Journal of Chemistry

Volume 2013 (2013), Article ID 486318, 6 pages

http://dx.doi.org/10.1155/2013/486318

Research Article

Crystal Structure of Ruthenium Phthalocyanine with Diaxial Monoatomic Ligand: Bis(Triphenylphosphine)Iminium Dichloro(Phthalocyaninato(2-))Ruthenium(III)

Derrick Ethelbhert Yu,¹ Akira Kikuchi,² Tetsuya Taketsugu,² and Tamotsu Inabe²

¹Department of Chemistry, College of Science, De La Salle University, 2401 Taft Avenue, Manila 1004, Philippines

²Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan

Received 27 June 2012; Accepted 6 September 2012

Academic Editor: Mitsushiro Nomura

Copyright © 2013 Derrick Ethelbhert Yu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Axially-ligated iron phthalocyanines have been found to be good molecular conductors with giant negative magnetoresistance (GNMR) which originates from a strong intramolecular -d interaction between the metal and phthalocyanine. Ab initio theoretical calculations showed that substitution of ruthenium into the phthalocyanine complex would result in a significant increase in the -d interaction of the system, potentially intensifying GNMR. This paper presents the crystal preparation and X-ray structural characterization of bis(triphenylphosphine)iminium dichloro(phthalocyaninato(2-))ruthenium(III), PNP [(Pc²⁻)Cl₂]. It is observed that [(Pc²⁻)Cl₂] system has a symmetric planar RuPc unit with perpendicular axial ligands which results in a unidirectional and uniform solid-state arrangement, suitable for -d interaction-based molecular conductors with potentially exceptional GNMR.

1. Introduction

Metallophthalocyanine complexes with mono- or diatomic linear diaxial ligands (Scheme 1) are suitable molecular conductors due to their ability to form a slip-stacked solid-state arrangement that permits intermolecular - overlap for electron conduction [1, 2]. Moreover, the existence of strong intramolecular -d interaction in axially ligated iron(III) phthalocyanine ((Pc)L₂; where L = CN, Cl, Br) molecular conductors has resulted in anisotropic giant negative magnetoresistance (GNMR) of up to 95% decrease in electrical resistance at 15 Tesla [3].

Scheme 1: Structure of (Pc)L₂ (where M = central metal and L = axial ligands).

Ab initio theoretical calculations using MOLPRO software package [4] performed on the (Pc)L₂ system corroborated experimental observation that the strength of GNMR is directly related to the strength of -d interaction in the order of L = CN > Cl > Br. On the electronic structure representation of [(Pc)L₂] species, the configuration gives two-fold degenerate ()²()²()¹ = ()²()¹()² while the HOMO is a singly occupied molecular orbital of the delocalized -system of the Pc. Electronic structure calculations using two state-averaged complete active space multiconfigurational SCF method (active space orbitals: Pc-, Fe- and ; Stuttgart-Köln ECP + DZ basis) resulted in (orbital energy difference between / and HOMO; intensity of the -d interaction) of 8.5450 eV, 8.3839 eV, and 7.8655 eV for L = Br, Cl, and CN, respectively. Using the same theoretical calculation framework to (Pc)L₂, which is electronically isostructural with the (Pc)L₂ species, the homologue system resulted in a remarkable increase of around two-fold in the -d interactions across all L₂ species (L: CN = 3.7518 eV, Cl = 3.8419 eV, Br = 3.9411 eV). Given that the intensity of the unique intramolecular -d interaction as the origin of the varying anisotropic GNMR in (Pc)L₂, thus the importance of the synthesis of ruthenium(III) phthalocyanine with linear axial ligands.

The synthesis of crystalline ruthenium phthalocyanine Ru(Pc) complexes has long been a challenge in phthalocyanine chemistry. Even upon the report of pure Ru(Pc) synthesis more than three decades ago, the ambiguities of its solid-state/materials science still remain as only very few crystal structures of 6-coordinated axially ligated Ru(Pc) complexes have been reported [5, 6]. However, these Ru(Pc) complexes have bulky and/or unsymmetrical axial ligands unsuitable for structure-property correlation studies. To date, only one axially-ligated magnetic Ru³⁺()-centered Pc crystal has been reported. Yet, this reported (Pc)L₂ crystal has unsymmetrical mixed axial cyano and pyridine ligands from an attempted identical di-axial ligation synthesis [7]. Herein, we report the crystal structure of ruthenium(III) phthalocyanine with identical di-axial linear ligands which can form symmetrical octahedral architecture that could be a potential component for magnetotransport material application.

