen donor nor the halogen acceptor is part of a charged species. Also, covalently bonded halogen atoms can interact with electrophiles; electrophiles tend to approach the halogen atom of the C
X bond (X = Cl, Br, or I) at an angle of around 90° (Scheme 1C). Another study showed that metal ions approach the halogen atom at an angle of around 100°.16 Some, but by no means all, scientists consider this interaction as a type of halogen bonding interaction.9,16,17 The arrangement of halogen 3 3 3 halogen synthons as well as the interaction of covalently bound halogen atoms with both nucleophiles and electrophiles can be traced back to the anisotropic distribution of electron density around the halogen atoms.15,18,19 Carbon attached halogen atoms have two different radii; the smaller radius occurs along the C
Y bond, and the longer radius is perpendicular to the first one. This distribution of electronic charge generates a positive electrostatic potential endcap and negative electrostatic potential ring in the π-region of the halogen atom. This electrostatic model describes the nucleophilic
electrophilic dual nature of halogen atoms and the arrangement of these supramolecular synthons inside crystals. We and others have shown by a series of publications that electrostatic forces are the major factors for determining the

a

Cu(2CP)2Cl2

Cu(2CP)2Br2

Cu(3CP)2Br2

C10H8Cl4CuN2 C10H8Cl2Br2CuN2 C10H8Cl2Br2CuN2

formula weight 361.52 diffractometer P4

450.44 P4

450.44 SMART APEX

Dcalc (Mg/m3) 1.806

2.141

2.281

T (K)

295

295

87

crystal system

triclinic

triclinic

monoclinic

space group

P1

P1

P21/c

a (Å)

8.4359(12)

8.4354(13)

3.9041(5)

b (Å)

8.4865(9)

8.8167(13)

13.8156(16)

c (Å) α (°)

10.5674(14) 76.876(11)

11.402(3) 70.088(16)

12.1585(14) 90

β (°)

70.044(11)

74.565(15)

90.521(2)

γ (°)

70.532(10)

62.103(12)

90

V (Å3)

664.95(15)

698.8(2)

655.77(14)

μ mm
1

2.422

7.640

8.142

ind reflections

2247

2430

1501

R (int)

0.0257

0.0406

0.0403

Z 2 goodness of fit 1.058

2 1.019

2 1.030

R1a [I > 2σI]

0.0338

0.0525

0.0364

wR2b [I > 2σI] 0.0765

0.1085

0.0783

R1 = ∑||Fo|
|Fc||/∑|Fo|. b wR2 ={∑[w(Fo2
Fc2)2]/∑[w(Fo2)2]}1/2.

relative strength of these interactions, even though, other forces such as charge transfer and dispersion forces cannot be ignored.5,18
26 Accordingly, the heavier the halogen atom, the better the halogen donor. We used this trend to explain the hierarchy of C
Y 3 3 3 X
M interactions in a series of crystal structures (nbp)2CuX4, (ncp)2CuX4, and Cu(nBP)2X2 (nbp = n-bromopyridinium cation, ncp = n-chloropyridinium cation, nBP = n-bromopyridine, n = 2, 3, and 4 and X = Cl, Br).20,27,28 Similarly, Espallargas et al. have used this hierarchy of halogen bond strengths to rationalize the crystal structures of 16 isomolecular salts (3yp)2MX4 (3yp = 3-halopyrdinium cation; M = Co, Zn; Y = F, Cl, Br, I; X = Cl, Br, I).23 In this article, we complement our previous work. The crystal structures of Cu(2CP)2X2 and Cu(3CP)2Br2 complexes are reported (2CP = 2-chloropyridine, 3CP = 3-chloropyridine, and X = Cl, Br). The structural analysis will be supported by theoretical calculations. Also Espallargus et al. recently have shown that the solids of Cu(3YP)2Cl2 react with HCl gas, which makes these materials a target in gas sorption studies.29

’ EXPERIMENTAL SECTION Synthesis and Crystal Growth. The following general procedure was followed to prepare the three complexes: 2 mmol of n-chloropyridine were dissolved in ∼15 mL of acetonitrile. One mmol of copper(II) halide (CuBr2 or CuCl2 3 2H2O) was dissolved in ∼20 mL of acetonitrile. The chloropyridine solution was added to the suitable copper(II) halide solution. This mixture was gently heated while stirring for about 15 min, and then the solution was left to slowly evaporate until crystals were formed. Blue crystals of Cu(2CP)2Cl2 and green crystals of Cu(2CP)2Br2 and Cu(3CP)2Br2 formed after two days. The actual and percent yields are (0.23 g; 64%), (0.34 g; 76%), and (0.25 g; 56%) for Cu(2CP)2Cl2, Cu(2CP)2Br2, and Cu(3CP)2Br2, respectively. 5317

