Polyhedron 81 (2014) 188–195

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Polyhedron

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Absorption spectra, luminescence properties and electrochemicalbehavior of Mn(II), Fe(III) and Pt(II) complexes with quaterpyridineligand

http://dx.doi.org/10.1016/j.poly.2014.05.0810277-5387/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +48 618291483; fax: +48 618291508.E-mail address: violapat@amu.edu.pl (V. Patroniak).

Ariel Adamski a, Monika Wałesa-Chorab a,b, Maciej Kubicki a, Zbigniew Hnatejko a, Violetta Patroniak a,⇑a Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61614 Poznan, Polandb Laboratoire de Caractérisation Photophysique des Matériaux Conjugués, Département de Chimie, Université de Montréal, CP 6128, Centre-ville, Montreal, QC H3C 3J7, Canada

a r t i c l e i n f o a b s t r a c t

Article history:Received 18 February 2014Accepted 14 May 2014Available online 11 June 2014

Keywords:Iron(III)Manganese(II)Platinum(II)Organoplatinum(II) complexQuaterpyridine

6,6000-Dimethyl-2,20;60 ,200;600,2000-quaterpyridine ligand L reacts with Mn(II) 1, Fe(III) 2 and Pt(II) 3, 4 ionswhat results in formation of mononuclear complexes. The reactions were carried out under differentconditions (various solvent, temperature, counterion), leading to new complexes [MnL(H2O)Cl][ClO4],[FeLCl2][FeCl4], [PtL][Pt(CH3CN)Cl3]2 in which dimethylquaterpyridine acts as tetradentate ligand. Theuse of more drastic reaction conditions leds to obtain of a novel organoplatinum(II) complex [Pt(L-

H)Cl], that reveal unique tridentate coordination mode C, N, N0. Obtained compounds were thoroughlystudied in terms of their structural studies. We also have investigated physicochemical and electrochem-ical properties of these complexes.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Polypyridines are considered as an unsually strong and themost versatile chelating ligands for transitions metal ions [1], thusgenerating diverse architectures of complexes [2] with rich usefulphysical properties [3]. Chelating properties of simple ligands suchas bi- and terpyridines have been extensively reviewed in the pastdecades [4], hence their widespread use as basic building block forthe construction of polymers [5], mesomorphic frameworks orhydrogen bond acceptors [6]. Additional number of pyridine unitsin ligand structures result in an increase of its chelate effect [7] andthe ability to form even more sophisticated architectures such ashelicates [8], cages [9] and related exotic framework [10].

Self-assembly of 6,6000-dimethyl-2,20;60,200;600,2000-quaterpyridinecontinues to surprise in terms generating of new complexstructures as a result of the disclosure of new coordination modes[11]. A characteristic structural feature of polypyridines is theirsteric rigidity and natural preference for adopting the planargeometry, which allows free movement of p electrons above andbelow whole plane, improving the optical absorption of lumines-cent polypyridine complexes [12]. Therefore, 6,6000-dimethyl-2,20;60,200;600,2000-quaterpyridine usually functions as a tetradentate

ligand with nearly planar structure, chelating ions especially inoctahedral or square-planar geometry, what leads to mononuclearcomplexes [13]. Such a quadridentate coordination mode is foundin well-defined structures of quaterpyridine complexes of Mn(II/III) [14] and Fe(II/III) [15], which the oxidation potential is success-ful applied to the catalytic formation O2 form water (WOCs) [16].Moreover complexes of Mn(III) and Fe(III) exhibits a high degreeof structural homology [17].

Fully planar structure of quaterpyridine complexes withplatinum(II) ion display a rich luminescent and photophysicalproperties [18,19], which are enhanced as the result of theirpropensity to exhibit weak metal–metal interactions [20]. Apartfrom these uses as supramolecular systems, polypyridineplatinum(II) complexes exhibit antitumor behavior due to theirefficient intercalating ability into DNA [21].

Highly interesting and unprecedented architecture is theformation of tetranuclear complex as a result of the coordinationof 6,6000-dimethyl-2,20;60,200;600,2000-quaterpyridine and Co(II) [22]ions. Another coordination model relies on coordination of tetrahe-dral ions Cu(I) [23] or Ag(I) [11] to 6,6000-dimethyl-2,20;60,200;600,2000-quaterpyridine leading to a more sophisticated helical architec-tures. Also helical privileged conformation of quaterpyridineprovides rack type complex of Cu(I) in the presence of terpyridine[24]. Helical complexes of polypyridines are used in various areassuch as asymmetric catalysis [25], DNA binding [26] or supramo-lecular functional devices [27].

A. Adamski et al. / Polyhedron 81 (2014) 188–195 189

The new coordination model was found in an organometallicstructure of 6,6000-dimethyl-2,20;60,200;600,2000-quaterpyridinecomplex of platinum(IV), which exhibits catalytic activity in thehydrosililation process [28]. Polypyridine ligands can coordinateas N-heterocyclic carbenes, what is the result of a strong activationof the C–H bond in the pyridine ring [29], leading to the ortho-metalation of the ligand [30]. This new coordination modes of qua-terpyridine based on the unit C, N, N0 deforms ligand barely, thusthat system is similar to the geometry of uncoordinated ligandmolecule [31].

Our extensive research on the effectiveness of 6,6000-dimethyl-2,20;60,200;600,2000-quaterpyridine L in the self-assembly with transi-tion metal ions results in the synthesis of a wide range of differentarchitectures [11,13,22,23,28,31] (Fig. 1).

