1. Introduction

ijms

International Journal of Molecular Sciences

Int. J. Mol. Sci.

1422-0067

Molecular Diversity Preservation International (MDPI)

10.3390/ijms12106966

ijms-12-06966

Article

Environmental Dependence of Artifact CD Peaks of Chiral Schiff Base 3d-4f Complexes in Soft Mater PMMA Matrix

Okamoto

Nidaira

Keisuke

Akitsu

Takashiro

* Department of Chemistry, Faculty of Science, Tokyo University of Science, 1–3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan

* Author to whom correspondence should be addressed; E-Mail: akitsu@rs.kagu.tus.ac.jp; Tel.: +81-3-5228-8271; Fax: +81-3-5261-4631.

2011

19 10 2011

12 10 6966 6979 13 9 2011 10 10 2011 14 10 2011

2011

This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).

Four chiral Schiff base binuclear 3d-4f complexes (NdNi, NdCu, GdNi, and GdCu) have been prepared and characterized by means of electronic and CD spectra, IR spectra, magnetic measurements, and X-ray crystallography (NdNi). A so-called artifact peak of solid state CD spectra, which was characteristic of oriented molecules without free molecular rotation, appeared at about 470 nm. Magnetic data of the complexes in the solid state (powder) and in PMMA cast films or solutions indicated that only GdCu preserved molecular structures in various matrixes of soft maters. For the first time, we have used the changes of intensity of artifact CD peaks to detect properties of environmental (media solid state (KBr pellets), PMMA cast films, concentration dependence of PMMA in acetone solutions, and pure acetone solution) for chiral 3d-4f complexes (GdCu). Rigid matrix keeping anisotropic orientation exhibited a decrease in the intensity of the artifact CD peak toward negative values. The present results suggest that solid state artifact CD peaks can be affected by environmental viscosity of a soft mater matrix.

chirality solid state CD soft mater schiff base complexes

1. Introduction

Organic/inorganic hybrid materials containing photochromic organic dyes and transition metal complexes such as models of chiral catalysts [1–3] and magnetic materials [4–8] have been developed widely aiming at photo-induced switching systems as supramolecules. As hybrid materials are essentially mixtures, overlapped strong absorption bands of π-π * and n-π * regions make it difficult to deal with individual components generally. To overcome this problem, we employed polarized electronic spectra [9–12] and polarized IR spectra [13,14] in order for selective detection of molecular orientation, or fluorescence spectra [15] as well as absorption spectra. Only CD spectra of chiral components can be observed selectively for hybrid materials of chiral and achiral ones, which show overlapped absorption spectra. Additionally, so-called artifact peaks may sometimes be a serious problem for solid state CD spectra [16–31], in which chiral molecules take anisotropic orientation without a degree of freedom for molecular motion. Although this problem has mainly been dealt with in view of improvement to reduce noise of CD spectra in the solid state, investigation in soft mater matrixes (intermediate between isotropic solutions and anisotropic solids) or positive applications for obtaining useful information have not been carried out so far.

By the way, chiral 3d-4f Schiff base complexes affording interesting structures [32–34] may also be appropriate candidates for distinguishable transitions for separate observation of CD bands. The analogous 3d-4f complexes have been investigated being focused on magnetic properties [35,36] or emission [37–39] resulting from 4f-electrons of lanthanide ions and their interactions to 3d electrons of transiton metal ions. It is well known that detailed treatment of superexchange interactions of 3d-4f molecule-based magnets is difficult because of spin-orbit interactions except for Gd(III) complexes. In order to overcome this, empirical estimation of magnetic interactions between 3d-4f ions are sometimes carried out. Although this may also be interesting for chiroptical or other CD spectroscopic studies, few studies have been reported to date.

In this paper, we report on preparations and characterization of new chiral Schiff base binuclear 3d-4f complexes, NdNi, NdCu, GdNi, and GdCu (Figure 1), including optical properties of 3d-4f moieties. We also prepared PMMA cast films containing these complexes and confirmed only the structure of GdCu was kept by means of magnetic measurement. We measured CD spectra of GdCu in a pure acetone, as acetone solutions of PMMA (different concentrations), and in the solid state (KBr pellets). Comparison with solid state and complete solution suggested so-called artifact peaks of solid state CD spectrum. As far as we know, we attempt to use the intensity of artifact CD peaks exhibiting environmental dependence of soft mater matrixes for the first time.

