Reduction of structural dimensionality through incorporation of auxiliary ligands in lanthanide tetracyanoplatinates

Inorganica Chimica Acta 370 (2011) 513–518

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Reduction of structural dimensionality through incorporation of auxiliary ligands in lanthanide tetracyanoplatinates Milorad Stojanovic, Nicholas J. Robinson, Xi Chen, Richard E. Sykora ⇑ Department of Chemistry, University of South Alabama, 6040 USA Drive South, Chemistry Building, Room 223, Mobile, AL 36688, USA

a r t i c l e

i n f o

Article history: Received 2 December 2010 Accepted 25 February 2011 Available online 4 March 2011 Keywords: Lanthanide Tetracyanoplatinate 1,10-Phenanthroline 2,20 -Bipyridine Auxiliary ligand Single-crystal X-ray diffraction

a b s t r a c t The synthesis of a series of lanthanide tetracyanoplatinates containing the auxiliary ligands 1,100 phenanthroline (phen) or 2,20 -bipyridine (bpy) have been carried out by reaction of Ln3+ nitrate salts with phen or bpy and potassium tetracyanoplatinate in solvent systems containing dimethylsulfoxide and dimethylformamide. The use of these solvents has lead to the isolation of [{Ln(DMSO)2(C12H8N2)(H2O)3}2Pt(CN)4](Pt(CN)4)22C12H8N24H2O (Ln = Eu (Eu-1), Tb (Tb-1), Yb(Yb-1)), [Ln(DMF)3(C12H8N2)(H2O)2NO3]Pt(CN)4 (Ln = La (La-2), Eu (Eu-2), Tb (Tb-2)), and [Ln(DMF)3(C10H8N2)(H2O)2NO3]Pt(CN)4 (Ln = La (La-3), Sm (Sm-3), Eu (Eu-3), Tb (Tb-3)) in the form of single crystals. Single-crystal X-ray diffraction has been used to investigate their structural features. The use of DMSO versus DMF as the solvent results in markedly different structural features. Eu-1 contains [{Eu(DMSO)2(C12H8N2)(H2O)3}2Pt(CN)4]2+ complex cations where the two Eu3+ centers are linked by a trans-bridging Pt(CN)42 anion to form a dimeric lanthanide complex cation. An additional uncoordinated Pt(CN)42 anion balances charge. Eu-2 and Eu-3 consist of zero-dimensional salts with [Eu(DMF)3(C12H8N2)(H2O)2(NO3)]2+ or [Eu(DMF)3(C10H8N2)(H2O)2(NO3)]2+ complex cations, respectively, and only non-coordinated Pt(CN)42 anions. Photoluminescence measurements illustrate that the Eu3+ and Tb3+ compounds for all three structure types display enhanced emission due to intramolecular energy transfer from the coordinated cyclic amines. Ó 2011 Elsevier B.V. All rights reserved.

1. Introduction A combination of the interesting structural and materials’ properties of cyanide-bridged, bimetallic f–d compounds have made this area heavily explored [1–4]. While magnetic applications predominantly involve transition-metal hexacyanides or the Prussian blue type compounds [5–9], catalytic and optical applications have been the focus regarding the tetracyanometallates of Pt, Pd, and Ni [10–24,25]. A wealth of synthetic [16–21], structural [17,19–21,25], spectroscopic [22–25], and catalytic [10–13,18] studies on lanthanide tetracyanometallates have been reported by the groups of Gliemann and Shore. One of our recent interests involves exploring the synthesis, structural chemistry, and spectroscopic properties of novel lanthanide compounds that incorporate two different ligand groups that can both undergo energy transfer to Ln3+ cations. Cooperative enhancement of the relatively weak Ln3+ emissions by these multiple donors is one goal. Recent efforts have focused on preparing Ln3+ compounds that contain both tetracyanoplatinate (TCP) and the auxiliary tridentate ligand 2,20 :60 ,200 -terpyridine, since each of these ⇑ Corresponding author. 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] (X. Chen), [email protected] (R.E. Sykora). 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.02.077

