Luminescent Cycloplatinated Complexes Containing Poly(pyrazolyl

ARTICLE pubs.acs.org/Organometallics

Luminescent Cycloplatinated Complexes Containing Poly(pyrazolyl)-borate and -methane Ligands
lvaro Díez, Elena Lalinde,* M. Teresa Moreno,* Santiago Ruiz, and Sergio S
anchez Jes
us R. Berenguer, A Departamento de Química - Grupo de Síntesis Química de La Rioja, UA-CSIC, Universidad de La Rioja, 26006, Logro~no, Spain

bS Supporting Information ABSTRACT:

Cycloplatinated neutral [Pt(C∧N){H2B(pz)2}] (1
3) [C∧N = benzoquinolate (bzq), 2-phenylpyridinate (ppy), and 2-phenylquinolate (pq)] and [Pt(pq){HB(pz)3}] 10 and cationic [Pt(C∧N){H2C(pz)2}]+ (4
6) and [Pt(C∧N){HC(pz)3}]+ (7
9) complexes were synthesized by the reaction of the corresponding precursors [Pt(C∧N)(μ-Cl)]2 with the adequate poly(pyrazolyl)-borate or -methane ligand. However, the reactions of [Pt(C∧N)(μ-Cl)]2 (C∧N = bzq, ppy) with [HB(pz)3]
evolve with B
N bond cleavage, yielding the binuclear systems [Pt(C∧N)(μ-pz)]2 as a mixture of cis and trans isomers. Complexes were characterized in solution by multinuclear and multidimensional NMR spectroscopy. The solid-state structures of 1, 3, 6, 7
9, and [Pt(bzq)(μ-pz)]2 were confirmed by X-ray single-crystal studies. The absorption, emission, and electrochemical properties of these complexes are mainly dominated by the nature of the cyclometalated ligand and the charge of the complex. On the basis of TD-DFT calculations (1, 7
9), the lowest-energy absorption for neutral 1 has been ascribed to a mixed 1ILCT/1MLCT transition, whereas for the cationic 7
9, it is mainly attributed to 1ILCT combined with some CT to both ligands in 9 (1MLCT/ML0 CT 9) or to the HC(pz)3 in 7 and 8 (1ML0 CT). These compounds are emissive in all media (except 4 and 10 in the solid state at 298 K). In the solid state at 298 K and at 77 K, these complexes display intense phosphorescence, which is typical of monomers. In deoxygenated CH3CN solutions at 298 K, phosphorescence is accompanied by higher-energy fluorescence in complexes 1, 4, and 8, which disappears at concentrated solutions and at 77 K. Complex 7 displays a special behavior, observing fluorescence and/or excimer fluorescence only at 298 K and excimeric emission (diluted glasses) and emission from aggregates in concentrated glasses. TD-DFT of the lowest-lying excited states responsible for the phosphorescence of 1 and 7
9 reveals a 3ILCT origin with a mixed 3 MLCT character for 1 and, in the case of the cationic 7
9, a 3ILCT transition mixed with 3ML0 CT (especially in 8) and with some 3MLCT in 9.

’ INTRODUCTION Cyclometalated square-planar platinum(II) complexes have attracted great interest in recent years due to their luminescent properties1
12 with potential applications in optoelectronic devices,2,3,7,10,11,13
25 photocatalysts,26 and chemical or biochemical sensors.27
31 Emission from these Pt(II) complexes is typically assigned to ligand-centered (3LC) and/or metal-to-ligand charge-transfer (3MLCT) states, although some degree of ligand-to-ligand0 charge-transfer (3LL0 CT) states is also possible. Additionally, the square-planar nature of these complexes facilitates the formation of dimers or aggregates through noncovalent π 3 3 3 π and/or Pt 3 3 3 Pt interplanar stacking interactions, both in the solid state and in solution.32
44 As a consequence, they exhibit rich photophysical behavior causing a marked red shift relative to the mononuclear emission spectra, derived from excimeric r 2011 American Chemical Society

ligand-to-ligand (3ππ) and/or metal
metal-to-ligand chargetransfer (3MMLCT) excited states. In this area, heteroleptic mononuclear Pt(II) complexes bearing a single cyclometalating ligand and a great variety of noncyclometalating ancillary ligands have been extensively investigated as phosphorescent materials both in solution and in the solid state.35,45
50 This type of complex shows a wide capability to tune photophysical characteristics (absorption, emission, and lifetimes) and even their solubility by modification of ancillary ligands and/or cyclometalated groups. On a different vein, poly(pyrazolyl)-borate or -methane ligands have been widely used as auxiliary ligands in coordination, organometallic, and bioinorganic chemistry,51
58 and they have Received: July 12, 2011 Published: October 06, 2011 5776

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Organometallics Scheme 1

shown an important role in a wide range of topics, such as C
H bond activation,59
66 catalytic processes,67
72 models for enzymatic reactions,73,74 metal extraction,52,54,55,58,75,76 and biomedical applications.73,77 However, there have been few reports on the influence of these ligands on the photophysical properties of metal complexes,78
81 and in particular, very few studies are related to square-planar cycloplatinated complexes.81,82 These ligands would be expected to introduce a remarkable steric hindrance above and below the square-planar coordination plane, disfavoring undesirable face-to-face intermolecular π 3 3 3 π and Pt 3 3 3 Pt interactions. In this paper, we report the preparation of a series of neutral and cationic cycloplatinated complexes [Pt(C∧N){L0 }]n containing poly(pyrazolyl)-borate or -methane ligands (L 0 = [H 2 B(pz)2]
/[HB(pz)3]
, n = 0; [H2C(pz)2]/[HC(pz)3], n = 1) and three distintive cyclometalating groups [C∧N = benzoquinolate (bzq), 2-phenylpyridinate (ppy), and 2-phenylquinolate (pq)]. Their structures and photophysical properties are discussed with the aim of understanding the relationship between structure
physical properties in the context of novel phosphorescent Pt(II) materials.

’ RESULTS AND DISCUSSION Synthesis. The synthetic routes to neutral and cationic cycloplatinated derivatives are illustrated in Scheme 1. Treatment of chloro-bridged binuclear complexes [Pt(C∧)(μ-Cl)]2 [C∧N = 7,8-benzoquinolate (bzq), 2-phenylpyridinate (ppy), and 2-phenylquinolate (pq)] with 2 equiv of K[H2B(pz)2] in acetone affords, after workup (see the Experimental Section), the series of bis(pyrazolyl)borate complexes [Pt(C∧N){H2B(pz)2}] [C∧N = bzq 1, ppy 2, pq 3) (Scheme 1i). It should be noted that the synthesis of complex 2 starting from (NBu4)[Pt(ppy)Cl (ppyH)] was reported when this work was in progress.81 Similar treatment of [Pt(C∧N)(μ-Cl)]2 with [H2C(pz)2] or [HC(pz)3] and NaPF6 (2 equiv) in acetone gives rise to the two families of cationic complexes, the bis-[Pt(C∧N){H2C(pz)2}]PF6

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Scheme 2

[C∧N = bzq 4, ppy 5, pq 6) (Scheme 1ii) and the tris-[Pt(C∧N){HC(pz)3}]PF6 [C∧N = bzq 7, ppy 8, pq 9) (Scheme 1iii) (pyrazolyl)methane series, respectively (see the Experimental Section for details). We have also attempted the synthesis of the related neutral cycloplatinated complexes [Pt(C∧N){HB(pz)3}] containing the tris(pyrazolyl)borate ligand. However, only the reaction of [Pt(pq)(μ-Cl)]2 with K[HB(pz)3] was clean, affording the expected complex [Pt(pq){HB(pz)3}] 10 in a 77% yield (Scheme 2i). To our surprise, the reaction of [Pt(bzq)(μ-Cl)]2 with K[HB(pz)3] evolves with B
N bond cleavage83,84 and the formation of mixtures containing mainly the previously described dimer [Pt(bzq)(μ-pz)]2 (mixture of cis and trans isomers), from which suitable crystals for X-ray diffraction studies of trans-[Pt(bzq)(μ-pz)]2 were obtained from slow crystallization of CH2Cl2/ hexane (Scheme 2ii). Similarly, the reaction of [Pt(ppy)(μ-Cl)]2 with K[HB(pz)3] affords a mixture from which the mononuclear product [Pt(ppy){HB(pz)3}] 12 (5%) and the binuclear complex [Pt(ppy)(μ-pz)]285,86 (mixture of cis and trans isomers) could be separated (Scheme 2iii). It is noteworthy that, although relatively rare in the chemistry of poly(pyrazolyl)borate ligands, the cleavage of B
N bonds evolving with formation of pyrazolate and/or pyrazole groups has many precedents.83,84 However, to our knowledge, there are no previous reports in platinum chemistry. Elemental analyses of 1
10 are consistent with the proposed formulation (see the Experimental Section). The positive mode MALDI-TOF spectra of 1
3 and 10 exhibit the anticipated molecular ion peaks ([M]+ or [M
H]+), whereas those of 4
9 show the presence of the corresponding cations [M
PF6]+ as the parent peak. The pyrazolyl borate complexes 1
3 and 10 exhibit, in their IR spectra, an intense ν(B
H) [2407 (1), 2413 (2), 2431 (3), 2419 cm
1 (10)], in agreement with the signal described by Trofimenko in poly(pyrazolyl)borate derivatives.51 Complexes were characterized by 1H (1
10) and 13C{1H} (1
6, 9, and 10) NMR spectroscopies, and the assignments 5777

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Figure 1. X-ray molecular structure of 1 (a), 3 (b), and 6+ (c).

Figure 2. X-ray molecular structure of 7+ (a), 8+ (b), and 9+ (c).

were made by comparison with those of the ligands, the values of the coupling constants, and 1H
1H COSY (1
10) and 1H
13C HSQC (1
3, 10) spectra. The schematic labeling used for the assignments is shown in Figure S1 (Supporting Information). The 1H NMR spectra of the bzq derivatives (1, 4, and 7) show two characteristic low-field doublets in the ranges of 9.01
9.08 and 8.70
8.82 ppm with platinum satellites in the first signal (3JPt
H = 32.9
41.0 Hz) due to the H2 and H4 protons. The H2 proton of the ppy ligand in complexes 2, 5, and 8 also appears as a doublet in the 8.66
8.74 ppm range with a 3JPt
H of 35.1
37.7 Hz, whereas the pq derivatives (3, 6, 9, and 10) exhibit two

characteristics H4/H3 low-field signals in the ranges of 8.50
8.79 and 8.02
8.32 ppm, respectively. Furthermore, complexes containing bis(pyrazolyl)-borate or -methane groups exhibit two high-field triplets (δ ranges of 6.20
6.88 and 5.96
6.87), assigned to the nonequivalent 40 and 400 protons of the coordinated pyrazolyl rings, whereas the tris(pyrazolyl)methane derivatives 0 00 broad show a coincident triplet for H4 and H4 and a high-field 000 singlet (6.23
6.63 ppm range) attributed to the H4 proton of the free pyrazolyl ring. The protons bonded to the bridgehead boron in 1 and 2 are seen as a very broad triplet 1:1:1 (1JB
H = 143.3
161.2 Hz) in the 3.88
3.97 ppm range and, in 3, as a 5778

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Figure 3. X-ray molecular structure of [Pt(bzq)(μ-pz)]2 (11).

