Synthesis of a Series of Heavy Lanthanide(III) Monoporphyrinato

Osaka University, Toyonaka, Osaka 560-0043, Japan. Inorg. Chem. , 2017, 56 (17), pp 10625–10632. DOI: 10.1021/acs.inorgchem.7b01546. Publication...
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Synthesis of a Series of Heavy Lanthanide(III) Monoporphyrinato Complexes with Tetragonal Symmetry Anas Santria, Akira Fuyuhiro, Takamitsu Fukuda, and Naoto Ishikawa* Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan S Supporting Information *

ABSTRACT: A series of heavy lanthanide(III) and yttrium(III) monoporphyrinato complexes formulated in [Ln(TPP)(cyclen)]Cl (Ln = Tb, Dy, Ho, Er, Tm, Yb, and Y; TPP = 5,10,15,20-tetraphenylporphyrinato), with cyclen, 1,4,7,10-tetraazacyclododecane, as a capping ligand, have been prepared in mild conditions and studied using single-crystal X-ray diffraction crystallography. The complexes exhibit an electronic absorption band (B(0,0)) in the range of 421−423 nm, showing a bathochromic shift associated with the increase of the ionic radii of the lanthanide, as well as two peaks of Q(1,0) and Q(0,0) bands between 548−586 nm. All of the complexes are isostructural, where both TPP and cyclen are coordinated to a lanthanide(III) or yttrium(III) ion giving an eight-coordinate square-antiprismatic (SAP) geometry (average skew angles are in the range of 43.01°−43.67°). The mean plane of the four nitrogen atoms of TPP (N4t) and that of the cyclen (N4c) are virtually parallel with a dihedral angle of less than 1°. The lanthanide(III) or yttrium(III) ions lie between N4t and N4c. The position of the metal ion is closer to the N4t plane, which is presumably caused by the different charges of the ligands, the size of the N4 square ligands, and the steric factor. The average Ln−N and interplanar distances (dN) decrease with decreasing lanthanide(III) ionic radii, showing the effect of lanthanide contraction. The skew angles, opening angles, and N−N distances are nearly unchanged, keeping the rigid square antiprismatic geometry throughout the series.

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INTRODUCTION Since the lanthanide(III) monoporphyrinato complexes were reported in 1974,1 studies on the compounds have been carried out from various aspects. In the beginning, these complexes were developed as a new NMR probe for use in biological systems.2,3 The studies have further spread to new areas such as photoluminescence4,5 and magnetism.6 Generally, the lanthanide(III) monoporphyrinato complexes were prepared via an intermediate obtained from a reaction between free-base porphyrin and lanthanide acetylacetonate (acac) at high temperature.7 The act of following reactions that displace acac with other ligands in mild conditions, however, is quite difficult. A prolonged reaction time employing a high temperature results in the formation of a large amount of double- and triple-decker side products instead of the desired monoporphyrinato complex.8 Other preparation methods using nondiketonate axial ligands that require more rigorous reaction conditions were reported in later years. Schaverien et al. reported methods using protonolysis of Ln(CH(SiMe3)2)3 (CH(SiMe3)2 = bis(trimethylsilyl)methyl) with octaethylporphyrin (OEPH2) in toluene.9 Boncella et al. reported the salt metathesis reaction of LnCl3·3(THF) (THF = tetrahydrofuran) with dilithiotetraphenylporphyrin bis-dimetoxyethane in toluene.10 This method gave a high product yield (75−85%) for the four heaviest lanthanides from holmium to ytterbium, but for lighter elements there was no data. It is desirable to establish methods which can be used for all lanthanide ions in less rigorous conditions. © 2017 American Chemical Society