2. Methodology

2.1. Crystallization

Dichloro(phthalocyaninato(1-)) ruthenium(III), (Pc¹⁻)Cl₂, was prepared via the method reported by Myers et al. in preparing various (Pc¹⁻)Cl₂ through the reaction of (Pc) with thionyl chloride oxidizing agent [8]. Pc (500 mg; 0.81 mmol) synthesized using the procedure of Farrell et al. [9], was suspended in nitrobenzene (10 mL). Thionyl chloride (2 mL; 28 mmol) was subsequently added to the reaction vessel and refluxed at 70°C for 3 hours. A 1 : 10 mole ratio of (Pc¹⁻)Cl₂ and bis(triphenylphosphine) iminium chloride (PNPCl) was dissolved in a 1 : 1 : 1 : 1 (volume) dimethylformamide : acetone : ethanol : hexane solvent system. The resulting solution was then left in an evacuated dessicator compartment at 25°C. Bis(triphenylphosphine)iminium dichloro(phthalocyaninato(2-)) ruthenium(III), PNP[(Pc²⁻)Cl₂], crystallized into dark blue crystals after 8 weeks.

2.2. X-Ray Crystal Structure Determination

A blue block crystal of PNP [(Pc²⁻)Cl₂] (Formula: C₆₈H₄₆N₉Cl₂RuP₂) having approximate dimensions of 0.15 × 0.10 × 0.05 mm was mounted on a glass fiber. All measurements were made on a Rigaku RAXIS RAPID imaging plate area detector with graphite monochromated Mo-Kα radiation. Indexing was performed from 3 oscillations that were exposed for 90 seconds. The crystal-to-detector distance was 127.40 mm. The data were collected at a temperature of 123 K to a maximum 2θ value of 49.0°. A total of 44 oscillation images were collected. A sweep of data was done using ω scans from 130.0 to 190.0° in 5.0° step, at ° and °. The exposure rate was 150.0 [sec/°]. A second sweep was performed using ω scans from 0.0 to 160.0° in 5.0° step, at ° and °. The exposure rate was 150.0 [sec/°]. The crystal-to-detector distance was 127.40 mm. Readout was performed in the 0.100 mm pixel mode. All post measurement data processing was performed using the CrystalStructure crystallographic software package [10].

3. Results and Discussion

The low solubility of (Pc)Cl₂ can be a cause of deterrent for the compound to be used as a precursor in synthesizing PNP[(Pc)Cl₂] salt crystal. However, the difficulty can be overcome by a delicate mixture of 1 : 1 : 1 : 1 dimethylformamide : acetone : ethanol : hexane crystallization solvent which produced the title compound.

In Figure 1, it can be observed that PNP[(Pc)Cl₂] units form ordered solid-state arrangement. Particularly, the anion component of the title compound, [(Pc)Cl₂]⁻, affords unidirectional orientation. The crystallographic parameters of PNP[Ru(Pc)Cl₂] are listed in Table 1. The crystal structure of PNP[Ru(Pc)Cl₂] is seen to be isostructural with its Fe homologue, PNP[(Pc)Cl₂], which also has a triclinic () crystal system [3].

Table 1: Crystallographic data collection parameters of PNP[RuIII(Pc)Cl₂] at 123 K.

Empirical formula
C₆₈H₄₆N₉Cl₂P₂Ru₁

Formula weight
1223.10

Crystal system
Triclinic

Lattice parameters
a = 10.4425(11)Å

b = 12.2391(11)Å

c = 13.159 (11)Å

= 75.523(3)°

= 64.686(3)°

= 65.883(3)°

= 1381.9(2)

Space group
(#2)

Z value
1

Calculated density
1.470 g/cm³

4.92 cm⁻¹

2
49.0°

Reflections collected/unique
10394/4588

[R(int) = 0.1173]

[> 2.00(I)]
0.0803

wR2 (all data)
0.2345

Goodness-of-fit indicator
1.105

Figure 1: Crystal structure of PNP[(Pc)Cl₂] (crystal system = triclinic; Z = 1).