2. Results and Discussion 2.1. Crystal Structure of NdNi

Typical reactions of Schiff base ligands, 3d (Ni(II) or Cu(II), and Zn(II)) ions, and 4f (Nd(III) or Gd(III)) ions gave rise to analogous binuclear 3d-4f complexes [39]. Since Nd(III) ion can coordinate to this ligand more rigidly than Gd(III) ion generally, which results in different features of crystal growth and dissociation in solutions. As depicted in Figure 2, the crystal structure could be determined only for NdNi (the other complexes must be similar binuclear structures). Unfortunately, suitable single crystals could not be obtained for other complexes. Asymmetric unit of NdNi contains two crystallographically independent molecules which are coupled with π-π stacking of ligands by noncovalent interactions. Therefore, intramolecular superexchange interactions between 3d and 4f ions can be expected in view of crystal structures (see later section). Ni(II) and Nd(III) ions afford a square planar trans-[NiN₂O₂] and ten-coordinated prism-like [GdO₁₀] coordination environment, as summarized in Table 1. Ni(II) ion coordinates no additional axial ligands. Each bond distance and angle of the ligand moieties including cyclohexyl groups connected to asymmetric carbon atoms of (R,R)-configuration are within normal values for analogous Schiff base complexes [32,33,39].

2.2. Magnetic Properties

Figures 3A and Figure 3B show the χ_MT vs T plots of Nd(III) (NdNi and NdCu) and Gd(III) (GdNi and GdCu) complexes including the differences of χ_MT values (χ_MT(NdCu)-χ_MT(NdNi) and χ_MT(GdCu)-χ_MT(GdNi)). As the data at 300 K suggested, Cu(II) ion and Ni(II) ion of four-coordinated square planar coordination environment are S = 1/2 (paramagnetic) and S = 0 (diamagnetic), respectively. The ground electronic state of Nd(III) ion is ⁴I_9/2 with S = 3/2, L = 6, J = 9/2 with λ = 290 cm⁻¹, while that of Gd(III) ion is ⁸S_7/2 with S = 7/2, L = 0, J = 7/2 with λ = 0 cm⁻¹, the total orbital angular momentum is zero and single ion anisotropy due to spin-orbit interaction should be negligible. Therefore, empirical proof of ferromagnetic superexchange interaction based on the differences of χ_MT values may be clear and reliable. Actually, the corresponding data of Nd(III) complexes (χ_MT(NdCu)-χ_MT(NdNi)) did not exhibit increasing of low-temperature region, while that of Gd(III) complexes (χ_MT(GdCu)-χ_MT(GdNi)) exhibited typical peak in the low-temperature region. Therefore, the 3d-4f binuclear moiety of GdCu can be judged to be ferromagnetic one.

Figure 3C shows comparison of the χ_MT vs T plots of GdCu as a bulk powder sample (identical to the data above) and GdCu as PMMA cast films. Contrary to other three complexes (not shown), only GdCu exhibited similar behavior regardless of bulk and film except for increasing of diamagnetic contribution of PMMA in the high-temperature region. The results suggest that coordination of lanthanide ion is kept only for GdCu. In this way, GdCu is suitable for the flowing discussion associated with CD spectroscopy because of these two conditions, namely, ferromagnetic interaction and rigidity of Gd(III) ion coordination.

2.3. CD Spectra in the Solid State

Figures 4 and 5 show solid state CD spectra and the corresponding diffuse reflectance electronic spectra of Ni(II) complexes (NdNi, GdNi, and the related mononuclear Ni complex having the identical chiral ligand) and Cu(II) complexes (NdCu, GdCu, and mononuclear Cu), respectively. The different features of d-d band around 500–600 nm for mononuclear Ni and Cu complexes are ascribed to conventional difference of square planar Schiff base Ni(II) and Cu(II) complexes. Indeed, the signs of the corresponding CD bands are opposite. When Nd(III) ions are introduced, sharp f-f peaks appeared at 580, 740, and 790 nm in the diffuse reflectance electronic spectra. When Nd(III) or Gd(III) ions are introduced or replaced, the region of charge transfer bands are affected predominantly. The corresponding CD bands are changed; in particular, the region of 500–550 nm for Ni(II) complexes exhibited clear shifts, which is not clear in the diffuse reflectance electronic spectra. When comparing this with the CD spectra in solutions (in which free molecular motion is permitted), so-called artifact CD peaks in the solid state (in which molecular motion is not permitted completely) can be assigned to the peaks around 470 nm, which is neighboring region of d-d bands around 500–600 nm and an important region for chiroptical features of binuclear 3d-4f systems.

2.4. CD Spectra in PMMA Films or Solutions

Figure 6B shows the CD and the corresponding electronic absorption spectra of GdCu measured as PMMA cast films, PMMA acetone solutions of various concentration (mass%), and acetone solution. PMMA cast film is a novel environment, having flexibility in which molecular orientation can be kept and simultaneously molecular motion (conformational changes) can be permitted. Furthermore, acetone solutions with a high concentration of PMMA lose its freedom of molecular motion. In these solutions, anisotropy of molecular orientation gradually may be increased to appear so-called artifact CD peaks, which is ascribed to losing isotropy of molecular orientation in rigid environment of a matrix. Little changes of the corresponding electronic absorption spectra also support that spectral changes of CD spectra are essentially ascribed to not reactions or changes of molecules but the principle of CD spectroscopy.