ligands have been shown to act as sensitizers for Ln3+ cations previously [22–31]. In compounds such as Eu(C15H11N3)(H2O)2(NO3)(Pt(CN)4)CH3CN and {Eu(C15H11N3)(H2O)3}2(Pt(CN)4)32H2O [32] where both donor groups have been simultaneously coordinated to a given Eu3+ cation, the emission from the Eu3+ has been shown to be enhanced, relative to direct Eu3+ excitation, via energy transfer by exciting either donor ligand. However, in cases where the 2,20 :60 ,200 -terpyridine ligand is coordinated to Eu3+ but the TCP anion is not [32,33], e.g. in [Eu(C15H11N3)(H2O)2(CH3COO)2]2Pt(CN)43H2O, emission enhancement of the Eu3+ cation was only observed by excitation of the terpy ligand. Our current work has been to explore alternate possibilities for the auxiliary multidentate ligand incorporated into the lanthanide tetracyanoplatinate frameworks in our materials. For various reasons, 2,20 -bipyridine (bpy) and 1,10-phenanthroline (phen) are being studied. First, both of these are chelating ligands that are known to readily coordinate in a bidentate fashion with Ln3+ cations [34–37] making them ideal candidates to incorporate into our materials. Second, and more importantly, both ligands are known to participate in ligand-to-metal charge transfer (LMCT) and thus enhance emission of Ln3+ (acceptor) cations via ligand (donor) excitation. In the case of bpy [38–40], LMCT and enhancement of luminescence intensity has been attributed to ligand chelation to the Ln3+ ion, which can effectively increase the rigidity of coordination polymers and reduce the loss of energy by

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radiationless decay. Additionally, enhancement in the excitedstate lifetime has been observed [39]. In addition, phen can act as a light harvesting module (antenna) due to its intense and tunable UV–Vis absorption features [41]. By means of this strategy, efficient sensitization of emission by acceptor cations via ligand absorption followed by energy transfer is accomplished [42]. Additionally, Ln3+–phenanthroline complexes have also been tested in solid-state matrices leading to remarkable luminescence performances [43,44]. Many of the previous lanthanide TCP compounds synthesized by the groups of Gliemann or Shore tend to be low-dimensional coordination polymers [19,45,46]. These compounds can be grouped into two broad classes: (1) those that contain pseudoone-dimensional chains consisting of planar TCP anions with short Pt  Pt (platinophilic) interactions and (2) compounds lacking Pt  Pt interactions. Whereas the former compounds tend to be heavily hydrated [25,45], the latter are typically anhydrous compounds solvated with DMF or DMA [19,46]. Herein we report on three lanthanide TCP structure types that incorporate bpy or phen auxiliary ligands, [{Ln(DMSO)2(C12H8N2)(H2O)3}2Pt(CN)4](Pt(CN)4)22C12H8N24H2O (Ln = Eu (Eu-1), Tb (Tb-1), Yb(Yb-1)), [Ln(DMF)3(C12H8N2)(H2O)2NO3]Pt(CN)4 (Ln = La (La-2), Eu (Eu-2), Tb (Tb-2)), and [Ln(DMF)3(C10H8N2)(H2O)2NO3]Pt(CN)4 (Ln = La (La-3), Sm (Sm-3), Eu (Eu-3), Tb (Tb-3)). Introducing these auxiliary ligands to the lanthanide TCP system has resulted in the isolation of the title compounds as zero-dimensional salts. The synthetic route, structures, and photoluminescence properties for representative members of these classes are discussed.

1,10-phenanthroline in a 20%:80% H2O:CH3CN solvent system. Slow evaporation of the solvent over a period of several days resulted in crystallization of plate-shaped crystals with yields varying from 33% to 48%, depending on the lanthanide used for the synthesis. Supplementary material contains detailed synthetic information, % yield, and IR data for each of the compounds. Representative IR (Eu-2, solid, cm1): 3331 (w, br), 2168 (s), 2037 (w, br), 1662 (w), 1472 (s), 1424 (s), 1308 (s), 1144 (m), 1105 (m), 1030 (m), 845 (s), 774 (m), 727 (s).

2. Experimental

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 [47] 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) [48]. The initial structure solutions were carried out using direct methods and the remaining atomic positions were located in difference maps. One of the DMF molecules in the Ln-2 and Ln-3 structure types is disordered over two orientations. The atomic sites were constrained such that the partial occupancies of the disordered atoms summed to full occupancy. The final refinements included anisotropic displacement parameters for all non-hydrogen atoms except for the carbon atoms on one dimethylsulfoxide in the Ln-1 structure type. Some crystallographic details are listed in Tables 1–3.

