Mercury(II) Complexes Containing the [Hg(L)2]2–, [Hg(L)(HL)]−, and

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Mercury(II) Complexes Containing the [Hg(L)2]2
, [Hg(L)(HL)]
, and [Hg(HL)2] Units [H2L = 3-(2-Chlorophenyl)-2-sulfanylpropenoic Acid]. Structural and Spectroscopic Effects of the Different Degrees of Ligand Protonation Jos
e S. Casas,† Ricardo Collazo,‡ María D. Couce,*,‡ Manuel García-Vega,† Agustín S
anchez,† Jos
e Sordo,*,† and Ezequiel M. V
azquez-L
opez‡ †

Departamento de Química Inorg
anica, Facultade de Farmacia, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain ‡ Departamento de Química Inorg
anica, Facultade de Química, Edificio de Ciencias Experimentais, Universidade de Vigo, 36310 Vigo, Galicia, Spain

bS Supporting Information ABSTRACT:

The reaction of mercury(II) acetate with 3-(2-chlorophenyl)-2-sulfanylpropenoic acid (H2Clpspa) in ethanol in the presence (or absence) of diisopropylamine or triethylamine yielded the compounds [HQ]2[Hg(Clpspa)2] (1), [HP][Hg(Clpspa)(HClpspa)] (2) (where HQ = diisopropylammonium and HP = triethylammonium cations), and [Hg(HClpspa)2] (3). All of the new compounds were characterized by elemental analysis, IR, and NMR (1H, 13C, 199Hg) spectroscopy. The crystal structures of 1, 2, and 3 3 4H2O were determined by X-ray diffractometry. Diisopropylammonium cations and [Hg(Clpspa)2]2
anions were detected in the first compound, triethylammonium cations and [Hg(Clpspa)(HClpspa)] anions were found in the second compound, and molecular [Hg(HClpspa)2] units were found in the third. The different degrees of ligand protonation modify the structural parameters of the Hg-kernel as well as the supramolecular association in the compounds. Furthermore, the spectroscopic characteristics of the compounds in the solid (IR) and in solution (NMR) are sensitive to this ligand protonation.

’ INTRODUCTION The unique and useful properties of mercury led to the industrial importance of this metal, its widespread presence, and subsequent concern about its toxicity.1 One of the most important chemical species of this element, Hg(II), has an extremely high affinity for compounds containing sulfhydryl groups, and this affinity influences several biological processes. Significant examples include the inhibition or inactivation of several enzymes,2 the detoxification process by metallothionein,3,4 the role of glutathione as a transport agent,5 and the role of cysteinylglycine and cysteine as accumulation and transport forms of the metal into kidney cells.6 All of these properties are all closely related with this Hg
S affinity. r 2011 American Chemical Society

The high Hg
S affinity is the reason why chelating agents used against mercury intoxication, such as dimercaptosuccinic (or dimercaptopropanesulfonic) acid7 or alternatives such as 3-(aryl)-2-sulfanylpropenoic acids,8,9 all contain thiol groups. Another common fragment in some of these compounds is the carboxylic acid group. The studies in solution on the stability constants for Hg(II) complexes,10,11 as well as for other elements of the group, Zn(II) and Cd(II),12 with this class of sulfanylcarboxylate ligands (H2L) are based on the existence of different Received: July 26, 2011 Revised: October 6, 2011 Published: October 10, 2011 5370

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Crystal Growth & Design Scheme 1

degrees of protonation for the ligand as a function of the pH. For example, species such as [M(L)2 ]2
, [M(L)(HL)]
, or [M(HL)2] have been postulated. This protonation takes place on the carboxylate group, as confirmed for cysteine by vibrational spectroscopy in the complex [Hg(cys)(Hcys)],13 by X-ray diffraction in [Hg(Hcys)(H2cys)]Cl 3 0.5H2O,14 and for thiosalicylic acid (H2tsa) by X-ray diffraction in [Hg(Htsa)2].15 In a previous paper,16 we described the interaction of a class of sulfanylcarboxylic acids, the 3-(aryl)-2-sulfanylpropenoic acids (H2xspa), with Hg(II) and the preparation of compounds of the type [HQ]2[Hg(xspa)2], where HQ = diisopropylammonium and the aryl groups of the acid are phenyl, 2-thiophene, and 2-furan. These compounds contain the anion [Hg(xspa)2]2
and the X-ray study showed the xspa fragment to be coordinated to the Hg atom through the S atom and one of the O atoms of the carboxylate group. In an effort to investigate the structural effects produced by the gradual protonation of the ligand in the specific case of the 3-(aryl)-2-sulfanylpropenoic acids (H2xspa), we elected to study 3-(2-chlorophenyl)-2-sulfanylpropenoic acid (H2Clpspa) (see Scheme 1, where the numbering scheme for crystallographic and NMR studies is used). This compound includes a potential hydrogen-bond acceptor as a substituent on the phenyl ring, and this would be able to create new interactions in the solid.17 The interaction of this ligand with Hg(II) under different conditions was studied. The reactions afforded complexes containing the three types of species previously mentioned: [Hg(Clpspa)2]2
, [Hg(Clpspa)(HClpspa)]
, and [Hg(HClpspa)2]. The structural characterization of these complexes enabled us to correlate the structural characteristics with spectroscopic properties in the solid and in solution.