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Crystal Growth & Design Scheme 2. The Two Different Starting Geometries for Optimizing Cu(nYP)2X2, the Two Y Groups Are in L-cis Position (A and C) and in L-trans Positions (B and D)

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Table 2. Selected Bond Distances (Å) and Angles (°) compound

a

Cu(2CP)2Cl2

Cu(2CP)2Br2

Cu(3CP)2Br2

Cu
X1

2.284(1)

2.423(1)

2.432(1)

Cu
X3

2.246(1)

2.391(1)

Cu
N1

2.033(3)

1.992(6)

Cu
N7

2.038(3)

2.006(7)

X1
Cu
X3

176.5(1)

171.7(1)

180.0a

N1
Cu
N7

170.1(1)

175.3(3)

180.0(2)b

N1
C2
Cl2

116.9(3)

115.7(6)

N7
C8
Cl8 Cu 3 3 3 Cl2

115.4(3) 3.331(1)

115.1(6) 3.181(2)

Cu 3 3 3 Cl8

3.129(1)

3.155(3)

2.016(4)

Br1
Cu
Br1A angle in Figure 1A. b N1
Cu
N1A angle in Figure 1A.

Figure 2. Illustration of chain structure of Cu(3CP)2Br2. The Cu 3 3 3 Br semicoordinate bonds are shown as thin lines.

Figure 1. The molecular units of the two complexes: (A) Cu(3CP)2Br2 and (B) Cu(2CP)2Cl2. Cu(2CP)2Cl2 and Cu(3CP)2Cl2 are isomorphous to Cu(2CP)2Br2 and Cu(3CP)2Br2, respectively. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at 50% probability.

Crystal Structure Determination. The crystal structures of Cu(2CP)2X2 were determined at room temperature. The data collection was carried out on a Syntex P21 diffractometer upgraded to Bruker P4 specifications. Lattice dimensions were obtained from 32 and 27 accurately centered reflections for Cu(2CP)2Cl2 and Cu(2CP)2Br2, respectively.30 Data were corrected for absorption utilizing Ψ-scan data assuming an ellipsoidal shaped crystal.31 Data for Cu(3CP)2Br2 were collected at 87(2) K using a Bruker/Siemens SMART APEX instrument (Mo Kα radiation, λ = 0.71073 Å) equipped with a Cryocool NeverIce low temperature device. Cell parameters were retrieved using SMART

software and refined using SAINTPlus on all observed reflections.32,33 Data reduction and correction for Lp and decay were performed using the SAINTPlus software. Absorption corrections were performed using SADABS.34 The structure were solved by direct methods and refined by least-squares method on F2 using the SHELXTL program package. Hydrogen atoms were placed at the calculated positions using a riding model. All non-hydrogen atoms were refined anisotropically. No decomposition was observed during data collection. Details of the data collection and refinement are given in Table 1. Theoretical Method. Gaussian 03 was used for geometry optimization.35 The molecular structures of the Cu(nYP)2X2 complexes were optimized using two different starting geometries (Scheme 2). The calculations were carried out using DFT/B3LYP method. Geometry optimizations were performed using different basis sets; cc-pvdz on carbon, hydrogen, and nitrogen atoms; aug-cc-pvdz on halogen atoms, aug = presence of diffuse function on the halogen atoms; 6-31g on copper atom.

’ RESULTS Structural Results. The structures of the two complexes, Cu(3CP)2X2, are based on the planar trans CuX2N2 geometries, as shown in Figure 1A. The structure of Cu(3CP)2Cl2 was reported by Espallargas et al.29 These two complexes are isomorphous with the analogous Cu(3BP)2X2 (3BP = 3-bromopyridine; X = Cl
or Br
).20 In contrast, Figure 1B shows that Cu(2CP)2X2 complexes have distorted trans square planar CuX2N2 geometry with approximate C2v symmetry, the trans angles range 170.9
176.5° (Table 2). Copper centers in 5318

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Crystal Growth & Design

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Figure 3. Chain structure of Cu(2CP)2Cl2. C
H 3 3 3 Br, Cu 3 3 3 Br, and Cl 3 3 3 Cl interactions are represented by blue, black, and red dotted lines, respectively.