In this paper we report a new quaterpyridine complexes ofmanganese(II) 1, iron(III) 2 and platinum(II) 3, 4. Such organome-tallic platinum(II) systems without steric hindrance above andbelow the plane of the square-planar Pt(II) complexes can facilitatethe substitution reaction [32], what results in enhancement oftheir potential catalytic reactivity. Whilst polypyridine complexesMn(II) and Fe(III) are common catalysts to photosynthetic wateroxidation [33].

2. Experimental

2.1. General

Ligand L, 6,6000-dimethyl-2,20:60,200:600,2000-quaterpyridine wasprepared in our laboratory [11]. The metal salts were used withoutfurther purification as supplied from Aldrich. NMR spectroscopicdata were run on a Varian Gemini 300 MHz spectrometer, andwere calibrated against the residual protonated solvent signal ([D6-

]DMSO: d = 2.50) and are given in ppm. Mass spectra were deter-mined by a Waters Micromass ZQ spectrometer in acetonitrile.The samples were run in the positive-ion mode. The concentrationsof the compounds were about 10�4 mol dm�3. Sample solutionswere introduced into the mass spectrometer source with a syringepump with a flow rate of 40 lL min�1 with a capillary voltage of+3 kV and a desolvation temperature of 300 �C. Source temperaturewas 120 �C. Cone voltage (Vc) was set to 30 V to allow transmissionof ions without fragmentation processes. Scanning was performedfrom m/z = 100 to 1000 for 6 s, and 10 scans were summed toobtain the final spectrum. Microanalyses were obtained by usinga Perkin-Elmer 2400 CHN microanalyser. IR spectra were obtainedwith a Perkin-Elmer 580 spectrophotometer and are reported incm�1. All electronic absorption spectra were recorded with aShimadzu UVPC 2001 spectrophotometer, between 200 and800 nm, in 10 � 10 mm quartz cells using solutions 2.5 � 10�5 Mwith respect to the metal ions. Excitation and emission spectrawere measured at room temperature on a Hitachi 7000

Fig. 1. The ligand L – C22H18N4.

spectrofluorimeter. The quantum yield for the Mn(II) complex 1was measured using a relative method with anthracene as thestandard [34]. Cyclic voltammetry measurements were performedon a multi-channel BioLogic VSP potentiostat. Tetrabutylammo-nium hexafluorophosphate (0.1 M) in acetonitrile was used asthe supporting electrolyte. A platinum electrode and a saturatedAg/AgCl electrode were used as auxiliary and reference electrodes,respectively.

2.2. Synthesis of complexes 1–4

2.2.1. Complex [MnL(H2O)Cl][ClO4] 1To a mixture of Mn(ClO4)2�6H2O (22 mg, 59 lmol) and MnCl2-

�6H2O (15 mg, 59 lmol) in acetonitrile (40 mL), ligand L (20 mg,59 lmol) in dichloromethane (20 mL) was added dropwise withstirring. The reaction was carried out for 24 h under reflux at argonatmosphere. The reaction mixture was evaporated to dryness andremaining solid was dissolved in boiling acetonitrile (10 mL), fil-tered under gravity and left to stand overnight for crystallization.Obtained crystals of complex 1 suitable for X-ray crystallographywere filtered off, washed with cold acetonitrile and dried to yield14.9 mg (46%). ESI-MS: m/z = 447 (55) [MnL(H2O)Cl]+, 429 (64)[MnLCl]+, 339 (71) [L+H]+, 361 (100) [L+Na]+. IR (KBr): ~m = 3065,2916, 1604, 1570, 1471, 1368, 1264, 1114, 1029, 985, 918, 797,640, 633, 432 cm–1. [Mn(C22H18N4)(H2O)Cl][ClO4] (546.26): Anal.Calc. C, 48.37; H, 3.69; N, 10.26. Found: C, 48.45; H, 3.72; N, 10.33%.

2.2.2. Complex [FeLCl2][FeCl4] 2A mixture of FeCl3�6H2O (41 mg, 152 lmol) and ligand L (26 mg,

76 lmol) in CH3CN/CH2Cl2 (1:1, 40 mL) was stirred at room tem-perature for 72 h. Then the excessive solvents were removed byevaporation under reduced pressure. Obtained residue was dis-solved in dichloromethane. Complex was isolated from filtrate byprecipitation with diethyl ether. Brown solid was washed withdiethyl ether and dried to yield 21.5 mg (86%). Single crystal ofcomplex Fe(III) suitable for X-ray crystallography was obtainedby slow diffusion of hexane into methanol solution of Fe(III) com-plex 2. ESI-MS: m/z = 456 (100) [Fe2L2Cl3(OH)]2+, 197 (30) [FeL]2+,429 (27) [FeLCl]+. IR (KBr): ~m = 3083, 2924, 1734, 1653, 1605,1571, 1472, 1388, 1334, 1256, 1108, 1015, 908, 787, 654, 634,434 cm–1. [Fe(C22H18N4)Cl2][FeCl4] (662.81): Anal. Calc. C, 39.87;H, 2.74; N, 8.45. Found: C, 39.95; H, 2.77; N, 8.60%.

