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Structural analysis and photoluminescence properties of low dimensional lanthanide tetracyanometallates
Inorganica Chimica Acta 376 (2011) 414–421
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Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Structural analysis and photoluminescence properties of low dimensional lanthanide tetracyanometallates Milorad Stojanovic a, Nicholas J. Robinson a, Zerihun Assefa b, Richard E. Sykora a,⇑ a b
Department of Chemistry, University of South Alabama, Mobile, AL 36688, USA Department of Chemistry, North Carolina A&T State University, Greensboro, NC 27411, USA
a r t i c l e
i n f o
Article history: Received 20 December 2010 Accepted 3 July 2011 Available online 12 July 2011 Keywords: Lanthanide Tetracyanoplatinate Tetracyanopalladate Single-crystal X-ray diffraction Photoluminescence
a b s t r a c t The synthesis of a number of lanthanide tetracyanometallate (TCM) compounds have been carried out by reaction of Ln3+ nitrate salts and potassium tetracyanometallates in solvent systems containing dimethylsulfoxide and water. These reactions result in the isolation of three distinct structure types: (1) monoclinic [Ln(DMSO)4(H2O)3M(CN)4](M(CN)4)0.52H2O (Ln = Eu, Tb and M = Pd, Pt), (2) orthorhombic {La(DMSO)3 (H2O)2(NO3)M(CN)4}1H2O (M = Pd, Pt), and (3) orthorhombic {Ln(DMSO)3(H2O)(NO3)M(CN)4}1 (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt) in the form of single crystals. Single-crystal X-ray diffraction has been used to investigate their structural features. Structure type 1 is a zero dimensional ionic compound with a M/Ln ratio of 1.5:1. It contains coordinated as well as uncoordinated [M(CN)4]2 (M = Pd, Pt) anions and features relatively long platinophilic interactions. Structure types 2 and 3 differ quite drastically from structure type 1, but they are very similar to each other. Both of the latter are one-dimensional in nature due to chains containing linkage of Ln3+ coordination spheres with trans-bridging [M(CN)4]2 anions. These coordination polymers both have a M/Ln ratio of 1:1, a lack of platinophilic interactions, and incorporation of a bidentate NO3 for charge balance. Photoluminescence properties for select Eu3+ and Tb3+ compounds have been investigated. They show characteristic absorption and emission for the Ln3+ ions, but no significant influence of the tetracyanometallate anions. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Cyanide-bridged lanthanide-transition-metal compounds have been an interesting area of research because of their potential magnetic, optical and catalytic properties. While magnetic applications predominantly involve first row transition metal hexacyanides or the Prussian blue like compounds [1–5], catalytic [6–9] and optical [10,11] applications have been the focus regarding the lanthanide tetracyanometallates of Pt, Pd, and Ni. Much of the synthetic, structural and catalytic work in this area has been done by the Shore group [5,6,9,12–17]. Some of our previous work as well as a current research focus of our group is to synthesize cyanide-bridged lanthanide/noble-metal cyanides containing additional chromophoric ligands, such as 2,20 :60 ,200 -terpyridine [18–20], that can cooperatively photosensitize lanthanide ion luminescence. The lanthanide tetracyanometallate compounds that will be discussed in this paper were initially created while attempting to synthesize cyanide-bridged lanthanide/ ⇑ Corresponding author. Address: Department of Chemistry, University of South Alabama, Chemistry Building, Room 223, Mobile, AL 36688, USA. Tel.: +1 251 460 7422; fax: +1 251 460 7359. E-mail addresses: [email protected] (M. Stojanovic), njr301@ jaguar1.usouthal.edu (N.J. Robinson), [email protected] (Z. Assefa), rsykora@ southalabama.edu (R.E. Sykora). 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.07.002
noble-metal complexes with 2,20 -bipyridine as a chromophoric ligand. They are structurally quite similar to many compounds reported previously by Shore including {(DMF)10Yb2[Pd(CN)4]3}1 [6], {[(DMF)16Yb6(l6-O)(l3-OH)8(l-NC)Pd(l-CN)(CN)2] [Pd(CN)4]34D MF}1 [17], and {(DMF)12Ce2[Pd(CN)4]3}1 [15]. While the bulk of these and related tetracyanometallate compounds prepared by Shore contain dimethylformamide or dimethylacetamide, we have focused on using solvent systems containing dimethylsulfoxide and water. One very important similarity to Shore’s compounds, produced in DMF or DMA, and our related DMSO compounds is the general lack of strong metallophilic (in particular Pt Pt) interactions [15,16]. These are quite different results from past research on lanthanide tetracyanoplatinates prepared in aqueous solution where many compounds [21–26] have been explored that contain pseudo-1-D columnar stacks of tetracyanoplatinate anions with very short Pt Pt distances as a dominant structural feature [27,28]. Such compounds exhibit luminescent properties which are caused by the Pt Pt interactions occurring between the adjacent anions via an intra-chain donor–acceptor interaction [29]. It has been established that the luminescence occurs as a result of excitation from the donor a1g (Pt–5dz2) to the acceptor a2u (Pt–6pz, CN–p⁄) in the electronic structure of the Pt Pt interaction. Several studies have shown that a strong correlation exists between the observed
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structural and optical properties in tetracyanoplatinate materials [21,28]. The spectroscopic properties (absorption and luminescence) of the salts are strongly dependent on the Pt Pt distances (3 to 3.8 Å) [26]. Some experiments have shown that those distances, and hence the associated spectroscopic properties, can be tuned by chemical and physical variations such as choice of counter cation [29] or applied pressure [23]. In this paper we report three novel lanthanide tetracyanometallate structure types that are all structurally low dimensional. Abbreviations that note the Ln element, noble-metal element, and structural family (e.g. EuPt1 for the Eu–Pt compound in structure type (1)) are used to simplify the presentation. Structural families include: (1) monoclinic [Ln(DMSO)4(H2O)3M(CN)4](M(CN)4)0.5 2H2O (Ln = Eu, Tb and M = Pd, Pt), (2) orthorhombic {La(DMSO)3(H2O)2(NO3)M(CN)4}1H2O (M = Pd, Pt), and (3) orthorhombic {Ln(DMSO)3(H2O)(NO3)M(CN)4}1 (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt). Synthetic routes, structural trends, and select photoluminescence properties are reported for isostructural members of these classes of compounds. 2. Experimental 2.1. Materials and methods La(NO3)36H2O (Strem, 99.9%), Eu(NO3)36H2O (Strem, 99.9%), Tb(NO3)3xH2O (Strem 99.9%), Er(NO3)36H2O (Strem, 99.9%), Yb(NO3)35H2O (Strem, 99.9%), K2Pt(CN)43H2O (Alfa Aesar, 99.9%), and K2Pd(CN)4xH2O (Alfa Aesar, 99.9%) were used as received without further purification. The reactions reported produced the highest observed yields of the respective compounds. IR spectra were obtained on neat crystalline samples at room temperature using a Jasco FT/IR-4100 with an ATR attachment. 2.2. Synthesis 2.2.1. [Ln(DMSO)4(H2O)3M(CN)4](M(CN)4)0.52H2O (Ln = Eu, Tb and M = Pd, Pt) All four reported compounds in structure type 1 were created by mixing 1 mL of a 0.10 M solution of the appropriate lanthanide nitrate in DMSO and 1 mL of 0.10 M K2[Pd(CN)4] or K2[Pt(CN)4] in H2O. Slow evaporation of the solvent over a period of 10–14 days resulted in crystallization of colorless needle shaped crystals. The recovered yield was in the range of 53–61%. Percent yields as well as IR data for individual compounds are provided in Supplementary material. 2.2.2. {La(DMSO)3(H2O)2(NO3)M(CN)4}1H2O (M = Pd, Pt) LaPd2 and LaPt2 were created by mixing 1 mL of a 0.10 M solution of lanthanum nitrate in DMSO and 1 mL of 0.10 M K2[Pd(CN)4] or K2[Pt(CN)4] in H2O. Slow evaporation of the solvent over a period of 17–21 days resulted in crystallization of colorless plate shaped crystals. The recovered yield was in the range of 66–69%. Percent yields as well as IR data for individual compounds are provided in Supplementary material. 2.2.3. {Ln(DMSO)3(H2O)(NO3)M(CN)4}1 (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt) All four compounds of structure type 3 were created by mixing 1 mL of a 0.10 M solution of the appropriate lanthanide nitrate in DMSO and 1 mL of 0.10 M K2[Pd(CN)4] or K2[Pt(CN)4] in H2O. Slow evaporation of the solvent over a period of 17–21 days resulted in crystallization of colorless plate shaped crystals. The recovered yield was in the range of 53–66%. Percent yields as well as IR data for individual compounds are provided in Supplementary material.