Table 3. Supramolecular Interactions Distances (Å) and Angles (°) compound Cu 3 3 3 X1
Cu 3 3 3 X1
Cu Cl 3 3 3 X1
(Å)

Cu(2CP)2Br2

Cu(3CP)2Br2

2.956(1)

3.710(2)a

3.116(1)

98.57(3)

100.18(4)

88.55(2) 3.661(1)

Ab

A

A

A

162.17(14)

A

A

117.54(2)

3.399(2)

3.555(3)

A

177.26(13) 104.60(13)

175.31(26) 107.15(29)

A A

Cl8 3 3 3 Cl8 C8
Cl8 3 3 3 Cl8

3.726(3)

3.377(4)

A

138.53(15)

149.24(3)

A

Cl8 3 3 3 Cl8
C8

138.53(15)

149.24(3)

A

C1
Cl1 3 3 3 X1
Cl1 3 3 3 X1
Cu Cl2 3 3 3 Cl8 C2
Cl2 3 3 3 Cl8 Cl2 3 3 3 Cl8
C8

a

Cu(2CP)2Cl2

Even though this distance is long, semicoordinate is assumed to be present because the structures of Cu(2CP)2Br2 and Cu(2CP)2Cl2 are isomorphous. b A = the interaction is absent.

Cu(3CP)2X2 complete their 4n + 2 coordination via Cu 3 3 3 X
semicoordinate bond. This results in formation of an infinite chain [CuL2X2]n (Figure 2). These chains run parallel to the a axis. Cu(2CP)2X2 complexes form a [Cu(2CP)2X2]2 dimer, because the sixth coordination site is blocked by the organic chlorine atoms on the ring (Figure 3). Hence, only one semicoordinate bond is possible. The supramolecular structure of the three complexes is developed based on the Cu 3 3 3 X semicoordinate bond, chlorine 3 3 3 chlorine interactions, chlorine 3 3 3 halide interactions, and other weak interactions like the nonclassical C
H 3 3 3 X hydrogen bond. The data summarizing these interactions are listed in Table 3. The Cu 3 3 3 X semicoordinate bond is present in all reported structures, though its role in the Cu(3CP)2X2 structures is more pronounced as indicated by the Cu 3 3 3 X1 distances; the Cu 3 3 3 Br1 distance in Cu(3CP)2Br2 is shorter than the analogous distance in Cu(2CP)2Br2 by 0.6 Å (Table 3). Inspection of halogen bonding interactions in the structures reveals that there are two different types; C
Cl 3 3 3 X
Cu present only in Cu(3CP)X2 and C
Cl 3 3 3 Cl
C in Cu(2CP)X2. In Cu(3CP)Br2 crystal structure, the role of the Cu 3 3 3 X
semicoordinate bond is complemented by C
Cl 3 3 3 X
Cu halogen bonding interactions. The fact that the Cl 3 3 3 Br distance in Cu(3CP)Br2 is longer than the sum of van der Waals radii of chlorine and bromine atoms by 0.06 Å does not negate the presence of attractive forces between these synthons, since the C
Cl 3 3 3 Br angle is in suitable arrangement for halogen

bonding interactions.21,28 In contrast, the role of the Cu 3 3 3 X semicoordinate bond in the supramolecular synthesis of Cu(2CP)X2 crystals is complemented by chlorine 3 3 3 chlorine interactions instead of C
Cl 3 3 3 X
Cu interactions. Examination of chlorine 3 3 3 chlorine interactions reveals that two patterns are present; (a) the symmetrical pattern with θ = θ1 = θ2, ca. θ = 144° (Scheme 1A). (b) The perpendicular pattern, with average θ1 = 176.3 and θ2 = 105.9°. Despite the fact that the two structures are isomorphous, there is a significant difference in chlorine 3 3 3 chlorine interactions in Cu(2CP)2X2 structures; the symmetrical arrangement is dominant in the Cu(2CP)2Br2 structure, and in contrast, the perpendicular arrangement is dominant in the Cu(2CP)2Cl2 structure as indicated by the inter-chlorine distances and angles of these interactions. The C
Cl 3 3 3 Cl angle of the symmetrical arrangement in Cu(2CP)2Br2 (ca. 149.3°) is closer to the perfect value 150°, with a short inter-chlorine distance of 3.377 Å, compared to that in the Cu(2CP)2Cl2 structure (138.53°) with inter-chlorine distances of 3.726 Å. Also the inter-chlorine distance of the perpendicular arrangement in the structure of Cu(2CP)2Cl2 is shorter than the corresponding distance in Cu(2CP)2Br2 by 0.15 Å. The isomeric nature of the chloropyridine ligands plays a crucial role in the hierarchy of these interactions in developing the supramolecular structures. In the Cu(3CP)2X2 structures, Cu 3 3 3 X connect the monomeric species into [Cu(3CP)2Cl2]n chains. These chains are subsequently linked into a threedimensional structure via C
Cl 3 3 3 X
Cu and via the weak nonclassical C
H 3 3 3 X
hydrogen bond. These semicoordinate bonds connect the Cu(2CP)2X2 to form dimers. These dimers are linked via chlorine 3 3 3 chlorine synthons to form a chain structure that extends along the 4 0 4 axis (Figure 3). These chains interact via C
H 3 3 3 X
hydrogen bond to form the three-dimensional structure. Theoretical Results. The molecular structure of the compounds Cu(nYP)X2 (where nYP denotes the n-substituted pyridine ligand, n = 2 or 3, Y = H, F, Cl, or Br and X = Cl
or Br
) was optimized for the L-cis and L-trans arrangements (Scheme 2); the L-trans and L-cis isomerism in this context refers to the arrangement of the organic halogen atoms rather than the inorganic halide ligands. Figure 4 shows representative examples of the optimized structures. The geometry around the Cu2+ center in Cu(HP)2X2 and L-trans Cu(3YP)X2 is square planar with N
Cu
N and X
Cu
X trans angles equal to 180°. In contrast, these trans angles are distorted from this perfect value in the rest of the complexes. The trans angles are avg = 153.2° (range 144.4
165.6°) and avg = 156.7° (range 148.6
163.5°) for X
Cu
X and N
Cu
N in Cu(2YP)X2, and the corresponding trans angles in L-cis-Cu(3YP)X2 complexes are 5319

