Cation-Induced Dimerization of Crown-Substituted Phthalocyanines

Oct 20, 2017 - Synopsis. The supramolecular dimeric complex [(μ-oxo)bis(tetra-15-crown-5-phthalocyaninato)(nicotinato)aluminum(III)]tetra(rubidium) b...
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Cation-Induced Dimerization of Crown-Substituted Phthalocyanines by Complexation with Rubidium Nicotinate As Revealed by X‑ray Structural Data Lyudmila A. Lapkina,† Vladimir E. Larchenko,† Gayane A. Kirakosyan,†,‡ Aslan Yu. Tsivadze,†,‡ Sergey I. Troyanov,*,§ and Yulia G. Gorbunova*,†,‡ †

Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow 119991, Russia Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskii pr. 31, bldg. 4, Moscow 119071, Russia § Chemistry Department, Moscow State University, Leninskie Gory, Moscow 119991, Russia ‡

S Supporting Information *

ABSTRACT: The supramolecular dimeric complex [(μoxo)bis(tetra-15-crown-5-phthalocyaninato)(nicotinato)aluminum(III)]tetra(rubidium) bis(nicotinate) was prepared by addition of an excess of a methanol solution of rubidium nicotinate to a chloroform solution of the aluminum crownphthalocyaninate, [(HO)Al(15C5)4Pc]. A single-crystal X-ray d iff raction study of {[Rb 4 (NicAl(15C5) 4 Pc) 2 (μO)]2+(Nic−)2}·2.36HNic·11H2O demonstrated that two molecules of the aluminum crown-phthalocyaninate nicotinate are connected through an Al−O−Al bridge supported by sandwiching of crown ether moieties by Rb+ cations.

T

alkali or alkaline-earth metal cations caused by their complexation with crown ether moieties of paramagnetic metal crownphthalocyanines. Thus, ESR spectroscopy reveals that the two paramagnetic centers are separated by 4.9 Å in VO(15C5)4Pc, 4.8 Å in Ag(15C5)4Pc, and 4.1 Å in Cu(15C5)4Pc in the presence of K+ in solution.7,8 Nevertheless, despite the 30-year history of studying cation-induced assembly of crown-Pc, to the best of our knowledge, X-ray characterization of such assemblies has not been reported. Here we report the investigation of alkali cation (K+, Rb+)induced assembly of aluminum(III) tetra-15-crown-5-phthalocyaninate [(HO)Al(15C5)4Pc]5 and the first structural characterization of such assemblies in the solid state by means of single-crystal X-ray diffraction (XRD) analysis. First, the cation-induced assembly of [(HO)Al(15C5)4Pc] in the presence of potassium or rubidium salts (nicotinate (Nic), pivalate, salicylate, sulfamate, and carbonate) in methanol was studied in chloroform solution by UV−vis and 1H NMR spectroscopy. In the UV−vis spectra, the blue shift of the Q band from 690 to 639 nm observed upon titration of a solution of [(HO)Al(15C5)4Pc] in chloroform with a solution of an alkali metal salt in methanol is indicative of the formation of a cofacial supramolecular complex (see Figure S2 in the Supporting Information). The formation of the supramolecular dimer was also proven by 1H NMR spectroscopy. In particular,

he recognition and transport of most common biological alkali cations are great challenges in the fields of inorganic and biological chemistry. In particular, a better understanding of their interactions with macromolecular ligands may lead to useful biomimetic models of ion transport in cells and can be further extended to the study of antibiotic systems in the field of biochemistry.1 To this end, the application of crown ethercontaining tetrapyrrolic ligands is very promising since it affords insight into the effects that arise from supramolecular assembly in nature.2 On the other hand, such a study provides novel approaches toward materials with outstanding properties. Indeed, crown-substituted phthalocyanines (crown-Pc), which were first reported in 1986,3 got a renaissance in the last few years due to growing understanding of the crucial role of cation-induced supramolecular assembly in the development of new materials with improved properties.4 In particular, trivalent metals (Al3+, Ga3+, In3+) containing crown-Pc have demonstrated unique recognition, photorefractive, nonlinear optical, and photosensitizing characteristics.5,6 The alkali-metal-induced assembly of crown-Pc in solution is well-detectable by UV−vis and NMR spectroscopy and has been widely reported. Kobayashi and Lever suggested a method for estimating the dipole−dipole splitting in cation-induced cofacial dimers of d-metal complexes with 15-crown-5phthalocyanine (M(15C5)4Pc, M = Cu, Zn, Ni), which allows one to evaluate the intermolecular distance (up to 4 Å in these complexes).7 Electron spin resonance (ESR) studies also indicate the formation of cofacial dimers in the presence of © 2017 American Chemical Society