There were very few studies on lanthanide(III) monoporphyrinato systems based on X-ray crystallography in the last two decades. Even the first X-ray crystal structure of complex system was determined only on a lutetium complex, (OEP)LuCH(SiMe3)2 (OEP = octaethylporphyrinato),9 17 years after the first lanthanide(III) monoporphyrinato report.1 Several years later, the crystal structures of others lanthanide(III) monoporphyrinato [Tb(β-Cl 8 TPP)(O 2 CMe)(Me 2 SO) 2 ] (Cl8TPP = octachloro-5,10,15,20-tetraphenylporphyrinato), 11 [Ln(TMPP)(H2O)3]Cl (Ln = Yb, Er, or Y ; TMPP = tetrakis(p-methoxyphenyl)porphyrinato),12 [Gd(TPP)(acac)· 8H2O·3TCB] (TPP = 5,10,15,20-tetraphenylporphyrinato; TCB = 1,2,4-trichlorobenzene),13 and [Ln(TPP)Tp] (Ln = Tm and Nd; Tp = hydridotris(1-pyrazolyl)borate) were reported.14 In the case of the [Gd(TPP)(acac)·8H2O·3TCB] complex, Adachi et al. reported the structural parameters only,13 and further properties were clarified by Benazeth et al. eight years later.15 Relatively recently, the crystal structures of dysprosium(III) and holmium(III) monoporphyrinato complexes were reported by Zuo et al.6 Since then, the crystal structures of the remaining series of lanthanide(III) have not been determined. To date, there has been no report of the preparation and crystal structure of a series of lanthanide(III) monoporphyrinato with the second ligand having 4-fold rotational symmetry Received: June 22, 2017 Published: August 14, 2017 10625

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The expected formulae for the 3a−3g complexes are in a good agreement with mass spectral data. The cationic peak which resulted from dissociation of [Ln(TPP)(cyclen)]Cl, appears with high intensity in all of the mass spectra of 3a−3g complexes as shown in Figures S1− S7. In the mass/charge (m/z) unit, the cationic peaks are at 943.4, 947.7, 950.5, 952.2, 954.6, 959.5, and 874.1 which correspond to [Tb(TPP)(cyclen)]+, [Dy(TPP)(cyclen)]+, [Ho(TPP)(cyclen)]+, [Er(TPP)(cyclen)]+, {[Tm(TPP)(cyclen)]+ + H0}, {[Yb(TPP)(cyclen)]+ + H0} and [Y(TPP)(cyclen)]+, respectively. In addition, the elemental analysis also gave a satisfactory result by adding some solvent molecules. Anal. Calcd for 3a·H2O·C6H14, C58H64N8ClTb: C, 64.29; H, 5.95; N, 10.34. Found: C, 64.20; H, 5.75; N, 10.35. Anal. Calcd for 3b·6H2O·DMF, C55H67N9ClDy: C, 56.75; H, 5.80; N, 10.83. Found: C, 56.37; H, 5.71; N, 11.08. Anal. Calcd for 3c·6H2O·C6H14, C58H74N8ClHo: C, 59.05; H, 6.32; N, 9.50. Found: C, 59.09; H, 6.22; N, 9.64. Anal. Calcd for 3d·4H2O·C6H14·2DMF, C64H84N10ClEr: C, 59.49; H, 6.55; N, 10.84. Found: C, 59.19; H, 6.48; N, 10.93. Anal. Calcd for 3e·9H2O·3DMF, C61H87N11ClTm: C, 53.45; H, 6.40; N, 11.24. Found: C, 53.11; H, 6.08; N, 11.14. Anal. Calcd for 3f·12H2O· 4DMF, C64H100N12ClYb: C, 51.18; H, 6.71; N, 11.19. Found: C, 51.47; H, 6.38; N, 11.47. Anal. Calcd for 3g·8H2O·C6H14·4DMF, C70H106N12ClY: C, 58.71; H, 7.46; N, 11.74. Found: C, 58.62; H, 7.42; N, 11.88. Single-Crystal X-ray Analysis. The single-crystal X-ray diffraction data of 3a−3g were collected at −73 ± 1 °C to a maximum 2θ value of 55.0° with total oscillation of 90. All of the structures were solved by direct methods16 and expanded using Fourier techniques. The nonhydrogen atoms were refined anisotropically. The riding model was used to refine hydrogen atoms. All calculations, except for refinement, were performed using the CrystalStructure17 crystallographic software package. Additionally, we used SHELXL Version 2014/718 to refine the structures.