broad singlet. The related H
C proton of the HC(pz)3 ligand in 7
9 is seen as a low-field singlet (9.40
9.53 ppm), whereas the nonequivalent H2C(pz)2 protons in 4
6 appear as the expected AB system (7.29
7.43 ppm). The 13C{1H} NMR spectra of the bzq and ppy derivatives display, as the most characteristic signals, the metalated C10 carbon at high frequency (bzq: δ 157.5 (1), 154.4 (4); ppy: 168.6 (2), 167.8 (5)) and the C2 and C9 carbon resonances, the latter with platinum satellites (C2 148.3
154.3 ppm, 2JPt
C = 19.7
26.7 Hz; C9 131.7
135.2 ppm, 2JPt
C = 56.3
64.6 Hz). For the pq derivatives, the most significant signals are those corresponding to C12 (ortho to the metalated carbon) (δ 134.8 (3), 134.1 (6), 133.0 ppm (9); 2JPt
C = 58.5
57.6 Hz), C9 (126.5 (3), 127.0 (6), 126.1 (9), 130.7 ppm (10); 3JPt
C = 35.8
27.6 Hz (3, 6, 9)), and C3 (117.9 (3), 118.1 (6), 117.2 (9), 122.0 ppm (10); 3JPt
C = 48.1
44.4 Hz (3, 6, 9)) carbon atoms. Molecular Structures. X-ray structural studies of 1, 3, 6, 7
9, and of [Pt(bzq)(μ-pz)]2 (11) were carried out. The structures of the neutral (1, 3) and complex cations (6+
9+) are illustrated in Figures 1
3, and selected structural bonding details are collected in Tables S1
S3 (Supporting Information). The structures of 1, 3, 6, 7, 8, and 9 show an approximately planar arrangement of the C and N atoms of the cyclometalated groups and the two coordinated N-donor atoms of the pyrazolyl ligand around the Pt center. Within the Pt(C∧N) fragment, the Pt
C bond distances [1.991(3)
2.010(3) Å] are slightly shorter than the platinum
pyridine ones [2.015(3)
2.046(7) Å], and in the chelating N
N ligand, the Pt
N lengths trans to the carbon atom are longer than the Pt
N distances trans to the pyridine N atom, in agreement with the higher trans influence exerted by the carbon C sp2. The cyclometalated ligands exhibit a small bite angle [range of 79.8(3)
82.0(1)°] similar to that observed in related cycloplatinated complexes.37,81,82,87
90 Platinum is slightly shifted with respect to the best PtN3C coordination plane (0.031 (1), 0.077 (3), 0.113 (6+), 0.029 (7+), 0.033 (8+), 0.087 Å (9+)). The cyclometalated ligands are distinctly twisted, showing a different interplanar angle between the two planar rings and with the Pt coordination plane. Thus, whereas the benzoquinolate (bzq) ligand is almost coplanar with the Pt coordination plane in 1 and 7+, the phenylquinolate (pq) ligand is always fluttered,

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forming dihedral angles of 21.6 (3), 19.1 (6+), and 21.2° (9+). The phenylpyridinate (ppy) exhibits an intermediate angle of 16.7° in 8+. In all mononuclear complexes, the six-membered PtN4Y (Y = B, C) ring adopts a typical boat conformation, the free pyrazolyl group exhibiting an endo orientation in relation to the Pt center in the complex cations 7+, 8+, and 9+. Similar structural features have been previously observed by Ma82 and Slugovc81 in related complexes. The relatively long Pt 3 3 3 H (B, C) distances in neutral (3.210 (1), 3.110 Å (3)) and cationic 6+ (2.982 Å) complexes excludes the occurrence of the backbiting hydrogen-bonding interaction of the sym oriented H atom. A distinguishing feature of these structures lies in their different packing arrangements. In 1 and 3 (neutral) and 7 (cationic) derivatives, the molecules are arranged as head-to-tail dimers through moderate intermolecular π 3 3 3 π interactions between bzq (1, 7) or pq (3) ligands [3.298(1) (1), 3.249 (3), 3.399 Å (7)] (Figures S2
S4, Supporting Information). In 7, these dimers form chains separated by PF6
anions. However, the cationic entities in complexes 6, 8, and 9 do not show π 3 3 3 π interactions between the corresponding cyclometalated ligands, perhaps due to the presence of PF6
anions and, in the case of 8 and 9, of the bulky free pyrazolyl group. A complete description of all types of secondary interactions and figures of the resulting supramolecular networks are shown in the Supporting Information (Figures S5
S7). The structure of the μ-pyrazolate binuclear complex [Pt(bzq) (μ-pz)]2 (11) has also been determined by X-ray crystallography (Figure 3, Table S3 (Supporting Information)). Two [Pt(bzq)] moieties are bridged by two pyrazolate ligands in an exobidentate fashion. The central six-membered “Pt2N4” core adopts a typical boat conformation similar to those previously found in related Pt(II) μ-pyrazolate derivatives.82,85,86,91
93 The molecule adopts a typical trans orientation. It should be noted that both trans ([Pt(ppy)(μ-pz)]2,86 [Pt(ppy)(μ-dmpz)]2,86 [Pt{(2,4-F2C6H2)py}(μ-3-Me,5-Butpz)]2,82 [Pt(thpy)(μ-pz)]2;85 Hdmpz = 3,5-dimethylpyrazol; thpy = thyenylpyridine) and cis ([Pt{(2,4-F2C6H2)py}(μ-R2pz)]2; R2pz = pz, dmpz, 3,5-But2pz)82 isomers have been previously found. The two bridging pyrazolate ligands form a dihedral angle of 82.47° and exhibit different Pt
N bond lengths, reflecting the different trans influence of the C(metalated) and N(pyridyl) donor atoms of the bzq ligand. The shorter Pt
N distances have the N atoms trans to N(bzq) [Pt(1)
N(3) 2.029(3) Å, Pt(2)
N(6) 2.005(3) Å], while the longer Pt
N bond lengths have the N(pz) trans to the C metalated atom [Pt(1)
N(5) 2.065(3) Å, Pt(2)
N(4) 2.080(3) Å]. As in complexes 1 and 7, the benzoquinolate ligands are coplanar with their platinum coordination planes, which form a dihedral angle of 82.47°. The Pt 3 3 3 Pt separation of 3.319 Å and the tilt angle are comparable to those found in related μ-pyrazolate complexes.82,85,86,91 Thompson et al. have shown that both the Pt 3 3 3 Pt distance and the tilt angle decrease due to the increasing demanding of the substituents of the bridging pyrazolate ligand (3- and 5-positions).82 As can be observed in Figure S8 (Supporting Information), the diplatinum complex generates an extended one-dimensional chain based on π 3 3 3 π staggered dimers, which are, in turn, formed by π 3 3 3 π (bzq) intermolecular interactions (3.345 Å), reinforced by secondary (C
H 3 3 3 π) type T interactions (see caption of Figure S8 (Supporting Information) for more details). Photophysical Properties. Absorption Spectra. For solubility reasons, absorption spectra for all complexes were carried out in CH3CN (5  10
5 M). For complexes that are soluble in 5779

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Figure 4. Low-energy zone of normalized UV
vis absorption spectra of [Pt(pq)L]n+ (n = 0 (3, 10); n = 1 (6, 9)) in 5  10
5 M CH3CN solutions.

other solvents, spectra have also been recorded in toluene and CH2Cl2. The absorption data are provided in the Supporting Information (Table S4) and representative spectra in Figures 4 and S9 (Supporting Information) (medium- and low-energy regions). In CH3CN, all of the complexes exhibit intense, high-energy bands at 229
330 nm, ascribable to ππ* intraligand transitions located on the cyclometalated (L) and poly(pyrazolyl)-borate or -methane (L0 ) ligands, perhaps somewhat perturbed by coordination to the metal and medium-energy absorptions at 330
370 nm, which are likely to have a mixed composition, as confirmed by TD-DFT theoretical studies (see below). They probably result from intraligand and/or metal-to-ligand and ligandto-ligand charge-transfer transitions. A detailed assignment based on TD-DFT calculation is provided for complexes 1 and 7
9 in Table S5 (Supporting Information). Furthermore, all compounds exhibit a low-energy broad band (ε = (1.4
4.2)  103 M
1 cm
1), which, in accordance with previous works, can be ascribed to a mixed 1IL/1MLCT manifold. This low-energy band shows a certain dependence on both the chelating N
N ligand (L0 ) and the cyclometalating group (L). Thus, this absorption maximum occurs at lower energy for the neutral complexes with the [H2B(pz)2]
ligand, whereas there is no appreciable variation within the cationic series containing the neutral ligands H2C(pz)2 and HC(pz)3 [H2B(pz)2/H2C(pz)2/HC(pz)3: 405/ 389 (1/4, 7); 389/377 (2/5, 8); 425/401/402 nm (3/6/9)] (Figure 4). Neutral 10 containing the [HB(pz)3]
group also shows a red shift in relation to that of cationic 6 and 9 with the same cyclometalated ligand (pq) [420 nm (10) vs 401 (6) and 402 (9) nm]. The blue shift in the cationic complexes relative to their neutral analogues is ascribed to an obviously increased contribution from the [π f π*(C∧N)] 1IL transition, together with a reduced 1MLCT character in the low-energy bands, which is supported by DFT studies (vide infra). The dependence of this low-energy band is clearer with the cyclometalated ligand (Figure S9, Supporting Information), which is red shifted on going from the 2-phenylpyridinate (ppy) complexes to the 2-phenylquinolate derivatives (λmax ppy < bzq < pq) [389 (2) < 405 (1) < 425 (3); 377 (5) < 389 (4) < 401 (6); 377 (8) < 389 (7) < 402 nm (9)]. This fact is in agreement with the higher electron delocalization of the bzq

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group in relation to the 2-phenylpyridinate group and with the better π-accepting capability of the 2-phenylquinolate group. As indicated in Figure S10 (Supporting Information) for 1, the lowenergy absorption bands are distinctly red shifted with the decrease of the solvent polarity [i.e., 1: 405 nm (CH3CN), 413 nm (CH2Cl2), 423 nm (toluene)], typical of a negative solvatochromic effect, suggesting a certain degree of a charge transference for this transition. TD-DFT theoretical calculations for selected complexes (1, 7
9) (see below) support a mixed contribution to this transition, mainly 1ILCT/1MLCT in neutral 1 containing the [H2B(pz)2]
group. However, in the cationic HC(pz)3 series (7
9), this transition is mainly 1ILCT combined with some degree of CT from Pt to both ligands (1MLCT/1 ML0 CT) for 9 or to the tris(pyrazolyl)methane ligand 1ML0 CT in 7 and 8. As was expected, a linear plot of absorbance versus concentration in the range of 5  10
5 to 10
3 M (Figure S11, Supporting Information) indicates that this low-energy band obeys Beer’s Law, excluding the presence of ground-state oligomerization processes in this range. However, very weak absorption bands (ε < 50 μ
1 cm
1) at longer wavelengths [462 (1), 445, 478 (2), 502, 537 (3), 459 (4), 443, 475 (5), 493, 532 (6), 494, 531 nm (9)] are discernible in very concentrated solutions (10
2 M, Figure S12 (Supporting Information) for 3). Although, to some extent, the formation of aggregates cannot be excluded, these bands could be tentatively attributed to the direct population of triplet states of mixed character favored by the high spin
orbital coupling associated with the Pt(II) ion. As depicted in Figure S13 (Supporting Information), the solid-state diffuse reflectance UV
vis spectra exhibit a pattern similar to those seen in solution, including the lowest-energy bands observed in very concentrated solutions (10
2 M), indicating that the possible π 3 3 3 π interactions between monomers do not affect the absorption maxima. Emission Properties. The photophysical data in the solid state and in acetonitrile solution (298 and 77 K) are shown in Table 1, and the data in other solvents [CH2Cl2 (1
6, 9, 10) and toluene (1, 2)] are included in the Supporting Information (Table S6). In the solid state at 298 K, all of the complexes (except 4 and 10) exhibit a broad structured band with the vibrational progressional spacing characteristic of the cyclometalated ligands, indicative of substantial involvement of these ligands in the emissive state. The variation of the cyclometalated ligand has a notable impact on the emission maximum, and a similar trend is observed in all series [Pt(C∧N)L2]n+. Thus, the emission maximum is red shifted, following the order of ppy < bzq < pq [490 (2), 519 (1), 580 nm (3) (Figure 5); 511 (5), 560 nm (6); 503 (8), 514 (7), 557 nm (9)], in agreement with a more extended conjugation of the cyclometalated ligand. The correlation of the emission maximum with the auxiliary poly(pyrazolyl)-borate or -methane ligands is less clear. In the bzq (1, 4, 7) and pq (3, 6, 9) series, the emissions occur at higher energies in the cationic complexes containing poly(pyrazolyl)methane groups than in the neutral ones with the bis(pyrazolyl)borate ligand [500 (4), 514 (7) vs 519 nm (1); 560 (6), 557 (9) vs 580 nm (3)] (Figure S14a, Supporting Information, for the pq series). This trend clearly suggests a remarkable character of Pt to C∧N CT in this emission (3MLCT). As expected, in the cationic complexes, the stabilization of the Pt/C∧N-based HOMO increases the HOMO
LUMO gap, making the charge transfer more difficult. Interestingly, as can be seen in Figure S14b (Supporting Information), in the ppy derivatives, emission occurs at higher energy in the 5780