2.2.3. Complex [PtL][Pt(CH3CN)Cl3]2 3A mixture of PtCl2 (35 mg, 132 lmol) and ligand L (15 mg,

44 lmol) in CH3CN/CH2Cl2 (1:1, 44 mL) was stirred at room tem-perature for 72 h. Then the excessive solvents were removed byevaporation under reduced pressure. Obtained residue was dis-solved in methanol. Complex was isolated from filtrate by precip-itation with diethyl ether. Grey solid was washed with diethylether and dried to yield 38.9 mg (72%). Single crystal of Pt(II)complex suitable for X-ray crystallography was obtained by slowdiffusion of dichloromethane into methanol solution of Pt(II) com-plex 3. ESI-MS: m/z = 361 (100) [L+Na]+, 267 (23) [PtL]2+. IR (KBr):~m = 3087, 2922, 1736, 1655, 1604, 1571, 1474, 1389, 1336, 1258,1110, 1013, 905, 788, 656, 633, 435 cm–1. 1H NMR: (300 MHz,d6-DMSO): d = 8.92 (t, 2H, J = 6.7 Hz, (HE and HE0)), 8.67 (d, 2H,J = 7.5 Hz, (HD, HD0)), 8.45 (t, 2H, J = 7.6, (HB, HB0)), 7.95 (d, 2H,J = 7.85, (HC, HC0)), 7.50–7.47 (m, 4H (HA, HA0, HF, HF0)), 2.74 (s, 6H,Me), 2.58 (s, 6H, Me0) ppm. [Pt(C22H18N4)][Pt(CH3CN)Cl3]2

(1218,46): Anal. Calc. C, 25.63; H, 1.99; N, 6.90. Found: C, 25.65;H, 2.01; N, 6.87%.

2.2.4. Complex [Pt(L-H)Cl] 4An equimolar mixture of PtCl2 (12 mg, 44 lmol) and ligand L

(15 mg, 44 lmol) in DMSO (10 mL) was heated at 60 �C for 24 h.

190 A. Adamski et al. / Polyhedron 81 (2014) 188–195

Then the excessive DMSO was removed by evaporation underreduced pressure. Obtained residue was dissolved in methanol,solids which did not dissolve were removed by filtration. Complexwas isolated from filtrate by precipitation with diethyl ether.Orange solid was washed with diethyl ether and dried to yield15.6 mg (62%). Single crystal of Pt(II) complex suitable for X-raycrystallography was obtained by slow diffusion of hexane intomethanol solution of Pt(II) complex 4. ESI-MS: m/z = 531 (15)[Pt(L�H)]+, 339 (40) [L+H]+), 361 (100) [L+Na]+. IR (KBr):~m = 3066, 2917, 1603, 1572, 1470, 1365, 1265, 1114, 1032, 988,921, 791, 645, 632, 432 cm–1. 1H NMR: (300 MHz, d6-DMSO):d = 8.90–8.72 (m, 3H, (HE, HD, HH)), 8.65–8.46 (m, 2H, (HG, HB),8.05(t, 1H, J = 7.8 Hz, (HJ)), 7.88(m, 1H, (HC)), 7.81 (d, 1H, J = 7.71,(HI)), 7.49–7.39 (m, 2H, (HF–HA)), 7.26 (d, 1H, J = 7.2, (HK), 2.75(s, 3H, Me), 2.69 (s, 3H, Me) ppm. [Pt(C22H17N4)Cl] (567.93): Anal.Calc. C, 46.53; H, 3.02; N, 9.87. Found: C, 46.67; H, 3.14; N, 9.96%.

2.3. Crystal structure determination of complexes 1–4

X-ray diffraction data were collected at 120(1) K (2), 130(1) K(3, 4) and at room temperature (1) by the x-scan technique on Agi-lent Technologies four-circle SuperNova diffractometer (Atlasdetector) with mirror-monochromatized Cu Ka radiation(k = 1.54178 Å). The data were corrected for Lorentz-polarizationand absorption effects [35]. Accurate unit-cell parameters weredetermined by a least-squares fit of 1147 (1), 10882 (2), 15169(3) and 4983 (4) reflections of highest intensity, chosen from thewhole experiment. The structures were solved with SIR92 [36]and refined with the full-matrix least-squares procedure on F2 bySHELXL97 [37]. Scattering factors incorporated in SHELXL97 were used.All non-hydrogen atoms were refined anisotropically, all hydrogenatoms were placed in the calculated positions, and refined as ‘rid-ing model’ with the isotropic displacement parameters set at 1.2(1.5 for methyl groups) times the Ueq value for appropriate non-hydrogen atom. The crystals of 1 were of poor quality, moreoverthe sample decomposed during data collection. Soft restraints havebeen applied to the displacement parameters, in our opinion thedata allowed for discussion of the principal structural features. Rel-evant crystal data are listed in Table 1, together with refinementdetails.

3. Results and discussion

The formation of self-assembled systems strongly depends onreaction conditions employed therein, therefore in this paper wereport structures and characterization of four new complexes ofMn(II), Fe(III) and Pt(II) obtained as a result of a variety of syntheticpathways. Generally, we noticed that the dimethylquaterpyridineligand L is function as tetradentate one, generating mononuclearcomplexes of Mn(II) 1, Fe(III) 2 and Pt(II) 3 in the presence of ace-tonitrile as solvent, whereas in organometallic complex of Pt(II) 4,obtained in the presence of DMSO, ligand L is acting as tridentateone.

In complexes of Mn(II) and Fe(III) metal ions provides a octahe-dral geometry, coordinating with all nitrogen atoms of ligand L inequatorial plane, whereas axial positions are occupied by differentligands, according to the applied reaction conditions. The introduc-tion of two various manganese(II) hydrated salt into refluxed reac-tion environment resulted in the formation of [MnL(H2O)Cl][ClO4]complex 1. Our strategy has been to use two kinds of manga-nese(II) salts to direct the self-assembly process, because earlywe obtained the crystals suitable for X-ray analysis when we useddifferent kinds of counterions [38]. Complex [FeLCl2][FeCl4] wasobtained in the reaction between ligand L and FeCl3�6H2O at roomtemperature. Reaction between ligand L and PtCl2 results in

formation of complex [PtL][Pt(CH3CN)Cl3]2 (by the use mildreaction conditions) or leads to orthometalation to provide newcomplex [Pt(L-H)Cl] when reaction conditions were more drastic(DMSO, 60 �C). In the crystal structure of both platinum(II)complexes 3 and 4 all metal ions have square-planer geometry,whereas ligands structures are planar too. In structure of organo-platinum(II) complex 4 the metal ion is situated in a distortedsquare-planar coordination environment comprising N,N-donorligand sets, one chloride and C–Pt bond and generation of five-membered metallocycles. We reported earlier the ability of PtCl2

to undergo orthometalation reaction with dimethylquaterpyridinein DMSO, when drastic reaction conditions leads to isomorphicorganoplatinum(IV) complex, that has proved to be effective andhighly selective catalyst precursor in the hydrosilylation of styreneand terminal alkynes [28].