in the literature. Herein we report the synthesis of a series of eight-coordinated lanthanide and yttrium complexes with a square-antiprismatic geometry, [Ln(TPP)(cyclen)]Cl (Ln = Tb, Dy, Ho, Er, Tm, Yb, Y; cyclen = 1,4,7,10-tetraazacyclododecane), through protonolysis of LnCl3·nH2O with 5,10,15,20tetraphenylporphyrin (H2TPP) in DMF/DBU (DMF = N,Ndimethylformamide; DBU = 1,8-diazabicyclo[5.4.0]undec-7ene). Through choosing cyclen and chloride as a second ligand and counteranion, respectively, we succeeded in establishing the preparation method and determined all of the crystal structures.

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EXPERIMENTAL SECTION

Materials and Instrumentation. The lanthanide(III) chlorides were synthesized from lanthanide oxide and hydrochloric acid. The H2TPP (1) and cyclen were purchased from commercial suppliers. As solvents in reaction, we used DMF, DBU, and methanol (MeOH). Dichloromethane (DCM) and hexane were used for crystallization. Elemental analysis (C, H, and N) was implemented on a Yanaco CHN Corder MT-5 and MT-6 Elemental Analyzer. Mass spectra were recorded using a Kratos PC Axima CFR V.2.3.5 (Shimadzu Corporation) operated in linear mode. Single-crystal X-ray diffraction measurements were executed on a Rigaku R-AXIS VII diffractometer using filtered Mo Kα radiation (λ = 0.71075 Å) at 45 kV and 55 mA. Absorption spectra were measured on a Shimadzu UV-1650PC UV− vis spectrophotometer. Synthesis of the Hydrous Lanthanide and Yttrium Chlorides. A solution of 35% HCl (113.3 mmol) was reacted with solid Ln2O3 or Y2O3 (1.34 mmol), and then heated at 100 °C for 2−3 h or until the reaction mixture became transparent. After evaporation, the precipitate was collected on a filter and washed with water. The white solid LnCl3·nH2O and YCl3·nH2O were obtained after drying in vacuo at 90 °C for several hours (6−8 h). General Procedure for Synthesis of Lanthanide and Yttrium Complexes. (See Scheme 1 for a schematic describing the synthesis

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RESULTS Synthesis. The complex compounds were synthesized from a corresponding metal chloride hydrate and two different ligands as described in the Experimental Section. The time of reaction is different for each lanthanide, i.e. Tb and Yb had the longest and shortest time of reaction, respectively. The slow crystallization using vapor or a liquid−liquid diffusion method was needed to get the crystals suitable for X-ray analysis. Single crystals were readily obtained in a temperature range of 20−28 °C without external disturbance. Finally, the dried crystal was obtained by exposure to air at room temperature for several hours. UV−vis Absorption Spectra. The absorption spectra of the 3a−3g complexes are shown in Figure 1 with comparison

Scheme 1. Synthetic Route for [Ln(TPP)(cyclen)]Cl, 3a−3g

of 3a−3g.) Under an argon atmosphere, a solution of H2TPP in DMF was mixed with solid LnCl3·nH2O (TPP/Ln = 1:6 in molar ratio), followed by the addition of DBU (20% of DMF volume), and heated at 200 °C with stirring for 12−36 h. The resulting compounds were cooled to the room temperature and then washed with H2O and filtered. The precipitate was collected on a filter and dried in vacuo at 90 °C for several hours. The dried compounds were dissolved in MeOH and filtered. To the resulting filtrate was added solid cyclen (some mg), followed by stirring for 10−30 min. The resultant solution was evaporated and dried in vacuo for 4−6 h, then dissolved in DCM. The 3a−3g complexes were obtained in a crystal form by liquid−liquid diffusion of hexane (C6H14) into the DCM solution.