At the molecular level (Figure 2), the regularity is brought about by the planarity of the RuPc and the linearity of the di-axial chloro ligands which give it a uniform octahedral architecture, that is, the central Ru³⁺ is aligned with the planarity of the Pc moiety which is manifested by the bond lengths, as well as the bond angles between the central Ru³⁺ and its adjacent nitrogen atoms being nearly equal (Tables 2 and 3). Furthermore, there is a linear 180° bond angle between the two axial chloro ligands which are perpendicular (90° ± 1.6) with respect to the central metal (Table 3), making [(Pc)Cl₂]⁻ suitable for slip-stacked intermolecular arrangement, with the cation bis(triphenylphosphine)iminium (PNP) serving as effective space-filler in the crystal system.

Table 2: Intramolecular bond lengths (Å) of PNP[RuIII(Pc)Cl₂].

Atom
Distance

Ru1–N3
1.982(9)

Ru1–N1
1.993(8)

P1–N5
1.552(3)

P1–C23
1.796(10)

N2–C8
1.335(12)

N3–C16
1.395(12)

N5–P1
1.552(3)

C2–C3
1.380(13)

C3–H3
0.9300

C5–C6
1.396(14)

C6–H6
0.9300

C10–C11
1.383(14)

C11–H11
0.9300

C13–C14
1.384(15)

C14–H14
0.9300

C17–C18
1.402(16)

C19–C20
1.353(19)

C20–H20
0.9300

C22–H22
0.9300

C24–C25
1.371(15)

C25–H25
0.9300

C27–C28
1.359(15)

C29–C30
1.375(13)

C30–H30
0.9300

C32–C33
1.354(14)

C33–H33
0.9300

Ru1–N3
1.982(9)

Ru1–Cl1
2.355(3)

P1–C17
1.767(12)

N1–C1
1.363(12)

N2–C9
1.349(12)

N4–C1
1.329(12)

C1–N4
1.329(12)

C2–C7
1.424(13)

C4–C5
1.373(15)

C5–H5
0.9300

C7–C8
1.463(13)

C10–C15
1.417(14)

C12–C13
1.406(15)

C13–H13
0.9300

C15–C16
1.449(14)

C18–C19
1.421(18)

C19–H19
0.9300

C21–C22
1.389(18)

C23–C28
1.382(13)

C24–H24
0.9300

C26–C27
1.391(16)

C27–H27
0.9300

C29–C34
1.403(14)

C31–C32
1.390(16)

C32–H32
0.9300

C34–H34
0.9300

Ru1–N1
1.993(8)

Ru1–Cl1
2.355(3)

P1–C29
1.789(10)

N1–C8
1.392(12)

N3–C9
1.365(13)

N4–C16
1.337(12)

C1–C2
1.463(13)

C3–C4
1.379(14)

C4–H4
0.9300

C6–C7
1.373(13)

C9–C10
1.481(13)

C11–C12
1.376(14)

C12–H12
0.9300

C14–C15
1.362(13)

C17–C22
1.384(16)

C18–H18
0.9300

C20–C21
1.34(2)

C21–H21
0.9300

C23–C24
1.386(14)

C25–C26
1.404(16)

C26–H26
0.9300

C28–H28
0.9300

C30–C31
1.398(15)

C31–H31
0.9300

C33–C34
1.361(15)

Table 3: Intramolecular bond angles (°) of PNP[RuIII(Pc)Cl₂].

Atom
Angle

N3 Ru1 N3
179.999(1)

N3 Ru1 N1
90.3(3)

N3 Ru1 Cl1
90.4(2)

N1 Ru1 Cl1
91.6(2)

N1 Ru1 Cl1
91.6(2)

N5 P1 C17
110.3(4)

N5 P1 C23
111.2(3)

C1 N1 C8
109.8(8)

C8 N2 C9
122.7(8)

C16 N3 Ru1
125.7(6)

N4 C1 N1
128.8(9)

C3 C2 C7
120.0(9)

C4 C3 C2
117.9(10)

C5 C4 C3
122.2(10)

C4 C5 C6
121.2(10)

C7 C6 C5
117.3(10)

C6 C7 C2
121.4(9)

N2 C8 N1
127.7(9)

N2 C9 N3
128.3(9)

C11 C10 C15
120.9(9)

C12 C11 C10
117.3(10)

C11 C12 C13
122.0(10)

C14 C13 C12
120.2(10)

C15 C14 C13
118.5(10)