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Figure 4. Optimized structure of (A) L-cis-Cu(2CP)2Br2, (B) L-trans-Cu(2CP)2Br2, (C) L-cis-Cu(3CP)2Cl2, (D) L-trans-Cu(3CP)2Cl2, (E) Cu(2HP)2Br2, and (F) L-cis-Cu(3FP)2Cl2.

Table 4. Calculated Destabilization Energya and Selected Bond Distances and Angles of the Optimized Cu(2YP)2X2 Molecular Structures structure L-cis-Cu(2FP)2Cl2 L-trans-Cu(2FP)2Cl2

ΔE (kJ/mol)a

Cu
X

Cu
N

X
Cu
X

N
Cu
N angle

H 3 3 3 Xb

0

2.234

2.038

146.1

148.6

2.799

10.4

2.227

2.041

158.37

152.9

3.505

2.393 2.388

2.026 2.027

144.8 155.06

150.4 151.5

3.003 3.329

L-cis-Cu(2FP)2Br2 L-trans-Cu(2FP)2Br2

0 9.91

2.387

2.033

L-cis-Cu(2CP)2Cl2

0

2.242

2.045

145.32

156.2

2.719

L-trans-Cu(2CP)2Cl2

7.93

2.232

2.042

164.39

162.5

3.525

2.232

2.047

L-cis-Cu(2CP)2Br2

0

2.406

2.033

144.40

160.1

2.867

L-trans-Cu(2CP)2Br2

7.24

2.396

2.032

161.5

161.3

3.583

145.5

158.6

2.680

165.6

164.2

3.509

144.5

162.2

L-cis-Cu(2BP)2Cl2

0

2.244

2.029 2.051

L-trans-Cu(2BP)2Cl2

5.55

2.231

2.044 2.051

L-cis-Cu(2BP)2Br2

0

2.402

2.041

2.409 L-trans-Cu(2BP)2Br2

4.29

2.395

2.815 2.815

2.031

163.1

163.5

3.575

2.036 a

The relative destabilization energy, ΔE = Eoptimized L‑trans
Eoptimized L‑cis. b H is the proton that is attached to C2 (Figure 4).

avg = 141.6° (range 136.4
144.7°) and avg = 135.2° (range 132.0
139.5°) for X
Cu
X and N
Cu
N, respectively (Tables 4 and 5). The deviation of these angles from the 180° value is greater in the case of the L-cis isomer with respect to the L-trans analogue. The average of these trans angles are 150.6° and 160.3° in the L-cis -and L-trans Cu(2YP)X2 isomers.