Figure 1. UV−vis absorption spectra of 3a−3g and H2TPP (1) measured in DCM. 10626

DOI: 10.1021/acs.inorgchem.7b01546 Inorg. Chem. 2017, 56, 10625−10632

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Inorganic Chemistry to that of H2TPP (1). The number of peaks are decreased by coordination to lanthanide(III) or yttrium(III). All of these complexes have a highest peak B(0,0) band with a shoulder due to small B(1,0) in range of 421−423 nm and two low peaks, Q(1,0) and Q(0,0) bands, between 548−586 nm. The positions of the B band peaks of the complexes are shifted to a longer wavelength (red-shifted) relative to the B bands of free-base TPP in the same solvent. The number of Q bands are decreased from four to two, of which the highest lies at the shorter wavelength. This is also observed in the other metallo-TPP complexes like [MIITPP] (M = Zn and Mg),19 [GaIII(TPP)R] (R = Cl, C(CH3)3, C4H9, C2H5, CH3, C6H5, pMeC6H4, C2H2C6H5, C2C6H5),20 [TlIII(TPP)X] (X = Cl and F).21,22 All of the peak positions are summarized in Table 1. As Table 1. UV−vis Absorption of 3a−3g Complexes Measured in DCM B bands (nm)

Q bands (nm)

compound

4f shell

B(1,0)

B(0,0)

Q(1,0)

Q(0,0)

3a 3b 3c 3d 3e 3f 3g

8

402.6 402.2 401.4 400.8 400.4 400.6 401.2

422.4 422.0 421.6 421.4 421.0 421.0 421.6

549.4 549.2 548.8 548.2 547.8 548.2 549.2

585.2 585.2 585.0 584.6 584.2 584.4 585.6

f f9 f10 f11 f12 f13

Figure 2. Crystal structure of 3a viewed along the c axis. Hydrogen atoms are omitted for clarity.

Molecular Structures. The molecular structure of 3a viewed along the 4-fold rotation axis is presented in Figure 3. The structures of 3a−3g are isostructural possessing one Ln3+ or Y3+ bound to the two different tetradentate ligands, TPP2− and cyclen. The TPP2− ligand, which is composed of four pyrroles, is slightly distorted from planarity and somewhat convex as seen from Figures S8−S14. The mean plane of the four nitrogen atoms of TPP, N4t, is not coplanar with the mean plane of four pyrroles. All of the dihedral angles between N4t and the pyrrole mean plane, which are symbolized by θp, are in the range of 7.00°−14.10° as seen from Table S1 in details. Also, the TPP2− has four phenyl rings with two opposite orientations, i.e. clockwise and counterclockwise. The phenyl rings which have a clockwise orientation are attached to C5, C10, and C20, while another phenyl ring is attached to C15 with counterclockwise orientation. Both rotation angles are less than 28° from the plane perpendicular to the N4t plane as listed in Table S2. The cyclen ligand, which is a macrocycle with 12 atoms, N5−C21−C22−N6−C23−C24−N7−C25−C26−N8− C27−C28, gives a square conformation [3333] (adopted from Dale’s ring conformation)24 where the square sides are formed

a comparison, the result also shows that the variation of lanthanide ions only gives a minor change to the absorption spectra. This result agrees with that of related complexes in previous reports.2,3,23 Crystal Structure. The single-crystal X-ray diffraction analysis showed that all of the complexes, 3a−3g, crystallized in a tetragonal crystal system and have the space group of P4̅21c (#114) with very similar lattice parameters, as seen in Table 2. Each single crystal contains discrete [Ln(TPP)(cyclen)]Cl molecules without unusual intramolecular contacts; only van der Waals contacts are observed. Figure 2 shows the crystal structure of 3a viewed along the c axis. Those of 3b−3g are similar to that of 3a. The chloride ion, Cl−, and [Ln(TPP)(cyclen)]+ are arranged in pairs and occupy the unit cell without any solvent in all of the crystals, 3a−3g. Table 2. Crystallographic Data for 3a−3g 3a formula Mw appearance crystal dimensions crystal system lattice type space group a(Å) c (Å) v (Å3) Z Dcalc (g/cm3) GOF R1 (I > 2.00σ(I)) wR2