C14 C15 C10
121.1(10)

N4 C16 N3
126.1(9)

C22 C17 C18
118.3(12)

C17 C18 C19
119.0(13)

C20 C19 C18
119.4(14)

C21 C20 C19
122.7(16)

C20 C21 C22
119.0(14)

C17 C22 C21
121.6(13)

C28 C23 C24
118.8(10)

C25 C24 C23
121.6(11)

C24 C25 C26
118.8(11)

C27 C26 C25
119.2(11)

C28 C27 C26
120.7(11)

C27 C28 C23
120.8(10)

C30 C29 C34
119.9(10)

C29 C30 C31
118.9(11)

C32 C31 C30
120.4(10)

C33 C32 C31
119.4(10)

C32 C33 C34
121.6(11)

C33 C34 C29
119.7(10)

N3 Ru1 N1
89.7(3)

N3 Ru1 N1
89.7(3)

N3 Ru1 Cl1
89.6(2)

N3 Ru1 Cl1
89.6(2)

N1 Ru1 Cl1
88.4(2)

N5 P1 C29
110.5(3)

C17 P1 C23
107.7(5)

C1 N1 Ru1
124.6(6)

C9 N3 C16
108.0(8)

C1 N4 C16
124.3(8)

N4 C1 C2
122.3(9)

C3 C2 C1
133.3(9)

C4 C3 H3
121.1

C5 C4 H4
118.9

C4 C5 H5
119.4

C7 C6 H6
121.4

C6 C7 C8
132.2(9)

N2 C8 C7
124.0(9)

N2 C9 C10
122.0(9)

C11 C10 C9
133.3(10)

C12 C11 H11
121.3

C11 C12 H12
119.0

C14 C13 H13
119.9

C15 C14 H14
120.7

C14 C15 C16
132.3(10)

N4 C16 C15
123.9(9)

C22 C17 P1
119.1(9)

C17 C18 H18
120.5

C20 C19 H19
120.3

C21 C20 H20
118.7

C20 C21 H21
120.5

C17 C22 H22
119.2

C28 C23 P1
122.3(8)

C25 C24 H24
119.2

C24 C25 H25
120.6

C27 C26 H26
120.4

C28 C27 H27
119.6

C27 C28 H28
119.6

C30 C29 P1
122.1(8)

C29 C30 H30
120.5

C32 C31 H31
119.8

C33 C32 H32
120.3

C32 C33 H33
119.2

C33 C34 H34
120.2

N3 Ru1 N1
90.3(3)

N1 Ru1 N1
179.999(1)

N1 Ru1 Cl1
88.4(2)

N3 Ru1 Cl1
90.4(2)

Cl1 Ru1 Cl1
179.999(1)

C17 P1 C29
108.2(5)

C29 P1 C23
108.8(5)

C8 N1 Ru1
125.4(6)

C9 N3 Ru1
126.1(7)

P1 N5 P1
179.999(1)

N1 C1 C2
108.9(8)

C7 C2 C1
106.6(8)

C2 C3 H3
121.1

C3 C4 H4
118.9

C6 C5 H5
119.4

C5 C6 H6
121.4

C2 C7 C8
106.3(8)

N1 C8 C7
108.3(8)

N3 C9 C10
109.7(9)

C15 C10 C9
105.8(9)

C10 C11 H11
121.3

C13 C12 H12
119.0

C12 C13 H13
119.9

C13 C14 H14
120.7

C10 C15 C16
106.5(8)

N3 C16 C15
109.9(9)

C18 C17 P1
122.6(9)

C19 C18 H18
120.5

C18 C19 H19
120.3

C19 C20 H20
118.7

C22 C21 H21
120.5

C21 C22 H22
119.2

C24 C23 P1
119.0(8)

C23 C24 H24
119.2

C26 C25 H25
120.6

C25 C26 H26
120.4

C26 C27 H27
119.6

C23 C28 H28
119.6

C34 C29 P1
118.0(7)

C31 C30 H30
120.5

C30 C31 H31
119.8

C31 C32 H32
120.3

C34 C33 H33
119.2

C29 C34 H34
120.2

Figure 2: ORTEP molecular structure representation of PNP[(Pc)Cl₂] (hydrogens are omitted for clarity).