The behavior of complexes 1–4 was studied in acetonitrilesolution by use ESI-MS technique, consequently was determinedthe presence of cations, respectively [MnL(H2O)Cl]+, [FeL]2+,[PtL]2+, and [Pt(L–H)]+.

3.1. 1H NMR spectroscopy

The 1H NMR spectrum of free ligand L in CDCl3 exhibit sevensets of signals of which six in the range d 8.64–7.22 ppm confirmsthe presence of pyridine protons of symmetric ligand, whereas onesharp singlet at d 2.67 ppm confirms the methyl substituents sinceboth methyl groups are equivalent.

The 1H NMR spectrum of complex 3 in d6-DMSO shows aro-matic protons in the range d 8.92–7.47 ppm and two types ofmethyl protons at d 2.74 ppm and d 2.58 ppm (cf. experimentalsection and Fig. 2).

Both methyl groups of the coordinated ligand L were observedat d 2.74 ppm as sharp singlet, whereas the resonance centeredat d 2.58 ppm were assigned to methyl protons of counterion. Acomparison of the free ligand spectrum with the platinum(II) com-plex spectrum confirmed a downfield of pyridine as well as methylprotons, what is a traid characteristic for complexation of pyridine-based ligands [39]. The 1H NMR spectrum of free ligand in CDCl3

shows six sets of signals in the aromatic region, appear as four dou-blets at d 7.22, 7.41, 7.76, 8.64 ppm and two triplets at d 7.98 ppmand d 8.46 ppm. In the aromatic region of spectrum of complex 3both triplets (corresponding to protons HE, HE0 and HB, HB) areshifted the most (respectively Dd = 0.47 and 0.46), what confirmthe coordination of the ligand to the metal centre by use four nitro-gen donor atoms, whereas the resonances of all the other pyridineprotons did not undergo significant shifts.

The 1H NMR spectrum of complex 4 in d6-DMSO exhibit 13 setsof signals indicating the disorder of symmetry of ligand L inorganoplatinum(II) complex (cf. experimental section and Fig. 3).

One missing proton is the result of orthometalation of one ofpyridine rings, leading to formation of platinum–carbon bonds.The spectrum of organoplatinum complex shows broadening ofthe aromatic region (compared to the spectrum of free ligand) thatincludes the range d 8.90–7.26 ppm. Two resonances centered at d2.69 ppm and d 2.75 ppm were assigned to both methyl groups ofasymmetric coordinated ligands. A comparison of the free ligandspectrum with the organoplatinum(II) complex spectrum con-firmed a downfield of pyridine as well as methyl protons. In thearomatic region of spectrum of complex 4 signals of HI, HJ, HK

did not undergo significant shifts, which indicates that the one pyr-idine ring does not participate in the coordination. The signals ofHB and HE are shifts the most (respectively Dd = 0.48 and0.44 ppm), what confirms coordination of platinum ion with twonitrogen donor atoms. For signals HA–HE increase the multiplicityand overlap signals HG and HH were observed. All these features

Table 1Crystal data, data collection and structure refinement.

Compound 1 2 3 4

Formula C22H20ClMnN4O�ClO4 C22H18Cl2FeN4�FeCl4 C22H18N4Pt�2(C2H3Cl3NPt) C22H17ClN4PtFormula weight 546.26 662.80 1218.48 567.93Crystal system triclinic triclinic monoclinic triclinicSpace group P�1 P�1 P21/n P�1a (Å) 7.181(2) 8.872(2) 16.389(3) 7.394(2)b (Å) 11.322(2) 12.662(3) 7.840(2) 9.957(2)c (Å) 29.862(4) 13.066(3) 24.659(4) 12.988(3)a (�) 82.05(2) 107.93(2) 90 81.20(2)b (�) 85.41(2) 109.56(2) 101.00(2) 83.10(2)c (�) 78.00(3) 91.84(2) 90 78.32(3)V (Å3) 2348.7(9) 1300.9(6) 3110.2(11) 921.4(4)Z 4 2 4 2Dcalc(g cm�3) 1.55 1.69 2.60 2.05F(000) 1116 664 2232 544l(mm�1) 7.03 14.78 29.71 15.70H range (�) 4.02–58.08 3.71–70.00 2.99–73.73 3.46 – 75.99hkl range �7 6 h 6 7, �10 6 h 6 10, �20 6 h 6 19, �9 6 h 6 8

�12 6 k 6 7, �15 6 k 6 15, �9 6 k 6 8, �12 6 k 6 8�32 6 l 6 24 �15 6 l 6 15 �30 6 l 6 28 �16 6 l 6 14

ReflectionsCollected 5394 15,107 22,068 6896Unique (Rint) 4217 (0.145) 4928 (0.026) 6227 (0.051) 3679 (0.039)With I > 2r(I) 2075 4678 5935 3443

No. of parameters 613 309 374 255Weighting scheme

A 0.14 0.0597 0.234 0.0524B 3.9 1.2965 0 2.4784

R(F) [I > 2r(I)] 0.150 0.033 0.063 0.035wR(F2) [I > 2r(I)] 0.349 0.091 0.170 0.092R(F) [aLl data] 0.228 0.034 0.065 0.037wR(F2) [all data] 0.397 0.092 0.173 0.094Goodness of fit (GOF) on F2 1.37 0.96 1.11 1.09Max/min Dq (e �3) 0.87/�0.61 0.63/�0.49 4.90/�3.43 1.74/�1.60

Fig. 2. The complex 3 with the designation scheme of hydrogen atoms.