C52H48ClN8Tb 979.38 dark-red, block 0.20 × 0.05 × 0.02 tetragonal primitive P4̅21c (#114) 26.4644(5) 14.7708(3) 10345.0(3) 8 1.258 1.094 0.0601 0.1229

3b

3c

3d

3e

3f

3g

C52H48ClN8Dy 982.96 dark-red, column 0.15 × 0.03 × 0.02 tetragonal primitive P4̅21c (#114) 26.4228(6) 14.8112(3) 10340.6(4) 8 1.263 1.040 0.0890 0.1820

C52H48ClN8Ho 985.39 dark-red, column 0.20 × 0.03 × 0.03 tetragonal primitive P4̅21c (#114) 26.4208(8) 14.6933(5) 10256.7(5) 8 1.276 1.023 0.0643 0.1268

C52H48ClN8Er 987.72 dark-red, column 0.12 × 0.05 × 0.04 tetragonal primitive P4̅21c (#114) 26.4365(6) 14.6970(3) 10271.6(4) 8 1.277 1.055 0.0608 0.1136

C52H48ClN8Tm 989.39 dark-red, column 0.20 × 0.05 × 0.04 tetragonal primitive P4̅21c (#114) 26.3973(8) 14.7441(4) 10274.0(5) 8 1.279 1.066 0.0951 0.1902

C52H48ClN8Yb 993.50 dark-red, column 0.15 × 0.03 × 0.02 tetragonal primitive P4̅21c (#114) 26.4092(6) 14.8489(3) 10356.3(4) 8 1.274 1.057 0.0617 0.1338

C52H48ClN8Y 909.36 dark-red, column 0.20 × 0.10 × 0.05 tetragonal primitive P4̅21c (#114) 26.4272(6) 14.7181(3) 10279.1(4) 8 1.175 1.001 0.0818 0.1822

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Å and relatively shorter than those in bis-TPP lanthanide complexes having ideal square antiprismatic geometry.25 The structural parameters of 3a−3g complexes such as skew angle and opening angle are also listed in Table 3. The skew angle as illustrated in Scheme 2a, ω1/ω2/ω3/ω4, is formed by two NTPP−Ln−N′TPP and Ncyclen−Ln−N′cyclen planes. The value of ω1 and ω2 are equal to ω3 and ω4, respectively, and give an average skew angle (ω) in the range of 43.01°−43.67°. This is very close to that of ideal square antiprismatic (45°). There are two types of opening angles as shown in Scheme 2b. Both types are the opening angle of NTPP−Ln−N′TPP (φt) and Ncyclen−Ln−N′cyclen (φc). The φt and φc are in the range of 118.30°−120.30° and 103.40°−104.60°, respectively. The distances between adjacent nitrogen donor atoms, N− N, are listed in Table S3. The atoms N1 to N4 belong to TPP and N5 to N8 to cyclen. It is seen that the average N−N distances in TPP and cyclen are nearly unchanged. The data shows that the effect of the change in ionic radii to the size of the N4 square is small.

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Figure 3. Molecular structure of 3a. The thermal ellipsoid plot with the probability level at 50%. Hydrogen atoms are omitted for clarity.