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2.3. Single-crystal X-ray diffraction studies Single crystals of the title compounds were selected, mounted on quartz fibers, and aligned with a digital camera on a Varian Oxford Xcalibur E single-crystal X-ray diffractometer. Intensity measurements were performed using Mo Ka radiation, from a sealed-tube Enhance X-ray source, and an Eos area detector. CrysAlisPro [30] was used for preliminary determination of the cell constants, data collection strategy, and for data collection control. Following data collection, CrysAlisPro was also used to integrate the reflection intensities, apply an absorption correction to the data, and perform a global cell refinement. For all structure analyses, the program suite SHELX was used for structure solution (XS) and least-squares refinement (XL) [31]. The initial structure solutions were carried out using direct methods and the remaining atomic positions were located in difference maps. All three structures contain some disorder in the DMSO solvent molecules. The refinements were constrained such that the partial occupancies of disordered sites summed to full occupancy. Some crystallographic details are listed in Tables 1–3. 2.4. Photoluminescence studies The luminescence data were collected using a Photon Technology International (PTI) QM-3 spectrometer. The PTI system utilizes both a pulsed and a steady-state Xe source for excitation and can be used to determine steady-state emission and excitation profiles and to conduct lifetime measurements. Selection of excitation and emission wavelengths are conducted by means of computer controlled autocalibrated ‘‘QuadraScopic’’ monochromators that are equipped with aberration corrected emission and excitation optics. Signal detection is accomplished with a PMT detector (model 928 tube) that can work either in analog or digital (photon counting) modes. All of the photoluminescence experiments were conducted at room temperature on neat crystalline samples held in sealed quartz capillary tubes. 3. Results and discussion 3.1. Synthesis Three different structure types that will be described shortly were all created under similar conditions. Structure type (1) was initially created by mixing 1 mL of a 0.10 M solution of Ln(NO3)3 in DMSO, 1 mL of 0.10 M K2[Pd(CN)4] or K2[Pt(CN)4] in H2O, and 1 mL of 0.10 M 2,20 -bipyridine in 19/1 mixture H2O/EtOH. After several days, needle-like crystals of LnM1 are isolated as well as microcrystalline 2,20 -bipyridine. This structure type can also be prepared without bipyridine present as was described in the experimental section. Structure type 1 has been observed with both Eu and Tb. LaPd2 and LaPt2 has been observed only with La, the structural difference presumably is a result of the larger La3+ ion since the reactions to produce these compounds are otherwise identical. {Ln(DMSO)3(H2O)(NO3)(Pt(CN)4)}1 (Ln = Tb, Er, Yb) and the Pd analog, (TbPd3), were created with the smaller lanthanide cations, Tb3+, Er3+, Yb3+. Reactions involving Tb3+ and [M(CN)4]2 form both structure types 1 and 3, similar to {(DMF)10Sm2[Ni(CN)4]3} [15] where two different structure types were isolated from one reaction. 3.2. Structures of [Ln(DMSO)4(H2O)3M(CN)4](M(CN)4)0.52H2O (Ln = Eu, Tb and M = Pd, Pt) (1) Since all compounds of formula [Ln(DMSO)4(H2O)3M(CN)4] (M(CN)4)0.52H2O are isostructural, the structures will be discussed
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Table 1 Crystallographic data for [Ln(DMSO)4(H2O)3M(CN)4](M(CN)4)0.52H2O (Ln = La, Eu, Tb; M = Pd, Pt). Compound code
EuPd1
EuPt1
TbPd1
TbPt1
Formula mass (amu) Color Crystal system Space group a (Å) b (Å) c (Å) F D
870.27 colorless triclinic (no. 2) P1 10.6687(8) 10.8590(7) 15.7951(8) 88.683(4) 73.590(5) 64.849(7) 1579.0(2) 2 290 0.71073 51.36 1.830 3.124 23 997 5961 5961/6/378 0.0236 0.0512
1003.31 colorless triclinic (no. 2) P1 10.6353(4) 10.8518(4) 15.7858(4) 88.632(2) 73.422(3) 64.938(4) 1571.84(11) 2 290 0.71073 51.36 2.120 8.948 28 233 5940 5940/6/379 0.0332 0.0860
877.23 colorless triclinic (no. 2) P1 10.6607(3) 10.8559(3) 15.7775(5) 88.809(2) 73.650(3) 64.812(3) 1575.17(8) 2 290 0.71073 51.36 1.850 3.385 23 155 5949 5949/6/378 0.0269 0.0652
1010.27 colorless triclinic (no. 2) P1 10.6239(3) 10.8215(3) 15.7717(3) 88.682(2) 73.466(2) 64.984(2) 1565.26(7) 2 290 0.71073 52.74 2.144 9.241 31 906 6404 6404/6/379 0.0240 0.0576
C V (Å3) Z T (K) k (Å) 2hmax qcalcd (g cm3) l (Mo Ka) (mm1) Reflections collected Independent reflections Data/restraints/parameters R(F) for Fo2 > 2r (Fo2)a Rw(Fo2)b a b
P P RðFÞ ¼ hjjF o j jF c jj= jF o j. i1=2 P P 2 2 Rw ðF o Þ ¼ ½wðF o F 2c Þ2 = wF 4o .
Table 2 Crystallographic data for {La(DMSO)3(H2O)2(NO3)M(CN)4}1H2O (M = Pd, Pt).
a b
Compound code
LaPd2
LaPt2
Formula mass (amu) Color Crystal system Space group a (Å) b (Å) c (Å) V (Å3) Z T (K) k (Å) 2hmax qcalcd (g cm3) l (Mo Ka) (mm1) Reflections collected Independent reflections Data/restraints/parameters R(F) for Fo2 > 2r (Fo2)a Rw(Fo2)b
699.83 colorless orthorhombic Pnma (no. 22) 17.9048(5) 15.1738(3) 9.3874(2) 2550.41(10) 4 290 0.71073 51.36 1.823 2.647 10 462 2516 2516/13/194 0.0190 0.0468
788.52 colorless orthorhombic Pnma (no. 22) 17.9283(7) 15.1865(7) 9.3721(4) 2551.72(19) 4 290 0.71073 51.44 2.053 7.417 12 905 2523 2523/13/181 0.0294 0.0782
P P RðFÞ ¼ hjjF o j jF c jj= jF o j. i1=2 P P Rw ðF 2o Þ ¼ ½wðF 2o F 2c Þ2 = wF 4o .
together using EuPt1 as the representative. The structure of EuPt1 is ionic in nature and consists of [Eu(DMSO)4(H2O)3Pt(CN)4]+ complex cations crystallized with Pt(CN)42 anions (Fig. 1) in a stoichiometry of 2:1. The distorted square antiprismatic coordination geometry around each Eu3+ center results from four monodentate DMSO molecules (two of them disordered because of the sulfur split site), three monodentate water molecules and one coordinated (monodentate) TCP, which provide a total of eight inner sphere atoms around the Eu3+ site. The structure is completed with the uncoordinated Pt(CN)42 anions and water molecules of hydration. Select bond distances for EuPt1 can be found in Table 4. Average Eu–N and Eu–O distances in EuPt1 are longer than the comparable Tb–N and Tb–O distances in TbPt1 as expected based on ionic radii differences [32]. The distances between Eu3+ and the various coordinating ligands within EuPt1 also show a clear trend. The longest distance is the Eu–N distance between Eu and the [Pt(CN)4]2 ligand (2.549(5) Å). Eu–O distances to the water molecules
(average of 2.436 Å) are longer than Eu–O bonds to the DMSO (average value of 2.358 Å). Pt–C distances vary little, ranging from 1.979(7) to 1.993(6) Å. They are slightly shorter than Pd–C distances which range from 1.985(4) to 2.003(4) Å. All of these bond distances are within normal ranges as found in previously reported lanthanide tetracyanoplatinate [15,21,33] and tetracyanopalladate structures [12]. In terms of packing, this zero-dimensional structure (Fig. 2) consists of TCP dimers, formed from coordinated TCP anions, where Pt atoms within each dimer are separated by 3.6390(3) Å. This Pt Pt distance is somewhat longer than previously reported distances in other lanthanide tetracyanoplatinates [34], which range from 3.3 to 3.5 Å. The dimers assemble with their Pt1 Pt10 interactions oriented along the a axis with inter-dimer distances of 7.0830(5) Å, this latter distance is too long to be considered an important platinophilic interaction. The dimer formation in this compound differs from similar TCP compounds reported in the past [21–26] which contain pseudo-1-D columnar stacks of tetracyanoplatinate anions with extended platinophilic interactions. The reason for this difference is the presence of multiple bulky DMSO molecules coordinated to the Ln3+ coordination spheres which interrupt true 1-D Pt chain formation in EuPt1. The uncoordinated Pt(CN)42 anions are positioned perpendicular to the dimers with average Pt Pt distances of 7.5890(3) Å. Within the structure, there are multiple hydrogen bonding interactions between O–H donors from the coordinated and uncoordinated water molecules and nitrogen acceptors of the [Pt(CN)4]2 anions and oxygen acceptors of uncoordinated water molecules. 3.3. Structure of {La(DMSO)3(H2O)2(NO3)M(CN)4}1H2O (M = Pd (LaPd2), Pt (LaPt2)) La3+ forms structure type 2, presumably due to its larger size relative to Eu3+ and Tb3+, which form structure type 1. {La(DMSO)3(H2O)2(NO3)M(CN)4}1H2O (Fig. 3) has several significant differences from structure type (1). The coordination geometry around each La3+ center in the type (2) structure is a nine coordinate tri-capped trigonal prism where one DMSO and one water molecule have been replaced by a bidentate NO3 anion, relative to structure type 1. Additionally, La3+ coordinates two [M(CN)4]2
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M. Stojanovic et al. / Inorganica Chimica Acta 376 (2011) 414–421 Table 3 Crystallographic data for {Ln(DMSO)3(H2O)(NO3)M(CN)4}1 (Ln = Tb, M = Pd, Pt; Ln = Er, Yb; M = Pt).
a b
Compound code
TbPd3
TbPt3
ErPt3
YbPt3
Formula mass (amu) Color Crystal system Space group a (Å) b (Å) c (Å) V (Å3) Z T (K) k (Å) 2hmax qcalcd (g cm3) l (Mo Ka) (mm1) Reflections collected Independent reflections Data/restraints/parameters R(F) for Fo2 > 2r (Fo2)a Rw(Fo2)b
683.81 colorless orthorhombic Pnma (no. 22) 19.5259(5) 15.7186(3) 7.4866(2) 2297.79(10) 4 290 0.71073 51.36 1.977 4.145 9555 2258 2258/4/140 0.0362 0.0977
772.50 colorless orthorhombic Pnma (no. 22) 19.5619(8) 15.7329(8) 7.4420(4) 2290.39(19) 4 290 0.71073 51.40 2.240 9.474 11 820 2247 2247/4/141 0.0279 0.0769
780.84 colorless orthorhombic Pnma (no. 22) 19.4456(8) 15.6345(8) 7.4270(4) 2257.97(19) 4 290 0.71073 51.32 2.297 10.195 11 521 2218 2218/4/141 0.0378 0.1017
786.62 colorless orthorhombic Pnma (no. 22) 19.4345(5) 15.5735(4) 7.4435(3) 2252.87(12) 4 290 0.71073 51.46 2.319 10.644 10 428 2226 2226/4/140 0.0422 0.1152
P P RðFÞ ¼ jjF o j jF c jj= jF o j. P P Rw ðF 2o Þ ¼ ½ ½wðF 2o F 2c Þ2 = wF 4o 1=2 .