The resulting unidirectional and ordered orientation of [(Pc)Cl₂]⁻ units is mainly attributed to the steric influence of small and linear axial ligands of the fully conjugated planar Pc from which electrical and magnetic property manifestations can be designed and modulated based on its bulkiness for corresponding intermolecular - overlap variations [11], as well as on the chemical properties founded on the ligand field energy [3] of the axial ligands.

4. Conclusion

The synthesis of the crystalline PNP[(Pc)Cl₂] revealed an ordered octahedral structural architecture of the Ru(Pc)Cl₂ moiety. The regularity of the structure, coupled with the steric influence of the linear axial ligands, could effectively result in a slip-stacked arrangement capable of intermolecular - orbital overlap for electron conduction. Furthermore, PNP[(Pc)Cl₂] is found to be isomorphous with its Fe homologue, thus opening prospects for the solid-state synthesis of other possible Fe(Pc)L₂ homologue species of ruthenium. The resulting Ru(Pc)L₂ is expected to have stronger -d interactions than its Fe counterparts that could result in molecular conductors with exceptional GNMR.

Appendix

CCDC 864862 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgments

This work was supported by the Hokkaido University Global Center of Excellence (GCOE) Program in chemistry and materials science (2007-2012) funded by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of the Japan Government.

References

T. Inabe and H. Tajima, “Phthalocyanines—versatile components of molecular conductors,” Chemical Reviews, vol. 104, no. 11, pp. 5503–5534, 2004.

D. E. C. Yu, M. Matsuda, H. Tajima, T. Naito, and T. Inabe, “Stable π-π dependent electron conduction band of TPP[M(Pc)L₂]₂ molecular conductors (TPP = tetraphenylphosphonium; M = Co, Fe; Pc = phthalocyaninato; L = CN, Cl, Br),” Dalton Transactions, vol. 40, no. 10, pp. 2283–2288, 2011.

D. E. C. Yu, M. Matsuda, H. Tajima et al., “Variable magnetotransport properties in the TPP[Fe(Pc)L₂]₂ system (TPP = tetraphenylphosphonium, Pc = phthalocyaninato, L = CN, Cl, and Br),” Journal of Materials Chemistry, vol. 19, no. 6, pp. 718–723, 2009.

H. J. Werner, P. J. Knowles, R. Lindh, F. R. Manby, and M. Schutz, “2006,” MOLPRO version 2006.1, a package of ab initio program, http://www.molpro.net/

L. R. Subramanian, “Tribute to Professor Dr Michael Hanack,” Journal of Porphyrins and Phthalocyanines, vol. 4, no. 3, pp. 300–309, 2000.

T. Rawling and A. McDonagh, “Ruthenium phthalocyanine and naphthalocyanine complexes: synthesis, properties and applications,” Coordination Chemistry Reviews, vol. 251, no. 9-10, pp. 1128–1157, 2007.

M. Weidemann, H. Hueckstaedt, and H. Homborg, “Darstellung und Eigenschaften von (Acido)(pyridin)phthalocyaninato(2–)ruthenaten(II); Kristallstruktur von Tetra(n-butyl)ammonium(cyano)(pyridin)phthalocyaninato(2–)ruthenat(II),” Zeitschrift für Anorganische Und Allgemeine Chemie, vol. 624, no. 5, pp. 846–852, 1998.

J. F. Myers, G. W. Canham, and A. B. P. Lever, “Higher oxidation level phthalocyanine complexes of chromium, iron, cobalt and zinc. Phthalocyanine radical species,” Inorganic Chemistry, vol. 14, no. 3, pp. 461–468, 1975.

N. P. Farrell, A. J. Murray, J. R. Thornback, D. H. Dolphin, and B. R. James, “Phthalocyanine complexes of ruthenium(II),” Inorganica Chimica Acta, vol. 28, pp. L144–L146, 1978.

D. J. Watkin, C. K. Prout, J. R. Carruthers, and P. W. Betteridge, “CrystalStructure 4.0: crystal structure analysis package, Rigaku and Rigaku/MSC (2010),” in CRYSTALS Issue 10, Chemical Crystallography Laboratory, Oxford, UK, 1996.

D. E. C. Yu, H. Imai, M. Ushio, S. Takeda, T. Naito, and T. Inabe, “One-step synthesis of partially oxidized cobalt(III) phthalocyanine salts with axial ligands,” Chemistry Letters, vol. 35, no. 6, pp. 602–603, 2006.