The relative energy of the optimized structures for the L-trans and L-cis pair was compared. The energy of the L-cis isomer was taken as a reference for each two L-trans and L-cis isomer pair. Henceforth, the energy difference between L-cis and L-trans isomers, which is destabilization energy, will be taken as a parameter to indicate the relative stability of these complexes. 5320

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Table 5. Calculated Destabilization Energya and Selected Bond Distances and Angles of the Optimized Cu(3YP)2X2 Molecular Structures compound

ΔE (kJ/mol)a

Cu
X1

Cu
X3

Cu
N

X
Cu
X

N
Cu
N

H(2) 3 3 3 X(1)

H(6) 3 3 3 X(3)

Φb

Cu(P)2Cl2

2.255

180

180

0

2.724

2.718

47.5

Cu(P)2Br2 L-cis-Cu(3FP)2Cl2

2.420 2.234

180 142.7

0 134.8

3.010 2.518

3.000 2.517

57.7

2.236

180 2.065

2.247

2.247

2.041

180

180

2.738

2.743

48.1

2.391

2.393

2.041

144.7

139.5

2.657

2.684

3.008

2.938

2.413

2.413

2.023

180

180

2.963

2.963

2.238

2.232

2.066

142.4

134.6

2.510

2.522

L-trans-Cu(3FP)2Cl2

13.12

L-cis-Cu(3FP)2Br2 L-trans-Cu(3FP)2Br2

13.15

L-cis-Cu(3CP)2Cl2

Θc 58.7436

55.6

L-trans-Cu(3CP)2Cl2

12.46

2.247

2.247

2.040

180

180

2.746

2.738

48.4

60.329

L-cis-Cu(3CP)2Br2 L-trans-Cu(3CP)2Br2

10.43

2.386 2.411

2.394 2.411

2.061 2.023

136.4 180

132.0 180

2.652 2.976

2.633 2.968

56.3

60.2

The relative destabilization energy, ΔE = Eoptimized L‑trans
Eoptimized L‑cis. b The angle between the plane of the aromatic systems and the coordination plane CuN2X2 of the optimized structures. c The angle between the plane of the aromatic systems and the coordination plane CuN2X2 of the structures obtained from structural analysis. a

These energy values are listed in Table 4. Three trends are observed in the calculated energies: (a) the L-trans isomer is less stable than the corresponding L-cis one. The destabilization energies of the L-trans isomer are avg = 9.45 kJ/mol (range 4.29
13.15 kJ/mol). (b) The destabilization energy of the complexes with chloride ligands (inorganic chloride) is more than the analogous value of the corresponding bromide complexes by avg = 1.12 kJ/mol (range 0.49
2.03 kJ/mol), except in Cu(3FP)2X2 complexes; both L-trans-Cu(3FP)2Cl2 and L-transCu(3FP)2Br2 have similar destabilization energies. (c) The lighter the organic halogen atom, the more stable the L-cis isomer with respect to the L-trans analogue; the L-trans-Cu(2FPy)2Cl2 isomer is less stable than L-cis-Cu(2FP)2Cl2 analogue by 10.4 kJ/ mol, and the corresponding destabilization energy value in L-trans-Cu(2BP)2Br2 is 4.3 kJ/mol.

’ DISSCUSION The data reported in this article will be discussed in the following sequence: (a) Comparing the optimized molecular structures with the experimental ones that were determined using X-ray crystallography. (b) Analysis of the weak intramolecular interactions; those are responsible for stabilizing the molecular structures. (c) Determining the role of intermolecular interactions in formation of the supramolecular structures of the reported structures in this article. The calculated destabilization energy of all investigated molecules in this articles is quite small (4.3
13.2 kJ/mol). Therefore, there is no perfect agreement between the calculated low energy isomer and the structure determined by X-ray crystallography. Moreover, the optimization process rules out the effect of intermolecular interactions which are expected to affect the molecular structure. In the case of Cu(2CP)2X2, the predicted structures (L-trans and L-cis isomersim) agree with those determined by structural analysis; The experimentally determined molecular structure of Cu(2CP)2X2 and the optimized structure are the L-cis isomers. Also, L-cis geometry was observed in a similar motif, Cu(2MP)2X2 (2MP = 2-methypyridine).37,38 In contrast, the molecular structure of Cu(2BP)2X2 is L-trans.20 This disagrees with the theoretical calculations; however, the destabilization energy is larger in the case of Cu(2CP)X2 than the corresponding energy values in Cu(2BP)2X2, and the average