’ EXPERIMENTAL SECTION Materials and Instrumentation. 2-Chlorobenzaldehyde, rhodanine (Aldrich), mercury(II) acetate, triethylamine, and diisopropylamine (Merck) were all used as supplied. 3-(2-Chlorophenyl)-2-sulfanylpropenoic acid (H2Clpspa) was prepared by condensation of the appropriate aldehyde with rhodanine,17 subsequent alkaline hydrolysis of the resulting 5-substituted rhodanine, and acidification with aqueous HCl.18 Elemental analysis was performed on a Fisons 1108 microanalyzer. Melting points were determined on a B€uchi apparatus and are uncorrected. IR spectra (KBr pellets or Nujol mulls) were recorded on a Bruker IFS66V FT-IR spectrophotometer and are reported in the Synthesis section. 1H and 13C NMR spectra were recorded in DMSOd6 at room temperature on a Bruker AMX 300 spectrometer operating at 300.14 and 75.40 MHz, respectively, using 5 mm o.d. tubes; chemical shifts are reported relative to TMS using the solvent signals (δ 1H = 2.50 ppm; δ 13C = 39.5 ppm for DMSO-d6) as reference. The numbering scheme is shown in Scheme 1. The splitting of proton resonances in the reported 1H NMR spectra are defined as s = singlet, d = doublet, dd = doublet of doublets, t = triplet, td = triplet of doublets, q = quadruplet,