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Table 1. Photophysical Data for Complexes 1
10 in the Solid State and in Acetonitrile Solutions compound 1

λem/nm (λexc/nm)

medium (Ta/K) solid (298) solid (77)

519max, 560, 590sh (330
470) 520max, 560, 600 (340
460)

10
3 M (298)

485max, 520, 550 (385
450)

5  10
5 M (298)a

τ/μs 11.4 (519); 12.3 (590) 11.4 (87%); 66.5 (13%) (520)

350, 365, 380, 485max, 500, 550sh (280) 485max, 500, 550sh (330
410)

c

2

3

5  10
5 M (77)b solid (298)

480max, 515, 560 (285
420) 490, 520max, 560, 590sh (310
410)

8.0 (490)

solid (77)

490, 524max, 560, 590sh (330
450)

9.5 (490); 9.2 (560)

10
3 M (298)

480max, 510, 560, 600sh (360
450)

5  10
5 M (298) a

430, 480max, 510, 545, 590sh (280
330) 480max, 515, 545, 600 (350
380)

5  10
5 M (77)b solid (298)

480max, 520, 560, 600sh (280
400) 580, 610max, 670sh (400
450)

8.8 (580)

solid (77)

580max, 610, 660sh (340
510)

9.8 (580)

10
3 M (298)

590max, 660sh (420
450)

5  10
5 M (298)

447, 590max (350
380) 590max, 660sh (420)

4

10
3 M (77)

580max, 610, 660sh (330
440)

5  10
5 M (77) solid (77)

560max, 600, 655sh (350
430) 500max, 537, 570, 612sh (350
460)

10
3 M (298) 5  10
5 M (298)a

474, 493d (362, 421) 350, 365max, 480br (280)

308 (500/570)

365max, 480br (330
350)

5

6

10
3 M (77)

500max, 535, 566, 620sh (330
400)

5  10
5 M (77) solid (298)

478max, 512, 550, 600sh (300
400) 511, 530max, 580sh (345
450)

10.2 (530)

solid (77)

507, 543max, 580 d (340
450)

11.3 (507)

10
3 M (298)

479max, 512, 546, 586sh (390)

5  10
5 M (298)a

479max, 512, 546, 586 (290
380)

5  10
5 M (77)b solid (298) solid (77)

487max, 522, 554d (330
380) 560, 591maxe (350
440) 555, 594maxe (350
440)

10
3 M (298) 5  10
3

10


5

7

8

565, 591maxe (440) a

M (298)

560 max, 590e (345
400) 563max, 605, 646she (355
420)

M (77)
5

8.6 (560/645) 14.7 (556)

5  10 M (77) solid (298)

556max, 598, 650she (355
420) 514, 552max, 590e (370
450)

9.5 (514); 12.4 (550)

solid (77)

505max, 546, 590 (370
450)

192 (64%), 18.7 (36%) (505)

10
3 M (298)

440max, 480sh, 520sh (360)

a

5  10
5 M (298)a

349max, 365, 383 (270
330)

10
3 M (77)

440br, (360) 496, 535, 612max, 660sh (360
430)

5  10
5 M (77) solid (298)

485max, 520, 560, 620 (340
400) 503, 528max, 566sh (330
390)

9.5 (503)

solid (77)

505max, 540, 575, 610 (370
440)

11.3 (505)

10
3 M (298)

477max, 511max, 530, 560sh (350
390)

5  10
5 M (298)

340 (290) 428, 478max, 512, 535, 560sh (330) 478max, 512, 535, 560 (360
380)

9

5  10
5 M (77)f solid (298) solid (77)

480max, 520, 550, 590sh (330
380) 557, 592max, 630sh (370
440) 590max, 630, 670sh (370
440)

10
3 M (298)

562, 592max, 640sh (440)

5  10
5 M (298)

561, 590max, 640sh (350
390)

5  10
5 M (77)f

561max, 597, 640 (350
420) 5781

8.7 (592) 12.3 (590)

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Table 1. Continued compound 10

λem/nm (λexc/nm)

medium (Ta/K) e

solid (77) 10
3 M (298)

604 (390
550) 590maxe (444)

5  10
5 M (298)a 5  10


5

b

M (77)

τ/μs 11.1 (604/665)

590maxe (350
420) 560max, 602, 652 (355
430)

The same spectrum at 10
4 M. b The same spectra at 10
3 and 10
4 M. c Data are consistent with that previously reported.81 d Tail to 650 nm. e Tail to 750 nm f The same spectrum at 10
3 M. a

Figure 5. Normalized emission spectra of [Pt(C∧N){H2B(pz)2}] (1, 2, and 3) in the solid state at (a) 298 and (b) 77 K (λex 390
400 nm).

neutral derivative (490 nm (2)) than in the cationic ones [511 (5) and 503 nm (8)], pointing to some contribution of the neutral bis- and tris(pyrazolyl)methane auxiliary ligand in the emission (3ML0 CT character). Upon cooling the solids (77 K), the emissions are more intense and the bands become better structured, following the same trends as previously commented. The neutral derivative [Pt(pq){HB(pz)3}] (10), which is nonemissive at 298 K, shows, at 77 K, an asymmetric broad band that is red shifted with regard to the related cationic complex [Pt(pq){HC(pz)3}]+ (9) [604 (10) vs 590 nm (9)], as in the rest of the pq series. The structured

emission bands, which are typical of monomers, and long luminescent lifetimes (8.0
11.4 μs, 298 K; 9.5
308 μs, 77 K), which are characteristics of triplet states, are indicative of emission with mixed intraligand and metal-to-ligand 3ILCT/3MLCT (L = cyclometalated ligand) parentage. However, it must be pointed out, that, previously indicated for complexes 2, 5, and 8 containing the less acceptor ppy ligand, a certain contribution of 3ML0 CT cannot be excluded [L0 = poly(pyrazolyl)-borate or -methane]. Furthermore, it is noteworthy that, whereas the values of the lifetime measurements are similar at 298 K in all series, at 77 K, the bzq derivatives show relatively longer lifetimes [66.5 (13%), 11.4 (87%) (1); 308 (4); 192 (64%), 18.7 (36%) μs (7)] than those of related ppy and pq complexes (see Table 1), suggesting a major intraligand contribution for complexes containing the benzoquinolate group. Similar longer lifetimes have been previously found for cationic benzoquinolate platinum(II) complexes with bis(diphenylphosphine)alkane ligands, in relation to those of related derivatives containing other heterocyclic groups.94
96 This fact has been attributed to the occurrence of a smaller excited-state, singlet
triplet splitting in the bzq compounds, which leads to higher intersystem crossing quantum yield and longer lifetimes.95,96 All complexes are emissive in fluid solution and in the glass state. Taking into account that 7 and 8 are only soluble in CH3CN, this solvent was chosen for the comparative photophysical study of all of the derivatives (shown in Table 1). Photophysical data in other solvents (1
6, 9, 10, CH2Cl2; 1, 2, toluene) are given in the Supporting Information (Table S6). As in the solid state, the emission energy is mainly tuned by the cyclometalated ligand, although, in some cases, a subtle dependence on the poly(pyrazolyl)-borate or -methane auxiliary ligand was also observed. The bzq series [Pt(bzq)L2]n+ (1, 4, 7) shows an interesting behavior. In 5  10
5 M degassed acetonitrile solutions, complexes 1 and 4 display a low-energy emission (485 (1), 480 nm (4)), which is sensitive to O2 (Figure 6) and is, therefore, ascribed to a normal triplet mixed 3ILCT/3MLCT excited state, and a high-energy structured emission band with λmax at ∼350 nm, attributed to fluorescence located on the benzoquinolate group. This kind of dual emission (fluorescence/phosphorescence) is rare, but not unusual.37,90 Time-resolved emission in the microsecond time scale shows similar decay for both bands (F/P) (Figure S15, Supporting Information), indicating that delayed fluorescence, a feature that has precedents in platinum complexes, is present.37,97 We noted that, under similar deoxygenated conditions, the contribution of fluorescence to the emission is higher in the cationic complex 4 than in the neutral 1. Curiously, the cationic compound 7 with the HC(pz)3 ligand does not show phosphorescence in diluted (5  10
5 M) degassed acetonitrile solution, probably due to the presence of the lone pair of the pendant pyridyl group that could interact with the Pt center, quenching the 3MLCT excited state. It exhibits one 5782

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Figure 6. Normalized excitation spectra (dotted lines) and emission spectra (solid lines) of 1 in CH3CN solution (5  10
5 M) at 298 K in deoxygenated and in aerated solutions.

fluorescence band from the bzq ligand (λmax ∼ 350 nm, λex < 330 nm) together with a small unstructured band at ∼440 nm, associated with maximum excitation at 370 nm (Figure S16, Supporting Information), which is tentatively ascribed to excimer fluorescence, as in [Pt(bzq)(NCMe)2]ClO4.90 When the concentration is increased (10
3 M), the fluorescence disappears and only the band at 440 nm, tentatively assigned to excimer fluorescence, is observed. An additional solvent-dependence emission study at 298 K in diluted solutions (5  10
5 M) has been carried out for 1 in CH2Cl2 and toluene, and the results are shown in Table S6 (Supporting Information). It is remarkable that, although dual fluorescence 1(ππ*) and slightly red shifted phosphorescence (3ILCT/3MLCT) is also observed in CH2Cl2 (485 nm CH3CN vs 487 nm CH2Cl2), in the less polar solvent (toluene), the fluorescence disappears and only the 3ILCT/3MLCT band shifted to 491 nm is observed. This result suggests that, in the less polar solvent (toluene), the triplet 3ILCT/3MLCT state is probably stabilized in relation to the singlet state, and thus the intersystem crossing is more effective compared with that observed in the more polar solvents. Moreover, in a nonpolar solvent, the formation of contact ions pairs could probably be somewhat enhanced, increasing the radiative decay and also contributing to the fact that the excited molecule mainly deactivates through the triplet state. In the ppy series (2, 5, and 8), the tendency to exhibit fluorescence in acetonitrile (5  10
5 M) decreases, being observed in complex 8 only. Complexes 2 and 5 exhibit a well-defined, structured emission in the green-blue region (480 (2), 479 nm (5)), assigned mainly to a mixed 3ILCT/3MLCT manifold (Figure S17, Supporting Information). However, the cationic complex 8 containing the HC(pz)3 ligand exhibits, in addition to the vibronic structured phosphorescence emission (3ILCT/3 MLCT) at 478 nm upon excitation to 360 nm, fluorescence from the bzq (∼340 nm, λexc 290 nm) and a broad band centered at 428 nm, upon excitation at higher energies. This structureless feature is tentatively assigned to excimer fluorescence (Figure S18, Supporting Information). The effect of the solvent was studied on 2, observing the same trend as that found in the bzq complexes with slightly red shifted maxima, by decreasing solvent polarity (480 nm CH3CN, 485 nm CH2Cl2, 487 nm toluene) (Figure S17, Supporting Information).