Figure 6A is magnification of the CD spectra (Figure 6B). It indicates concentration or viscosity-dependence of the CD spectra of PMMA acetone solutions of GdCu. As PMMA cast film and solutions, intensity changes (negative decreasing of θ values) with a CD peak around 470 nm assigned as an artifact CD peak of solid state indicated, depending on viscosity of matrix. In this way, the intensity of so-called artifact peaks is changed as the degree of restriction of molecular motion in correlation with concentration of viscous PMMA concentration or environment of a soft mater or complete solid state.

3. Experimental Section 3.1. General Procedures

Chemicals of the highest commercial grade available (solvents from Kanto Chemical, organic compounds from Tokyo Chemical Industry and metal sources from Wako) were used as received without further purification.

3.2. Preparations 3.2.1. Preparation of NdNi

To a solution of o-vanillin (0.3069 g, 2.00 mmol) dissolved in methanol (40 mL), (1R,2R)-(−)-1,2-cyclohexandiamine (0.1231 g, 1.00 mmol) was added dropwise and stirred at 313 K for 2 h to give yellow solution of ligand. Nickel(II) acetate tetrahydrate (0.2493 g, 1.00 mmol) was added to give rise to orange solution of the complex. After stirring for 2 h, neodymium (III) nitrate hexahydrate (0.4552 g, 1.00 mmol) was added and refluxed at 373 K for 4 h to yield orange solution with orange precipitates. This crude orange compound was filtered and recrystallized from methanol/diethyl ether to give orange prismatic single crystals suitable for X-ray analysis containing solvents. Yield 0.5804 g (89.9%). IR (KBr (cm⁻¹)): 451, 565, 667, 740, 748, 785, 856, 965, 1031, 1078, 1166, 1232, 1307, 1381, 1468, 1624(C=N), 1652, 1699, 2413, 2848, 2927. UV-vis (nm (Abs)): (acetone) 332 (0.96). (methanol) 331 (0.46). (chloroform) 339 (0.73). CD (nm (θ/mdeg)): (acetone) 394 (−25.5), 450 (4.66), 568 (5.47). (methanol) 391 (−10.2), 456 (1.22), 559 (3.13). (chloroform) 404 (−5.42), 459 (1.03), 566 (1.51).

3.2.2. Preparation of NdCu

To a solution of o-vanillin (0.3054 g, 2.00 mmol) dissolved in methanol (40 mL), (1R,2R)-(−)-1,2-cyclohexandiamine (0.1171 g, 1.00 mmol) was added dropwise and stirred at 313 K for 2 h to give yellow solution of ligand. Copper (II) acetate monohydrate (0.2048 g, 1.00 mmol) was added to give rise to purple-red solution of the complex. After stirring for 2 h, neodymium (III) nitrate hexahydrate (0.4493 g, 1.00 mmol) was added and refluxed at 373 K for 4 h to yield red solution with red precipitates. This crude red compound was filtered and recrystallized from methanol/diethyl ether to give red precipitates. Yield 0.6333 g (97.4%). IR (KBr (cm⁻¹)): 400, 433, 560, 642, 740, 759, 849, 950, 1022, 1072, 1223, 1280, 1380, 1458, 1603, 1628(C=N), 1652, 1699, 2412, 2843, 2942. UV-vis (nm (Abs)): (acetone) 346 (2.37). (methanol) 347 (0.30). (chloroform) 358 (0.52). CD (nm (θ/mdeg)): (acetone) 374 (−91.5), 490 (7.61), 598 (11.9). (methanol) 372 (−11.4), 491 (0.92), 606 (2.27). (chloroform) 389 (−25.4), 483 (2.21), 605 (4.32).

3.2.3. Preparation of GdNi

To a solution of o-vanillin (0.3124 g, 2.00 mmol) dissolved in methanol (40 mL), (1R,2R)-(−)-1,2-cyclohexandiamine (0.1358 g, 1.00 mmol) was added dropwise and stirred at 313 K for 2 h to give yellow solution of ligand. Nickel (II) acetate tetrahydrate (0.2517 g, 1.00 mmol) was added to give rise to orange solution of the complex. After stirring for 2 h, gadolinium (III) nitrate hexahydrate (0.4640 g, 1.00 mmol) was added and refluxed at 373 K for 4h to yield orange solution with orange precipitates. This crude orange compound was filtered and recrystallized from methanol/diethyl ether to give orange precipitates. Yield 0.5859 g (89.0%). IR (KBr (cm⁻¹)): 419, 452, 565, 667, 739, 784, 856, 1033, 1076, 1164, 1232, 1308, 1380, 1471, 1508, 1619(C=N), 1652, 1699, 2412, 2831, 2928. UV-vis (nm (Abs)): (acetone) 331 (1.86). (methanol) 331 (0.46). (chloroform) 340 (0.65). CD (nm (θ/mdeg)): (acetone) 392 (−44.5), 444 (8.65), 555 (10.1). (methanol) 397 (−6.34), 458 (1.08), 555 (1.91). (chloroform) 404 (−13.6), 459 (2.41), 574 (3.55).