Table 4 Selected bond distances (Å) for [Eu(DMSO)4(H2O)3Pt(CN)4](Pt(CN)4)0.52H2O (EuPt1). Eu1–O1 Eu1–O2 Eu1–O3 Eu1–O4 Eu1–O5 Eu1–O6 Eu1–O9
2.433(4) 2.406(4) 2.468(4) 2.371(4) 2.390(4) 2.323(4) 2.347(5)
Eu1–N1 Pt1–C1 Pt1–C2 Pt1–C3 Pt1–C4 Pt1–C5 (x2) Pt1–C6 (x2)
2.549(5) 1.988(6) 1.993(6) 1.989(7) 1.983(6) 1.993(6) 1.979(7)
Fig. 2. Packing diagram for EuPt1 showing dimers of coordinated [Pt(CN)4]2and the uncoordinated [Pt(CN)4]2, approximately perpendicular to each other. In addition, the hydrogen atoms from the water molecules serve as H-bond donors to nitrogen atoms of the [Pt(CN)4]2 anion. Disordered methyl groups from DMSO have been removed for clarity.
Fig. 1. Molecular structure of EuPt1 showing the eight coordinate Eu3+ environment and the uncoordinated Pt(CN)42 anion. Disorder of the DMSO molecules are not shown for clarity. Symmetry code: (a) 2 x, 1 y, z.
anions and the compounds have a lower M/Ln ratio than structure type (1) (1:1 compared to 1.5:1). Linkage of La3+ coordination spheres with trans-bridging Pt(CN)42 anions makes this compound one-dimensional in nature which is significantly different from the zero-dimensional ionic structure type 1. These zigzag chains (Fig. 4) are similar to those previously described in the type A compound, {(DMF)5Sm[Ni(CN)4]Cl} [35] which also contains chains formed via trans-bridging
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Fig. 3. Structural building unit of LaPt2 showing the nine coordinate La3+ cation environment. Disorder of one DMSO is shown and the others are not shown for clarity. Symmetry codes: (a) x, ½ y, z; (b) 1 x, 1 y, 1 z; (c) 1 x, ½ + y, 1 z.
tetracyanometallate anions. Whereas the bridging angle (Pt1–La1– Pt1a) within our zigzag chains in LaPt2 is 81.7°, an indication of the zigzag nature, the chains within {(DMF)5Sm[Ni(CN)4]Cl} are more linear with a bridging angle of 146.2°. The difference is attributed to the presence of slightly bulkier and distorted DMSO molecules and the bidentate nitrate anion in LaPt2. The packing diagram shows that the one-dimensional chains are stacked parallel to each other in the structure. Additionally, an uncoordinated water molecule is positioned between the chains. It contains two types of hydrogen bonding interactions. First, water molecules coordinated to the lanthanide serves as Hdonors to the oxygen of the uncoordinated water molecule and second, hydrogens of the uncoordinated water molecule serve as H-bond donors to nitrogen acceptors of the [Pt(CN)4]2 anions. The trends in La–O(H2O), La–O(DMSO), and La–N bond distances, which are given in Table 5, are equivalent to those that have been previously described for structure type (1).
Fig. 4. Packing of one-dimensional zigzag chains in LaPt2, illustrating the transbridging of La3+ by Pt(CN)42 anions. Additionally, an uncoordinated water molecule is located between the chains. Hydrogen atoms from the coordinated as well as uncoordinated water molecules serve as H-bond donors to nitrogen atoms of the [Pt(CN)4]2 anion and to oxygen atoms of uncoordinated water molecules. Only one orientation of the disordered DMSO molecules, with H-atoms removed, are shown for clarity.
Table 5 Selected bond distances (Å) for {La(DMSO)3(H2O)2(NO3)Pt(CN)4}1H2O (LaPt2). La1–O2 (x2) La1–O3 La1–O4 La1–O6
2.638(4) 2.531(5) 2.554(5) 2.450(5)
La1–O7 (x2) La1–N1 (x2) Pt1–C1 (x2) Pt1–C2 (x2)
2.451(3) 2.691(5) 1.979(5) 1.966(5)
3.4. Structure of {Ln(DMSO)3(H2O)(NO3)M(CN)4}1 (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt) (3) While La forms structure type (2) in these systems, smaller lanthanides form structure type 3, {Ln(DMSO)3(H2O)(NO3)(M(CN)4)}1 (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt) (Fig. 5). These two structure types are very similar. TbPt3 will be used as a representative member to describe structure type 3. The coordination geometry around each Tb3+ center is an eight coordinate distorted square antiprism made of three DMSO molecules, a bidentate nitrate anion, a water molecule, and two TCP anions. The reduced number of coordinated water molecules relative to the La3+ cations in LaPt2, which reduces the Tb3+ coordination number to eight, is consistent with the smaller size of the heavier lanthanides. Whereas the larger lanthanides are usually nine coordinate, smaller lanthanides are often eight coordinate [36]. The structure also forms one-dimensional chains due to TCP bridging of Tb3+ coordination spheres in a ‘‘trans’’ orientation very reminiscent of the chains in structure type 2. The Pt1–Tb1–Pt1a
Fig. 5. The one-dimensional chains in TbPt3 are very similar to those in structure type 2. The H-bonding interactions between the chains are the major difference due to the reduced water content in TbPt3. Symmetry codes: (a) x, ½ y, z; (b) x, y, z; (c) x, ½ + y, z.
bridging angle of 89.9° is larger than the (Pt1–La1–Pt1a) angle of LaPt2, largely because Tb3+ is smaller than La3+ and because of reduced number of coordinated water molecules relative to LaPt2 as noted above.
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shifted relative to some Eu3+ systems, and signifies a strong electric dipole contribution in EuPt1. While observance of this 0–0 transition usually indicates a low symmetry site occupation for the Eu3+ ion, the existence of a single band for this transition is indicative of a single site occupation for the Eu3+ ion, even at the luminescence time scale. This observation is consistent with the crystallographic result that shows a single (C1) site occupation for Eu3+. The complete removal of the degeneracy of the 5D0 ? 7F1 transition and observance of three Stark components is also consistent with a low symmetry site (C1) occupation [40,41]. In EuPt1 the overall 7 F1 splitting is 260 cm1. The most intense transition, 5D0 ? 7F2, does not show the expected splitting into five Stark components at room temperature, however at 77 K splitting of this band does occur. Although the overall emission profile of EuPd1 is similar to that described for the platinum system, some subtle differences are prevalent. The major difference lies in the ratios of the emission intensities of the electric dipole versus magnetic dipole allowed transitions. A qualitative picture of the extent of covalency in the crystal field can be obtained by comparing the ratio of the intensity of the hypersensitive 5D0 ? 7F2 transition to that of the magnetic dipole 5D0 ? 7F1 transition [42–48] as this ratio is closely correlated with the polarizability of the coordination sphere. For EuPt1 and EuPd1, these ratios are 3.2 and 1.7, respectively, indicating the dominant role of the electric dipole component in the former. Since the cyanides are the common ligands in both cases, the differences in the ratio can be attributed to the difference in the central transition metal atom’s ability to withdraw electron density from the CN ligand. The experimental data appears to suggest that the Pd system withdraws electron density from the cyanide ligands more than the Pt system and decreases the electrostatic contribution to the Eu3+ ion. Moreover, the difference in lifetimes of the Eu3+ emission from the two complexes, 394 ls for EuPt1 versus 271 ls for EuPd1, can also be explained by this rationale. Nevertheless, it is important to note that other features of the emission behavior remain almost identical for EuPt1 and EuPd1, including the extent of splitting of the 7F1 state (which is 260 cm1 in both compounds) and the positions of the 0–0 transitions. One reason can be attributed to the absence of or minimal M–M interactions in both systems, since a stronger M–M interaction might have induced a more effective electrostatic contribution. The excitation spectrum of EuPt1 was measured by monitoring the emission at 618 nm. Only characteristic Eu3+ absorption was observed. The individual band positions and assignments for both the emission and excitation spectra can be found in Table 7. Similar data is also provided for the EuPd1 system. Both EuPt1 and EuPd1 demonstrate excitation spectra that contain bands assignable only to the Eu3+ f–f transitions, although the compounds contain both coordinated and uncoordinated Pt(CN)42 and Pd(CN) 42 groups, respectively, in their structures. It is likely that the lack of significant metallophilicity between the tetracyanometallate groups negates the possibility of donor–acceptor energy transfer in these systems.