DISCUSSION Ln−N Bond Lengths. All eight Ln−N bonds are different in length to each other as shown in Figure S15 and summarized in Table 4. But Ln−N bond lengths in the same ligand (TPP or cyclen) are almost the same. The average bond length between Ln and nitrogen atoms in TPP, Ln−Nt, are slightly shorter than those in cyclen, Ln−Nc. The former lengths are in the range of 2.362−2.414 Å and the latter 2.506−2.591 Å. This indicates that the pophyrin ring has more binding ability than the cyclen ring, which is presumably due to the different charges of the ligands, i.e. −2 for porphyrin and neutral for cyclen. In addition, other factors such as the size of the N4 squares and the steric effect from hydrogen on the cyclen side can reasonably contribute to make different Ln−N bond lengths. The size of the N4 squares is directly related to their opening angle, φ. Additionally, as shown in Figures S8−S14, the N donor atoms of the cyclen are bound to a hydrogen atom, which is located on the near side to the metal ion. This causes a steric hindrance and thus leads to a longer Ln−N distances and a smaller opening angle φ on the cyclen side. Figure 4 plots the average Ln−N bond lengths against the reciprocal ionic radii of the lanthanide atoms.26 The average

of three consecutive bonds with carbon atoms as its square corners (see Figure 3). Each ethylenediamine bridge (N−C− C−N) of cyclen is in a λ conformation with the average torsion angles (ψ) in range of (−53°)−(−59°) as summarized in Table 3 and Table S2 for details. The mean plane of the four nitrogen atoms of cyclen (henceforth, designated as N4c) and N4t are essentially planar and almost parallel to each other with their dihedral angle of less than 1°. The planarity is indicated by the small values (less than 0.01 Å) of the mean absolute deviation of the N atoms from N4t or N4c, which are shown as MADN−N4t and MADN−N4c in Table 3. The chloride anion is placed on the cyclen side about 6 Å from Ln, nearly along the axis that passes through Ln and perpendicular to N4c. The yttrium(III) or lanthanide(III) ions are sandwiched by TPP and cyclen ligands forming an eight coordinate structure. They sit in the range of 1.17−1.23 Å and 1.54−1.60 Å from the N4t and N4c planes, respectively, as seen from Table 3 in details. The eight Ln−N bond lengths of each complex and the average Ln−N length are compared in Table 4. The average values for 3a−3g symbolized by Ln−Na are in the range of 2.445−2.490 Table 3. Distances (Å) and Angles (Deg) in 3a−3ga 3a

3b

3c

3d

3e

3f

3g

0.0053 0.0000 1.2005 1.5653 2.7658 5.9750

0.0007 0.0082 1.1950 1.5538 2.7488 5.9730

0.0071 0.0072 1.1799 1.5424 2.7223 5.9140

0.0003 0.0013 1.2075 1.5789 2.7864 5.9630

0.372 43.062 43.695 43.378 119.33 104.10 −57.66

0.287 43.515 43.692 43.603 119.82 104.50 −57.49

0.234 42.599 43.432 43.015 120.25 104.59 −53.19

0.781 43.321 43.616 43.468 119.14 104.09 −56.88

distances MAD

N−N4t N−N4c Ln−N4t Ln−N4c dN Ln−Cl

0.0068 0.0000 1.2320 1.5946 2.8266 5.9670

0.0076 0.0089 1.2144 1.5778 2.7922 5.9250

0.0048 0.0039 1.2134 1.5782 2.7916 5.9770

N4t−N4c ω1,3 ω2,4 ω φt φc ψ

0.329 42.842 43.535 43.188 118.32 103.40 −58.14

0.972 42.587 43.811 43.199 118.85 103.77 −53.31

0.326 43.638 43.697 43.667 119.06 103.76 −57.95

MAD

angles

a

MAD = mean absolute deviation of the atoms from the plane, (−) is sign for counterclockwise. 10628

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Inorganic Chemistry Table 4. Selected Bond Lengths of Ln−N in 3a−3g Ln−N1 (Å) Ln−N2 (Å) Ln−N3 (Å) Ln−N4 (Å) Ln−N5 (Å) Ln−N6 (Å) Ln−N7 (Å) Ln−N8 (Å) ∑(Ln−N) Ln−Na Ln−Nt Ln−Nc