3.2.4. Preparation of GdCu

To a solution of o-vanillin (0.3022 g, 2.00 mmol) dissolved in methanol (40 mL), (1R,2R)-(-)-1,2-cyclohexandiamine (0.1143 g, 1.00 mmol) was added dropwise and stirred at 313 K for 2 h to give yellow solution of ligand. Copper (II) acetate monohydrate (0.2089 g, 1.00 mmol) was added to give rise to purple-red solution of the complex. After stirring for 2 h, gadolinium (III) nitrate hexahydrate (0.4634 g, 1.00 mmol) was added and refluxed at 373 K for 4 h to yield red solution with red precipitates. This crude red compound was filtered and recrystallized from methanol/diethyl ether to give red precipitates. Yield 0.5220 g (78.0%). IR (KBr (cm⁻¹)): 430, 560, 667, 740, 758, 838, 949, 1020, 1072, 1165, 1222, 1303, 1374, 1460, 1527, 1605, 1624, 1652, 2420, 2842, 2924. UV-vis (nm (Abs)): (acetone) 346 (2.06). (methanol) 346 (2.04). (chloroform) 360 (0.79). CD (nm (θ/mdeg)): (acetone) 375 (−73.9), 483 (6.39), 569 (9.46). (methanol) 374 (−62.8), 487 (5.28), 604 (12.4). (chloroform) 397 (−35.6), 481 (3.47), 609 (1.94).

3.3. Physical Measurements

Infrared spectra were recorded as KBr pellets on a JASCO FT-IR 4200 plus spectrophotometer in the range of 4000–400 cm⁻¹ at 298 K. Absorption (and diffuse reflectance) electronic spectra were measured on a JASCO V-570 UV/VIS/NIR spectrophotometer (equipped with an integrating sphere) in the range of 800–200 nm at 298 K. Circular dichroism (CD) spectra were measured on a JASCO J-820 spectropolarimeter in the range of 800–200 nm at 298 K. Magnetic properties were investigated with a Quantum Design MPMS-XL superconducting quantum interference device magnetometer (SQUID). DC magnetic susceptibility data were measured at 5–300 K under 5000 Oe (measured at Institute for molecular Science and Institute for Solid State Physics, the University of Tokyo).

3.4. X-ray Crystallography

Orange prismatic single crystals of NdNi was glued on top of a glass fiber and coated with a thin layer of epoxy resin to measure the diffraction data. Intensity data were collected on a Bruker APEX2 CCD diffractometer with graphite monochromated Mo Kα radiation (λ = 0.71073 Å). Data analysis was carried out with a SAINT program package. The structures were solved by direct methods with a SHELXS-97 [40] and expanded by Fourier techniques and refined by full-matrix least-squares methods based on F² using the program SHELXL-97 [40]. An empirical absorption correction was applied by a program SADABS. All non-hydrogen atoms were readily located and refined by anisotropic thermal parameters. All hydrogen atoms were located at geometrically calculated positions and refined using riding models. Unfortunately, appropriate single crystals could not be obtained for other metal complexes.

Crystallographic data for NdNi. C₂₂H₂₄N₅NdNiO₁₃, crystal size 0.15 mm × 0.13 mm × 0.12 mm, M_w = 769.41, triclinic, space group P1, a = 9.3035(11) Å, b = 12.1272(14) Å, c = 12.2122(14) Å, α = 101.6500(10) °, β = 96.2000(10) °, γ = 90.0350(10) °, V = 1341.2(3) Å ³, Z = 2, D_calc = 1.905 mg/m ³, F(000) = 766, R₁ = 0.0224, wR₂ = 0.0675 (6137 reflections), S = 0.582, Flack parameter = −0.005(13). (where R₁ = ∑||F_o|−|F_c||/∑|F_o|. R_w = (∑w(|F_o|−|F_c|)² /∑w|F_o|²)^1/2, w = 1/(σ ²(F_o) + (0.1P)²), P = (F_o2 + 2F_c2)/3).

4. Conclusions

In summary, among four chiral 3d-4f complexes reported herein, only GdCu was confirmed to be suitable for CD spectroscopy experiments in various environmental matrixes. In comparison with acetone solution and solid state CD spectra, the bands at about 470 nm in the solid state spectra could be assigned as a so-called artifact CD peak in the solid state. In this PMMA polymer matrixes system, that suggests anisotropic molecular orientation as well as restricted molecular motion, we have shown matrix viscosity-dependence of the intensity of artifact peaks resulting from chiroptical features of 3d-4f complexes for the first time. Rigid matrix maintaining anisotropic orientation exhibited a decrease in intensity of the artifact CD peak toward negative θ values.