2.1. Materials and methods La(NO3)36H2O (Strem, 99.9%), Sm(NO3)36H2O (Alfa Aesar, 99.9%), Eu(NO3)36H2O (Strem, 99.9%), Tb(NO3)3xH2O (Strem, 99.9%), Yb(NO3)35H2O (Strem, 99.9%), 2,20 -bipyridine (Alfa Aesar, 99%), 1,10-phenanthroline monohydrate (Alfa Aesar, 99+%), and K2Pt(CN)43H2O (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 a diamond ATR attachment. 2.2. Synthesis of [{Ln(DMSO)2(C12H8N2)(H2O)3}2Pt(CN)4](Pt(CN)4)2 2C12H8N24H2O (C12H8N2 = 1,10-phenanthroline; Ln = Eu (Eu-1), Tb (Tb-1), Yb (Yb-1)) The syntheses of the compounds were carried out by mixing 1 mL of a 0.10 M solution of the appropriate lanthanide nitrate in DMSO, 1 mL of 0.10 M K2[Pt(CN)4] in water, and 1 mL of 0.10 M 1,10-phenanthroline in a 20%:80% H2O:CH3CN solvent system. Slow evaporation of the solvent over a period of several days resulted in crystallization of colorless plate-shaped crystals with yields of 65%. Supplementary material contains detailed synthetic information, % yield, and IR data for each of the compounds. Representative IR (Eu-1, solid, cm1): 3150 (m, br), 2171 (m), 2133 (s), 1627 (w), 1591 (w), 1520 (s), 1479 (s), 1423 (s), 1300 (w), 1223 (w), 1147 (w), 1105 (s), 1003 (s), 962 (s), 836 (s), 769 (m), 725 (s). 2.3. Synthesis of [Ln(DMF)3(C12H8N2)(H2O)2NO3]Pt(CN)4 (C12H8N2 = 1,10-phenanthroline; Ln = La (La-2), Eu (Eu-2), Tb (Tb-2)) The synthesis of each compound was carried out by mixing 1 mL of a 0.10 M solution of the appropriate lanthanide nitrate in DMF, 1 mL of 0.10 M K2[Pt(CN)4] in water, and 1 mL of 0.10 M

2.4. Synthesis of [Ln(DMF)3(C10H8N2)(H2O)2NO3]Pt(CN)4 (C10H8N2 = 2,20 -bipyridine; Ln = La (La-3), Sm (Sm-3), Eu (Eu-3), Tb (Tb-3)) The synthesis of each compound was carried out by mixing 1 mL of a 0.10 M solution of the appropriate lanthanide nitrate in DMF, 1 mL of 0.10 M K2[Pt(CN)4] in water, and 1 mL of 0.10 M 2,20 -bipyridine in a 95%:5% water:ethanol solvent system. Slow evaporation of the solvent over a period of several days resulted in crystallization of plate-shaped crystals with yields varying from 45% to 74%, depending on the lanthanide used for the synthesis. Supplementary material contains detailed synthetic information, % yield, and IR data for the individual compounds. Representative IR (Eu-3, solid, cm1): 3214 (m, br), 2170 (s), 1650 (m), 1569 (m), 1575 (w), 1476 (s), 1432 (s), 1310 (s, br), 1156 (w), 1109 (w), 1014 (s), 816 (m), 760 (s).

2.5. Single-crystal X-ray diffraction studies

2.6. Photoluminescence studies The luminescence data were collected using a Photon Technology International (PTI) QM-3 spectrometer. The PTI system utilizes a steady-state Xe source for excitation. 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.

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M. Stojanovic et al. / Inorganica Chimica Acta 370 (2011) 513–518 Table 1 Crystallographic data for [{Ln(C12H8N2)(H2O)3(DMSO)2}2Pt(CN)4](Pt(CN)4)22C12H8N24H2O (Ln = Eu, Tb, Yb). Identification c

Eu-1

Tb-1

Yb-1

Chemical formula Formula weight (amu) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z T (K) k (Å) qcalcd (g cm3) l(Mo Ka) (mm1)

C68H76Eu2N20O14Pt3S4 2414.92 triclinic  (No. 2) P1 8.8650(1) 15.6051(2) 15.6989(2) 106.008(1) 93.922(1) 94.525(1) 2071.82(4) 1 295 0.71073 1.936 6.709 0.0275

C68H76N20O14Pt3S4Tb2 2428.84 triclinic  (No. 2) P1 8.8575(3) 15.5768(6) 15.6827(5) 105.929(3) 94.108(3) 94.524(3) 2064.35(12) 1 295 0.71073 1.954 6.927 0.0315

C68H76N20O14Pt3S4Yb2 2457.08 triclinic  (No. 2) P1 8.8273(2) 15.5620(5) 15.6583(6) 105.737(3) 94.366(2) 94.600(2) 2052.92(11) 1 295 0.71073 1.987 7.521 0.0278

0.0731

0.0769

0.0738

R(Fo) for F 2o > 2r ðF 2o Þa Rw ðF 2o Þb a b

RðF o Þ ¼

P

P

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 2 Crystallographic data for [Ln(DMF)3(C12H8N2)(H2O)2NO3]Pt(CN)4 (Ln = La, Eu, Tb).