Table 6 Selected bond distances (Å) for {Tb(DMSO)3(H2O)(NO3)Pt(CN)4}1 (TbPt3). Tb1–O1 (x2) Tb1–O2 Tb1–O3 Tb1–O4 (x2)
2.309(4) 2.317(7) 2.347(6) 2.446(6)
Tb1–N1 (x2) Pt1–C1 (x2) Pt1–C2 (x2)
2.492(5) 1.977(6) 1.991(7)
Fig. 6. Room temperature, solid-state emission spectra of EuPt1 and TbPt1. The emission spectra were collected upon excitation of EuPt1 at 393 nm and TbPt1 at 369 nm.
The main difference in structure types 2 and 3 is in regards to the packing of the chains. There are not lattice waters of hydration in structure type 3. Therefore the reduced water content, both in terms of coordinated and uncoordinated, leads to a reduction in the number of inter-chain H-bonding interactions in TbPt3 relative to LaPt2. H-bonding interactions only exist between O–H donors, coordinated to the lanthanides, and N acceptors of the terminal nitrogen atoms of the [Pt(CN)4]2 anions in neighboring chains (Fig. 5). The trends in La–O(H2O), La–O(DMSO), and La–N bond distances, which are given in Table 6, are equivalent to those that have been previously described in structure types 1 and 2. The Ln–O and Ln–N bond distances decrease among the isostructural members of the series, consistent with the decreasing size of the Ln3+ cations [32] as also described above for structure types 1 and 2. 3.5. Photoluminescence studies The photoluminescence spectrum of EuPt1 (Fig. 6) was measured with direct excitation of the Eu3+ into the 5L6 state at 393 nm. The spectrum shows characteristic sharp f–f emissions (Table 7) originating from two different excited states [37–39]. The 0–0 transition between 5D0 ? 7F0 is observed at 577 nm, blue Table 7 Band locations (nm) and assignments for EuPd1 and EuPt1. Excitation
Emission
Assignment 5
EuPd1
7
H3 F0 7 L10 F0 7 D4 F0 5 5 L7, G(3.2) 5 7 L6 F0 5 7 D3 F0 5 5
7
F0
317 339 362, 366 375, 380, 384 394 416
EuPt1
Assignment
EuPd1
EuPt1
317 346 360, 365 374, 381 393 415
5
524 534 551, 555 577 582.3588.7590.7 612, 617 649, 652 690, 697
524 535 551, 556 577 582.3588.5591.2 612, 618 650, 652 689, 698
7
D1 ? F 0 D1 ? 7F1 D1 ? 7F2 5 D0 ? 7F0 5 D0 ? 7F1 5 D0 ? 7F2 5 D0 ? 7F3 5 D0 ? 7F4 5 5
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Table 8 Band locations (nm) and assignments for TbPd1 and TbPt1. Excitation
Acknowledgments
Emission
Assignment
TbPd1
TbPt1
Assignment
TbPd1
TbPt1
5
D1 5 D2
7
D4 ? 7 F 6 5 D4 ? 7 F 5
487 541
488 543
7
317, 327 341, 351, 359 369, 377
5
5
319, 328 342, 351, 359 369, 377
5
581, 586 619
583, 587 618, 620 645, 652 667 678
D3
F6 7 F6 F6
D4 ? 7 F 4
5
D4 ? 7 F 3
5
D4 ? 7 F 2
5
7
D4 ? F 1 D4 ? 7 F 0
5
643, 651 667 677
The emission spectrum of TbPt1 (Fig. 6) (band locations and assignments given in Table 8) was measured at an excitation wavelength of 369 nm. The spectrum shows characteristic green Tb3+ emission [49,50] which displays the full range of 5D4 ? 7FJ (J = 0– 6) transitions. The strongest emission band is located at 543 nm which is a characteristic band for the Tb3+ 5D4 ? 7F5 transition [41]. This emission band in TbPt1 has a lifetime of 1 ms, whereas the comparable band in TbPd1 has a lifetime of 953 ls. The excitation spectrum of TbPt1 was measured by monitoring the Tb3+ emission at 543 nm. Both the TbPt1 and TbPd1 complexes display nearly identical excitation profiles, with only minor changes in the band positions and/or relative intensities. As was the case with EuPt1, the excitation spectra provide only characteristic Ln3+ absorption bands displaying Tb3+ 7F6 ? 5DJ (J = 0–4) transitions which are tabulated in Table 8. Apart from the characteristic f–f transitions a very weak and broad band located at 415 nm is also evident in the emission spectra of both TbPt1 and EuPt1. These bands display excitation maxima of 285 nm. While these bands cannot be assigned to any Ln3+ ion f–f transitions, they most likely correspond to excitation/emission associated with the Pt(CN)42 groups. Potential broad MMLCT-based Pt(CN)42 emission and excitation bands, around 500 and 385 nm, respectively [51], are not present in EuPt1 and TbPt1. Such bands have been well established for compounds that contain one-dimensional stacks of Pt(CN)42 with short Pt Pt distances of 3.1–3.3 Å [26] or for compounds that have slightly longer Pt Pt distances (3.5 Å) in dimeric TCP units [34]. In the present case the Pt Pt distance of 3.6390(3) Å between the TCP dimers of EuPt1 and TbPt1 proved to be too long to observe any MMLCT-based bands. Finally, excitation and emission spectra for EuPt3 were also obtained to probe for possible donor–acceptor energy transfer, but none was observed, or expected, considering that EuPt3 does not have any Pt Pt distances shorter than 7 Å. Only Eu3+ based emission via direct excitation was observed, similar to that reported for EuPt1. 4. Conclusion Reactions of Ln(NO3)3 and [M(CN)4]2 (M = Pd and Pt) in DMSO/ H2O solvent system have created three different structure types. Structure type 1 is a zero-dimensional ionic compound while structure types 2 and 3 are one dimensional. Tb3+ forms structure type 1 as well as structure type 3. Introduction of DMSO has prevented forming of strong Pt Pt interactions and thus directly influenced the photoluminescent properties compared to the hydrated lanthanide tetracyanoplatinates. Photoluminescence studies of Eu3+ and Tb3+ of structure type (1) have shown characteristic Eu3+ and Tb3+ emission and absorption bands as well as lack donor–acceptor energy transfer between tetracyanometallate ligands and Ln3+ cations.
The authors gratefully acknowledge the National Science Foundation for their generous support (NSF-CAREER Grant to R.E.S., CHE-0846680). Appendix A. Supplementary material CCDC 802937, 802938, 802939, 802940, 802941, 802942, 802943, 802944, 802945, and 802946 contain (EuPd1), (EuPt1), (TbPd1), (TbPt1), (LaPd2), (LaPt2), (TbPd3), (TbPt3), (ErPt3), and (YbPt3). These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac. uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2011. 07.002. References [1] T. Akitsu, Y. Einaga, Inorg. Chim. Acta 359 (2006) 1421. [2] S. Pal, D. Jagadeesan, K.L. Gurunatha, M. Eswaramoorthy, T.K. Maji, J. Mater. Chem. 18 (2008) 5448. [3] G. Li, T. Akitsu, O. Sato, Y. Einaga, J. Coord. Chem. 57 (2004) 855. [4] H.Z. Kou, S. Gao, X. Jin, Inorg. Chem. 40 (2001) 6295. [5] D.C. Wilson, S. Liu, X. Chen, E. Meyers, X. Bao, A.V. Prosvirin, K.R. Dunbar, C.M. Hadad, S.G. Shore, Inorg. Chem. 48 (2009) 5725. [6] S.G. Shore, E. Ding, C. Park, M.A. Keane, J. Mol. Catal. A: Chem. 212 (2004) 291. [7] A. Rath, E. Aceves, J. Mitome, J. Liua, U.S. Ozkanb, S.G. Shore, J. Mol. Catal. A: Chem. 165 (2001) 103. [8] H. Imamura, Y. Miura, K. Fujita, Y. Sakata, S. Tsuchiya, J. Mol. Catal. A: Chem. 140 (1999) 81. [9] S.G. Shore, E. Ding, C. Park, M.A. Keane, Catal. Commun. 3 (2002) 77. [10] Y. Sadaoka, H. Aono, E. Traversa, M. Sakamoto, J. Alloys. Compd. 278 (1998) 135. [11] P. Shuk, A. Vecher, V. Kharton, L. Tichonova, H.D. Wiemhofer, U. Guth, W. Gopel, Sens. Actuators B 16 (1993) 401. [12] B. Du, E. Ding, E.A. Meyers, S.G. Shore, Inorg. Chem. 40 (2001) 3637. [13] B. Du, E.A. Meyers, S.G. Shore, Inorg. Chem. 39 (2000) 4639. [14] S. Liu, P. Poplaukhin, E. Ding, C.E. Plecnik, X. Chen, M.A. Keane, S.G. Shore, J. Alloys Compd. 418 (2006) 21. [15] J. Liu, D.W. Knoeppel, S. Liu, E.A. Meyers, S.G. Shore, Inorg. Chem. 40 (2001) 2842. [16] S.G. Shore, D.W. Knoeppel, H. Deng, J. Liu, J.P. White III, S.-H. Chun, J. Alloys Compd. 249 (1997) 25. [17] J. Liu, S. Liu, E.A. Meyers, S.G. Shore, Inorg. Chem. 37 (1998) 5410. [18] B.A. Maynard, P.A. Smith, R.E. Sykora, Acta Crystallogr., Sect. E 65 (2009) m1132. [19] B.A. Maynard, P.A. Smith, A. Jaleel, L. Ladner, R.E. Sykora, J. Chem. Crystallogr. 40 (2010) 616. [20] B.A. Maynard, K. Kalachnikova, K. Whitehead, Z. Assefa, R.E. Sykora, Inorg. Chem. 47 (2008) 1895. [21] A. Loosli, M. Wermuth, H.-U. Güdel, S. Capelli, J. Hauser, H.-B. Bürgi, Inorg. Chem. 39 (2000) 2289. [22] W. Daniels, H. Yersin, H.V. Philipsborn, G. Gliemann, Solid State Commun. 30 (1979) 353. [23] H. Yersin, M. Stock, J. Chem. Phys. 76 (1982) 2136. [24] W. von Ammon, I. Hidvegi, G. Gliemann, J. Chem. Phys. 80 (1984) 2837. [25] H. Yersin, J. Chem. Phys. 68 (1978) 4707. [26] W. von Ammon, G. Gliemann, J. Chem. Phys. 77 (1982) 2266. [27] A.S. Mocanu, M. Ilisß, F. Dumitrasßcu, M. Ilie, V. Cîrcu, Inorg. Chim. Acta 363 (2010) 729. [28] G. Gliemann, H. Yersin, Struct. Bond. 62 (1985) 87. [29] H. Yersin, W. von Ammon, M. Stock, G. Gliemann, J. Lumin. 18–19 (1979) 774. [30] Oxford Diffraction, Oxford Diffraction Ltd., Xcalibur CCD System, CrysAlisPro Software System, Version 1.171.33.66, 2010. [31] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112. [32] R.D. Shannon, Acta Crystallogr., Sect. A 32 (1976) 751. [33] W. Holzapfel, H. Yersin, G. Gliemann, Z. Kristallogr. 157 (1981) 47. [34] B.A. Maynard, P.A. Smith, L. Ladner, A. Jaleel, N. Beedoe, C. Crawford, Z. Assefa, R.E. Sykora, Inorg. Chem. 48 (2009) 6425. [35] D.W. Knoeppel, J. Liu, E.A. Meyers, S.G. Shore, Inorg. Chem. 37 (1998) 4828. [36] S.A. Cotton, C. R. Chim. 8 (2005) 129. [37] K. Binnemans, K. Van Herck, C. Gorller-Walrand, Chem. Phys. Lett. 266 (1997) 297. [38] J.G. Bunzli, D. Plancherel, G.O. Pradervand, J. Phys. Chem. 93 (1989) 980. [39] B. Yan, Y.Y. Bai, J. Fluorine 15 (2005) 605. [40] D.J. Qian, W.N. Leng, Y. Zhang, Z. Chen, Spectrochim. Acta, Part A 56 (2000) 2645. [41] C. Djordjevic, S.A. Craig, E. Sinn, Inorg. Chem. 24 (1985) 1283. [42] K. Sheng, G. Korenowski, J. Phys. Chem. 92 (1988) 50.