3a

3b

3c

3d

3e

3f

3g

2.412(7) 2.399(7) 2.400(7) 2.402(7) 2.591(7) 2.587(8) 2.564(7) 2.555(8) 19.910 2.4888 2.4032 2.5743

2.376(11) 2.383(11) 2.414(11) 2.374(11) 2.572(11) 2.567(13) 2.546(12) 2.538(13) 19.770 2.4712 2.3868 2.5558

2.405(7) 2.387(8) 2.388(7) 2.387(7) 2.573(7) 2.569(9) 2.543(8) 2.545(8) 19.792 2.4746 2.3917 2.5575

2.381(7) 2.383(7) 2.374(7) 2.369(7) 2.561(7) 2.561(8) 2.532(8) 2.527(8) 19.688 2.4610 2.3767 2.5453

2.392(12) 2.391(13) 2.374(12) 2.373(11) 2.534(12) 2.548(13) 2.524(12) 2.547(13) 19.683 2.4604 2.3825 2.5383

2.362(7) 2.373(8) 2.369(8) 2.366(8) 2.539(8) 2.531(9) 2.514(8) 2.506(9) 19.560 2.4450 2.3675 2.5225

2.375(6) 2.386(6) 2.394(6) 2.378(6) 2.584(6) 2.562(7) 2.552(6) 2.569(7) 19.800 2.4750 2.3833 2.5667

interplanar distances of 3a−3g are in range of 2.78−2.83 Å and are shown in Table 3 for details. Figure 5 shows the relationship between reciprocal ionic radii of the central atoms and dN. The interplanar distances of 3a−3g

Scheme 2. Structural Parametersa,b

a

Skew angle, ω. bOpening angle, φ

Figure 5. Plots of the interplanar distances (dN) against the reciprocal ionic radii of central atoms (1/rion). The full black squares, blue squares, and red circles indicate the 3a−3g, bis-TPP, and bis-OEP complexes, respectively.

and some bis-porphyrin complexes (M(TPP)2/M(TPP)2− and M(OEP)2/M(OEP)2−)8,25,30−33 decrease linearly with shortening ionic radii. This feature is in good agreement with a related previous report29 and is more substantive than Ln−N bond length to support lanthanide contraction existence. Skew Angles. As we mentioned earlier, the skew angles of 3a−3g are around 43°. In the same coordination number, the skew angles of 3a−3g change is quite different from that of the bis-TPP complexes,30,31 but almost similar to that of bisOEP8,31−33 and mixed TPP-OEPH complexes34,35 (OEPH = protonated octaethylporphyrinato) as shown in Figure S16 and Table 5 in detail. As the dN value increases, the skew angles of bis-TPP complexes get smaller and the eclipsed configuration is stabilized, whereas the 3a−3g, bis-OEP and mixed TPP-OEPH complexes stay in staggered configuration. This is probably due to a minimum or even absent interplanar steric repulsion between the phenyl rings on the TPP and the neighboring atoms on the second ligand. Therefore, the skew angle does not depend on the central lanthanide ion. In the case of the 3a−3g complexes, steric repulsion between phenyl rings and the neighboring hydrogen atoms on cyclen is very small, as seen in

Figure 4. Average lengths between lanthanide and nitrogen atoms (Ln−N) against the reciprocal ionic radii of the lanthanide atoms (1/ rion). The blue squares, purple circles, and red triangles are the Ln−Nc, Ln−Na, and Ln−Nt, respectively.

Ln−N bond length steadily decreases from Tb3+ to Yb3+ with decreasing ionic radii. The decrease of the average Ln−N bond length is in good accordance with a previous related report that focused on lanthanide contraction.27 Interplanar Distances. In sandwich-type complexes composed of cyclic multidentate ligands such as porphyrin and cyclen, the Ln−N bond lengths and the interplanar distance are both important geometric factors. In this report, we define the interplanar distance as the distance between N4t and N4c planes, which is symbolized by dN, in a similar way to that in the report for the bisphthalocyanine complexes.28,29 The 10629

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Inorganic Chemistry Table 5. Structural Properties of 3a−3g and Bis-Porphyrin Complexes in Eight Coordination Structure complex

ionic radius, Å

dN, Å

average of skew angle, °

ref.