3.1. Structural similarities and differences

Identification code

La-2

Chemical formula Formula weight (amu) Crystal system Space group a (Å) b (Å) c (Å) b (°) V (Å3) Z T (K) k (Å) qcalcd (g cm3) l(Mo Ka) (mm1)

C25H33LaN10O8Pt C25EuH33N10O8Pt C25H33N10O8PtTb 935.61 948.66 955.62

R(Fo) for F 2o >

Eu-2

Tb-2

monoclinic P21/m (No. 11) 8.5882(1) 19.5666(4) 10.1355(2) 97.220(1) 1689.68(5) 2 295 0.71073 1.839 5.441 0.0239

monoclinic P21/m (No. 11) 8.5389(1) 19.3879(2) 10.1108(1) 97.087(1) 1661.07(3) 2 295 0.71073 1.897 6.136 0.0197

monoclinic P21/m (No. 11) 8.5414(2) 19.3440(5) 10.0932(3) 96.989(2) 1655.26(8) 2 295 0.71073 1.917 6.400 0.0259

0.0504

0.0421

0.0606

2r ðF 2o Þa Rw ðF 2o Þb a b

RðF o Þ ¼

P

3. Results and discussion

P

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 .

Three different isostructural families of compounds are reported with formulae [{Ln(DMSO)2(C12H8N2)(H2O)3}2Pt(CN)4](Pt(CN)4)22C12H8N24H2O (C12H8N2 = 1,10-phenanthroline; Ln = Eu (Eu-1), Tb (Tb-1), Yb (Yb-1)), [Ln(DMF)3(C12H8N2)(H2O)2NO3]Pt(CN)4 (C12H8N2 = 1,10-phenanthroline; Ln = La (La-2), Eu (Eu-2), Tb (Tb-2)), and [Ln(DMF)3(C10H8N2)(H2O)2NO3]Pt(CN)4 (C10H8N2 = 2,20 -bipyridine; Ln = La (La-3), Sm (Sm-3), Eu (Eu-3), Tb (Tb-3)), abbreviated as structure types Ln-1, Ln-2, and Ln-3, respectively. While Ln-2 and Ln-3 are not rigorously isostructural because of the substitution of phen for bipy, these compounds are otherwise very similar. All three structure types will be discussed together below using the Eu3+ member of each class as the representative. Similarities, differences, and trends among the compounds will be discussed where appropriate. The structure of Eu-1 is an ionic salt and consists of a ‘‘dimeric’’ [{Eu(DMSO)2(C12H8N2)(H2O)3}2Pt(CN)4]2+ complex cation whereby two Eu sites are linked by a trans-bridging Pt(CN)42 anion

Table 3 Crystallographic data for [Ln(DMF)3(C10H8N2)(H2O)2NO3]Pt(CN)4 (Ln = La, Sm, Eu, Tb). Identification code

La-3

Sm-3

Eu-3

Tb-3

Chemical formula Formula weight (amu) Crystal system Space group a (Å) b (Å) c (Å) b (deg.) V (Å3) Z T (K) k (Å) qcalcd (g cm3) l(Mo Ka) (mm1)

C23H33LaN10O8Pt 911.59 monoclinic P21/m (No. 11) 8.8271(10) 20.182(2) 9.3598(15) 97.666(12) 1652.5(4) 2 295 0.71073 1.832 5.560 0.0458

C23H33N10O8PtSm 923.03 monoclinic P21/m (No. 11) 8.8158(6) 20.1026(9) 9.3049(6) 98.079(6) 1632.65(17) 2 295 0.71073 1.878 6.118 0.0284

C23H33EuN10O8Pt 924.64 monoclinic P21/m (No. 11) 8.8085(3) 20.1138(7) 9.2869(3) 98.273(3) 1628.26(10) 2 295 0.71073 1.886 6.257 0.0436

C23H33N10O8PtTb 931.60 monoclinic P21/m (No. 11) 8.8051(3) 20.0486(7) 9.2540(3) 98.385(3) 1616.15(9) 2 295 0.71073 1.914 6.552 0.0207

0.1168

0.0511

0.1000

0.0342

R(Fo) for F 2o > 2r ðF 2o Þa Rw ðF 2o Þb a b

RðF o Þ ¼

P

P

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 .