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Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Structural analysis and photoluminescence properties of low dimensional lanthanide tetracyanometallates Milorad Stojanovic a, Nicholas J. Robinson a, Zerihun Assefa b, Richard E. Sykora a,⇑ a b
Department of Chemistry, University of South Alabama, Mobile, AL 36688, USA Department of Chemistry, North Carolina A&T State University, Greensboro, NC 27411, USA
a r t i c l e
i n f o
Article history: Received 20 December 2010 Accepted 3 July 2011 Available online 12 July 2011 Keywords: Lanthanide Tetracyanoplatinate Tetracyanopalladate Single-crystal X-ray diffraction Photoluminescence
a b s t r a c t The synthesis of a number of lanthanide tetracyanometallate (TCM) compounds have been carried out by reaction of Ln3+ nitrate salts and potassium tetracyanometallates in solvent systems containing dimethylsulfoxide and water. These reactions result in the isolation of three distinct structure types: (1) monoclinic [Ln(DMSO)4(H2O)3M(CN)4](M(CN)4)0.52H2O (Ln = Eu, Tb and M = Pd, Pt), (2) orthorhombic {La(DMSO)3 (H2O)2(NO3)M(CN)4}1H2O (M = Pd, Pt), and (3) orthorhombic {Ln(DMSO)3(H2O)(NO3)M(CN)4}1 (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt) in the form of single crystals. Single-crystal X-ray diffraction has been used to investigate their structural features. Structure type 1 is a zero dimensional ionic compound with a M/Ln ratio of 1.5:1. It contains coordinated as well as uncoordinated [M(CN)4]2 (M = Pd, Pt) anions and features relatively long platinophilic interactions. Structure types 2 and 3 differ quite drastically from structure type 1, but they are very similar to each other. Both of the latter are one-dimensional in nature due to chains containing linkage of Ln3+ coordination spheres with trans-bridging [M(CN)4]2 anions. These coordination polymers both have a M/Ln ratio of 1:1, a lack of platinophilic interactions, and incorporation of a bidentate NO3 for charge balance. Photoluminescence properties for select Eu3+ and Tb3+ compounds have been investigated. They show characteristic absorption and emission for the Ln3+ ions, but no significant influence of the tetracyanometallate anions. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Cyanide-bridged lanthanide-transition-metal compounds have been an interesting area of research because of their potential magnetic, optical and catalytic properties. While magnetic applications predominantly involve first row transition metal hexacyanides or the Prussian blue like compounds [1–5], catalytic [6–9] and optical [10,11] applications have been the focus regarding the lanthanide tetracyanometallates of Pt, Pd, and Ni. Much of the synthetic, structural and catalytic work in this area has been done by the Shore group [5,6,9,12–17]. Some of our previous work as well as a current research focus of our group is to synthesize cyanide-bridged lanthanide/noble-metal cyanides containing additional chromophoric ligands, such as 2,20 :60 ,200 -terpyridine [18–20], that can cooperatively photosensitize lanthanide ion luminescence. The lanthanide tetracyanometallate compounds that will be discussed in this paper were initially created while attempting to synthesize cyanide-bridged lanthanide/ ⇑ Corresponding author. Address: Department of Chemistry, University of South Alabama, Chemistry Building, Room 223, Mobile, AL 36688, USA. Tel.: +1 251 460 7422; fax: +1 251 460 7359. E-mail addresses: [email protected] (M. Stojanovic), njr301@ jaguar1.usouthal.edu (N.J. Robinson), [email protected] (Z. Assefa), rsykora@ southalabama.edu (R.E. Sykora). 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.07.002
noble-metal complexes with 2,20 -bipyridine as a chromophoric ligand. They are structurally quite similar to many compounds reported previously by Shore including {(DMF)10Yb2[Pd(CN)4]3}1 [6], {[(DMF)16Yb6(l6-O)(l3-OH)8(l-NC)Pd(l-CN)(CN)2] [Pd(CN)4]34D MF}1 [17], and {(DMF)12Ce2[Pd(CN)4]3}1 [15]. While the bulk of these and related tetracyanometallate compounds prepared by Shore contain dimethylformamide or dimethylacetamide, we have focused on using solvent systems containing dimethylsulfoxide and water. One very important similarity to Shore’s compounds, produced in DMF or DMA, and our related DMSO compounds is the general lack of strong metallophilic (in particular Pt Pt) interactions [15,16]. These are quite different results from past research on lanthanide tetracyanoplatinates prepared in aqueous solution where many compounds [21–26] have been explored that contain pseudo-1-D columnar stacks of tetracyanoplatinate anions with very short Pt Pt distances as a dominant structural feature [27,28]. Such compounds exhibit luminescent properties which are caused by the Pt Pt interactions occurring between the adjacent anions via an intra-chain donor–acceptor interaction [29]. It has been established that the luminescence occurs as a result of excitation from the donor a1g (Pt–5dz2) to the acceptor a2u (Pt–6pz, CN–p⁄) in the electronic structure of the Pt Pt interaction. Several studies have shown that a strong correlation exists between the observed
M. Stojanovic et al. / Inorganica Chimica Acta 376 (2011) 414–421
structural and optical properties in tetracyanoplatinate materials [21,28]. The spectroscopic properties (absorption and luminescence) of the salts are strongly dependent on the Pt Pt distances (3 to 3.8 Å) [26]. Some experiments have shown that those distances, and hence the associated spectroscopic properties, can be tuned by chemical and physical variations such as choice of counter cation [29] or applied pressure [23]. In this paper we report three novel lanthanide tetracyanometallate structure types that are all structurally low dimensional. Abbreviations that note the Ln element, noble-metal element, and structural family (e.g. EuPt1 for the Eu–Pt compound in structure type (1)) are used to simplify the presentation. Structural families include: (1) monoclinic [Ln(DMSO)4(H2O)3M(CN)4](M(CN)4)0.5 2H2O (Ln = Eu, Tb and M = Pd, Pt), (2) orthorhombic {La(DMSO)3(H2O)2(NO3)M(CN)4}1H2O (M = Pd, Pt), and (3) orthorhombic {Ln(DMSO)3(H2O)(NO3)M(CN)4}1 (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt). Synthetic routes, structural trends, and select photoluminescence properties are reported for isostructural members of these classes of compounds. 2. Experimental 2.1. Materials and methods La(NO3)36H2O (Strem, 99.9%), Eu(NO3)36H2O (Strem, 99.9%), Tb(NO3)3xH2O (Strem 99.9%), Er(NO3)36H2O (Strem, 99.9%), Yb(NO3)35H2O (Strem, 99.9%), K2Pt(CN)43H2O (Alfa Aesar, 99.9%), and K2Pd(CN)4xH2O (Alfa Aesar, 99.9%) were used as received without further purification. The reactions reported produced the highest observed yields of the respective compounds. IR spectra were obtained on neat crystalline samples at room temperature using a Jasco FT/IR-4100 with an ATR attachment. 2.2. Synthesis 2.2.1. [Ln(DMSO)4(H2O)3M(CN)4](M(CN)4)0.52H2O (Ln = Eu, Tb and M = Pd, Pt) All four reported compounds in structure type 1 were created by mixing 1 mL of a 0.10 M solution of the appropriate lanthanide nitrate in DMSO and 1 mL of 0.10 M K2[Pd(CN)4] or K2[Pt(CN)4] in H2O. Slow evaporation of the solvent over a period of 10–14 days resulted in crystallization of colorless needle shaped crystals. The recovered yield was in the range of 53–61%. Percent yields as well as IR data for individual compounds are provided in Supplementary material. 2.2.2. {La(DMSO)3(H2O)2(NO3)M(CN)4}1H2O (M = Pd, Pt) LaPd2 and LaPt2 were created by mixing 1 mL of a 0.10 M solution of lanthanum nitrate in DMSO and 1 mL of 0.10 M K2[Pd(CN)4] or K2[Pt(CN)4] in H2O. Slow evaporation of the solvent over a period of 17–21 days resulted in crystallization of colorless plate shaped crystals. The recovered yield was in the range of 66–69%. Percent yields as well as IR data for individual compounds are provided in Supplementary material. 2.2.3. {Ln(DMSO)3(H2O)(NO3)M(CN)4}1 (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt) All four compounds of structure type 3 were created by mixing 1 mL of a 0.10 M solution of the appropriate lanthanide nitrate in DMSO and 1 mL of 0.10 M K2[Pd(CN)4] or K2[Pt(CN)4] in H2O. Slow evaporation of the solvent over a period of 17–21 days resulted in crystallization of colorless plate shaped crystals. The recovered yield was in the range of 53–66%. Percent yields as well as IR data for individual compounds are provided in Supplementary material.