ARTICLE

Figure 7. Normalized excitation spectra (dotted lines) and emission spectra (solid lines) of 6 in CH3CN solution (10
3 and 5  10
5 M) at 298 K.

For the pq complexes (3, 6, 9, and 10), only phosphorescence was observed, appearing notably red shifted in relation to that observed for the related bzq and ppy derivatives (∼590 (3); 560, 590 (6); 561, 590 (9), and ∼590 nm (10)) (Figure 7 for 6), in agreement with the presence of a low-lying π-accepting quinoleine group on the cyclometalated pq ligand. The emission in the cationic 6 is clearly more structured and, as expected, blue shifted in relation to the neutral 3, suggesting a major 3MLCT character for the latter. Upon excitation at higher energies, an additional fluorescence (excimer) at 447 nm is also seen in acetonitrile, but not in CH2Cl2 or toluene, for complex 3 only. We have also performed a concentration-dependent study on the luminescence properties at 298 K. When the concentration increases to 10
3 M, only the phosphorescence band is observed, except, as indicated, for complex 7 (see Table 1 for data), but it is necessary to reach this concentration because, at 10
4 M, fluorescence is still observed in complexes 1 and 4. In general, the emission profiles of the 3ILCT/3MLCT manifold are similar to those obtained in diluted solutions, and it should be noted that in no case were low-energy bands due to π 3 3 3 π or Pt 3 3 3 Pt aggregates found. The most significant change observed by increasing the concentration in these solutions is that the excitation profile usually differs from that obtained when monitoring diluted solutions. The reason for these changes in the excitation spectra are not completely understood, but, presumably, they may point to the presence of different absorbing species when the concentration increases. By way of illustration, the normalized emission and excitation spectra in degassed acetonitrile solutions (5  10
5 and 10
3 M) for complex 1 are shown in Figure S19 (Supporting Information). When diluted solutions are frozen (77 K), 1(ππ*) fluorescence and intermediate (∼440 nm) emissions disappear for all complexes, indicating effective falling to low-lying emissive manifolds. The bzq (1, 4) and pq (3, 6, 9, and 10) complexes exhibit, in diluted acetonitrile solutions, the expected 3ILCT/3 MLCT as a well-structured band slightly blue shifted in relation to that seen at 298 K, whereas in the phenylpyridinate derivatives, the maxima do not change (2) or are only slightly red shifted. Similar effects were observed in other solvents (see Table S6, Supporting Information). The presence of an additional lowenergy broad manifold (525
560 nm), which could be attributed to excimeric 3(ππ*) emission in the rigid matrix (Figure 8a), 5783

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Table 2. Electrochemical Data for Complexes 1
10 in MeCNa Epred/V

Epox/V

[Pt(bzq){H2B(pz)2}] 1


1.70

+1.38b

[Pt(ppy){H2B(pz)2}] 2 [Pt(pq){H2B(pz)2}] 3


1.90
1.50

+1.49b +1.49b

complex

[Pt(bzq){H2C(pz)2}]PF6 4


1.54

+1.68

[Pt(ppy){H2C(pz)2}]PF6 5


1.73

+1.90

[Pt(pq){H2C(pz)2}]PF6 6


1.33

[Pt(bzq){HC(pz)3}]PF6 7


1.52

[Pt(ppy){HC(pz)3}]PF6 8


1.72

[Pt(pq){HC(pz)3}]PF6 9


1.32

[Pt(pq){HB(pz)3}] 10


1.48

+0.90

All measurements were carried out at 25 °C with 0.1M NBu4PF6. Scan rate is 100 mV s
1 and vs Ag/AgCl reference electrode. b Together with other small irreversible waves (1.10, 1.64 V (1); 1.00, 1.82 V (2); 1.00, 1.70 V (3)). a

Figure 8. Excitation spectra (dotted lines) and emission spectra (solid lines) of 7 in CH3CN solution at 77 K: (a) 5  10
5 and (b) 10
3 M.

was only observed in the case of the benzoquinolate complex 7 with [HC(pz)3] ligand. In keeping with this notion, the excitation spectra monitored at 480 and 560 nm are similar. As can be seen in Figure 8b, upon increasing the concentration to 10
3 M, a clear, broad feature develops at ca. 620 nm. The excitation spectrum monitored at this new low-energy feature is different to that monitored at the 490 nm band and also at the excimeric band at ∼560 nm, suggesting that it originates from an emissive state resulting from ground-state aggregation of the complex, probably through the occurrence of π 3 3 3 π stacking interactions between the Pt(bzq) fragments of the cations 7+.98 By contrast, the emission profiles of 1 and of the ppy complexes 2, 5, and 8 are not modified in concentrated solutions, and only a slight red shift of the maxima band was found for the pq derivatives (3, 6, 9, and 10). In the case of the bzq complex 4, a structured, broader, and red shifted profile was observed upon increasing the concentration to 10
3 M (CH3CN, 500, 535, 566 nm, 10
3 M, 77 K vs 478, 512, 550 nm, 5  10
5 M, 77 K). The shape and energy of these bands are very similar to those observed in the solid state at 77 K (500, 537, 570 nm), so a crystallization process cannot be discarded in the formation of the glass. Electrochemistry. The electrochemical properties of the complexes were examined using cyclic voltammetry, and the

redox data in CH3CN are given in Table 2. Most complexes described here show an irreversible reduction wave between
1.32 and
1.90 V and irreversible oxidation between +0.9 and +1.90 V (except in 6
9), together with other small waves observed in the reverse scan, probably due to electrogenerated byproduct. For cyclometalated derivatives, it is generally considered that reduction is localized on the C∧N ligand, whereas oxidation occurs at the Pt(II) center.49,99
101 This electrochemical behavior is consistent with a description of ligand-based LUMO states and a HOMO with a certain metal character, as seen in DFT calculations (see below). In general, in all series, the irreversible reduction potential is strongly dependent on the cyclometalated ligand. The pq derivative is the easiest to reduce, whereas the ppy derivative is the most difficult (for example, [Pt(C∧N){H2B(pz)2}], C∧N = pq (3):
1.50 V; bzq (1):
1.70 V; ppy (2):
1.90 V). As the conjugated π-system of the C∧N ligand is increased, complexes show a decrease in reduction potential. Probably, the decrease in reduction potential is due to a greater stabilization of the negative charge on the more delocalized π-orbital system. This sequence is in agreement with the dependence observed in the low-energy band absorption and in the emission maximum in the solid state at 298 K with the cyclometalated ligand. As expected, the cationic derivatives are easier to reduce than the related neutral derivatives (i.e., in the pq series: 6 (
1.33 V), 9 (
1.32 V) vs 3 (
1.50 V), 10 (
1.48 V)). However, as can be observed in Table 2, related complexes with the same cyclometalated ligand and a different coligand show similar potential reductions [i.e., 3 (
1.50 V) vs 10 (
1.48 V)], which would suggest the negligible influence of the coligands, in accordance with the emission results. In relation to the irreversible oxidation process, we note that, as expected, the cationic derivatives (4, 5) were harder to oxidate than the neutral ones (1
3, 10), and probably for this reason, no band was observed in the window studied for most of the cationic complexes. Molecular Orbital Calculations. To gain further insight into the nature of the absorption and emission characters of these complexes in CH3CN, DFT and time-dependent DFT (TDDFT) calculations were performed on selected neutral (1) and cationic complexes (7, 8, and 9) using the B3LYP method with the LandL2DZ basis set for Pt and the 6-31G (d,p) basis set for 5784

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Table 3. Composition (%) of Frontier MOs in the Ground State for 1 and 7+
9+ 7+

1 MO

pz

8+ Pt

9+

Pt

bzq

pz

Pt

bzq

pz

ppy pz

LUMO+4

52 26

22

19 51

30

25 50

LUMO+3

40 36

24

89

2

10

96

2

2

25

Pt

pq

17 48 36 94

2

LUMO+2 LUMO+1

6 1

6 3

88 95

16 70

3 3

81 27

6 85

1 3

93 11

1 86

2 97 4 11

LUMO

1

3

95

18

27

4 87

HOMO

8 29

63

HOMO
1 39 45

17

4

77

2 14

84

1

9

89

6 91

4

8 86

6

HOMO
3 52 13

35

9 38

54

HOMO
2

HOMO
4 60

5

35

22 54

HOMO
5 72

2

26

95

2

4

6

67

9

5 23

73

1 19 80

4

6 21 73

8

88

17 79

5

1 11 88

96

3

1

7 81 12

24

29 56

15

3

82 15

2

98

1

1

18 51 31

the ligand atoms. The optimized S0 and T1 structures (Figures S20
S23), the optimized coordinates for S0 and T1 states (Table S7), and the main geometrical parameters (Table S8), which are close to experimental values, are reported in the Supporting Information. Some selected frontier molecular orbitals have been drawn in the Supporting Information (Figures S24
S27), and their relative composition in terms of ligands and metals is indicated in Table 3. The HOMO and LUMO orbitals, which illustrate the differences between the neutral (1) and cationic complexes (7
9), are shown in Figure 9. As can be seen, while, in all of the complexes, the HOMO orbitals have a similar π*[dπ(Pt)
π*(C∧N)] character with a negligible contribution of the pyrazolyl ligand (8% (1), 2% (7), 5% (8), 1% (9)), the metal contribution is higher in the neutral complex (1) and particularly remarkable in the ppy cationic complex 8 [Pt (29% (1), 14% (7), 23% (8), 19% (9)); C∧N (63% bzq (1), 84% bzq (7), 73% ppy (8), 80% pq (9)]. In addition, whereas in 7
9, the HOMO
1 is still mainly localized on the cyclometalated ligand (89% (7), 88% (8), 73% (9)), in 1, the HOMO
1 has a remarkable contribution from the Pt (45%) and the pyrazolyl groups (39%). With respect to the LUMOs, in the neutral complex 1, both, the LUMO and the L+1, are mainly composed of the bzq ligand with a small contribution of Pt (bzq 95%, Pt 3%). However, in the cationic complexes 7
9, the LUMOs are generated from the cyclometalating ligand with an increasing contribution of the pyrazolyl groups from 9 to 8 (9% (9), 18% (7), 27% (8)) and the LUMO+1's are primarily composed from the pyrazolyl groups (86% (9), 85% (8), 70% (7)), with a notable decrease in the contribution of the C∧N ligand (11% (9), 11% (8), 27% (7)). The calculated transition energies in CH3CN solution (first singlets) with strong oscillator strengths, which have a higher contribution to the absorption spectra, are collected in Table S5 (Supporting Information). Selected allowed transitions are shown in bars together with the experimental absorption maxima in Figure 10. The calculated values of the low-energy absorptions 390 (1), 383 (7), 362 (8), 402 nm (9)) are close, although slightly blue shifted, to the experimental values (405 (1), 389 (7), 377 (8), 402 nm (9)). In all complexes, the major contribution to this band (∼90%) involves the HOMO f LUMO transition. Therefore, for the neutral complex 1, this band can be assigned to an admixture of 1ILCT (L = bzq) with a remarkable contribution of 1MLCT (Pt f bzq), whereas for cationic complexes 7
9, the