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(illustrated in Fig. 1), crystallized along with an additional uncoordinated Pt(CN)42 anion, an uncoordinated phen molecule, and waters of hydration. The slightly-distorted, square-antiprismatic coordination geometry around each Eu3+ center results from one bidentate phen ligand, two O-bound DMSO molecules, three water molecules, and the N-bound Pt(CN)42 anion, which provide a total of eight inner sphere atoms around the Eu3+ site. Pt1, from the trans-bridging Pt(CN)42, is located on an inversion center and therefore both Eu coordination polyhedra in the complex cation are related by symmetry. A thermal ellipsoid plot of the asymmetric unit of Eu-2, also representative of Eu-3, with the included atomic labeling scheme is illustrated in Fig. 2. The structures of Eu-2 and Eu-3 are also zerodimensional and ionic in nature and consist of either [Eu(DMF)3(C12H8N2)(H2O)2(NO3)]2+ or [Eu(DMF)3(C10H8N2)(H2O)2(NO3)]2+ complex cations, respectively, crystallized with a Pt(CN)42 anion. The distorted tri-capped trigonal prismatic coordination geometry around each Eu3+ center results from one bidentate amine ligand, one bidentate nitrate anion, two water molecules, and three O-bound DMF molecules, which provide a total of nine inner sphere atoms around the Eu3+ sites. The largest structural difference between these latter two families of compounds and the Ln-1 family is the lack of direct Pt(CN)42 coordination in Ln-2 and Ln-3 which results in the absence of bridging of the Ln3+ sites. Select bond distances for Eu-1 can be found in Table 4. As expected based on ionic radii differences [49] the average EuN and EuO distances in Eu-1 are longer than the comparable LnN and LnO distances in Tb-1 and Yb-1. For Eu-1, a clear trend in the EuO and EuN distances among the various coordinating groups is observed. EuO(DMSO) distances are shorter (average of 2.347 Å) than the EuO(H2O) distances (average of 2.408 Å), while the EuN distance with Pt(CN)42 is shorter by an average of 0.05 Å compared with the EuN distances to 1,10-phenanthroline. Similar trends in the EuO(H2O) and EuO(DMF) distances for Eu2 and Eu-3 are also observed, whereas the EuO(NO3) distances are the longest (Tables 5 and 6). The PtC distances vary little, ranging from 1.981(6) to 2.001(5) Å with an average value of 1.992 Å for all compounds reported here. All of these bond distances are within normal ranges as found in previously reported lanthanide tetracyanoplatinate structures [19,25,45]. As mentioned earlier, the TCP anion is not coordinated to Eu3+ in either Eu-2 or Eu-3. Further, the arrangement of the TCP anions does not result in quasi-one-dimensional TCP stacks [25,26,45] in any of the structures reported here, as has been observed in many previous TCP structures. The structures even lack the presence of Pt

C6 O3

C4

C3

O1

C2

C5 N2 O2

C1

N1 Eu1

O4 O5 C11 N3

C9

O6

C10

C12A

N6 C8

N5 C7

N4 C13A

Pt1

Fig. 2. A thermal ellipsoid plot (30%) of Eu-2 illustrating the coordination environment of the Eu and Pt sites. Eu1 is located on a mirror plane and Pt1 is located on an inversion center. The figure is also representative of La-2 and Tb-2 since they are isostructural with Eu-2. The related compounds La-3, Sm-3, Eu-3, and Tb-3, while not completely isostructural, are related in that a 2,20 -bipyridine molecule replaces the 1,10-phenanthroline molecule in Eu-2. Only one orientation of each disordered DMF molecule is given for clarity.

dimers containing one Pt  Pt interaction, as observed in some uranyl [1] or lanthanide [32] TCP compounds. The lack of Pt  Pt interactions can be attributed to the presence of the bulky complex cations in the structures that do not allow for the close packing of the square planar anions. A similar situation has been observed previously in TCP compounds where large complex cations are crystallized as tetracyanoplatinate salts [33]. All three of the structure types presented here are stabilized by strong H-bonding networks. In the case of Ln-2 and Ln-3, the number of H-bonds are maximized via the formation of four H-bonds between the four

C8

C5 C4

C6 C7 N3

C3

C12 C13

N4 C14

Eu1 O1

O2 O4

C2 N2

C10 C11

O3

C1 N1

Pt1

C9

O5

S2

C15 S1

C18

C16

C17 Fig. 1. A thermal ellipsoid plot (30%) of Eu-1 illustrating the coordination environment of the Eu and Pt sites. Pt1 is located on an inversion center. The figure is also representative of Tb-1 and Yb-1 since they are isostructural with Eu-1.