Fig. 3. The complex 4 with the designation scheme of hydrogen atoms.

A. Adamski et al. / Polyhedron 81 (2014) 188–195 191

of the spectrum indicate the presence of a unique tridentatecoordination mode N, N, C, that we reported earlier [28].

3.2. Crystal date

The perspective view of the complexes are shown in Figs. 4–7;Table 2 lists the relevant geometrical parameters.

In the crystal structure of 1 there are two symmetry-independent MnL(H2O) cations and two perchlorates in theasymmetric part of the unit cell.

The geometrical features of the analogous moieties are quitesimilar, the precision of the geometrical parameters is anywayrelatively low due to the poor quality of the crystals. Mn is six-coordinated, in quite deformed octahedral fashion (in fact, thegeometry more resembles the pentagonal bipyramid with onecoordination center unoccupied). The L molecules are almost pla-nar, dihedral angles between terminal ring planes are 7.2(9)� inmolecule A and 9.9(9)� in B. The water molecules take part, asthe hydrogen bond donors, in the interactions with the perchlorateoxygen atoms. Also weak C–H� � �O and stacking interactions areadd to the final crystal architecture (Fig. 4a).

In the structure of [FeLCl2][FeCl4] the central iron(III) atom inthe cation is six-coordinated in a distorted octahedral manner,while in the anion FeCl4

� the iron in almost ideal tetrahedralenvironment).

The ligand molecule is significantly less folded, but the dihedralangle between the planes of terminal ring is still relatively large, of

Fig. 4. One of symmetry-independent cations in 1(A), with the numbering scheme;the ellipsoids are drawn at the 33% probability level, hydrogen atoms are shown asspheres of arbitrary radii. (a) The crystal packing of [MnL(H2O)Cl][ClO4] as seenalong y-direction; thin blue lines represent hydrogen bonds. (Color online.)

Fig. 5. The complex cation in 2 with the numbering scheme; the ellipsoids aredrawn at the 50% probability level, hydrogen atoms are shown as spheres ofarbitrary radii.

Fig. 6. The complex cation in 3 with the numbering scheme; the ellipsoids aredrawn at the 50% probability level, hydrogen atoms are shown as spheres ofarbitrary radii.

Fig. 7. The complex 4 with the numbering scheme; the ellipsoids are drawn at the50% probability level, hydrogen atoms are shown as spheres of arbitrary radii.

Table 2Relevant geometric parameters (Å, �) with s.u.’s in parentheses.

1Mn1A–N1A 2.394(19) Mn1B–N1B 2.336(19)Mn1A–N8A 2.275(16) Mn1B–N8B 2.233(18)Mn1A–N14A 2.189(19) Mn1B–N14B 2.294(17)Mn1A–N20A 2.39(2) Mn1B–N20B 2.42(2)Mn1A–O1A 2.160(17) Mn1B–O1B 2.186(16)Mn1A–Cl1A 2.438(7) Mn1B–Cl1B 2.539(9)N1A–Mn1A–N14A 140.5(8) N1B–Mn1B–N14B 143.1(8)N8A–Mn1A–N20A 141.4(7) N8B–Mn1B–N20B 139.3(7)O1A–Mn1A–Cl1A 155.1(4) O1B–Mn1B–Cl1B 154.2(5)N1A–Mn1A–N20A 147.2(7) N1B–Mn1B–N20B 146.4(6)

2Fe1–N1 2.279(2) Fe1–N8 2.120(2)Fe1–N14 2.122(2) Fe1–N20 2.273(2)Fe1–Cl1 2.2339(8) Fe1–Cl2 2.2762(8)N1–Fe1–N14 147.09(8) N8–Fe1–N20 146.98(8)Cl1–Fe1–Cl2 162.11(3)

3Pt1–N1 2.081(7) Pt1–N8 1.943(7)Pt1–N14 1.957(6) Pt1–N20 2.085(7)N1–Pt1–N14 159.8(3) N8–Pt1–N20 160.8(3)

4Pt1–N1 2.200(5) Pt1–N8 1.978(5)Pt1–C18 1.982(6) Pt1–Cl1 2.3163(15)N1–Pt1–C18 160.0(2) N8–Pt1–Cl1 174.43(15)

192 A. Adamski et al. / Polyhedron 81 (2014) 188–195

22.10(10)�. The conformation of L differs from that observed in[PtL][Pt(CH3CN)Cl3]2 one pair of rings is almost coplanar whilethe other two are twisted by 9.38(9)�. The N atoms are also inall-cis disposition. In the crystal structure basically the sameinteractions are important: electrostatic and weak C–H� � �Cl andp� � �p ones. As before, the latter interactions are observed in thecentrosymmetric ‘dimer’).