Supplementary Data

CCDC 837663 contains the supplementary crystallographic data. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44-1223-336-033; or E-Mail: deposit@ccdc.cam.ac.uk.

References 1

Akitsu

Einaga

Syntheses, crystal structures, and electronic properties of a series of copper(II) complexes with 3,5-halogen-substituted Schiff base ligands and their solutions

Polyhedron20052429332943

10.1016/j.poly.2005.06.018

Akitsu

Einaga

Synthesis, crystal structures, and electronic properties of Schiff base nickel(II) complexes: towards solvatochromism induced by photochromic solute

Polyhedron20052418691877

10.1016/j.poly.2005.06.019

Akitsu

Photofunctional supramolecular solution systems of chiral Schiff base nickel(II), copper(II), and zinc(II) complexes and photochromic azobenzenes

Polyhedron20072625272535

10.1016/j.poly.2006.12.031

Akitsu

Einaga

Novel photo-induced aggregation behavior of a supramolecular system containing iron(III) magnetic ionic liquid and azobenzene

Inorg. Chem. Commun2006911081110

10.1016/j.inoche.2006.07.018

Akitsu

Nishijo

The first observation of photoinduced tuning of AC magnetization for organic/inorganic hybrid materials composed of Mn₁₂-acetate and azobenzene

J. Magn. Magn. Mater200731595100

10.1016/j.jmmm.2007.03.189

Akitsu

Nishijo

The first detection of photomodulation by both DC and in-phase AC susceptibility for organic/inorganic hybrid materials containing cyano-bridged Gd-Cr complex and azobenzene

J. Magn. Magn. Mater200832015861590

10.1016/j.jmmm.2008.01.008

Akitsu

The tuning of quantum magnetization for organic/inorganic hybrid materials composed of Mn12-acetate and azobenzene casted into PMMA films on PVA films

J. Magn. Magn. Mater2008321207212 8

Akitsu

Ishioka

Itoh

Polarized Spectroscopy of Hybrid Materials of Mn₁₂ Single-Molecule Magnet and Azobenzene or Disperse Red 1 in PMMA Films

Cent. Eur. J. Chem20097690696

10.2478/s11532-009-0075-2

Akitsu

Itoh

Polarized spectroscopy of hybrid materials of chiral Schiff base cobalt(II), nickel(II), copper(II), and zinc(II) complexes and photochromic azobenzenes in PMMA films

Polyhedron201029477487

10.1016/j.poly.2009.06.050

Akitsu

Ishioka

Manipulation and Observation by Polarized Light: Hybrid Materials of Chiral Schiff Base Mn(III) Complexes and Azobenzene in PMMA

Asian Chem. Lett2010143751 11

Aritake

Takanashi

Yamazaki

Akitsu

Polarized spectroscopy and hybrid materials of chiral Schiff base Ni(II), Cu(II), Zn(II) complexes with included or separated azo-groups

Polyhedron201130886894

10.1016/j.poly.2010.12.015

Akitsu

Miura

Polarized electronic spectra of organic/inorganic hybrid materials of chiral Schiff base Ni(II) or Cu(II) complexes and disperse red 1 or azobenzene in PMMA films

J. Chem. Chem. Eng20115443450 13

Akitsu

Tanaka

Polarized Electronic and IR Spectroscopy of Hybrid Materials of Chiral Cu(II) and Mn₁₂ Complexes and Some Photochromic Compounds in PMMA Films

Asian Chem. Lett201014235254 14

Akitsu

Tanaka

Polarized Electronic and IR Spectra of Hybrid Materials of Chiral Mn(II) Complexes and Different Types of Photochromic Dyes Showing Photoisomerization or Weigert Effect

Curr. Phys. Chem201118289

10.2174/1877946811101020082

Akitsu

Yoshida

Detection of Intermolecular Interaction Between Pd(II) Complexes Having Imidate and Amine Ligands and Photochromic Dyes in Hybrid Solution Systems by Absorption and Fluorescence Spectra

Curr. Phys. Chem201117681

10.2174/1877946811101020076

Kuroda

Harada

Shindo

A solid-strate dedicated circular dichroism spectrophotometer: Development and application

Rev. Sci. Instr20017238023810

10.1063/1.1400157

Schellaman

Jensen

Optical spectroscopy of oriented molecules

Chem. Rev19878713591399

10.1021/cr00082a004

Tinoco

Mickols

Maestre

Bustamante

Absorption, scattering, and imaging of biomolecular structures with polarized light

Annu. Rev. Biophys. Biophys. Chem198716319349

10.1146/annurev.bb.16.060187.001535

3297087

Claborn

Isborn

Kaminsky

Kahr

Optical rotation of achiral comounds

Angew. Chem. Int. Ed. Engl20084757065717

18600811

Kaminsky

Experimental and phenomenological aspects of circular birefringence and related properties in transparent crystals