destabilization energy is 7.6 and 4.9 kJ/mol for Cu(2CP)X2 and Cu(2BP)X2, respectively (Table 4). The crystal structure of the complexes Cu(2FP)2X2 is not known; calculation predicts this structure to be in L-cis arrangement. The structures of Cu(3YP)2X2 indicates that the arrangement of Y groups is the L-trans arrangement which disagrees with the theoretical calculations. This disagreement might be because the opti mization process ignores the intermolecular forces and the L-trans arrangement facilitates the formation of a Cu 3 3 3 X semicoordinate bond. The optimized molecular structure is one in which attractive forces are maximized. The major weak intramolecular attractive forces present in Cu(nYP)2X2 are C
H 3 3 3 X-Cu, and C
H 3 3 3 Y hydrogen bonding interactions and C
Y 3 3 3 Cu interactions (Figure 4 and Scheme 1C). C
H 3 3 3 X interactions are the major factors that are responsible for the stability of the L-cisCu(2YP)2X2, Cu(P)2X2, and Cu(3YP)2X2 complexes; in contrast, the L-trans-Cu(2YP)2X2 isomers are stabilized by C
H 3 3 3 Y hydrogen bonding interactions and C
Y 3 3 3 Cu interactions (Figure 4, Scheme 1C). This would indicate the C
H 3 3 3 X
Cu hydrogen bonding interaction to be stronger than C
Y 3 3 3 Cu and C
H 3 3 3 Y
C interactions since the L-cis isomer is more stable than the corresponding L-trans one. In the L-cis isomers, the H 3 3 3 X distances are always shorter than the corresponding distances in the trans isomers. For example, in the L-cis-Cu(3YP)2X2 complexes, the H 3 3 3 X distances are shorter than the corresponding distance in the L-trans isomers by ∼0.3 Å. This proves the assumption that the extra stability of the L-cis isomer with respect to the L-trans one is due to C
H 3 3 3 X
Cu hydrogen bond interactions. Also, this trend in energy of interactions explains why the destabilization energy of the chloride complexes is larger than that of the corresponding bromide complexes. Breaking C
H 3 3 3 Cl
Cu hydrogen bonding interaction is more endothermic than breaking the analogous C
H 3 3 3 Br
Cu interactions. Theoretical calculations indicate that C
Y 3 3 3 Cu interactions are stronger than C
Y 3 3 3 H
C hydrogen bonding interactions. The L-trans isomers are stabilized by C
Y 3 3 3 Cu interactions and C
Y 3 3 3 H
C hydrogen bonding interactions. C
F 3 3 3 H
C hydrogen bonding interactions are stronger than C
Br 3 3 3 H
C. Therefore, based on this factor alone, it is expected that the destabilization energy of L-trans-Cu(2FP)2X2 would be 5321

dx.doi.org/10.1021/cg200893n |Cryst. Growth Des. 2011, 11, 5316–5323

Crystal Growth & Design Scheme 3. Illustration of the Cu 3 3 3 X Semicoordinate Bond, C
Y 3 3 3 X
Cu and Cl 3 3 3 Cl Interactions in Cu(3YP)2X2 (A), Cu(2CP)2X2 (B), and Cu(2BP)2X2 (C)

smaller than that of L-trans-Cu(2BP)2X2, which is not the case. The other type of weak interaction which stabilizes the L-trans isomer is C
Y 3 3 3 Cu. As the halogen atom gets heavier, this interaction gets stronger, since heavier halogen atoms are softer. This explains why the destabilization energy decreases steadily as the organic halogen atom gets heavier. The experimentally determined molecular structures agree with the analogous optimized molecular structures. In the L-trans-Cu(3YP)2X2 structures, both the optimized structures and the experimentally determined ones indicate that the two aromatic rings are located on the same plane. Also, the plane of the aromatic rings is rotated out of the coordination plane CuN2X2. The angle of rotation is avg = 61.2° and avg = 52.5° for the optimized and experimentally determined structures. In the case of L-cis-Cu(2CP)2X2 structures, the two aromatic planes are not located on the same plane, and the angle between the two aromatic planes are avg = 54.9° and 25.6° for the optimized and experimentally determined structures, respectively. The X1
Cu
X3 trans angles are 144.7°and 174.1° for the optimized and experimentally determined structures. These differences are

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because the role of the semicoordinate bond is ruled out in the optimized structures. The semicoordinate bond pushes for further opening of the X1
Cu
X3 angle in the experimental structures. This would indicate that the rationalization of these molecular structures using the previously described weak noncovalent interaction is justified. Analysis of halogen 3 3 3 halogen and halogen 3 3 3 halide interactions in the structures reported in this article and a comparison of them with those published in the literature, Cu(nBP)2X2 and Cu(4CP)2Cl2,20,39 indicate that C
Cl 3 3 3 X
Cu interactions are of a comparable strength to C
Cl 3 3 3 Cl
C interactions. The pattern of these interactions in Cu(3BP)2X2 is similar to that of Cu(3CP)2X2 (Scheme 3); these four structures are isomorphous. In these four structures, halogen 3 3 3 halide interactions complement the role of the Cu 3 3 3 X semicoordinate bond in developing the three-dimensional structure. Similarly, C
Br 3 3 3 X
Cu rather than C
Br 3 3 3 Br
C interactions play the major role in the supramolecular structure of Cu(2BP)2X2. In contrast, chlorine 3 3 3 chlorine interactions instead of chlorine 3 3 3 halide interactions complement the role of the X 3 3 3 Cu semicoordinate bond in developing the chain structures in Cu(2CP)2X2 and Cu(4CP)2Cl2,39 and the C
Cl 3 3 3 X interactions are absent in these structures. This demonstrates that the C
Cl 3 3 3 Cl
C and C
Cl 3 3 3 X
Cu interactions are of similar strength.