415
2.3. Single-crystal X-ray diffraction studies Single crystals of the title compounds were selected, mounted on quartz fibers, and aligned with a digital camera on a Varian Oxford Xcalibur E single-crystal X-ray diffractometer. Intensity measurements were performed using Mo Ka radiation, from a sealed-tube Enhance X-ray source, and an Eos area detector. CrysAlisPro [30] was used for preliminary determination of the cell constants, data collection strategy, and for data collection control. Following data collection, CrysAlisPro was also used to integrate the reflection intensities, apply an absorption correction to the data, and perform a global cell refinement. For all structure analyses, the program suite SHELX was used for structure solution (XS) and least-squares refinement (XL) [31]. The initial structure solutions were carried out using direct methods and the remaining atomic positions were located in difference maps. All three structures contain some disorder in the DMSO solvent molecules. The refinements were constrained such that the partial occupancies of disordered sites summed to full occupancy. Some crystallographic details are listed in Tables 1–3. 2.4. Photoluminescence studies The luminescence data were collected using a Photon Technology International (PTI) QM-3 spectrometer. The PTI system utilizes both a pulsed and a steady-state Xe source for excitation and can be used to determine steady-state emission and excitation profiles and to conduct lifetime measurements. Selection of excitation and emission wavelengths are conducted by means of computer controlled autocalibrated ‘‘QuadraScopic’’ monochromators that are equipped with aberration corrected emission and excitation optics. Signal detection is accomplished with a PMT detector (model 928 tube) that can work either in analog or digital (photon counting) modes. All of the photoluminescence experiments were conducted at room temperature on neat crystalline samples held in sealed quartz capillary tubes. 3. Results and discussion 3.1. Synthesis Three different structure types that will be described shortly were all created under similar conditions. Structure type (1) was initially created by mixing 1 mL of a 0.10 M solution of Ln(NO3)3 in DMSO, 1 mL of 0.10 M K2[Pd(CN)4] or K2[Pt(CN)4] in H2O, and 1 mL of 0.10 M 2,20 -bipyridine in 19/1 mixture H2O/EtOH. After several days, needle-like crystals of LnM1 are isolated as well as microcrystalline 2,20 -bipyridine. This structure type can also be prepared without bipyridine present as was described in the experimental section. Structure type 1 has been observed with both Eu and Tb. LaPd2 and LaPt2 has been observed only with La, the structural difference presumably is a result of the larger La3+ ion since the reactions to produce these compounds are otherwise identical. {Ln(DMSO)3(H2O)(NO3)(Pt(CN)4)}1 (Ln = Tb, Er, Yb) and the Pd analog, (TbPd3), were created with the smaller lanthanide cations, Tb3+, Er3+, Yb3+. Reactions involving Tb3+ and [M(CN)4]2 form both structure types 1 and 3, similar to {(DMF)10Sm2[Ni(CN)4]3} [15] where two different structure types were isolated from one reaction. 3.2. Structures of [Ln(DMSO)4(H2O)3M(CN)4](M(CN)4)0.52H2O (Ln = Eu, Tb and M = Pd, Pt) (1) Since all compounds of formula [Ln(DMSO)4(H2O)3M(CN)4] (M(CN)4)0.52H2O are isostructural, the structures will be discussed
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Table 1 Crystallographic data for [Ln(DMSO)4(H2O)3M(CN)4](M(CN)4)0.52H2O (Ln = La, Eu, Tb; M = Pd, Pt). Compound code
EuPd1
EuPt1
TbPd1
TbPt1
Formula mass (amu) Color Crystal system Space group a (Å) b (Å) c (Å) F D
870.27 colorless triclinic (no. 2) P1 10.6687(8) 10.8590(7) 15.7951(8) 88.683(4) 73.590(5) 64.849(7) 1579.0(2) 2 290 0.71073 51.36 1.830 3.124 23 997 5961 5961/6/378 0.0236 0.0512
1003.31 colorless triclinic (no. 2) P1 10.6353(4) 10.8518(4) 15.7858(4) 88.632(2) 73.422(3) 64.938(4) 1571.84(11) 2 290 0.71073 51.36 2.120 8.948 28 233 5940 5940/6/379 0.0332 0.0860
877.23 colorless triclinic (no. 2) P1 10.6607(3) 10.8559(3) 15.7775(5) 88.809(2) 73.650(3) 64.812(3) 1575.17(8) 2 290 0.71073 51.36 1.850 3.385 23 155 5949 5949/6/378 0.0269 0.0652
1010.27 colorless triclinic (no. 2) P1 10.6239(3) 10.8215(3) 15.7717(3) 88.682(2) 73.466(2) 64.984(2) 1565.26(7) 2 290 0.71073 52.74 2.144 9.241 31 906 6404 6404/6/379 0.0240 0.0576
C V (Å3) Z T (K) k (Å) 2hmax qcalcd (g cm3) l (Mo Ka) (mm1) Reflections collected Independent reflections Data/restraints/parameters R(F) for Fo2 > 2r (Fo2)a Rw(Fo2)b a b
P P RðFÞ ¼ hjjF o j jF c jj= jF o j. i1=2 P P 2 2 Rw ðF o Þ ¼ ½wðF o F 2c Þ2 = wF 4o .
Table 2 Crystallographic data for {La(DMSO)3(H2O)2(NO3)M(CN)4}1H2O (M = Pd, Pt).
a b
Compound code
LaPd2
LaPt2
Formula mass (amu) Color Crystal system Space group a (Å) b (Å) c (Å) V (Å3) Z T (K) k (Å) 2hmax qcalcd (g cm3) l (Mo Ka) (mm1) Reflections collected Independent reflections Data/restraints/parameters R(F) for Fo2 > 2r (Fo2)a Rw(Fo2)b
699.83 colorless orthorhombic Pnma (no. 22) 17.9048(5) 15.1738(3) 9.3874(2) 2550.41(10) 4 290 0.71073 51.36 1.823 2.647 10 462 2516 2516/13/194 0.0190 0.0468
788.52 colorless orthorhombic Pnma (no. 22) 17.9283(7) 15.1865(7) 9.3721(4) 2551.72(19) 4 290 0.71073 51.44 2.053 7.417 12 905 2523 2523/13/181 0.0294 0.0782
P P RðFÞ ¼ hjjF o j jF c jj= jF o j. i1=2 P P Rw ðF 2o Þ ¼ ½wðF 2o F 2c Þ2 = wF 4o .