Rep. Prog. Phys20006315751640

10.1088/0034-4885/63/10/201

Shindo

Nakagawa

On the artifacts in circularly polarized emission spectroscopy

Appl. Spectrosc1985393238

10.1366/0003702854249358

Shindo

Nakagawa

Ohmi

On the problems of CD spectropolarimeters.II: artifacts in CD spectrometers

Appl. Spectrosc198539860868

10.1366/0003702854250022

Hipps

Crosby

Applications of the photoelastic modulator to polarization spectroscopy

J. Phys. Chem197983555562

10.1021/j100468a001

Goldstein

Polarized LightMarcel Drekker

New York, NY, USA

2003 25

Kobayashi

Uesu

Takehara

A new optical method and apparatus “HAUP” for measuring simultaneously optical activity and birefringence of crystals. II. Application to triglycine-sulphuric acid (NH₂CH₂CO₂H)₃.H₂SO₄

J. Appl. Crystallogr198316212219

10.1107/S0021889883010274

Kaminsky

Claborn

Kahr

Polarimetric imaging of crystals

Chem. Soc. Rev200433514525

10.1039/b201314m

15480475

Kahr

Bing

Kaminsky

Viterbo

Turinese stereochemistry: Eligio Perucca’s enantioselectivity and Primo Levi’s asymmetry

Angew. Chem. Int. Ed20094837443748

10.1002/anie.200801840

Bing

Selassie

Paradise

Isborn

Kramer

Sadilek

Kaminsky

Kahr

Circular dichroism tensor of a triarylmethyl propeller in sodium chlorate

J. Am. Chem. Soc201013274547465

10.1021/ja1018892

20446684

Kaminsky

Geday

Herreros-Cedrés

Kahr

Optical rotatory and circular dichroic scattering

J. Phys. Chem. A200310728002807

10.1021/jp026364q

Kaminsky

Herreros-Cedrés

Geday

Kahr

Dispersion of anomalous azimuthal rotation and circular extinction contrast in dyed K₂SO₄ crystals

Chirality200416S55S61

10.1002/chir.20054

15239074

Claborn

Chu

Jang

Kaminsky

Kahr

Circular extinction imaging: determination of the absolute orientation of embedded chromophores in enantiomorphously twinned LiKSO₄ crystals

Cryst. Growth Des2005521172123

10.1021/cg050145n

Hazra

Koner

Nayak

Sparkes

Howard

JAK

Mohanta

Cocrystallized dinuclear-mononuclear Cu^II₃Na^I and double-decker-triple-decker Cu^II₅K^I₃ complexes derived from N,N’-Ethylenebis(3-ethoxysalicylaldimine)

Cryst. Growth Des2009936033608

10.1021/cg900341r

Akine

Taniguchi

Nabeshima

Cooperative formation of trinuclear Zinc(II) complexes via complexation of a tetradentate oxime chelate ligand, salamo, and Zinc(II) acetate

Inorg. Chem20044361426144

10.1021/ic049282k

15446856

Jana

Majumder

Carrella

Nayak

Weyhermueller

Dutta

Schollmeyer

Rentschler

Koner

Mohanta

Syntheses, structures, and magnetic properties of diphenoxo-bridged Cu^IILn^III and Ni^II(Low-Spin)Ln^III compounds derived from a compartmental ligand (Ln = Ce-Yb)

Inorg. Chem20104990129025

10.1021/ic101445n

20812685

Andruh

Costes

Diaz

Gao

3d-4f combined chemistry: synthetic strategies and magnetic properties

Inorg. Chem20094833423359

10.1021/ic801027q

19361237

Burrow

Burchell

Lin

Habib

Wernsdorfer

Clerac

Murugesu

Salen-Based [Zn₂Ln₃] complexes with fluorescence and single-molecule-magnet properties

Inorg. Chem20094880518053

10.1021/ic9007944

19678667

Yang

Jones

Wong

Lynch

Oye

Holmes

Design and synthesis of a near infra-red luminescent hexanuclear Zn-Nd prism

Chem Commun200618361838 38

Wong

Yang

Jones

Rivers

Lynch

Xiao

Oye

Holmes

Multinuclear luminescent schiff-base Zn-Nd sandwich complexes

Inorg. Chem20064543404345

10.1021/ic051866e

16711681

Pasatoiu

Madalan

Kumke

Tiseanu

Andruh

Temperature switch of lmct role: from quenching to sensitization of europium emission in a Zn^II-Eu^III binuclear complex

Inorg. Chem20104923102315

10.1021/ic902169s

20121211

Sheldrick

A short history of SHELX

Acta Cryst. A200764112122

Figures and Table Figure 1

Molecular structures of complexes (NdNi, NdCu, GdNi, and GdCu denote Ln and M metal ions). Crystalline water molecules were omitted for clarity.