In the Pt complex 3, quite unusual counterion was formed,namely [PtCl3(MeCN)]�. There are only few examples of suchanions structurally characterized. In both cation and anions, Pt is4-coordinated (by four molecules of N atoms in cation, and bythree chlorides and acetonitrile nitrogen in anions) in a squareplanar fashion. These coordination is almost ideal in anions (fourcoordination centers are in the same plane within 0.031(3) Å in

200 300 400 500 600 700 800

(3) (2) (4) (1) (L)

Abso

rban

ce

λ [nm]

Fig. 8. The absorption spectra of studied compounds.

Table 4The UV–Vis absorption bands (kmax) and molar absorption coefficients (e) of theligand, L, and its metal complexes.

Compound kmax [nm] (e[104 dm3 mol�1 cm�1])

L 252 (2.03), 292 (3.13)1 206 (4.01), 235 (2.64), 305 (2.43), 336 (1.32), 346 (1.38)2 223 (4.78), 303 (3.12), 349 (1.55)3 232 (3.25), 288 (0.35)4 222 (2.79), 264 (0.50)

200 250 300 350 400 450 500 550 6000

2000

4000

6000

8000

10000

600 620 640 660 680 700 7200

20

40

60

80

100

(1) (2) (3) (4)

Emiss

ion

Inte

nsity

[a.u

.]λ [nm]

Emissionspectra

Excitation spectra

(3) (2) (4) (1) (L)

Inte

nsity

[a.u

.]

λ[nm]

Fig. 9. The excitation and luminescence spectra of complexes 1–4 and ligand L; theinsert shows the red emission bands. (Color online.)

A. Adamski et al. / Polyhedron 81 (2014) 188–195 193

anion B and 0.053(3) Å in C, the ‘‘diagonal’’ angles are not smallerthan 177.24(10)�), while in the cation one can notice moresignificant deformation. Even though the four nitrogen atoms liein the same plane within 0.129(4) Å, and the Pt is situated almostideally in this plane (deviation 0.009(2) Å), the angles are morespread, obviously due to the spatial demands of the L molecule.The ligand molecule itself is significantly folded, with the dihedralangles between subsequent pyridine planes of 11.6(4)�, 11.2(4)�and 14.6(4)�. The dihedral angle between the planes of terminalrings – which can be to some extent regarded as the measure ofthe overall twist of L molecule – is 35.9(3)�. Four N atoms in theL molecule are in all-cis disposition. The dihedral angles are com-pared in Table 3.

In the crystal structure, besides the coulombic interactionsbetween charged species, some weak but directional C–H� � �Clhydrogen bonds are observed as well as p� � �p interactions betweenthe molecules related by center of symmetry at 0.5,0,0.5).

The organometallic molecule [Pt(L-H)Cl] the Pt cation is still 4-coordinated, in the distorted square-planar environment, but thecoordination centers are two nitrogen atoms from L molecule,chloride anion, and the fourth one is actually filled by Pt–C bond.This change causes the different conformation of L; not only it isalmost, within 0.091(6) Å planar as the whole (dihedral anglebetween terminal ring planes is 2.7(3)�) but also the dispositionof nitrogen atoms is cis–trans–trans. This allows for more regularsquare-planar coordination, four centers are planar within0.018(3) Å and Pt atoms is 0.017(2) Å out of this plane. C–H� � �N(as there are nitrogen atoms available as potential acceptors ofhydrogen bonds in this molecule) and C–H� � �Cl hydrogen bondsare observed in the crystal structure; interestingly no stackinginteractions could be found.

3.3. Electronic absorption spectra and luminescence properties

Fig. 8 shows the UV–Vis absorption spectra of the investigatedligand L and complexes 1–4 in CH2Cl2 and CH3CN solutions,respectively.

Selected data (maximum absorption wavelengths, kmax, molarabsorption coefficients, e) are summarized in Table 4.

The UV–Vis spectrum of CH2Cl2 solution containing the free Lligand was dominated by two intense absorption bands atk = 251.5 and 292.0 nm which are attributed to the p–p⁄ transi-tions of the aromatic ring. In the presence of transition metal ionsthe absorption bands had no or slight shift as compared to the freeligand L. The complexes of 1 and 2 also displayed a broad bandscentered at about 350 nm which are associated with the formationof complexes of transition metal ions with terpyridine ligand, whatwas observed earlier [40]. The broad absorption band in the visibleregion at k = 508 nm, in the complex 2, is assigned to an MLCT elec-tronic transition [41].

The photoluminescence study of solutions of obtained systemswas carried out at room temperature (Fig. 9).

Free L ligand displayed a broad emission band at kem = 350attributed to the p–p⁄ transitions upon photoexcitation atkex = 292 nm. The corresponding complexes 1 and 3 showedemission bands at the same wavelengths when were excitated atkex = 315 nm. The similar emission of 1 and 3 is due to similarcoordination environments around Mn(II) and Fe(III) centers. Theemission band maxima of 2 and 4 were red- and blue-shifted

Table 3NCCN dihedral angles in the L molecules.

1 2 3 4A 4B

N1–C6–C7–N8 �0.5(11) 1.5(3) �0.8(8) �3(3) 4(3)N8–N9–C13–N14 �9.8(11) �9.4(3) �179.5(5) 2(4) 3(4)N14–C15–C19–N20 3.3(11) �7.7(3) 177.5(6) 3(3) 9(4)

(kex = 335 and 285 nm respectively). From Fig. 9 it can be seen thatthe presence of transition metal ions decreased the luminescenceemission intensity of L. From studied complexes the intensity ofemission bands was the strongest in complex 1 with the low valueof quantum yield, equal 0.018, determined relative to anthraceneas standard. All complexes presents also a very weak red emissionbands, while the free ligand L does not present the emission. Thisemission is probably due to the metal–ligand or halide–metalcharge transfer [42,43].