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M. Stojanovic et al. / Inorganica Chimica Acta 370 (2011) 513–518 Table 4 Selected bond distances (Å) for [{Eu(C12H8N2)(H2O)3(DMSO)2}2Pt(CN)4](Pt(CN)4)2 2C12H8N24H2O (Eu-1). Distances (Å) Eu1–N1 Eu1–N3 Eu1–N4 Eu1–O1 Eu1–O2 Eu1–O3 Eu1–O4 Eu1–O5 Pt1–C1 Pt1–C2

2.525(3) 2.594(3) 2.547(3) 2.384(2) 2.419(2) 2.422(2) 2.369(3) 2.325(2) 1.988(3) 1.982(3)

Pt2C19 Pt2C20 Pt2C21 Pt2C22 C1N1 C2N2 C19N5 C20N6 C21N7 C22N8

1.996(4) 1.993(4) 1.988(4) 1.991(4) 1.143(4) 1.149(5) 1.126(5) 1.143(5) 1.143(5) 1.133(5)

Table 5 Selected bond distances (Å) for [Eu(DMF)3(C12H8N2)(H2O)2NO3]Pt(CN)4 (Eu-2). Distances (Å) Eu1–O1 Eu1–O2 Eu1–O4 Eu1–O40 Eu1–O5 Eu1–O50 Eu1O6

2.502(3) 2.541(3) 2.462(2) 2.462(2) 2.363(2) 2.363(2) 2.358(4)

Eu1–N1 Eu1–N10 Pt1C7 (2) Pt1C8 (2) C7N5 (2) C8N6 (2)

2.639(2) 2.639(2) 1.994(3) 1.999(4) 1.133(4) 1.131(4)

Fig. 3. Packing diagram for Eu-3 illustrating the strong OH  N H-bonding interactions in the structure. Only one orientation is shown for the disordered DMF molecules.

OH donors of the complex cations with four cyanide groups from the TCP anion as shown in Fig. 3 for Eu-3. Likewise for Eu-1, every terminal cyanide from each TCP anion is involved in H-bonding with an OH donor from either a coordinated or uncoordinated water molecule.

Eu-1 Eu-2 Eu-3

3.2. Photoluminescence studies The solid-state emission spectra of Eu-1, Eu-2, and Eu-3 shown in Fig. 4 (band locations and assignments given in Table S1) illustrate that all three compounds display the characteristic red emission associated with Eu3+. As expected, direct Eu3+ excitation at 395 nm provides relatively weak emission due to low absorption of the f-element ion. Exciting Eu-1 or Eu-2 with higher energy UV radiation in the range of 260–370 nm (260–340 nm for Eu-3) leads to similar Eu3+ emission profiles, albeit with greater intensities (Fig. 4). The increased Eu3+ emission upon exciting in the higher energy UV, coupled with the lack of observed phen fluorescence [41] in Eu-1 and Eu-2, are evidence for the intramolecular energy transfer in these compounds. In all three compounds, the 5 D0 ? 7F2 transition centered around 616 nm is the most intense indicating a lack of inversion symmetry of the Eu3+ ion [50], which is in line with the findings from the structural analyses. Fig. 5 illustrates the solid-state emission spectra for the related Tb3+ compounds, Tb-1, Tb-2, and Tb-3 (band positions and assignments given in Table S2). For all three compounds, strong green emission is visible upon excitation in the same UV range as noted above for the related Eu3+ compounds. The four strong emission bands are reminiscent of the Tb3+ cation and can be thus assigned.

400

Distances (Å) Eu1–O1 Eu1–O2 Eu1–O4 Eu1–O40 Eu1–O5 Eu1–O50 Eu1O6

2.463(5) 2.599(5) 2.449(3) 2.449(3) 2.384(4) 2.384(4) 2.349(5)

Eu1–N1 Eu1–N10 Pt1C6 (2) Pt1C7 (2) C6N5 (2) C7N6 (2)

2.639(4) 2.639(4) 1.990(5) 1.997(6) 1.136(7) 1.149(7)

600 Wavelength (nm)

700

Fig. 4. Room temperature, solid-state emission spectra for Eu-1, Eu-2, and Eu-3 upon mid-UV excitation.

Tb-1 Tb-2 Tb-3

400 Table 6 Selected bond distances (Å) for [Eu(DMF)3(C10H8N2)(H2O)2NO3]Pt(CN)4 (Eu-3).

500

450

500 550 600 Wavelength (nm)

650

700

Fig. 5. Room temperature, solid-state emission spectra of Tb-1, Tb-2, and Tb-3 upon mid-UV excitation.