Figure 9. HOMO and LUMO orbitals plots for 1 (a), 7 (b), 8 (c), and 9 (d). 1

ILCT transition is combined with some platinum CT to both ligands in 9 [1MLCT/1ML0 CT; L = bzq, L0 = HC(pz)3] or mainly to the 1ML0 CT in 7 and 8. Inspection of Table S5 (Supporting Information) suggests that the contribution of 1 ML0 CT increases from 9 to 8 (8 > 7 > 9), whereas the 1ILCT contribution goes from 8 to 9 (9 > 7 > 8). The geometry of the lowest-energy triplet state T1 was found to be close to that of the ground-state structure in all complexes (Table S8, Supporting Information). The calculated phosphorescence emissions for 1 and 7
9 (Table 4), based on the triplet unrestricted U-B3LYP optimization, are slightly red shifted when compared to the experimental data, but they follow the same tendency (In 7, the comparison is made with the low-temperature emission, because no phosphorescent band was observed at 298 K in CH3CN solution). The single-electron transition diagrams, based on TD-DFT calculations (CH3CN), for the lowest-energy emission of 1 and 7
9 are collected in Figures S28
S31 (Supporting Information) with the orbital labels referenced to S0 for a better understanding. The analysis of this study indicates that the lowest-lying triplet is mainly contributed by the HSOMO (LUMO in S0 notation) to the LSOMO (HOMO in S0 notation) transition, together with other minor transitions. In neutral complex 1, the LSOMO orbital is mainly located at the bzq (72%) with some contribution of the Pt (22%) and the pyrazolyl ligand (6%), whereas the HSOMO is mostly centered at the bzq ligand (97%). This emission mainly has a 3 ILCT origin with mixing 3MLCT character. In the case of the cationic [HC(pz)3] complexes 7
9, the LSOMO orbitals are also located in the C∧N ligand (91% (7), 76% (8), 85% (9)) with a smaller contribution from the Pt center (8% (7), 17% (8), 14% (9)) and a negligible contribution from pyrazolyl ligands (1% (7, 9), 7% (8)). The HSOMO orbitals are mainly located on the C∧N ligand (90% (7), 72% (8), 91% (9)), but in contrast to 1, there is also some contribution from the pyrazolyl group, increasing from 9 to 8 (7% (7), 22% (8), 5% (9)). In view of these results, we propose that the phosphorescent emission of 5785

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Figure 10. Experimental UV
vis spectra in CH3CN (5  10
5 M) at 298 K and calculated absorption spectra (bars) in CH3CN of 1 (a), 7 (b), 8 (c), and 9 (d).

the cationic complexes would arise from a 3ILCT transition mixed with 3ML0 CT (more important in 8) and with some of 3 MLCT in 9.

’ CONCLUSIONS In summary, three series of neutral [Pt(C∧N){H2B(pz)2}] (1
3) and cationic [Pt(C∧N){H2C(pz)2}]+ (4
6) and [Pt(C∧N){HC(pz)3}]+ (7
9) (C∧N = bzq, ppy, pq) cyclometalated complexes containing poly(pyrazolyl)-borate and -methane as ancillary ligands have been prepared by bridge splitting and chloride substitution reactions from the precursors [Pt(C∧N)(μ-Cl)]2 and the corresponding ligand. The neutral tris(pyrazolyl)borate [Pt(pq){HB(pz)3}] 10 complex was also prepared following a similar methodology, but the related benzoquinolate and phenylpyridinate derivatives were inaccessible by this route due to the ease of formation of binuclear systems [Pt(C∧N)(μ-pz)]2. The photophysical properties have been modulated by the cyclometalating and chelating ligands. Both, absorption and emission features, are distinctly red shifted, following the energy order (pq < bzq < ppy) and hence are mainly associated with

mixed IL/MLCT (L = cyclometalated ligand) transitions. Compared with the neutral complexes (1
3, 10), energy absorption and emission in most of the related cationic derivatives are blue shifted, in agreement with an increased contribution from the IL state and a decrease in the MLCT character. These trends are correlated with electrochemical measurements. This study reveals that, in diluted fluid solution, the complexes containing the planar bzq ligand (1, 4, 7) and some of the derivatives with the tris(pyrazolyl)methane group [HC(pz)3] also exhibit fluorescence and/or excimer fluorescence. Time-resolved emission studies suggest that the fluorescence is delayed fluorescence. This is also coherent with an additional solvent-dependence study on complex 1, which indicates that, in the less polar solvent used (toluene), the fluorescence disappears and the 3ILCT/3MLCT is stabilized. In the glass state, the triplet manifold is also stabilized and only phosphorescence emission is observed. Probably due to steric hindrance of the bulky ligands, no low-energy emissions due to excimer and/or aggregates are found (298 K, 77 K) even in concentrated solutions. Only in the cationic [HC(pz)3] complex 7, excimeric emission is observed even in diluted glasses (77 K) and emission from aggregates also appears at a longer wavelength in concentrated glasses. 5786

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Table 4. Calculated Phosphorescent Emissions of 1 and 7+
9+ with the TD-DFT/PCM (CH3CN) (in Parentheses, the First Calculated Triplet Transition with S0 Geometry), Together with Experimental Values in Acetonitrile Solutions (5  10
5 M) at 298 K compound 1

configuration (|CI coeff.|) 95 f 94 (0.64)

calculated/nm

transition character

experimental λem/nm

612 (464)

3

3

485

620 (461)

3

ILCT/3MLCT

485a

590 (449)

3

478

720 (514)

3

561

ILCT/ MLCT

95 f 93 (0.32) 96 f 94 (0.30) 7+

112 f 111 (0.66) 112 f 110 (0.33) 113 f 111 (0.29)

8+

106 f 105 (0.75)

+

119 f 118 (0.77)

9

ILCT/3MLCT ILCT/3MLCT/3ML’CT

119 f 117 (0.21) a

In glass at 77 K.

TD-DFT calculations have been carried out on the neutral 1 and the cationic 7
9 complexes. On the basis of these calculations, the lowest-energy absorption is suggested to be 1ILCT/1 MLCT in nature in 1 and, in the [HC(pz)3] series (7
9), this transition is mainly 1ILCT combined with 1MLCT/1ML0 CT for 9 or ML0 CT for 7 and 8. The TD-DFT calculations of the optimization of the lowest-lying triplet excited states responsible for the phosphorescence of these complexes indicate that, whereas in the neutral derivative 1, this emission has mainly a 3ILCT origin with mixing 3MLCT character, in the cationic derivatives 7
9, it would arise from a 3ILCT transition mixed with 3ML0 CT (specially in 8) and with some of 3MLCT in 9.

’ EXPERIMENTAL SECTION Materials and Methods. All reactions were carried out under an argon atmosphere using standard Schlenk techniques and solvents from a solvent purification system (MBRAUN MB SPS-800). Elemental analyses were carried out with a Carlo Erba EA1110 CHNS/O microanalyzer. Mass spectra were recorded on a Microflex MALDI-TOF Bruker (MALDI) spectrometer operating in the linear and reflector modes using dithranol as the matrix. Conductivities were measured in acetonitrile solutions using a Crison GLP31 conductimeter. IR spectra were recorded on a Nicolet Nexus FT-IR spectrometer from Nujol mulls between polyethylene sheets. NMR spectra were recorded on Bruker ARX 300 or ARX 400 spectrometers at 298 K. Chemical shifts are reported in parts per million (ppm) relative to external tetramethylsilane, SiMe4, and coupling constants in Hz. The NMR spectral assignments of the ligands follow the numbering scheme shown in Figure S1 (Supporting Information). The UV
vis absorption spectra were carried out in a Hewlett-Packard 8453 spectrophotometer. Diffuse reflectance UV
vis (DRUV) data of pressed powder were recorded on a Shimadzu (UV-3600 spectrophotometer with a Harrick Praying Mantis accessory) and recalculated following the Kubelka
Munk function. Excitation and emission spectra were obtained on a PerkinElmer LS50B or in a Jobin-Yvon Horiba Fluorolog 3-11 Tau-3 spectrofluorimeter. The lifetime measurements were performed in a Jobin Yvon Horiba Fluorolog operating in the phosphorimeter mode (with an F1-1029 lifetime emission PMT assembly, using a 450 W Xe lamp). Cyclic voltammetry measurements were carried out in 0.1 M NBu4PF6 solutions as the supporting electrolyte, using a three-electrode configuration (Pt disk as working electrode, Pt-wire counter electrode, Ag/AgCl reference electrode) on a Voltalab PST 050. The ferrocene/ferrocenium couple served as the internal reference (+0.46 V vs Ag/AgCl). Complexes [Pt(η32Me-C3H4)(μ-Cl)]2,102 [Pt(bzq)(μ-Cl)]2,103 [Pt(ppy)(μ-Cl)]2,104 K[H2B(pz)2],51 K[HB(pz)3],51 [HC(pz)3],105 and [H2C(pz)2]106 were prepared as reported in the literature.