’ CONCLUSIONS The results presented in this article indicate that weak noncovalent interactions play a major role in determining molecular structures and hence the crystal structure of Cu(nYP)2X2 complexes. The molecular structures are stabilized by three weak intramolecular interactions, C
H 3 3 3 X
Cu (X = Cl or Br), C
H 3 3 3 Y
C (Y = Cl or Br) hydrogen bonding interactions, and C
Y 3 3 3 Cu interactions (Scheme 1C). The C
H 3 3 3 X
Cu hydrogen bonding interactions are stronger than C
Y 3 3 3 Cu and C
H 3 3 3 Y
C interactions, since the optimized molecular structures L-cis-Cu(2YP)2X2 isomers are more stable than the corresponding L-trans ones (Scheme 2 and Figure 4). The L-cis isomers are stabilized by C
H 3 3 3 X
Cu hydrogen bonding interactions; in contrast, the L-trans isomers are stabilized by C
Y 3 3 3 Cu and C
H 3 3 3 Y
C interactions. C
Y 3 3 3 Cu interactions are stronger than C
H 3 3 3 Y
C interactions. The L-trans-Cu(2YP)2X2 isomers are stabilized by these two types of interactions. If the structure is only stabilized by C
H 3 3 3 Y
C hydrogen bonding interactions, the destabilization energy of L-trans-Cu(2FP)2X2 with respect to the L-cisanalogue will be lower than that of Cu(2BP)2X2, which is not the case. The destabilization energies are 10.4 and 5.6 kJ/mol for Cu(2FP)2X2 and Cu(2BP)2X2. The C
Y 3 3 3 Cu interaction gets stronger as the organic halogen is heavier. This explains why the destabilization energy of Cu(2FP)2X2 is larger than that of Cu(2BP)2X2. The intermolecular interactions affect the molecular structures. The calculations indicate separate L-cis-Cu(3YP)2X2 molecules are more stable than the corresponding L-trans isomers. The experimentally determined structure is the L-trans isomer. This is because the L-trans isomer facilitates the formation of the Cu 3 3 3 X semicoordinate bond. Analysis of the crystal structures indicates that the C
Cl 3 3 3 Cl
C interactions are of comparable strength to C
Cl 3 3 3 X
Cu. The supramolecular structures of Cu(3CP)2X2 are developed based on C
Cl 3 3 3 X
Cu interactions. In contrast, 5322

dx.doi.org/10.1021/cg200893n |Cryst. Growth Des. 2011, 11, 5316–5323

Crystal Growth & Design the molecular structure of Cu(2CP)2X2 are developed based on C
Cl 3 3 3 Cl
C interactions. This pattern has been observed in a similar motif, Cu(4CP)2Cl2.39