3.4. Cyclic voltammetry

Electrochemical measurements of complexes were performedin anhydrous deaerated acetonitrille solutions at concentration of

Fig. 10. Cyclic voltammograms of complexes Fe(III) 2 (A) and Mn(II) 1 (B).

194 A. Adamski et al. / Polyhedron 81 (2014) 188–195

complexes 0.1 mmol/dm3 with 0.1 M TBA-PF6 (tetrabutylammo-nium hexafluorophosphate) as a supporting electrolyte at scan rate100 mV/s. Cyclic voltammogram of ligand L did not show anyoxidation and reduction waves in the range �2.5 to +2.5 V. CV ofcomplexes exhibit oxidation and reduction peaks, which are attrib-uted to the different redox states of the metal ions and are showedin Fig. 10 and Fig 11.

For Mn(II) complex 1 two irreversible oxidation waves weredetected at +0.3 and +1.35 V (Fig. 10B). These oxidation peakscan be attributed to oxidation processes Mn(II)?Mn(III) (+0.3 V)and Mn(III)?Mn(IV) (+1.35 V) [44]. In the negative range of poten-tials there is one reduction peak at �0.65 V similar to this observedfor another mononuclear Mn(II) complexes [45]. In the CV of Fe(III)complex 2 (Fig. 10A) there are two cathodic peaks in the negativerange of potential, corresponding to reduction processes Fe(III)?Fe(II) of two Fe(III) metal ions in complex 2: Fe(III)–Fe(III) toFe(III)–Fe(II) followed by Fe(III)–Fe(II) to Fe(II)–Fe(II) process [46].Cyclic voltammograms of Pt(II) complexes 3 and 4 are similar(Fig. 11).

Fig. 11. Cyclic voltammograms of complexes Pt(II) 3 (A) and 4 (B).

There are irreversible oxidation waves around +2.0 V which canbe assigned to Pt(II)?Pt(IV) oxidation process. Cathodic peaks cor-responding to Pt(II)?Pt(0) reduction process appear around�0.6 Vfor both complexes. This value is similar to reduction potentialobserved for Pd(II)?Pd(0) process [47]. For Pt(II) complex 3 thereare also another weak reduction peaks at �0.18 and �0.34 V whichcan be assigned to Pt(II)?Pt(0) of [Pt(CH3CN)Cl3]� anions.

4. Conclusion

We report the synthesis of new mononuclear complexes ofMn(II), Fe(III) and Pt(II) with dimethylquaterpyridine ligand Land influence of various reaction conditions on the formation ofself-assembled crystal structures. The utilization of mild reactionconditions (acetonitrile as solvent) provides to formation ofcomplexes 1–3 in which dimethylquaterpyridine acts as tetraden-tate ligand by adopting flat shape around coordinated cation. Astrong tendency to adopt the flat shape of the ligand L is imple-mented by orthometalation process in more drastic conditions alsoleading to the formation of five-membered metallocycles inorganoplatinum(II) complex.

Acknowledgement

Cyclic voltammetry measurements were done at Universite deMontreal in the Laboratoire de Caractérisation Photophysique desMatériaux Conjugués, Prof. Will G. Skene is gratefully acknowl-edged. This research was carried out as a part of the NationalScience Center project (Grant No. 2011/03/B/ST5/01036).

Appendix A. Supplementary data

CCDC 974461, 974460, 974459, 974549 contain the supplemen-tary crystallographic data for compounds 1, 2, 3, 4, respectively.These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallo-graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.

References

[1] E.C. Constable, C.E. Housecroft, M. Neuburger, P.J. Rosel, S. Schaffner, DaltonTrans. (2009) 4918.

[2] C.R.K. Glasson, G.V. Meehan, C.A. Motti, J.K. Clegg, P. Turner, P. Jensen, L.F.Lindoy, Dalton Trans. 40 (2011) 12153.

[3] Y.-W. Zhong, C.-J. Yao, H.-J. Nie, Coord. Chem. Rev. 257 (2013) 1357.[4] C. Kaes, A. Katz, M.W. Hosseini, Chem. Rev. 100 (2000) 3553.[5] A. Maier, H. Fakhrnabavi, A.R. Rabindranath, B. Tieke, J. Mater. Chem. 21 (2011)

5795.[6] R. Ziessel, F. Camerel, B. Donnio, Chem. Rec. 9 (2009) 1.[7] R.D. Hancock, Chem. Soc. Rev. 42 (2013) 1500.[8] H.-L. Yeung, K.-C. Sham, W.-Y. Wong, C.-Y. Wong, H.-L. Kwong, Eur. J. Inorg.

Chem. (2011) 5112.[9] C.R.K. Glasson, G.V. Meehan, J.K. Clegg, L.F. Lindoy, P. Turner, M.B. Duriska, R.

Willis, Chem. Commun. (2008) 1190.[10] R. Ziessel, D. Matt, L. Toupet, Chem. Comm. (1995) 2033.[11] A.R. Stefankiewicz, M. Wałesa, P. Jankowski, A. Ciesielski, V. Patroniak, M.

Kubicki, Z. Hnatejko, J.M. Harrowfield, J.-M. Lehn, Eur. J. Inorg. Chem. (2008)2910.

[12] C. Coluccini, N. Manfredi, M.M. Salamone, R. Ruffo, M.G. Lobello, F. Angelis, A.Abbotto, J. Org. Chem. 77 (2012) 7945.

[13] A. Ciesielski, A.R. Stefankiewicz, M. Wałesa-Chorab, V. Patroniak, M. Kubicki, Z.Hnatejko, J.M. Harrowfield, Supramol. Chem. 21 (2009) 48.