Preparation of [Pt(pq)(μ-Cl)]2. A suspension of [Pt(η3-2MeC3H4)(μ-Cl)]2 (1 g, 1.75 mmol) in xylene (10 mL) was treated with 2-phenylquinoline (0.718 g, 3.50 mmol), and the mixture was refluxed for 2 h. The resulting orange solid was filtered and washed with xylene (5 mL) and diethyl ether (2 mL) (1.3 g, 86%). Anal. Calcd for C30H20N2Pt2Cl2 (868.03): C, 41.47; H, 2.32; N, 3.23. Found: C, 41.41; H, 2.13; N, 3.25. MALDI-TOF (+): m/z (%) 869.7 (100) [M]+, 833.68 (86) [M
Cl]+. The low solubility of this complex precludes its characterization by NMR spectroscopy. Preparation of [Pt(bzq){H2B(pz)2}] (1). To a yellow suspension of [Pt(bzq)(μ-Cl)]2 (0.500 g, 0.612 mmol) in acetone (30 mL) was added 0.455 g (2.446 mmol) of K[H2B(pz)2]. After 30 min of reaction, the white solid precipitated (KCl) was filtered through Celite and the yellow solution was evaporated to dryness. The residue was treated with CH2Cl2 (30 mL) and filtered again through Celite. Evaporation of the resulting filtrate and addition of EtOH (10 mL) yielded 1 as a yellow solid (0.273 g, 43%). Anal. Calcd for C19H16N5BPt (520.25): C, 43.86; H, 3.10; N, 13.46. Found: C, 43.67; H, 3.21; N, 13.17%. MALDI-TOF (+): m/z (%) 519.1 (100) [M
H]+. IR (cm
1): ν(B
H)st 2407 (s). 1 H NMR (δ, 300.13 MHz, CD3COCD3): 9.01 (d, JH
H = 5.4, 3JPt
H = 0 32.9, 1H, H2bzq), 8.70 (d, JH
H = 7.8, 1H, H4bzq), 7.98 (s, 2 H, H5 pz, 500 5 6 H pz), 7.89 (AB, JH
H = 10.2, δA = 7.95, δB = 7.83, 2H, H bzq, H bzq), 0 00 7.80 (s, 2H, H3 pz, H3 pz), 7.78 (d, JH
H = 7.1, 1H, H3bzq), 7.73 (d, JH
H = 7.9, 1H, H7bzq), 7.56 (t, JH
H = 7.5, 1H, H8bzq), 7.48 (d, 3JPt
H = 37.8, 0 00 JH
H = 7.2, 1H, H9bzq), 6.45 (t, JH
H = 1.8, 1H, H4 /4 pz), 6.41 (t, JH
H = 40 /400 13 1 2.0, 1H, H pz), 3.89 (tbr, JB
H = 161.2, 2H, HBH2). C{ H} NMR 10 2 (δ, 75.5 MHz, CDCl3): 157.5 (s, C bzq), 148.3 (s, JPt
C = 26.7, C2bzq), 0 142.0 (s, 2JPt
C = 79.1, C3 pz), 140.3 (s, C10b bzq), 140.0 (s, 2JPt
C = 24.3, 00 0 300 4 C pz), 137.7 (s, C bzq), 136.5 (s, C5 pz), 136.3 (s, 3JPt
C = 35.0, C5 pz), 10a 2 9 6 133.8 (s, C bzq), 131.7 (s, JPt
C = 64.6, C bzq), 130.0 (s, C bzq + C6abzq), 129.3 (s, 4JPt
C = 54.0, C7bzq), 127.1 (s, C4abzq), 123.1 (s, C5bzq), 122.2 (s, C8bzq), 120.9 (s, 3JPt
C = 38.0, C3bzq), 105.7 (s, 3JPt
C = 00 0 18.2, C4 pz, 3JPt
C = 50.15, C4 pz). Preparation of [Pt(ppy){H2B(pz)2}] (2). The synthesis of this complex has been previously described.81 In this work, 2 was obtained as a yellow solid, following the same procedure than that described for 1, starting from [Pt(ppy)(μ-Cl)]2 (0.200 g, 0.252 mmol) and K[H2B(pz)2] (0.189 g, 1.008 mmol) (0.096 g, 79%). Anal. Calcd for C17H16N5BPt (496.24): C, 41.15; H, 3.25; N, 14.11. Found: C, 40.78; H, 2.99; N, 13.82%. MALDI-TOF (+): m/z (%) 495.1 (52) [M
H]+. IR (cm
1): ν(B
H)st 2413 (s). 1H NMR (δ, 300.13 MHz, CD3COCD3): 8.68 (d, JH
H = 5.7, 3JPt
H = 37, 1H, H2ppy), 8.15 (t, = 8, 1H, H4ppy), 8.08 (d,0 JH
H 00= 7.3, 1H, H5ppy), 7.80 (s, 1H, JH
H 300 30 H pz), 7.75 (m, 4H, H pz, H5 pz, H5 pz, H6ppy), 7.39 (t, JH
H = 5.7, H3ppy), 7.20 (d, JH
H = 3.6, 3JPt
H = 35.6, 1H, H9ppy), 7.16 (d, JH
H = 4.3, 1H, H7/8 ppy), 7.14 (d, JH
H = 4.7, 1H, H7/8 ppy), 6.39 (t, JH
H = 2.0, 5787

dx.doi.org/10.1021/om200624v |Organometallics 2011, 30, 5776–5792

Organometallics 00

ARTICLE 0

1H, H4 pz), 6.36 (t, JH
H = 1.8, 1H, H4 pz), 3.88 (tbr, JB
H = 143.3, 2H, HBH2). 13C{1H} NMR (δ, 75.5 MHz, CD3COCD3): 168.6 (s, C10ppy), C2ppy), 146.6 (s, C12ppy), 144.2 (s, C11ppy), 142.8 150.5 (s, 2JPt
C = 19.7, 2 30 2 300 (s, JPt
C = 80.4, C pz), 141.3 (s, JPt
C = 24.5, C pz), 140.3 (s, 4JPt
C = 0 4 3 500 7.8, C ppy), 137.0 (s, JPt
C = 10.5, C pz), 136.8 (s, 3JPt
C = 30.1, C5 pz), 134.5 (s, 2JPt
C = 58.4, C9ppy), 130.1 (s, 3JPt
C = 51.9, C8ppy), 124.6 (s, JPt
C = 38.6, C6ppy, C7ppy), 123.6 (s, 3JPt
C =0 33.4, C3ppy), 120.200 (s, 3 JPt
C = 42.1, C5ppy), 106.5 (s, 3JPt
C = 51.4, C4 pz, 3JPt
C = 18.1, C4 pz). Preparation of [Pt(pq){H2B(pz)2}] (3). The complex was prepared as an orange solid in a similar way to 1, starting from [Pt(pq)(μCl)]2 (0.200 g, 0.229 mmol) and K[H2B(pz)2] (0.173 g, 0.920 mmol) (0.192 g, 76%). Anal. Calcd for C21H18N5BPt (546.31): C, 46.17; H, 3.32; N, 12.82. Found: C, 45.92; H, 3.15; N, 12.63%. MALDI-TOF (+): m/z (%) 545.1 (100) [M
H]+. IR (cm
1): ν(B
H)st 2431 (m, br). 1 H NMR (δ, 400.17 MHz, CD3COCD3): 8.53 (d, JH
H = 8.6, 2H, H3/4pq), = 7.6, H8pq), 7.76 (d, 8.07 (d, JH
H = 8.6, 2H, H3/4pq), 7.88 (d, JH
H 9 50 = 5.4, H pq), 7.63 (d, JH
H = 2.4, H pz), 7.61 (d, J0 H
H = 1.8, JH
H 00 H5 pz), 7.54 (d, JH
H = 9.1, H5pq), 7.51 (d, JH
H = 1.5, H3 pz), 7.41 (t, JH
H = 7, H7pq), 7.22 (t, JH
H = 7.1, H6pq), 7.12 (t, JH
H = 4.0, H10pq), 7.10 (t,00 JH
H = 4, H12pq), 7.09 (d, 0JH
H = 3.4, H11pq), 6.70 (d,00 JH
H = 1.7, H3 pz), 6.20 (t, JH
H = 2.3, H4 pz), 5.96 (t, JH
H = 2.1, H4 pz), 3.97 (br, 2H, HBH2). 13C{1H} NMR (δ, 75.5 MHz, CD3COCD3): 170.0 (s, C2pq), 149.2 (s, 0C8apq), 148.4 (s, C13pq), 147.900 (s, C14pq), 142.8 (s, 2 JPt
C = 83.0, C3 pz), 142.3 (s, 2JPt
C 0 = 29.6, C3 pz), 140.9 (s, 4JPt
C = 00 4.1, C4pq), 137.2 (s, 3JPt
C = 16.7, C5 pz), 136.3 (s, 3JPt
C = 8.1 C5 pz), 134.8 (s, 2JPt
C = 58.5, C12pq), 130.2 (s, C6pq), 130.1 (s, 3JPt
C = 50.7, C11pq), 129.0 (s, C8pq), 129.0 (s, C4apq), 127.6 (s, 4JPt
C = 30.3, C5pq, C7pq), 126.5 (s, 3JPt
C = 35.7, C9pq), 124.00 (s, C10pq), 117.9 (s, 4JPt
C = 44.4, C3pq), 106.2 (s, 3JPt
C = 52.5, C4 pz), 105.9 (s, 3JPt
C = 20.2, 400 C pz). Preparation of [Pt(bzq){H2C(pz)2}]PF6 (4). This complex was prepared as a yellow solid following the procedure described for 1, but using [Pt(bzq)(μ-Cl)]2 (0.200 g, 0.245 mmol), [H2C(pz)2] (0.109 g, 0.735 mmol), and NaPF6 (0.123 g, 0.735 mmol) (0.245 g, 75%). Anal. Calcd for C20H16N5PtPF6 (666.43): C, 36.05; H, 2.42; N, 10.51. Found: C, 36.18; H, 2.08; N, 10.80%. ESI-MS (+): m/z (%) 521.1 (100) [M
PF6]+, 589.4 (24) [M
PF6 + pz]+. ΛM (CH3CN): 149.3 Ω
1 cm
2 mol
1. 1H NMR (δ, 400.17 MHz, CD3COCD3): 9.08 (d, JH
H = 5.3, 3 2 4 JPt
H = 41.0, 1H, H ), 8.56 (d, JH
H = bzq), 8.82 (d, JH
H = 8.1, 1H, H bzq 0 00 50 500 2.3, 2H, H pz, H pz), 8.48 (d, JH
H = 2.1, 2H, H3 pz, H3 pz), 8.0 (AB JH
H = 8.8, δA = 8.04, δB = 7.93, 2H, H5bzq, H6bzq), 7.86 (m, 2H, H3bzq, H7bzq), 7.64 (t, JH
H = 7.6, 1H, H8bzq), 7.45 (d, JH
H = 7.3, 3JPt
H = 34.7, 1H, H9bzq), 7.35 (AB, JH
H 0 = 14.7, δA = 7.33, δB = 7.37, 002H, HCH2), 6.88 (t, JH
H = 4.77, 1H, H4 pz), 6.87 (t, JH
H = 5.16, 1H, H4 pz). 13 C{1H} NMR (δ, 75.5 MHz, CD3COCD3): 154.4 (s, C10bzq), 154.3 (s, 0 2 JPt
C =00 23.8, C2bzq), 150.2 (s, 2JPt
C = 68.3, C3 pz), 149.0 (s, 2JPt
C = 19.0, C3 pz), 148.2 00(s, C10bbzq), 144.4 (s, C4bzq), 139.9 (s, 3JPt
C = 17.2, 50 C pz), 139.7 (s, C5 pz), 138.7 (s, C10abzq), 135.2 (s, 2JPt
C = 65.1, C9bzq), 134.4 (s, C6bzq, C6abzq), 134.0 (s, C7bzq), 132.1 (s, C4abzq), 128.8 C3bzq), 114.1 (s, (s, C5bzq), 128.2 0(s, C8bzq), 127.2 (s, 3JPt
C = 27.0, 3 4 3 400 JPt
C = 49.7, C pz), 113.9 (s, JPt
C = 16.0, C pz), 68.6 (s, 3JPt
C = 28.0, CCH). Preparation of [Pt(ppy){H2C(pz)2}]PF6 (5). This complex was prepared as a yellow solid in a similar way to complex 4, starting from [Pt(ppy)(μ-Cl)]2 (0.250 g, 0.325 mmol), [H2C(pz)2] (0.145 g, 0.975 mmol), and NaPF6 (0.164 g, 0.975 mmol) (0.294 g, 70%). Anal. Calcd for C18H16N5PtPF6 (642.41): C, 33.65; H, 2.51; N, 10.90. Found: C, 33.27; H, 2.24; N, 10.66%. MALDI-TOF (+): m/z (%) 497.1 (100) [M
PF6]+. ΛM (CH3CN): 137.2 Ω
1 cm
2 mol
1. 1H NMR (δ, 400.17 3 1H, H2ppy), 8.51 MHz, CD3COCD 3): 8.74 (d, JH
H = 5.7, JPt
H =0 37.7, 0 500 3 /300 , H ), 8.38 (d, J = 2.0, 1H, H ), (m, 2H, H5 pz pz H
H pz 8.28 (d, JH
H = 0 00 1.9, 1H, H 3 /3 pz), 8.22 (m, 2H, H4ppy, H5ppy), 7.83 (d, JH
H = 7.4, 1H, H9ppy), 7.52 (t, JH
H = 7.4, 1H, H3ppy), 7.29 (AB, JH
H = 14.4, δA = 7.32, δB = 7.27, 2H, HCH2), 7.25 (m, JH
H = 7.1, 2H, H7ppy, H8 ppy), 7.16