together using EuPt1 as the representative. The structure of EuPt1 is ionic in nature and consists of [Eu(DMSO)4(H2O)3Pt(CN)4]+ complex cations crystallized with Pt(CN)42 anions (Fig. 1) in a stoichiometry of 2:1. The distorted square antiprismatic coordination geometry around each Eu3+ center results from four monodentate DMSO molecules (two of them disordered because of the sulfur split site), three monodentate water molecules and one coordinated (monodentate) TCP, which provide a total of eight inner sphere atoms around the Eu3+ site. The structure is completed with the uncoordinated Pt(CN)42 anions and water molecules of hydration. Select bond distances for EuPt1 can be found in Table 4. Average Eu–N and Eu–O distances in EuPt1 are longer than the comparable Tb–N and Tb–O distances in TbPt1 as expected based on ionic radii differences [32]. The distances between Eu3+ and the various coordinating ligands within EuPt1 also show a clear trend. The longest distance is the Eu–N distance between Eu and the [Pt(CN)4]2 ligand (2.549(5) Å). Eu–O distances to the water molecules
(average of 2.436 Å) are longer than Eu–O bonds to the DMSO (average value of 2.358 Å). Pt–C distances vary little, ranging from 1.979(7) to 1.993(6) Å. They are slightly shorter than Pd–C distances which range from 1.985(4) to 2.003(4) Å. All of these bond distances are within normal ranges as found in previously reported lanthanide tetracyanoplatinate [15,21,33] and tetracyanopalladate structures [12]. In terms of packing, this zero-dimensional structure (Fig. 2) consists of TCP dimers, formed from coordinated TCP anions, where Pt atoms within each dimer are separated by 3.6390(3) Å. This Pt Pt distance is somewhat longer than previously reported distances in other lanthanide tetracyanoplatinates [34], which range from 3.3 to 3.5 Å. The dimers assemble with their Pt1 Pt10 interactions oriented along the a axis with inter-dimer distances of 7.0830(5) Å, this latter distance is too long to be considered an important platinophilic interaction. The dimer formation in this compound differs from similar TCP compounds reported in the past [21–26] which contain pseudo-1-D columnar stacks of tetracyanoplatinate anions with extended platinophilic interactions. The reason for this difference is the presence of multiple bulky DMSO molecules coordinated to the Ln3+ coordination spheres which interrupt true 1-D Pt chain formation in EuPt1. The uncoordinated Pt(CN)42 anions are positioned perpendicular to the dimers with average Pt Pt distances of 7.5890(3) Å. Within the structure, there are multiple hydrogen bonding interactions between O–H donors from the coordinated and uncoordinated water molecules and nitrogen acceptors of the [Pt(CN)4]2 anions and oxygen acceptors of uncoordinated water molecules. 3.3. Structure of {La(DMSO)3(H2O)2(NO3)M(CN)4}1H2O (M = Pd (LaPd2), Pt (LaPt2)) La3+ forms structure type 2, presumably due to its larger size relative to Eu3+ and Tb3+, which form structure type 1. {La(DMSO)3(H2O)2(NO3)M(CN)4}1H2O (Fig. 3) has several significant differences from structure type (1). The coordination geometry around each La3+ center in the type (2) structure is a nine coordinate tri-capped trigonal prism where one DMSO and one water molecule have been replaced by a bidentate NO3 anion, relative to structure type 1. Additionally, La3+ coordinates two [M(CN)4]2
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M. Stojanovic et al. / Inorganica Chimica Acta 376 (2011) 414–421 Table 3 Crystallographic data for {Ln(DMSO)3(H2O)(NO3)M(CN)4}1 (Ln = Tb, M = Pd, Pt; Ln = Er, Yb; M = Pt).
a b
Compound code
TbPd3
TbPt3
ErPt3
YbPt3
Formula mass (amu) Color Crystal system Space group a (Å) b (Å) c (Å) V (Å3) Z T (K) k (Å) 2hmax qcalcd (g cm3) l (Mo Ka) (mm1) Reflections collected Independent reflections Data/restraints/parameters R(F) for Fo2 > 2r (Fo2)a Rw(Fo2)b
683.81 colorless orthorhombic Pnma (no. 22) 19.5259(5) 15.7186(3) 7.4866(2) 2297.79(10) 4 290 0.71073 51.36 1.977 4.145 9555 2258 2258/4/140 0.0362 0.0977
772.50 colorless orthorhombic Pnma (no. 22) 19.5619(8) 15.7329(8) 7.4420(4) 2290.39(19) 4 290 0.71073 51.40 2.240 9.474 11 820 2247 2247/4/141 0.0279 0.0769
780.84 colorless orthorhombic Pnma (no. 22) 19.4456(8) 15.6345(8) 7.4270(4) 2257.97(19) 4 290 0.71073 51.32 2.297 10.195 11 521 2218 2218/4/141 0.0378 0.1017
786.62 colorless orthorhombic Pnma (no. 22) 19.4345(5) 15.5735(4) 7.4435(3) 2252.87(12) 4 290 0.71073 51.46 2.319 10.644 10 428 2226 2226/4/140 0.0422 0.1152
P P RðFÞ ¼ jjF o j jF c jj= jF o j. P P Rw ðF 2o Þ ¼ ½ ½wðF 2o F 2c Þ2 = wF 4o 1=2 .
Table 4 Selected bond distances (Å) for [Eu(DMSO)4(H2O)3Pt(CN)4](Pt(CN)4)0.52H2O (EuPt1). Eu1–O1 Eu1–O2 Eu1–O3 Eu1–O4 Eu1–O5 Eu1–O6 Eu1–O9
2.433(4) 2.406(4) 2.468(4) 2.371(4) 2.390(4) 2.323(4) 2.347(5)
Eu1–N1 Pt1–C1 Pt1–C2 Pt1–C3 Pt1–C4 Pt1–C5 (x2) Pt1–C6 (x2)
2.549(5) 1.988(6) 1.993(6) 1.989(7) 1.983(6) 1.993(6) 1.979(7)
Fig. 2. Packing diagram for EuPt1 showing dimers of coordinated [Pt(CN)4]2and the uncoordinated [Pt(CN)4]2, approximately perpendicular to each other. In addition, the hydrogen atoms from the water molecules serve as H-bond donors to nitrogen atoms of the [Pt(CN)4]2 anion. Disordered methyl groups from DMSO have been removed for clarity.
Fig. 1. Molecular structure of EuPt1 showing the eight coordinate Eu3+ environment and the uncoordinated Pt(CN)42 anion. Disorder of the DMSO molecules are not shown for clarity. Symmetry code: (a) 2 x, 1 y, z.
anions and the compounds have a lower M/Ln ratio than structure type (1) (1:1 compared to 1.5:1). Linkage of La3+ coordination spheres with trans-bridging Pt(CN)42 anions makes this compound one-dimensional in nature which is significantly different from the zero-dimensional ionic structure type 1. These zigzag chains (Fig. 4) are similar to those previously described in the type A compound, {(DMF)5Sm[Ni(CN)4]Cl} [35] which also contains chains formed via trans-bridging
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Fig. 3. Structural building unit of LaPt2 showing the nine coordinate La3+ cation environment. Disorder of one DMSO is shown and the others are not shown for clarity. Symmetry codes: (a) x, ½ y, z; (b) 1 x, 1 y, 1 z; (c) 1 x, ½ + y, 1 z.
tetracyanometallate anions. Whereas the bridging angle (Pt1–La1– Pt1a) within our zigzag chains in LaPt2 is 81.7°, an indication of the zigzag nature, the chains within {(DMF)5Sm[Ni(CN)4]Cl} are more linear with a bridging angle of 146.2°. The difference is attributed to the presence of slightly bulkier and distorted DMSO molecules and the bidentate nitrate anion in LaPt2. The packing diagram shows that the one-dimensional chains are stacked parallel to each other in the structure. Additionally, an uncoordinated water molecule is positioned between the chains. It contains two types of hydrogen bonding interactions. First, water molecules coordinated to the lanthanide serves as Hdonors to the oxygen of the uncoordinated water molecule and second, hydrogens of the uncoordinated water molecule serve as H-bond donors to nitrogen acceptors of the [Pt(CN)4]2 anions. The trends in La–O(H2O), La–O(DMSO), and La–N bond distances, which are given in Table 5, are equivalent to those that have been previously described for structure type (1).
Fig. 4. Packing of one-dimensional zigzag chains in LaPt2, illustrating the transbridging of La3+ by Pt(CN)42 anions. Additionally, an uncoordinated water molecule is located between the chains. Hydrogen atoms from the coordinated as well as uncoordinated water molecules serve as H-bond donors to nitrogen atoms of the [Pt(CN)4]2 anion and to oxygen atoms of uncoordinated water molecules. Only one orientation of the disordered DMSO molecules, with H-atoms removed, are shown for clarity.
Table 5 Selected bond distances (Å) for {La(DMSO)3(H2O)2(NO3)Pt(CN)4}1H2O (LaPt2). La1–O2 (x2) La1–O3 La1–O4 La1–O6
2.638(4) 2.531(5) 2.554(5) 2.450(5)
La1–O7 (x2) La1–N1 (x2) Pt1–C1 (x2) Pt1–C2 (x2)
2.451(3) 2.691(5) 1.979(5) 1.966(5)
3.4. Structure of {Ln(DMSO)3(H2O)(NO3)M(CN)4}1 (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt) (3) While La forms structure type (2) in these systems, smaller lanthanides form structure type 3, {Ln(DMSO)3(H2O)(NO3)(M(CN)4)}1 (Ln = Tb and M = Pd, Pt; Ln = Er, Yb and M = Pt) (Fig. 5). These two structure types are very similar. TbPt3 will be used as a representative member to describe structure type 3. The coordination geometry around each Tb3+ center is an eight coordinate distorted square antiprism made of three DMSO molecules, a bidentate nitrate anion, a water molecule, and two TCP anions. The reduced number of coordinated water molecules relative to the La3+ cations in LaPt2, which reduces the Tb3+ coordination number to eight, is consistent with the smaller size of the heavier lanthanides. Whereas the larger lanthanides are usually nine coordinate, smaller lanthanides are often eight coordinate [36]. The structure also forms one-dimensional chains due to TCP bridging of Tb3+ coordination spheres in a ‘‘trans’’ orientation very reminiscent of the chains in structure type 2. The Pt1–Tb1–Pt1a
Fig. 5. The one-dimensional chains in TbPt3 are very similar to those in structure type 2. The H-bonding interactions between the chains are the major difference due to the reduced water content in TbPt3. Symmetry codes: (a) x, ½ y, z; (b) x, y, z; (c) x, ½ + y, z.
bridging angle of 89.9° is larger than the (Pt1–La1–Pt1a) angle of LaPt2, largely because Tb3+ is smaller than La3+ and because of reduced number of coordinated water molecules relative to LaPt2 as noted above.