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brs = broad singlet, and vbr = very broad. 119Hg NMR spectra were recorded in DMSO-d6 at room temperature on a Bruker AMX 500 spectrometer operating at 89.47 MHz. Chemical shifts are reported relative to pure dimethylmercury(II) as an external standard. All the physical measurements were carried out by the RIAIDT services of the University of Santiago de Compostela (USC). Synthesis. The compounds were prepared by reacting H2Clpspa with Hg(OAc)2 in the absence and in the presence of diisopropylamine or triethylamine in ethanol. The molar ratios used were 2:1:2 when diisopropylamine or triethylamine were added and 2:1 in the absence of base. The solid formed after stirring of the reaction mixture at r.t. was filtered off and vacuum-dried. [HQ]2[Hg(Clpspa)2] (1). H2Clpspa (0.90 g, 4.20 mmol), Hg(OAc)2 (0.67 g, 2.10 mmol), diisopropylamine (0.42 g, 4.20 mmol), ethanol (50 mL), 2 h stirring, gray solid, yield: 39%, M.p.: 223 °C. Anal. found: C, 42.9; H, 5.0; N, 3.7; S, 7.3. Calc. for C30H42N2O4S2Cl2Hg: C, 43.4; H, 5.1; N, 3.4; S, 7.7%. IR (cm
1): νasym(CO2
) 1549 s; νsym(CO2
) 1346 vs; δ(NH2+) 1621 s. 1H NMR (DMSO-d6, ppm): δ 7.83 (s, 2H, C(3)H); 7.42 (dd, 2H, C(6)H, 3J = 8.1 Hz); 7.34 (td, 2H, C(7)H, 3 J = 7.4 Hz); 7.20 (td, 2H, C(8)H, 3J = 7.4 Hz); 8.35 (d, 2H, C(9)H, 3J = 7.4 Hz); 8.4 (vbr (NH2+)); 3.30 (q, 4H, CH); 1.20 (d, 24H, CH3). 13 C, δ 169.8 C(1); 140.8 C(2); 125.4 C(2), 132.7 C(4); 136.0 C(5); 128.8 C(6); 126.2 C(7); 127.6 C(8); 130.5 C(9); 46.1 CH; 18.8 CH3. 199 Hg: δ
775.0. Crystals suitable for the X-ray study were obtained from a solution of the complex in chloroform/dimethylformamide. [HP][Hg(Clpspa)(HClpspa)](2). H2Clpspa (0.1 g, 0.47 mmol), Hg(OAc)2 (0.074 g, 0.23 mmol), triethylamine (0.045 g, 0.47 mmol), ethanol (5 mL), 24 h. stirring, white solid, yield: 82%. M.p.: 188 °C. Anal. found: C, 39.3; H, 3.3; N, 1.8; S, 8.4. Calc. for C24H27NO4S2Cl2Hg: C, 39.5; H, 3.7; N, 1.9; S, 8.8%). IR (cm
1): ν(CdO) 1664 s; νasym(CO2
) 1543 s; δ(OH) 1436 m; νsym(CO2
) 1345 vs; ν(C
O) 1280 m. 1H NMR (DMSO-d6, ppm): 1H, 7.86 (s, 2H, C(3)H); 7.44 (d, 2H, C(6)H, 3 J = 7.6 Hz); 7.35 (t, 2H, C(7)H, 3J = 7.4 Hz); 7.23 (t, 2H, C(8)H, 3J = 7.3 Hz); 8.27 (d, 2H, C(9)H, 3J = 7.1 Hz); 3.0 (q, 6H, CH2, 3J = 6.7 Hz); 1.13 (t, 9H, CH3, 3J = 7.0 Hz). 13C: δ 172.9, 170.6 C(1); 139.1 C(2); 128.3 C(3); 133.6 C(4), 136.1 C(5); 129.8 C(6); 127.2 C(7); 129.2 C(8); 131.4 C(9); 45.5 CH2; 8.6 CH3; 199Hg: δ
884.2. Crystals of [HP][Hg(Clpspa)(HClpspa)] (2) suitable for the X-ray study were isolated from the mother liquor. [Hg(HClpspa)2] (3). H2Clpspa (0.08 g, 0.37 mmol), Hg(OAc)2 (0.059 g, 0.18 mmol), ethanol (5 mL), 2 h stirring, yellow solid, yield: 72%, M.p.: 235 °C. Anal. found: C, 34.3; H, 1.9; S, 10.1. Calc. for C18H12O4S2Cl2Hg: C, 34.4; H, 1.9; S, 10.2%. IR (cm
1): ν(CdO) 1665 s; δ(OH) 1437 s; ν(C
O) 1286 s. 1H NMR (DMSO-d6, ppm): 1 H, δ 13.74 (brs, 1H, C(1)OH); 7.95 (s, 1H, C(3)H); 7.54 (dd, 2H, C(6)H, 3J = 8.0 Hz); 7.44 (td, 2H, C(7)H, 3J = 7.5 Hz); 7.37 (td, 2H, C(8)H, 3J = 7.8 Hz); 8.25 (dd, 2H, C(9)H, 3J = 7.8 Hz). 13C: δ 170.5 C(1); 132.1 C(2); 132.7 C(3); 133.4 C(4), 133.7 C(5); 129.4 C(6); 126.8 C(7); 130.1 C(8); 131.2 C(9). 199Hg NMR: δ
1030.0. Crystals of [Hg(HClpspa)2] 3 4H2O (3 3 4H2O) suitable for the X-ray study were isolated from the mother liquor. Structure Determination. Single crystals of 1, 2, and 3 3 4H2O were mounted on glass fibers in a Bruker Smart 1000 CCD automatic diffractometer. Data were collected at 293 K using Mo
Kα radiation (λ = 0.71073 Å). The crystal data, experimental details and refinement results are summarized in Table 1. Corrections for Lorentz effects, polarization,19 and absorption (SADABS)20 were carried out. The structures were solved using direct methods and in the refinement the non-H atoms were treated anisotropically.21 The scattering factors were taken from International Tables for Crystallography.22 For 3 3 4H2O, occupancy factors for a water molecule were refined with common anisotropic temperature factors until convergence at 35 and 65% and fixed in the last stage of refinement. The hydrogen atoms of these water molecules were not included in the model. The main calculations were 5371

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Table 1. Crystal and Structure Data Refinement for [HQ]2[Hg(Clpspa)2] (1), [HP][Hg(Clpspa)(HClpspa)] (2), and [Hg(HClpspa)2] 3 2H2O (3 3 4H2O) compound

[HQ]2[Hg(Clpspa)2] (1)

[HP][Hg(Clpspa)(HClpspa)] (2)

[Hg(HClpspa)2] 3 2H2O (3 3 4H2O)

empirical formula

C30H42Cl2HgN2O4S2

C24H27Cl2HgNO4S2

C18H16Cl2HgO8S2

formula weight crystal system

830.27 monoclinic

729.08 monoclinic

695.92 monoclinic

space group

P21/c

P21/n

P21/n

a (Å)

13.150(1)

15.200(1)

4.0068(1)

b (Å)

14.207(1)

10.5386(9)

13.5443(4)

c (Å)

18.496(1)

18.604(2)

24.6328(7)

β (°)

97.294(2)

113.418(2)

90.326(1)

volume (Å3)

3472.5(5)

2734.7(4)

1336.78(6)

Z (Mg/m3) calculated density (g 3 cm
3) absorption coefficient (mm
1)