00

(d, JH
H = 7.2, 1H, H6 ppy), 6.83 (t, JH
H = 2.5, 1H, H4 pz), 6.81 (t, JH
H = 40 2.6, 1H, H pz). 13C{1H} NMR (δ, 75.5 MHz, CD3COCD3): 167.80 (s, C10ppy), 150.9 (s, 2JPt
C =00 20.2, C2ppy), 146.1 (s, 2JPt
C = 68.7, C3 pz), 144.8 (s, 2JPt
C = 15.1, C3 pz), 141.700 (s, C4ppy), 139.7 (s, C12ppy), 136.1 4 50 (s, JPt
C = 42.1, C pz), 135.5 (s, C5 pz), 133.7 (s, 2JPt
C = 56.3, C9ppy), 131.0 (s, C11ppy), 130.7 (s, 3JPt
C = 50.5, C8ppy), 126.1 (s, C7 ppy), 125.1 C3ppy), 120.7 (s, 3JPt
C = (s, 3JPt
C = 35.7, C6 ppy), 124.4 (s, 3JPt
C = 26.5, 5 3 40 44.8, C ppy), 110.0 (s, JPt
C = 48.6, C pz), 109.8 (s, 3JPt
C = 16.2, 00 C4 pz), 64.6 (s, 3JPt
C = 26.7, CCH). Preparation of [Pt(pq){H2C(pz)2}]PF6 (6). This complex was prepared as an orange solid in a similar way to complex 4, starting from [Pt(pq)(μ-Cl)]2 (0.200 g, 0.230 mmol), [H2C(pz)2] (0.102 g, 0.690 mmol), and NaPF6 (0.116 g, 0.690 mmol) (0.226 g, 71%). Anal. Calcd for C22H18N5PtPF6 (692.47): C, 38.16; H, 2.62; N, 10.11. Found: C, 38.44; H, 2.37; N, 10.50%. ESI-MS (+): m/z (%) 547.1 (100) [M
PF6] +. ΛM (CH3CN): 136.8 Ω
1 cm
2 mol
1. 1H NMR (δ, 400.17 H3/4pq), 8.53 (d, JH
H = MHz, CD3COCD 3): 8.79 (d, JH
H = 8.6, 2H, 0 00 2.6, 1H, H5 pz), 8.48 (d, JH
H = 2.4, 1H, H5 pz), 8.32 (d, JH
H = 8.6, 02H, H3/4pq), 8.13 (d, JH
H = 8.3, 1H, H8pq), 8.09 (d, JH
H = 2.1, 1H, H3 pz), 8.00 (d, JH
H = 8.7, 1H, H5pq), 7.99 (d, JH
H = 6.4, 1H, H9pq), 7.66 (d, = JH
H = 7.4, 1H, H7pq), 7.51 (t, JH
H = 8.4, 1H, H6pq), 7.49 (AB, JH
H 00 15.7, δA = 7.59, δB = 7.38, 2H, HCH2), 7.45 (d, JH
H = 1.9, 1H, H3 pz), 7.34 (t, JH
H = 7.4, 1H, H10pq), 7.31 (t, JH
H = 7.4, 1H, H11pq), 7.200 (d, JH
H = 7.4, 3JPt
C = 32.0, 1H,00H12pq), 6.79 (t, JH
H = 2.5, 1H, H4 pz), 6.57 (t, JH
H = 2.3, 1H, H4 pz). 13C{1H} NMR (δ, 100.67 MHz, C2pq), 147.9 (s,00 C8apq), 147.4 (s, C13pq), 146.3 CD3COCD3): 169.9 (s, 2 30 (s, JPt
C = 73.9, C pz), 145.8 0(s, C3 pz), 144.500 (s, C14pq), 142.3 (s, C4pq), 136.0 (s, 3JPt
C = 16.5, C5 pz), 135.0 (s, C5 pz), 134.1 (s, 2JPt
C = 57.6, C12pq), 131.2 (s, C6pq), 130.8 (s, 3JPt
C = 52.4, C11pq), 129.6 (s, C8pq), 129.1 (s, C4apq), 128.2 (s, 4JPt
C = 36.9, C5/7pq), 127.4 (s, 4JPt
C = (s, C10pq), 00118.1 (s, 28.7, C5/7pq), 127.0 (s, 3JPt
C = 27.6, C9pq), 126.2 0 3 JPt
C = 47.7, C3pq), 109.7 (s, 3JPt
C = 51.4, C4 pz), 109.3 (s, C4 pq), 64.7 (s, 3JPt
C = 27.4, C8 CH). Preparation of [Pt(bzq){HC(pz)3}]PF6 (7). A mixture of [HC(pz)3] (0.157 g, 0.734 mmol), NaPF6 (0.123 g, 0.734 mmol), and [Pt(bzq)(μ-Cl)]2 (0.300 g, 0.367 mmol) was stirred in acetone (20 mL) for 1 h. The final mixture was evaporated to dryness and treated with CH2Cl2 (15 mL), yielding a yellow solid, which was washed with H2O (3  5 mL) and EtOH (3  5 mL). Recrystallization of the crude solid in a mixture of CH3CN/iPrOH at
30 °C yielded 7 as a yellow microcrystalline solid (0.366 g, 68%). Anal. Calcd for C23H18N7PtPF6 (732.50): C, 37.71; H, 2.48; N, 13.39. Found: C, 37.34; H, 2.54; N, 13.14%. ESI-MS (+): m/z (%) 587.1 (100) [M
PF6] +. ΛM (CH3CN): 126.0 Ω
1 cm
2 mol
1. 1H NMR (δ, 300.13 MHz, CD3COCD3): 9.45 (s, (d,00 JH
H = 5.3, 3JPt
H = 39.9, 1H, H2bzq), 8.95 (d, JH
H0 = 1H, HCH), 9.04 0 2.7,00 2H, H5 pz, H5 pz), 8.77000(d,000JH
H = 8.1, 1H, H4bzq), 8.67 (s, 2H, H3 pz, H3 pz), 8.29 (s, br, 1H, H3 /5 pz), 7.90 (AB, JH
H = 8.8, δA = 7.93, δB = 7.87, 2H, H5bzq, H6bzq), 7.84 (s, 1H, H3bzq), 7.82 (d, JH
H = 2.4, 1H, 000 000 H3 /5 pz), 7.78 (d, JH
H = 7.6, 1H, H7bzq), 7.57 (t, JH
H = 7.6, 1H, = 7.3, 3JPt
H = 33.8, 1H, H9bzq), 7.06 (t, JH
H = H8bzq), 7.360 (d, JH
H 4 400 4000 2.5, 2H, H pz, H pz), 6.23 (s, br, 1H, H pz). The low solubility of this complex precludes its characterization by 13C{1H} NMR. Preparation of [Pt(ppy){HC(pz)3}]PF6 (8). Complex 8 was prepared as a yellow solid by a similar procedure to 7 from [Pt(ppy)(μCl)]2 (0.300 g, 0.390 mmol), [HC(pz)3] (0.167 g, 0.780 mmol), and NaPF6 (0.131 g, 0.780 mmol). In this case, the solid obtained after washing with H2O and EtOH is analytically pure (0.383 g, 70%). Anal. Calcd for C21H18N7PtPF6 (708.47): C, 35.60; H, 2.56; N, 13.84. Found: C, 35.63; H, 2.47; N, 13.75%. ESI-MS (+): m/z (%) 563.1 (100) [M
PF6]+. ΛM (CH3CN): 137.0 Ω
1 cm
2 mol
1. 1H NMR (δ, 300.13 0 MHz, CD3COCD3): 9.40 (s, 1H, HCH), 8.90 (d, JH
H = 2.5, 2H, H5 pz, 500 3 2 3 JH
H = 5.4, JPt
H = 35.1, 1H, H bzq), 8.45 (s, JPt
H = H pz), 8.66 (d, 0 00 000 000 = 7.8, 1H, 31.0, 2H, H3 pz, H3 pz), 8.27 (s, 1H, H5 /3 pz), 8.20 (t, 000JH
H 000 H4bzq), 8.10 (d, JH
H = 7.8, 1H, H5bzq), 7.87 (s, 1H, H5 /3 pz), 7.73 (d, 5788