Figure 2

Crystal structures of NdNi showing selected atom labeling scheme. Hydrogen atoms are omitted clarity.

Figure 3

(A) The χ_MT vs T plots for NdNi and NdCu as powder and the differences of χ_MT(NdCu-NdNi) at 0.5 T; (B) The χ_MT vs T plots for GdNi and GdCu as powder and the differences of χ_MT(GdCu-GdNi) at 0.5 T; (C) The χ_MT vs T plots for GdCu as powder and as a PMMA cast film at 0.5 T.

Figure 4

The CD and diffuse reflectance electronic spectra of NdNi and GdNi (and the corresponding mononuclear Ni complex for comparison) measured as KBr pellets.

Figure 5

The CD and diffuse reflectance electronic spectra of NdCu and GdCu (and the corresponding mononuclear Cu complex for comparison) measured as KBr pellets.

Figure 6

(A) Concentration (viscosity) dependence of the CD spectra of PMMA film, PMMA acetone solutions, and acetone solution of GdCu (magnified); (B) Concentration (viscosity) dependence of CD and the corresponding electronic absorption spectra of PMMA film, PMMA acetone solutions, and acetone solution of GdCu.

Table 1

Selected bond distance (Å) and angles (°) of NdNi.

Nd1-O6 = 2.374(7)	Nd1-O8 = 2.377(6)	Nd1-O20 = 2.468(8)	Nd1-O18 = 2.470(7)
Nd1-O23 = 2.477(7)	Nd1-O21 = 2.482(7)	Nd1-O26 = 2.510(7)	Nd1-O24 = 2.514(7)
Nd1-O5 = 2.528(6)	Nd1-O7 = 2.543(6)	Nd1-N8 = 2.873(8)	Nd1-N9 = 2.902(8)
Nd2-O2 = 2.337(7)	Nd2-O4 = 2.395(7)	Nd2- O11 = 2.463(9)	Nd2-O9 = 2.478(7)
Nd2-O15 = 2.504(7)	Nd2-O1 = 2.507(6)	Nd2-O14 = 2.518(6)	Nd2-O3 = 2.522(7)
Nd2-O12 = 2.523(7)	Nd2-O17 = 2.533(9)	Nd2-N5 = 2.921(11)	Nd2-N7 = 2.942(9)
Ni1-O4 = 1.838(6)	Ni1-N2 = 1.843(7)	Ni1-N1 = 1.844(8)	Ni1-O2 = 1.876(7)
Ni2-O8 = 1.833(6)	Ni2-N4 = 1.849(8)	Ni2-N3 = 1.855(8)	Ni2-O6 = 1.861(7)
O4-Ni1-N2 = 94.3(3)	O4-Ni1-N1 = 175.9(3)	N2-Ni1-N1 = 88.7(3)	O4-Ni1-O2 = 81.9(3)
N2-Ni1-O2 = 175.8(3)	N1-Ni1-O2 = 95.2(3)	O8-Ni2-N4 = 95.3(3)	O8-Ni2-N3 = 175.7(3)
N4-Ni2-N3 = 85.9(3)	O8-Ni2-O6 = 82.8(3)	N4-Ni2-O6 = 175.3(3)	N3-Ni2-O6 = 96.3(3)
O6-Nd1-O8 = 61.9(2)	O6-Nd1-O20 = 117.0(3)	O8-Nd1-O20 = 118.6(2)	O6-Nd1-O18 = 73.6(3)
O8-Nd1-O18 = 74.9(2)	O20-Nd1-O18 = 51.4(3)	O6-Nd1-O23 = 110.7(2)	O8-Nd1-O23 = 144.0(2)
O20-Nd1-O23 = 96.5(2)	O18-Nd1-O23 = 139.6(2)	O6-Nd1-O21 = 161.2(2)	O8-Nd1-O21 = 134.3(2)
O20-Nd1-O21 = 66.8(3)	O18-Nd1-O21 = 116.6(3)	O23-Nd1-O21 = 51.0(2)	O6-Nd1-O26 = 68.1(2)
O8-Nd1-O26 = 77.1(2)	O20-Nd1-O26 = 164.3(2)	O18-Nd1-O26 = 139.9(2)	O23-Nd1-O26 = 68.1(2)