’ ASSOCIATED CONTENT

bS

Supporting Information. Crystal data in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT The Bruker (Siemens) SMART CCD diffraction facility was established at the University of Idaho with the assistance of the NSF-EPSCoR program and the M. J. Murdock Charitable Trust, Vancouver, WA, USA. ’ REFERENCES (1) Aaker€oy, C. B.; Beaty, A. M. Aust. J. Chem. 2001, 54, 409. (2) Bertani, R.; Sgarbossa, P.; Venzo, A.; Lelj, F.; Resnati, G.; Pilati, T.; Metrangolo, P.; Terraneo, G. Coord. Chem. Rev. 2010, 254, 677. (3) Braga, D.; Grepioni, F. Making Crystals by Design; Wiley-VCH Verlag GmbH & Co.: Weinheim, 2007. (4) Brammer, L. Chem. Soc. Rev. 2004, 33, 476. (5) Brisdon, A. K. Annu. Rep. Prog. Chem., Sect. A 2007, 103, 126. (6) Desiraju, G. R. Crystal Engineering, The Design of Organic Solids; Elsevier Science Publishers B. V: Amsterdam, 1989. (7) Fourmigue, M. Curr. Opin. Solid State Mater. Sci. 2009, 13, 36. (8) Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati, G. Acc. Chem. Res. 2005, 38, 386. (9) Metrangolo, P.; Resnati, G. Halogen Bonding Fundamentals and Applications; Springer: Heidelberg, 2008; Vol. 126, pp 1
15. (10) Tiekink, E. R. T.; Vittal, J.; Zaworotko, M. Organic Crystal Engineering, Frontiers in Crystal Engineering; John Wiley & Sons Ltd: Chichester, United Kingdom, 2010. (11) Aaker€oy, C. B.; Champness, N. R.; Janiak, C. CrystEngComm 2010, 12, 22. (12) Merz, K.; Vasylyeva, V. CrystEngComm 2010, 12, 3989. (13) Yamamoto, H. M.; Kosaka, Y.; Maeda, R.; Yamaura, J.; Nakao, A.; Nakamura, T.; Kato, R. ACS Nano 2008, 2 (1), 143. (14) Yamamoto, H. M.; Yamaura, J.; Kato, R. J. Am. Chem. Soc. 1998, 120, 5905. (15) Awwadi, F. F.; Willett, R. D.; Peterson, K. A.; Twamley, B. Chem.—Eur. J. 2006, 12, 8952. (16) Ramasubbu, N.; Parthasarathy, P.; Murray-Rust, P. J. Am. Chem. Soc. 1986, 108, 4308. (17) Pigge, F. C.; Vangala, V. R.; Swenson, D. C. Chem. Commun. 2006, 2123. (18) Bosch, E.; Barnes, C. L. Cryst. Growth Des. 2002, 2, 299. (19) Politzer, P.; Murray, J. S.; Clark, T. Phys. Chem. Chem. Phys. 2010, 12, 7748. (20) Awwadi, F. F.; Willett, R. D.; Haddad, S. F.; Twamley, B. Cryst. Growth Des. 2006, 6, 1833. (21) Awwadi, F. F.; Willett, R. D.; Peterson, K.; Twamley, B. J. Phys. Chem. A 2007, 111, 2319. (22) Espallargas, G.; Brammer, L.; Sherwood, P. Angew. Chem., Int. Ed. Engl. 2006, 45, 435. (23) Espallargas, G.; Zordan, F.; Marin, L.; Adams, H.; Shankland, K.; Streek, J.; Brammer, L. Chem.—Eur. J. 2009, 15, 7554. (24) Libri, S.; Jasim, N.; Perutz, R.; Brammer, L. J. Am. Chem. Soc. 2008, 130, 7842.

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(25) Lu, Y.-X.; Zou, J.-W.; Wang, Y.-H.; Jiang, Y.-J.; Yu, Q.-S. J Phys. Chem. A 2007, 111 (42), 10781. (26) Rosokha, S. V.; Neretin, I. S.; Rosokha, T. Y.; Hecht, J.; Kochi, J. K. Heteroatom Chem. 2006, 17, 449. (27) Awwadi, F. F.; Willett, R. D.; Twamley, B. Cryst. Growth Des. 2007, 7, 624. (28) Willett, R. D.; Awwadi, F. F.; Butcher, R.; Haddad, S. F.; Twamley, B. Cryst. Growth Des. 2003, 3, 301. (29) Espallargas, G.; Barnes, C. L.; Van de Streek, J.; Shankland, K.; Florence, A.; Adams, H. J. Am. Chem. Soc. 2006, 128, 9584. (30) XSCANS, Siemen Analytical X-ray Instrument, Inc., Version 2.00, Madison, WI, USA, 1993. (31) SHELXTL (XCIF, XL, XP, XPREP, XS), Version 6.10, Bruker AXS Inc., Madison, WI, USA, 2002. (32) SAINTPlus V 6.22, Bruker AXS, Inc., Madison, WI, USA, 2001. (33) SMART, Version 5.625 Bruker AXS Inc., Madison, WI, USA, 2002. (34) SADABS, V 2.03, Bruker AXS Inc., Madison, WI, USA, 2001. (35) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A. Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Strat-mann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; D Malick, K.; Rabuck,, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Iashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision D.01.; Gaussian, Inc.: Pittsburgh, PA, 2003. (36) Morosin, B. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1975, 31, 632. (37) Marsh, W. E.; Hatfield, W. E.; Hodgson, D. J. Inorg. Chem. 1982, 21, 2679. (38) Singh, P.; Jeter, D. Y.; Hatfield, W. E.; Hodgson, D. J. Inorg. Chem. 1972, 11, 1657. (39) Victorica-Yrezabal, I. J.; Sullivan, R. A.; Purver, S. L.; Curfs, C.; Tang, C. C.; Brammer, L. CrystEngComm 2011, 13, 3189.

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