Received: August 3, 2017 Published: October 20, 2017 82

DOI: 10.1021/acs.inorgchem.7b01983 Inorg. Chem. 2018, 57, 82−85

Article

Inorganic Chemistry the introduction of ∼10 equiv of RbNic in CD3OD into a solution of [(HO)Al(15C5)4Pc] in CDCl3 leads to narrowing of one resonance signal of aromatic protons (singlet at 8.83 ppm) with its simultaneous high-field shift (Figure S3). At the same time, the α-CH2 signal of the crown ether splits into two signals for exo and endo protons, which is consistent with the formation of a supramolecular dimer.7 It should be noted that we succeeded in growing single crystals suitable for XRD analysis only for the [(HO)Al(15C5)4Pc]−RbNic pair. Indeed, slow evaporation of a solution of [HOAl(15C5)4Pc] with an excess of RbNic in a chloroform/methanol/ethyl acetate mixture (10:1:1 v/v/v) at room temperature led to the formation of green single crystals that were studied by XRD using synchrotron radiation (see the Supporting Information for more crystallographic details). The XRD analysis revealed the crystal and molecular structure of the obtained supramolecular complex as {[Rb 4 (NicAl(15C5)4Pc)2(μ-O)]2+(Nic−)2}·2.36HNic·11H2O.9 The crystal consists of the [Rb4(NicAl(15C5)4Pc)2(μ-O)]2+ dication ([1]2+), two uncoordinated nicotinate counterions, nicotinic acid and solvate water molecules (Figure 1). The HNic

Table 1. Comparison of Al−Niso Distances (in Å) in the Tetraaza Coordination Cores of Phthalocyanine Ligands complexa

CNb

Al−N1

Al−N5

Al−N3

Al−N7

Al−Nmean

[1](Nic)2 212 311 414 514 613

6 6 5 5 5 5

1.963 1.961 1.959 1.952 1.948 1.993

1.956 1.961 1.951 1.952 1.952 1.968

1.958 1.952 1.964 1.965 1.942 1.979

1.957 1.952 1.961 1.956 1.940 1.972

1.958 1.956 1.956 1.956 1.946 1.978

a 2, [(NO 2 ) 2 AlPc(Bu 4 N)]; 3, [(MeO)Al((15C5)4Pc)]; 4, [(OC6H4NO2)AlPc]; 5, [(OC6F5)AlPc]; 6, [(AlPc)2O]. bAl coordination number.

Table 2. Coordination Environment of Al Atoms (in Å) (Axial Coordination) complexa

CNb

Al−μ(O)c

Al−OXd

Al−N4e

[1](Nic)2 212 716 817 311 414 514 613 915

6 6 6 6 5 5 5 5 5

1.881

1.911 1.927 1.848

0.031 0 0 0 0.407 0.422 0.390 −0.459 −0.441

1.861 1.756 1.761 1.766 1.679 1.675

a

7, [(PhCOO)AlTPP·EtOH]; 8, [NicAlTPP]n; 9, [(TTDPzAl)2O]. Al coordination number. cAl−O distance in the Al−O−Al moiety. d Bond length with the donor atom of the acido ligand. eMean plane of the Pc nitrogen donors. b

aluminum and the four isoindole nitrogens of the phthalocyanine range from 1.956(3) to 1.963(3) Å and are comparable with the corresponding distances in [(MeO)Al(15C5)4Pc] (1.951(4)−1.964(5) Å)11 and [(NO2)2AlPc(Bu4N)] (1.952− 1.961 Å)12 (Table 1) but slightly shorter than those in [(PcAl)2O] (1.968−1.993 Å).13 The Al atoms are located almost in the plane of the macrocycle. The aluminum center is displaced only by 0.031 Å from the mean plane of the Pc nitrogen donors (N4). By contrast, in the known five-coordinate aluminum phthalocyanine compounds, the metal center is 0.390−0.459 Å out of the phthalocyanine plane (Table 2).11,13,14 An interesting feature of the crystal structure of supramolecular dication [1]2+ is the existence of the Al−O−Al moiety (alumoxane) together with the coordination of two axially bound nicotinates. The angle of the Al−O−Al axis with respect to the plane of the (15C5)4Pc2− macrocycle is 89.14°. The Al−μ(O) distance is 1.881(1) Å, whereas the bond length of the nicotinate oxygen trans to the aluminum metal center, Al−ONic, is elongated to 1.911(3) Å. The Pc rings in [1]2+ are eclipsed and lie in parallel planes, with an interplanar distance of 3.697 Å. Similar alumoxane units have been found in the structures of [(PcAl)2O]13 and [(TTDPzAl)2O]15 (TTDPz = tetrakis(thiadiazole)porphyrazinato), even if with five-coordinate Al atoms (Table 2). The Al−O distances in the Al−O−Al moiety of the μ-oxo dimers are 1.679 and 1.675 Å with interplanar distances of 4.276 and 4.227 Å, respectively. The elongation of the Al−μ(O) bond in [1]2+ is due to the additional coordination of nicotinate anion and the presence of the large Rb+ cations between the crown ether moieties. The Al−ONic bond length of 1.911 Å in [1]2+ is close to the