O21-Nd1-O26 = 103.5(2)	O6-Nd1-O24 = 111.9(2)	O8-Nd1-O24 = 77.6(2)	O20-Nd1-O24 = 130.3(2)
O18-Nd1-O24 = 144.6(2)	O23-Nd1-O24 = 73.3(2)	O21-Nd1-O24 = 69.8(3)	O26-Nd1-O24 = 50.2(2)
O6-Nd1-O5 = 63.2(2)	O8-Nd1-O5 = 124.0(2)	O20-Nd1-O5 = 78.2(2)	O18-Nd1-O5 = 80.4(2)
O23-Nd1-O5 = 68.0(2)	O21-Nd1-O5 = 101.7(2)	O26-Nd1-O5 = 92.4(2)	O24-Nd1-O5 = 134.3(2)
O6-Nd1-O7 = 123.8(2)	O8-Nd1-O7 = 64.4(2)	O20-Nd1-O7 = 76.1(2)	O18-Nd1-O7 = 77.9(2)
O23-Nd1-O7 = 122.2(2)	O21-Nd1-O7 = 74.8(2)	O26-Nd1-O7 = 114.3(2)	O24-Nd1-O7 = 70.2(2)
O5-Nd1-O7 = 153.2(2)	O6-Nd1-N8 = 97.3(2)	O8-Nd1-N8 = 95.4(2)	O20-Nd1-N8 = 25.7(2)
O18-Nd1-N8 = 26.1(3)	O23-Nd1-N8 = 120.5(2)	O21-Nd1-N8 = 90.8(2)	O26-Nd1-N8 = 165.4(2)
O24-Nd1-N8 = 141.1(2)	O5-Nd1-N8 = 81.3(2)	O7-Nd1-N8 = 72.3(2)	O6-Nd1-N9 = 137.1(2)
O8-Nd1-N9 = 145.1(2)	O20-Nd1-N9 = 81.6(2)	O18-Nd1-N9 = 132.8(3)	O23-Nd1-N9 = 26.4(2)
O21-Nd1-N9 = 24.6(2)	O26-Nd1-N9 = 85.2(2)	O24-Nd1-N9 = 68.0(2)	O5-Nd1-N9 = 86.1(2)
O7-Nd1-N9 = 97.3(2)	N8-Nd1-N9 = 107.3(2)	O2-Nd2-O4 = 61.9(2)	O2-Nd2-O11 = 119.4(3)
O4-Nd2-O11 = 118.3(3)	O2-Nd2-O9 = 76.9(2)	O4-Nd2-O9 = 72.9(3)	O11-Nd2-O9 = 52.0(3)
O2-Nd2-O15 = 79.1(2)	O4-Nd2-O15 = 114.1(2)	O11-Nd2-O15 = 127.0(3)	O9-Nd2-O15 = 147.3(2)
O2-Nd2-O1 = 62.8(2)	O4-Nd2-O1 = 121.8(2)	O11-Nd2-O1 = 75.8(3)	O9-Nd2-O1 = 78.6(2)
O15-Nd2-O1 = 70.7(2)	O2-Nd2-O14 = 141.3(3)	O4-Nd2-O14 = 111.1(2)	O11-Nd2-O14 = 97.8(3)
O9-Nd2-O14 = 140.3(2)	O15-Nd2-O14 = 69.5(2)	O1-Nd2-O14 = 122.9(2)	O2-Nd2-O3 = 123.2(2)
O4-Nd2-O3 = 61.9(2)	O11-Nd2-O3 = 81.3(3)	O9-Nd2-O3 = 79.7(3)	O15-Nd2-O3 = 132.5(2)
O1-Nd2-O3 = 155.2(2)	O14-Nd2-O3 = 69.5(2)	O2-Nd2-O12 = 134.9(2)	O4-Nd2-O12 = 160.91(19)
O11-Nd2-O12 = 65.1(3)	O9-Nd2-O12 = 116.2(3)	O15-Nd2-O12 = 68.2(3)	O1-Nd2-O12 = 77.2(2)
O14-Nd2-O12 = 50.7(2)	O3-Nd2-O12 = 101.9(2)	O2-Nd2-O17 = 74.6(3)	O4-Nd2-O17 = 67.3(3)
O11-Nd2-O17 = 166.0(3)	O9-Nd2-O17 = 138.5(3)	O15-Nd2-O17 = 51.6(2)	O1-Nd2-O17 = 113.1(3)
O14-Nd2-O17 = 68.3(3)	O3-Nd2-O17 = 91.3(3)	O12-Nd2-O17 = 105.3(2)	O2-Nd2-N5 = 96.9(3)
O4-Nd2-N5 = 95.2(3)	O11-Nd2-N5 = 27.2(3)	O9-Nd2-N5 = 24.8(3)	O15-Nd2-N5 = 143.0(3)
O1-Nd2-N5 = 74.8(3)	O14-Nd2-N5 = 121.8(3)	O3-Nd2-N5 = 80.5(3)	O12-Nd2-N5 = 91.6(3)
O17-Nd2-N5 = 162.5(3)	O2-Nd2-N7 = 76.9(2)	O4-Nd2-N7 = 92.1(3)	O11-Nd2-N7 = 149.4(3)
O9-Nd2-N7 = 153.6(2)	O15-Nd2-N7 = 25.0(3)	O1-Nd2-N7 = 92.0(3)	O14-Nd2-N7 = 65.1(2)
O3-Nd2-N7 = 112.7(2)	O12-Nd2-N7 = 85.0(2)	O17-Nd2-N7 = 26.7(3)