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shifted relative to some Eu3+ systems, and signifies a strong electric dipole contribution in EuPt1. While observance of this 0–0 transition usually indicates a low symmetry site occupation for the Eu3+ ion, the existence of a single band for this transition is indicative of a single site occupation for the Eu3+ ion, even at the luminescence time scale. This observation is consistent with the crystallographic result that shows a single (C1) site occupation for Eu3+. The complete removal of the degeneracy of the 5D0 ? 7F1 transition and observance of three Stark components is also consistent with a low symmetry site (C1) occupation [40,41]. In EuPt1 the overall 7 F1 splitting is 260 cm1. The most intense transition, 5D0 ? 7F2, does not show the expected splitting into five Stark components at room temperature, however at 77 K splitting of this band does occur. Although the overall emission profile of EuPd1 is similar to that described for the platinum system, some subtle differences are prevalent. The major difference lies in the ratios of the emission intensities of the electric dipole versus magnetic dipole allowed transitions. A qualitative picture of the extent of covalency in the crystal field can be obtained by comparing the ratio of the intensity of the hypersensitive 5D0 ? 7F2 transition to that of the magnetic dipole 5D0 ? 7F1 transition [42–48] as this ratio is closely correlated with the polarizability of the coordination sphere. For EuPt1 and EuPd1, these ratios are 3.2 and 1.7, respectively, indicating the dominant role of the electric dipole component in the former. Since the cyanides are the common ligands in both cases, the differences in the ratio can be attributed to the difference in the central transition metal atom’s ability to withdraw electron density from the CN ligand. The experimental data appears to suggest that the Pd system withdraws electron density from the cyanide ligands more than the Pt system and decreases the electrostatic contribution to the Eu3+ ion. Moreover, the difference in lifetimes of the Eu3+ emission from the two complexes, 394 ls for EuPt1 versus 271 ls for EuPd1, can also be explained by this rationale. Nevertheless, it is important to note that other features of the emission behavior remain almost identical for EuPt1 and EuPd1, including the extent of splitting of the 7F1 state (which is 260 cm1 in both compounds) and the positions of the 0–0 transitions. One reason can be attributed to the absence of or minimal M–M interactions in both systems, since a stronger M–M interaction might have induced a more effective electrostatic contribution. The excitation spectrum of EuPt1 was measured by monitoring the emission at 618 nm. Only characteristic Eu3+ absorption was observed. The individual band positions and assignments for both the emission and excitation spectra can be found in Table 7. Similar data is also provided for the EuPd1 system. Both EuPt1 and EuPd1 demonstrate excitation spectra that contain bands assignable only to the Eu3+ f–f transitions, although the compounds contain both coordinated and uncoordinated Pt(CN)42 and Pd(CN) 42 groups, respectively, in their structures. It is likely that the lack of significant metallophilicity between the tetracyanometallate groups negates the possibility of donor–acceptor energy transfer in these systems.
Table 6 Selected bond distances (Å) for {Tb(DMSO)3(H2O)(NO3)Pt(CN)4}1 (TbPt3). Tb1–O1 (x2) Tb1–O2 Tb1–O3 Tb1–O4 (x2)
2.309(4) 2.317(7) 2.347(6) 2.446(6)
Tb1–N1 (x2) Pt1–C1 (x2) Pt1–C2 (x2)
2.492(5) 1.977(6) 1.991(7)
Fig. 6. Room temperature, solid-state emission spectra of EuPt1 and TbPt1. The emission spectra were collected upon excitation of EuPt1 at 393 nm and TbPt1 at 369 nm.
The main difference in structure types 2 and 3 is in regards to the packing of the chains. There are not lattice waters of hydration in structure type 3. Therefore the reduced water content, both in terms of coordinated and uncoordinated, leads to a reduction in the number of inter-chain H-bonding interactions in TbPt3 relative to LaPt2. H-bonding interactions only exist between O–H donors, coordinated to the lanthanides, and N acceptors of the terminal nitrogen atoms of the [Pt(CN)4]2 anions in neighboring chains (Fig. 5). The trends in La–O(H2O), La–O(DMSO), and La–N bond distances, which are given in Table 6, are equivalent to those that have been previously described in structure types 1 and 2. The Ln–O and Ln–N bond distances decrease among the isostructural members of the series, consistent with the decreasing size of the Ln3+ cations [32] as also described above for structure types 1 and 2. 3.5. Photoluminescence studies The photoluminescence spectrum of EuPt1 (Fig. 6) was measured with direct excitation of the Eu3+ into the 5L6 state at 393 nm. The spectrum shows characteristic sharp f–f emissions (Table 7) originating from two different excited states [37–39]. The 0–0 transition between 5D0 ? 7F0 is observed at 577 nm, blue Table 7 Band locations (nm) and assignments for EuPd1 and EuPt1. Excitation
Emission
Assignment 5
EuPd1
7
H3 F0 7 L10 F0 7 D4 F0 5 5 L7, G(3.2) 5 7 L6 F0 5 7 D3 F0 5 5
7
F0
317 339 362, 366 375, 380, 384 394 416
EuPt1
Assignment
EuPd1
EuPt1
317 346 360, 365 374, 381 393 415
5
524 534 551, 555 577 582.3588.7590.7 612, 617 649, 652 690, 697
524 535 551, 556 577 582.3588.5591.2 612, 618 650, 652 689, 698
7
D1 ? F 0 D1 ? 7F1 D1 ? 7F2 5 D0 ? 7F0 5 D0 ? 7F1 5 D0 ? 7F2 5 D0 ? 7F3 5 D0 ? 7F4 5 5
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Table 8 Band locations (nm) and assignments for TbPd1 and TbPt1. Excitation
Acknowledgments
Emission
Assignment
TbPd1
TbPt1
Assignment
TbPd1
TbPt1
5
D1 5 D2
7
D4 ? 7 F 6 5 D4 ? 7 F 5
487 541
488 543
7
317, 327 341, 351, 359 369, 377
5
5
319, 328 342, 351, 359 369, 377
5
581, 586 619
583, 587 618, 620 645, 652 667 678
D3
F6 7 F6 F6
D4 ? 7 F 4
5
D4 ? 7 F 3
5
D4 ? 7 F 2
5
7
D4 ? F 1 D4 ? 7 F 0
5
643, 651 667 677
The emission spectrum of TbPt1 (Fig. 6) (band locations and assignments given in Table 8) was measured at an excitation wavelength of 369 nm. The spectrum shows characteristic green Tb3+ emission [49,50] which displays the full range of 5D4 ? 7FJ (J = 0– 6) transitions. The strongest emission band is located at 543 nm which is a characteristic band for the Tb3+ 5D4 ? 7F5 transition [41]. This emission band in TbPt1 has a lifetime of 1 ms, whereas the comparable band in TbPd1 has a lifetime of 953 ls. The excitation spectrum of TbPt1 was measured by monitoring the Tb3+ emission at 543 nm. Both the TbPt1 and TbPd1 complexes display nearly identical excitation profiles, with only minor changes in the band positions and/or relative intensities. As was the case with EuPt1, the excitation spectra provide only characteristic Ln3+ absorption bands displaying Tb3+ 7F6 ? 5DJ (J = 0–4) transitions which are tabulated in Table 8. Apart from the characteristic f–f transitions a very weak and broad band located at 415 nm is also evident in the emission spectra of both TbPt1 and EuPt1. These bands display excitation maxima of 285 nm. While these bands cannot be assigned to any Ln3+ ion f–f transitions, they most likely correspond to excitation/emission associated with the Pt(CN)42 groups. Potential broad MMLCT-based Pt(CN)42 emission and excitation bands, around 500 and 385 nm, respectively [51], are not present in EuPt1 and TbPt1. Such bands have been well established for compounds that contain one-dimensional stacks of Pt(CN)42 with short Pt Pt distances of 3.1–3.3 Å [26] or for compounds that have slightly longer Pt Pt distances (3.5 Å) in dimeric TCP units [34]. In the present case the Pt Pt distance of 3.6390(3) Å between the TCP dimers of EuPt1 and TbPt1 proved to be too long to observe any MMLCT-based bands. Finally, excitation and emission spectra for EuPt3 were also obtained to probe for possible donor–acceptor energy transfer, but none was observed, or expected, considering that EuPt3 does not have any Pt Pt distances shorter than 7 Å. Only Eu3+ based emission via direct excitation was observed, similar to that reported for EuPt1. 4. Conclusion Reactions of Ln(NO3)3 and [M(CN)4]2 (M = Pd and Pt) in DMSO/ H2O solvent system have created three different structure types. Structure type 1 is a zero-dimensional ionic compound while structure types 2 and 3 are one dimensional. Tb3+ forms structure type 1 as well as structure type 3. Introduction of DMSO has prevented forming of strong Pt Pt interactions and thus directly influenced the photoluminescent properties compared to the hydrated lanthanide tetracyanoplatinates. Photoluminescence studies of Eu3+ and Tb3+ of structure type (1) have shown characteristic Eu3+ and Tb3+ emission and absorption bands as well as lack donor–acceptor energy transfer between tetracyanometallate ligands and Ln3+ cations.
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