[14] C.-W. Chan, C.-M. Che, S.-M. Peng, Polyhedron 12 (18) (1993) 2169.[15] C.-M. Che, C.-W. Chan, S.-M. Yang, C.-X. Guo, C.-Y. Lee, S.-M. Peng, J. Chem. Soc.,

Dalton Trans. (1995) 2961.[16] E.L.-M. Wong, G.-S. Fang, C.-M. Che, N. Zhu, Chem. Commun. (2005) 4578.[17] M. Sjödin, J. Gätjens, L.C. Tabares, P. Thuéry, V.L. Pecoraro, S. Un, Inorg. Chem.

47 (2008) 2897.[18] C.-W. Chan, C.-M. Che, M.-C. Cheng, Y. Wang, Inorg. Chem. 31 (1992) 4874.[19] X.-H. Li, L.-Z. Wu, L.-P. Zhang, C.-H. Tunga, C.-M. Che, Chem. Commun. (2001)

2280.

A. Adamski et al. / Polyhedron 81 (2014) 188–195 195

[20] V.W.-W. Yam, R.P.-L. Tang, K.M.-C. Wong, K.-K. Cheung, Organometallics 20(2001) 4476.

[21] Y.-C. Lo, T.-P. Ko, W.-C. Su, T.-L. Su, A.H.-J. Wang, J. Inorg. Biochem. 103 (2009)1082.

[22] A. Ciesielski, V. Patroniak, M. Kubicki, J. Chem. Crystallogr. 41 (2011) 1884.[23] M. Wałesa-Chorab, V. Patroniak, G. Schroeder, R. Franski, Eur. J. Mass

Spectrom. 16 (2010) 163.[24] E.C. Constable, C.E. Housecroft, J.R. Price, J.A. Zampese, Inorg. Chem. Commun.

13 (2010) 683.[25] T. Hasegawa, Y. Furusho, H. Katagiri, E. Yashima, Angew. Chem. 119 (2007)

5989.[26] A.C.G. Hotze, B.M. Kariuki, M.J. Hannon, Angew. Chem. 118 (2006) 4957.[27] F. Cardinalli, H. Mamlouk, Y. Rio, N. Armaroli, J.-F. Nierengarten, Chem.

Commun. (2004) 1582.[28] A. Adamski, M. Kubicki, P. Pawluc, T. Grabarkiewicz, V. Patroniak, Catal.

Commun. 42 (2013) 79.[29] K.J.H. Young, S.K. Meier, J.M. Gonzales, J. Oxgaard, W.A. Goddard III, R.A.

Periana, Organometallics 25 (2006) 4734.[30] P. Pattanayak, S.P. Parua, D. Patra, J.L. Pratihar, P. Brandão, V. Felix, S.

Chattopadhyay, Polyhedron 70 (2014) 1.[31] A. Ciesielski, A.R. Stefankiewicz, V. Patroniak, M. Kubicki, J. Mol. Struct. 930

(2009) 110.[32] A. Hofmann, D. Jaganyi, O.Q. Munro, G. Liehr, R. van Eldik, Inorg. Chem. 42

(2003) 1688.[33] R. Tagore, R.H. Crabtree, G.W. Brudvig, Inorg. Chem. 47 (2008) 1815.

[34] W.R. Dawson, M.W. Windsor, J. Phys. Chem. 72 (1968) 3251.[35] Agilent Technologies (2011) CRYSALIS PRO (Version 1.171.33.36d). Agilent

Technologies Ltd.[36] A. Altomare, G. Cascarano, C. Giacovazzo, A. Gualardi, J. Appl. Cryst. 26 (1993)

343.[37] G.M. Sheldrick, SHELXL-2013, A Program for the Refinement of Crystal Structures

from Diffraction Data, Univ. of Gottingen, Germany, 2013.[38] V. Patroniak, M. Kubicki, A. Mondry, J. Lisowski, W. Radecka-Paryzek, Dalton

Trans. (2004) 3295.[39] I. Eryazici, C.N. Moorefield, G.R. Newkome, Chem. Rev. 108 (2008) 1834.[40] M. Wałesa-Chorab, A.R. Stefankiewicz, D. Ciesielski, Z. Hnatejko, M. Kubicki, J.

Kłak, M.J. Korabik, V. Patroniak, Polyhedron 30 (2011) 730.[41] V. Kalsani, M. Schmittel, A. Listorti, G. Accorsi, N. Armaroli, Inorg. Chem. 45

(2006) 2061.[42] Z. Yang, Y. Chen, C.-Y. Ni, Z.-G. Ren, H.-F. Wang, H.-X. Li, J.-P. Lang, Inorg. Chem.

Commun. 14 (2011) 1537.[43] X.-H. Bu, H. Liu, M. Du, K.M.-C. Wong, V.W.-W. Yam, Inorg. Chim. Acta 333

(2002) 32.[44] C.G. Oliveira, P.I. da S. Maia, P.C. Souza, F.R. Pavan, C.Q.F. Leite, R.B. Viana, A.A.

Batista, O.R. Nascimento, V.M. Deflon, J. Inorg. Biochem. 132 (2014) 21.[45] M.N. Kopylovich, M.F.C. Guedes de Silva, L.M.D.R.D. Martins, M.L. Kouznetsov,

K.T. Mahmudov, A.J.L. Pombeiro, Polyhedron 50 (2013) 374.[46] T. Karimpour, E. Safaei, A. Wojtczak, P. Cotic, J. Mol. Struct. 1038 (2013) 230.[47] T.V. Magdesieva, O.M. Nikitin, A.V. Yakimansky, M.Y. Goikhman, I.V. Podeshvo,

Electrochim. Acta 56 (2011) 3666.