Figure 1. X-ray structure of the dication [1]2+: (a) side view; (b) top view. Hydrogen atoms have been omitted for clarity, and disorder of the crown ether moieties is not shown.

molecules stabilize the nicotinate counterions by hydrogen bonding via the formation of [Nic·HNic]− associates, as was found earlier for the [K(B15C5)2]+[35-Dnb(35-DnbH)2]− structure (35-DnbH = 3,5-dinitrobenzoic acid).10 Figure 1 shows side and top views of supramolecular dication [1]2+. The bond lengths in the coordination environment of the aluminum atom and their comparison with the corresponding values in known aluminum phthalocyaninate structures are given in Tables 1 and 2. Each of the aluminum atoms has a slightly distorted octahedral coordination sphere formed by four N donor atoms of phthalocyanine, the oxygen atom of the nicotinate group, and the μ-oxygen atom symmetrically bridging two Al atoms. The Al−Niso bond lengths involving 83

DOI: 10.1021/acs.inorgchem.7b01983 Inorg. Chem. 2018, 57, 82−85

Inorganic Chemistry

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Al−ONO2 bond length of 1.927 Å in the structure of [(NO2)2AlPc(Bu4N)],12 which also has a six-coordinate aluminum atom, and exceeds the Al−OOMe distance of 1.756 Å in [(MeO)Al(15C5)4Pc]11 and the Al−OOPh distances of 1.761 and 1.766 Å in [(PhO)AlPc]14 for pentacoordinated aluminum atoms. The bridging position of nicotinates in onedimensional (1-D) coordination polymers containing aluminum(III) porphyrins16 results in an Al−ONic bond length equal to 1.861 Å, which is very close to the distance in the bridging Al−O−Al moiety of [1]2+ (Table 2). A similar distance between Al and the carboxylate oxygen (1.848 Å) is observed in the six-coordinate aluminum complex [(C6H5COO)AlTPP·EtOH].17 In [1]2+, the rubidium ions induce the formation of typical sandwich-structured complexes with crown ether units. Rubidium ions exhibit a coordination number of 10 as a result of the coordination to the two crown ether moieties (Rb−O, 2.873 to 3.200 Å). All of the crown ether moieties are somewhat pushed out from the Pc planes (Figure 1). The distance between the two mean planes containing the basal crown oxygens is approximately 3.7 Å. The bond distances between the oxygen atoms adjacent to the benzene rings and Rb+ (3.023 and 3.024 Å) are longer than the other crown Rb−O distances (2.909 to 2.969 Å), as expected because of the electron-withdrawing effect of the aromatic rings well-established for sandwich complexes of Rb+ with benzo-15crown-5.18,19 The nearest oxygen atom from one of the uncoordinated charge-compensating nicotinate anions is located at a distance of more than 6.5 Å from the rubidium atom. The same Rb···ONO3 distance was found in the crystal of Rb(B15C5)2NO3·H2O.18 Rubidium cations in the sandwiches with neutral crown ether ligands reveal decreased charge density. In summary, we have succeeded in preparing the μ-oxo supramolecular complex of aluminum tetra(15-crown-5)phthalocyaninate with rubidium nicotinate, which is the first X-ray structurally characterized complex in a large series of cation-induced supramolecular assemblies of crown-phthalocyanines. An interesting feature of this complex is the simultaneous formation of a sandwich complex containing four Rb+−(15-crown-5)2 moieties as well as an Al−O−Al bridging fragment. A detailed investigation of the behavior of similar compounds in solution and their properties will be published soon.

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Article

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Tel: +74959395396. Fax: +74959391240. *E-mail: [email protected]. Tel/Fax: +74959554874. ORCID

Sergey I. Troyanov: 0000-0003-1663-0341 Yulia G. Gorbunova: 0000-0002-2333-4033 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by programs of the Russian Academy of Sciences and the Council for Grants of the President of the Russian Federation for support of leading scientific schools (Grant NSh-8675.2016.3).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01983. UV−vis, NMR, and HR-ESI spectra (PDF) Accession Codes

CCDC 1566600 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by e-mailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax: +44 1223 336033. 84

DOI: 10.1021/acs.inorgchem.7b01983 Inorg. Chem. 2018, 57, 82−85

Article

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DOI: 10.1021/acs.inorgchem.7b01983 Inorg. Chem. 2018, 57, 82−85