dx.doi.org/10.1021/om200624v |Organometallics 2011, 30, 5776–5792

Organometallics JH
H = 6.3, 1H, H9bzq), 7.45 (t, JH
H = 5.9, 1H, H3bzq), 7.19 (d, JH
H = 5.8, 1H, H8bzq), 7.17 (t, JH
H00 = 6.0,0 1H, H7bzq), 7.06 (d,000JH
H = 7.1, 1H, H6bzq), 6.99 (s, 2H, H4 pz, H4 pz), 6.34 (s, 1H, H4 pz). Its low solubility precludes its characterization by 13C{1H} NMR. Preparation of [Pt(pq){HC(pz)3}]PF6 (9). A mixture of [HC(pz)3] (0.172 g, 0.804 mmol), NaPF6 (0.135 g, 0.804 mmol), and [Pt(pq)(μ-Cl)]2 (0.350 g, 0.402 mmol) in acetone (20 mL) was stirred for 1.5 h. The solvent was removed and the complex extracted with CH2Cl2 (20 mL) and filtered through Celite to eliminate NaCl. The resulting orange filtrate was evaporated to dryness and treated with EtOH (10 mL) to give 9 as an orange solid, which was filtered and washed with diethyl ether (5 mL) (0.453 g, 74%). Anal. Calcd for C25H20N7PtPF6 (758.53): C, 39.59; H, 2.66; N, 12.93. Found: C, 39.87; H, 2.48; N, 12.57%. ESI-MS(+): m/z (%) 614.2 (100) [M
PF6]+. ΛM (CH3CN): 131.6 Ω
1 cm
2 mol
1. 1H NMR 0(δ, 300.13 MHz, 5 500 (s, 2H, H , H ), 8.72 (d, CD3COCD3): 9.53 (s, 1H, C-HCH), 8.96 pz pz 30 300 (s, 2H, H , H ), 8.23 (d, J = 8.6, 2H, JH
H = 8.6, 2H, H3/4pq), 8.36 pz pz H
H 000 000 = 7.8, 1H, H8pq), 7.91 (d, H3/4pq), 8.12 (s, br, 1H, H3 /5 pz), 8.07 (d,000 JH
H 9 3 /5000 JH
H = 7.1, 1H, H pq), 7.71 (s, br, 1H, H pz), 7.65 (d, JH
H = 7.2, 1H, = 7.7, 1H, H7pq), 7.26 H5pq), 7.61 (t, JH
H = 6.2, 1H, H6pq), 7.49 (t, JH
H 0 00 (m,000 3H, H10pq, H11pq, H12pq), 7.02 (s, 2H, H4 pz, H4 pz), 6.63 (s, 1H, H4 pz). 13C{1H} NMR (δ, 100.67 MHz,0 CD3COCD3): 168.9 (s, 2JPt
C = 84.5, C2pq), 147.8 (s, 2JPt
C = 61.8, C3 pz), 147.0 (s, JPt
C = 47.6, C13pq, C14pq), 146.3 (s, Cpz), 143.7 (s, Cpz), 141.4 (s, C4pq), 137.9 (s, Cpz), 133.0 (s, 2JPt
C = 53.0, C12pq), 130.2 (s, C6pq), 129.7 (s, 3JPt
C = 49.1, C11pq), 128.6 (s, C8pq), 128.1 (s, 2JPt
C = 20.7, C4apq), 127.3 (s, C5/7pq), 126.5 (s, 4 JPt
C = 24.5, C5/7pq), 126.1 (s, 3JPt
C = 35.8, C9pq), 125.3 (s, C10pq), 117.2 00 3 3 3 40 (s, 000 JPt
C = 48.1, C pq), 109.6 (s, JPt
C = 44.7, C pz), 108.3 (s, C4 pz, 4 C pz), 80.7 (s, CCH). Preparation of [Pt(pq){HB(pz)3}] (10). Complex 10 was prepared as an orange solid in a similar way to complex 9, starting from [Pt(pq)(μ-Cl)]2 (0.250 g, 0.287 mmol) and K[HB(pz)3] (0.147 mg, 0.575 mmol) by stirring for 30 min (0.270 g, 77%). Anal. Calcd for C24H20N7PtB (612.15): C, 47.05; H, 3.29; N, 16.01. Found: C, 46.50; H, 3.46; N 15.41%. ESI-MS(+): m/z (%) 612.5 (100) [M]+. IR 1 H NMR (δ, 300.13 MHz, (cm
1): ν(B
H)st 2419 (m,0 br). 3 /300 CD3COCD3): 8.50 (s, br, 2H, H pz), 8.50 (d, JH
H0 = 008.6, 2H, H3/4pq), 2H, H3/4pq), 8.02 (s, br, 2H, H5 /5 pz), 7.84 (s, br, 8.02 (d, JH
H000= 8.6, 8 3 /5000 9 3000 /5000 2H, H pq, H pz), 7.73 (s, br, 1H, H pq), 7.68 (s, br, 2H, H pz), 7.47 (d, JH
H = 8.8, 1H, H5 pq), 7.39 (t, JH
H = 7.3, 1H, H7 pq), 7.19 (t, (m, 3H, H10/11/12pq),0 6.76 (s, br, 1H, br, 000JH
H = 7.2, 1H, H6 pq,),0 7.10 4 4 /400 4 /400 13 C{1H} H pz), 6.34 (s, br, 1H, H pz), 6.02 (s, br, 1H, H pz). NMR (δ, 100.67 MHz, CD3COCD3): 152.6 (s), 151.9 (s), 148.6 (s, Cpz), 147.3 (s, Cpz), 145.2 (s, C4pq), 138.8 (s, C10/11/12pq), 134.5 (s, C10/11/12pq), 134.2 (s, C6pq), 133.1 (s, C8pq), 131.9 (s, C5pq,0 C7pq),00 130.7 (s, C9pq), 129.1 (s, C10/11/12pq), 122.0 (s, C3pq), 110.2 (s, C4 pz, C4 pz). Reaction of [Pt(bzq)(μ-Cl)]2 with K[HB(pz)3]. A yellow suspension of [Pt(bzq)(μ-Cl)]2 (0.250 g, 0.306 mmol) in 20 mL of acetone was treated with 0.150 g (0.612 mmol) of K[HB(pz)3] and stirred for 30 min. The mixture was evaporated to dryness, treated with CH2Cl2 (15 mL), and filtered over Celite. The orange filtrate was evaporated to dryness and the residue treated with EtOH (10 mL). The resulting orange solid was recrystallized from a mixture of CH2Cl2/hexane at
30 °C to precipitate yellow crystals identified as trans-[Pt(bzq)(μpz)]2 11 (0.040 g). From the ethanolic filtrate, an additional pale orange solid was obtained (0.100 g), identified as a mixture of cis- and trans[Pt(bzq)(μ-pz)]2. Reaction of [Pt(ppy)(μ-Cl)]2 with K[HB(pz)3]. A 0.199 g (0.780 mmol) portion of K[HB(pz)3] was added to a yellow suspension of [Pt(ppy)(μ-Cl)]2 (0.300 g, 0.400 mmol) in acetone. After 30 min, the mixture was evaporated to dryness, treated with CH2Cl2 (20 mL), and filtered over Celite. The filtrate was evaporated to dryness, and the residue was treated with EtOH (10 mL), causing the precipitation of a yellow solid identified as a mixture of trans-[Pt(ppy)(μ-pz)]2,

ARTICLE

cis-[Pt(ppy)(μ-pz)]2, and [Pt(ppy){HB(pz)3 }] (12). After successive crystallizations, 12 was separated as a pure solid in low yield (0.027 g, 5%). X-ray Crystallography. Details of the structural analyses for all complexes are summarized in Table S1 (Supporting Information). Yellow (1, 7, 8, 11) or orange (3, 6, 9) crystals were obtained by slow diffusion at room temperature of n-hexane (1, 3, 11), EtOH (6, 8, 9), or i-PrOH (7) into solutions of the complexes in acetone (1), CH2Cl2 (3, 6, 11), or acetonitrile (7, 8, 9). In all the cases, graphite-monochromatic Mo
Kα radiation was used. For complexes 1 and 11, X-ray intensity data were collected with an Oxford Diffraction Xcalibur CCD diffractometer, the diffraction frames integrated and corrected for absorption using the Crysalis RED package.107 For the rest of derivatives, data collection was performed on a NONIUS-kCCD area-detector diffractometer, and the images were processed using the DENZO and SCALEPACK suite of programs,108 the absorption corrected at this point for 7 and 8. For the rest of the crystals, the absorption correction was performed using XABS2109 (3, 6) or MULTI-SCAN110 (9), with the WINGX program suite.111 The structures were solved by direct and Patterson methods using SIR2004112 (1) or DIRDIF96113 (3, 6, 7, 8, 11) or by direct methods using SHELXS-97114 (9) and refined by fullmatrix least-squares on F2 with SHELXL-97.114 All non-hydrogen atoms were assigned anisotropic displacement parameters. For complexes 1, 7, 8, and 11, the correct assignment of the position of the C and N atoms bonded to platinum in the benzoquinolate and 2-phenylpyridinate ligands, and, for complexes 7, 8, and 9, that of the C and N atoms of the terminal pyrazolate group of the tris(pyrazolyl)methane ligands, was confirmed by examination of the ΔMSDA values for bonds involving these atoms,115,116 after refining each case in three different ways (with the identities of the C and N in one position, reversed, and with a 50/50 hybrid scattering factor at each of the affected atomic sites). All the hydrogen atoms were constrained to idealized geometries, fixing isotropic displacement parameters 1.2 times the Uiso value of their attached carbon, except for the methine H20 in the structure of 7, which was located from difference maps and assigned isotropic parameters. Finally, except for 7 and 8, the structures show some residual peaks greater than 1 e A
3 in the vicinity of the platinum atoms (or the hexafluorophosphate anion for 9), but with no chemical meaning. Computational Details for Theoretical Calculations. DFT and TD-DFT calculations were performed on complex 1 and the cations of complexes 7
9 with Gaussian 03 (revision E.01).117 Geometries in the S0 ground state and T1 excited state were optimized using the restricted B3LYP (S0) or unrestricted U-B3LYP (T1) Becke’s three-parameter functional combined with Lee
Yang
Parr’s correlation functional.118
120 No negative frequency was found in the vibrational frequency analysis. The basis set used for the platinum centers was the LanL2DZ effective core potential121 and 6-31G (d,p) for the ligand atoms. The solvent effect of the acetonitrile in the TD-DFT calculations was taken in consideration by the polarizable continuum model (PCM).122

’ ASSOCIATED CONTENT

bS

Supporting Information. Crystal data and structure refinement parameters for complexes 1, 3, 6, 7, 8, 9, and 11 (Table S1); selected distances and angles for 1, 3, 6, 7, 8, 9 (Table S2), and for 11 (Table S3); absorption data for compounds 1
10 at 298 K (5  10
5 M solutions and solid state) (Table S4); selected low-lying singlet excited states (Sn) computed by TDDFT/CPCM (CH3CN) with the orbitals involved, vertical excitation energies (nm), and assignments for 1 and 7
9 (Table S5); photophysical data for complexes 1
6, 9, and 10 in other solvents at 298 and 77 K (Table S6); DFT-optimized coordinates for the ground state (S0) and for T1 of 1, 7, 8, and 9 5789

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Organometallics (Table S7); comparative geometrical parameters of the experimental and the DFT calculated structures (S0 and T1) of 1, 7, 8, and 9 (Table S8); numbering scheme for NMR spectra assignments (Figure S1); supramolecular structure of complexes 1, 6
9, and 11 (Figures S2
S8); low-energy zone of UV
vis absorption spectra of 1, 2, and 3 in CH3CN solutions (5  10
5 M) (Figure S9); low-energy zone of normalized absorption spectra of 1 in different solvents (5  10
5 M) solutions, showing a negative solvatochromic effect (Figure S10); low-energy zone of normalized absorption spectra in CH2Cl2 solutions at different concentrations and lineal fit of the absorbance at the 392 nm band versus concentration for 4 (Figure S11); lowenergy zone of normalized UV
vis absorption spectra of 3 in CH2Cl2 solutions (10
2
10
3 M) (Figure S12); normalized absorption spectra calculated from the diffuse reflectance spectra of 1, 2, and 3 in the solid state (Figure S13); emission spectra of the pq derivatives (3, 6, and 9) and ppy derivatives (2, 5, and 8) in the solid state at 298 K (Figure S14); time-resolved emission spectra of 1 in CH3CN solution (5  10
5 M) at 298 K (Figure S15); normalized excitation and emission spectra of 7 in CH3CN solution (5  10
5 M) at 298 K (Figure S16); normalized excitation and emission spectra of 2 in different solvents (5  10
5 M) at 298 K (Figure S17); normalized excitation and emission spectra of 8 in CH3CN (5  10
5 M) at 298 K (Figure S18); normalized excitation and emission spectra of 1 in CH3CN solutions at 5  10
5 and 10
3 M at 298 K (Figure S19); DFToptimized structures (S0 and T1) of 1 and 7
9 (Figures S20
S23); representative frontier orbitals involved in the absorption of 1 and 7
9 (Figures S24
S27); diagrams of the singleelectron transitions according to TD-DFT calculations (CH3CN) for the lowest-energy emission of 1 and 7
9 (Figures S28
S31); and complete reference for Gaussian 03 (revision E.01). This material is available free of charge via the Internet at http:// pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected] (E.L.), [email protected] (M.T.M.). Fax: (+34) 941-299621.

’ ACKNOWLEDGMENT This work was supported by the Spanish MICINN (Project CTQ2008-06669-C02-02/BQU and a grant for A.D. and S.R.). S.S. thanks CSIC for a grant. The authors also thank CESGA for computer support. ’ REFERENCES (1) Williams, J. A. G. Top. Curr. Chem. 2007, 281, 205. (2) Williams, J. A. G.; Develay, S.; Rochester, D. L.; Murphy, L. Coord. Chem. Rev. 2008, 252, 2596. (3) Williams, J. A. G. Chem. Soc. Rev. 2009, 38, 1783. (4) McGuire, R., Jr.; McGuire, M. C.; McMillin, D. R. Coord. Chem. Rev. 2010, 254, 2574. (5) Chi, Y.; Chou, P. T. Chem. Soc. Rev. 2010, 39, 638. (6) Yersin, H.; Donges, D. Top. Curr. Chem. 2004, 241, 81. (7) Lai, S. W.; Che, C. M. Top. Curr. Chem. 2004, 241, 27. (8) Muro, M. L.; Rachford, A. A.; Wang, X.; Castellano, F. N. Top. Organomet. Chem. 2010, 29, 159. (9) Ma, B.; Djurovich, P. I.; Thompson, M. E. Coord. Chem. Rev. 2005, 249, 1501.

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dx.doi.org/10.1021/om200624v |Organometallics 2011, 30, 5776–5792