Ta(OEP)2+ Zr(TPP)2 Ce(OEP)2 3f 3e 3d 3c 3g 3b 3a Tb(TPP)2− Th(OEP)2 Th(TPP)2 Gd(TPP)(OEPH) Eu(OEP)2− Sm(TPP)(OEPH)

0.74 0.840 0.970 0.985 0.994 1.004 1.015 1.019 1.027 1.040 1.040 1.050 1.050 1.053 1.066 1.079

2.398 2.534 2.752 2.722 2.749 2.766 2.792 2.786 2.792 2.827 2.8430 2.887 2.9220 2.946 2.849 2.990

44.63 37.38 41.83 43.02 43.60 43.38 43.67 43.47 43.20 43.19 45.00 41.88 34.75 43.12 42.68 44.28

32 30 8 this work this work this work this work this work this work this work 25 31 31 35 33 34

band peak with a shoulder in range of 421−423 nm and two Qband peaks in 548−586 nm. The crystal structures of the complexes belong to the tetragonal system. The lanthanide(III) and yttrium(III) ions are sandwiched by TPP and cyclen ligands through four nitrogen donor atoms with each ligand forming a square antiprismatic (SAP) geometry (ω in range of 43.01°−43.67°). The different charge of the ligands, size of N4 square ligands, and steric factor lead the lanthanide ions closer to N4t plane than N4c. The effect of lanthanide contraction has been observed through Ln−N and dN, which decrease with decreasing lanthanide(III) ionic radii. The N−N distances are nearly unchanged with decreasing ionic radii, and hence, the size of the N4 square is almost kept constant.

Figure S17. This is why the 3a−3g complexes have square antiprismatic geometry with skew angles close to 45°. The effect of the steric repulsion in 3a−3g may be indicated by the dihedral angle between the phenyl ring and C12 mean planes (henceforth is symbolized by θph). The C12 mean plane is calculated from four carbon atoms attached to phenyl rings and the eight neighboring carbon atoms on pyrroles, C1−C4− C5−C6−C9−C10−C11−C14−C15−C16−C19−C20. The θph values of the complexes are in the range of 63.9°−80.9° (see Table S4 in detail). Interestingly, as the average θph value increases, the average skew angle tends to linearly increase as shown in Figure 6. This shows that there is a relationship

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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.7b01546. Mass spectra of 3a−3g, ORTEP drawing of 3a−3g, Ln− N (TPP) and Ln−N (cyclen) bond lengths of 3a−3g, plots of the skew angles against the reciprocal ionic radii of porphyrin complexes, space-fill representation of 3a, and selected distances and angles (PDF) Accession Codes

CCDC 1556182−1556188 contain 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 emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

Figure 6. Plots of the average skew angles (ω) against the average θph of 3a−3g.

between the skew angle and the steric repulsion. This is also in line with the previous observation, which was reported in the structural analysis of [Ln(TPP)(TPPH)] (TPPH = protonated tetraphenylporphyrinato).36

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AUTHOR INFORMATION

Corresponding Author

*Phone: +81(6)6850-5408; Fax: +81(6)6850-5408; E-mail: [email protected]

CONCLUSIONS Seven novel isostructural lanthanide(III) and yttrium(III) monoporphyrinato complexes with a strict 4-fold symmetry axis were successfully obtained under mild conditions and characterized by absorption spectroscopy and single-crystal Xray diffraction. The absorption spectra in the dichloromethane solution have shown that all of the complexes have one Soret

ORCID

Anas Santria: 0000-0003-0140-0850 Naoto Ishikawa: 0000-0002-3490-4222 Notes

The authors declare no competing financial interest. 10630

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Inorganic Chemistry

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ACKNOWLEDGMENTS The authors would like to thank the Japanese Government (MEXT) for financial support for A.S.

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