As is most commonly observed, the 5D4 ? 7F5 transition at 542 nm is the strongest for all three Tb3+ compounds studied here. Since direct f-level excitation of the Tb3+ ion in Tb-1, Tb-2, and Tb-3 leads to emission spectra with greatly reduced intensities, relative to the indirect ligand excitation, it can be concluded

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that the ligand systems in these compounds also act as light absorbing antennae to sensitize the lanthanide luminescence. Both 1,10-phenanthroline and 2,20 -bipyridine are known to coordinate Eu3+ and Tb3+ ions and sensitize their emission via energy transfer [42]. Due to the lack of Pt  Pt interactions, and therefore lack of possible MMLCT transitions [25], the TCP anions are not expected to significantly contribute to the energy transfer mechanisms operable in these compounds. 4. Conclusions Three isostructural series of lanthanide tetracyanoplatinate compounds, [{Ln(DMSO)2 (C12 H8N 2)(H2O)3} 2Pt(CN) 4](Pt(CN) 4) 2 2C12H8N24H2O (Ln = Eu, Tb, Yb), [Ln(DMF)3(C12H8N2)(H2O)2NO3]Pt(CN)4 (Ln = La, Eu, Tb), and [Ln(DMF)3(C10H8N2)(H2O)2NO3]Pt(CN)4 (Ln = La, Sm, Eu, Tb), have been prepared and structurally characterized. The structural analyses revealed that all of these compounds are zero-dimensional ionic salts containing cationic Ln3+ complexes and uncoordinated [Pt(CN)4]2 anions. The photoluminescence of the Eu3+ and Tb3+ compounds have been investigated. The latter measurements indicate that a sensitization process involving phen or bpy absorption followed by energy transfer to the Eu3+ or Tb3+ cations is present in all of these compounds. Acknowledgments 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

[6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32]

[33]

CCDC 761859, 761860, 761861, 761862, 761863, 761864, 761865, 761866, 761867, or 761868 contain the supplementary crystallographic data for Eu-1, Tb-1, Yb-1, La-2, Eu-2, Tb-2, La-3, Sm-3, Eu-3, or Tb-3, respectively. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Further experimental details including percent yield, IR, and photoluminescence data. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2011.02.077.

[34]

References

[44]

[1] B.A. Maynard, R.E. Sykora, J.T. Mague, A.E.V. Gorden, Chem. Commun. 46 (2010) 4944. [2] B.Q. Ma, S. Gao, G. Su, G.X. Xu, Angew. Chem. 40 (2001) 434. [3] M.D. Ward, Coord. Chem. Rev. 251 (2007) 1663. [4] Z. Assefa, R.G. Haire, R.E. Sykora, J. Solid State Chem. 181 (2008) 382. [5] M. Hernandez-Molina, J. Long, L.-M. Chamoreau, J.-L. Cantin, J. von Bardeleben, V.J. Marvaud, New J. Chem. 33 (2009) 1301.

[35] [36] [37] [38] [39] [40] [41] [42] [43]

[45] [46] [47] [48] [49] [50]

T. Akitsu, Y. Einaga, Inorg. Chim. Acta 359 (2006) 1421. G. Li, T. Akitsu, O. Sato, Y. Einaga, J. Coord. Chem. 57 (2004) 855. H.Z. Kou, S. Gao, X. Jin, Inorg. Chem. 40 (2001) 6295. D.C. Wilson, S. Liu, X. Chen, E.A. Meyers, X. Bao, A.V. Prosvirin, K.R. Dunbar, C.M. Hadad, S.G. Shore, Inorg. Chem. 48 (2009) 5725. S.G. Shore, E. Ding, C. Park, M.A. Keane, J. Mol. Catal. A: Chem. 212 (2004) 291. A. Rath, E. Aceves, J. Mitome, J. Liua, U.S. Ozkanb, S.G. Shore, J. Mol. Catal. A: Chem. 165 (2001) 103. H. Imamura, Y. Miura, K. Fujita, Y. Sakata, S. Tsuchiya, J. Mol. Catal. A: Chem. 140 (1999) 81. S.G. Shore, E. Ding, C. Park, M.A. Keane, Catal. Commun. 3 (2002) 77. Y. Sadaoka, H. Aono, E. Traversa, M. Sakamoto, J. Alloys Compd. 278 (1998) 135. P. Shuk, A. Vecher, V. Kharton, L. Tichonova, H.D. Wiemhofer, U. Guth, W. Gopel, Sens. Actuators B 16 (1993) 401. B. Du, E. Ding, E.A. Meyers, S.G. Shore, Inorg. Chem. 40 (2001) 3637. B. Du, E.A. Meyers, S.G. Shore, Inorg. Chem. 39 (2000) 4639. S. Liu, P. Poplaukhin, E. Ding, C.E. Plecnik, X. Chen, M.A. Keane, S.G. Shore, J. Alloys Compd. 418 (2006) 21. J. Liu, D.W. Knoeppel, S. Liu, E.A. Meyers, S.G. Shore, Inorg. Chem. 40 (2001) 2842. S.G. Shore, D.W. Knoeppel, H. Deng, J. Liu, J.P. White III, S.-H. Chun, J. Alloys Compd. 249 (1997) 25. J. Liu, S. Liu, E.A. Meyers, S.G. Shore, Inorg. Chem. 37 (1998) 5410. H. Yersin, J. Chem. Phys. 68 (1978) 4707. H. Yersin, W. von Ammon, M. Stock, G. Gliemann, J. Lumin. 18–19 (1979) 774. H. Yersin, M. Stock, J. Chem. Phys. 76 (1982) 2136. G. Gliemann, H. Yersin, Struct. Bond. 62 (1985) 87. and references therein. A. Loosli, M. Wermuth, H.-U. Güdel, S. Capelli, J. Hauser, H.-B. Bürgi, Inorg. Chem. 39 (2000) 2289. W. Daniels, H. Yersin, H. Von Philipsborn, G. Gliemann, Solid State Commun. 30 (1979) 353. W. von Ammon, I. Hidvegi, G. Gliemann, J. Chem. Phys. 80 (1984) 2837. W. von Ammon, G. Gliemann, J. Chem. Phys. 77 (1982) 2266. T. Gunnlaugsson, F. Stomeo, Org. Biomol. Chem. 5 (2007) 1999. and references therein. U.S. Schubert, H. Hofmeier, G.R. Newkome, Modern Terpyridine Chemistry, Wiley-VCH Verlag GmbH & Co. KgaA, Weinheim, 2006. (a) B.A. Maynard, P.A. Smith, L. Ladner, A. Jaleel, N. Beedoe, C. Crawford, Z. Assefa, R.E. Sykora, Inorg. Chem. 48 (2009) 6425; (b) B.A. Maynard, K. Kalachnikova, K. Whitehead, Z. Assefa, R.E. Sykora, Inorg. Chem. 47 (2008) 1895. M. Stojanovic, N.J. Robinson, X. Chen, P.A. Smith, R.E. Sykora, J. Solid State Chem. 183 (2010) 933. S. Biju, D.B.R. Ambili, M.L.P. Reddy, C.K. Jayasankar, A.H. Cowley, M. Findlater, J. Mater. Chem. 19 (2009) 1425. S.A. Cotton, O.E. Noy, F. Liesener, P.R. Raithby, Inorg. Chim. Acta 344 (2003) 37. H.M. Ye, N. Ren, J.J. Zhang, S.J. Sun, J.F. Wang, New J. Chem. 34 (2010) 533. Y. Zhang, X. Li, Y. Li, J. Coord. Chem. 62 (2009) 583. E.C. Yang, P.X. Dai, X.G. Wang, X.J. Zhao, Z. Anorg. Allg. Chem. 635 (2009) 346. V. Bekiari, G. Pistolis, P. Lianos, Chem. Mater. 11 (1999) 3189. C. Zhuqi, D. Fei, H. Feng, G. Ming, B. Zuqiang, D. Bei, H. Chunhui, New J. Chem. 34 (2010) 487. G. Accorsi, A. Listorti, K. Yoosaf, N. Armaroli, Chem. Soc. Rev. 38 (2009) 1690. D. Parker, J.A.G. Williams, J. Chem. Soc., Dalton Trans. (1996) 3613. G. Accorsi, N. Armaroli, A. Parisini, M. Meneghetti, R. Marega, M. Prato, D. Bonifazi, Adv. Funct. Mater. 17 (2007) 2975. L. Armelao, G. Bottaro, S. Quici, M. Cavazzini, M.C. Raffo, F. Barigellettic, G. Accorsi, Chem. Commun. (2007) 2911. W. Holzapfel, H. Yersin, G. Gliemann, Z. Kristallogr. 157 (1981) 47. D.W. Knoeppel, J. Liu, E.A. Meyers, S.G. Shore, Inorg. Chem. 37 (1998) 4828. Oxford Diffraction, Oxford Diffraction Ltd., Xcalibur E CCD system, CrysAlisPro Software System, Version 1.171.33.66, 2010. G.M. Sheldrick, Acta Crystallogr. A 64 (2008) 112. R.D. Shannon, Acta Crystallogr. A 32 (1976) 751. G.-D. Qian, M.-Q. Wang, Mater. Res. Bull. 36 (2001) 2289.