4 1.609

4 1.771

2 1.729

4.804

6.006

6.149

F(000)

1656

1424

668

crystal size (mm3)

0.17  0.08  0.04

0.38  0.28  0.27

0.30  0.09  0.80

theta range for data collection (°)

1.56
28.04

1.47
28.00

1.65
26.40

index ranges


17 e h e 16


20 e h e 19


5 e h e 5


18 e k e 11


13 e k e 13


16 e k e 16

reflections collected/unique


24 e 1 e 24 18116/7585 [R(int) = 0.0822]


24 e l e 16 17390/6500 [R(int) = 0.0435]


30 e l e 30 2713/2058 [R(int) = 0.0496]

absorption correction

semiempirical

semiempirical

semiempirical

refinement method

full-matrix least-squares on F2

full-matrix least-squares on F2

full-matrix least-squares on F2

data/parameters

7585/374

6500/310

2713/146

goodness-of-fit on F2

0.740

1.038

1.143

final R indices [I > 2σ (I)]

R1 = 0.0469, wR2 = 0.0608

R1 = 0.0381, wR2 = 0.0721

R1 = 0.0501, wR2 = 0.1243

R indices (all data)

R1 = 0.1866, wR2 = 0.0799

R1 = 0.0812, wR2 = 0.0878

R1 = 0.0701, wR2 = 0.1369

largest diff peak and hole (e 3 Å
3)

1.063 and
0.649

1.300 and
0.877

2.436 and
0.923

performed with SHELXL-9721 and PLATON23 and figures were plotted with ZORTEP24 and MERCURY.25

’ RESULTS AND DISCUSSION Crystal Structures. The crystal of [HQ]2[Hg(Clpspa)2] (1) consists of diisopropylammonium cations and [Hg(Clpspa)2]2
anions. The numbering scheme for the [Hg(Clpspa)2]2
anion is shown in Figure 1a, and selected bond lengths (Å) and angles (°) are listed in Table 2. The Hg atom is tetracoordinated in an HgO2S2 environment, with the ligand (which acts as a bidentate chelate) bound to the Hg atom through an O atom of the carboxylate group and the S atom of the deprotonated SH group. The Hg
S bond lengths [2.342(2), 2.324(2) Å] adopt values that are slightly shorter than the sum of the corresponding covalent radii (2.37 Å).26 The Hg
O bond lengths [2.550(6), 2.608(5) Å] are longer than the sum of the covalent radii (1.98 Å)26 but shorter than the sum of the van der Waals radii of Hg and O (3.4 Å).27,28 Regarding the angles around the metal, the lowest values correspond to the bite angle of the ligand, S
Hg
O [77.46(14), 76.84(14)°], and the widest is the S
Hg
S angle [170.85(10)°]. These bond lengths and angles are close to those previously found for mercury complexes with other sulfanylcarboxylate ligands16 that also define a nido-trigonal bipyramidal or seesaw-shaped geometry. The structural parameters of the two L2
fragments are slightly different (Table 2). Comparison of these parameters with those previously found29 for the free H2Clpspa shows that the most marked changes affect

the COOH group. Upon deprotonation and formation of a carboxylate group the two C
O bond distances, 1.312(9) and 1.206(8) Å in the free acid, adopt very similar values, ranging between 1.232(8) and 1.257(8) Å. The planarities of the two L2
fragments present in the anion are also different. The two chelate HgSCCO rings, for which the angle between planes is 72.9(1)°, have different planarities [HgS(1)C(12)C(11)O(11) (rms: 0.112); HgS(2)C(22)C(21)O(21) (rms: 0.076)] and the angles with the corresponding Cl
C6H4 plane are also different: 60.3(2) in the first case and 27.7(3) in the second (32.83° in the free acid). The parameters for the diisopropylammonium cation are comparable with those described previously.16 The [Hg(L)]2
anions and the [HQ]+ cations are hydrogen bonded through the NH2 group of the cation and the O atoms of the carboxylate group [N(1)
H(11B) 3 3 3 O(12): 0.90, 1.89, 2.778(8) Å, 167.6°; N(1)
H(11A) 3 3 3 O(21)#1: 0.90, 1.88, 2.779(9) Å, 172.6°; N(2)
H(21A) 3 3 3 O(22)#1: 0.90, 1.87, 2.760(9) Å, 168.5°; N(2)
H(21B) 3 3 3 O(11): 0.90, 1.92, 2.815(9) Å, 170.6°; #1 x,
y + 1/2, z
1/2]. These interactions give rise to the polymeric structure depicted in Figure 1b. An alternative view of the chain from the c axis is shown in Figure S1, Supporting Information. This interaction is reminiscent of that previously found 16 for [HQ]2[Hg(pspa)2] [H2pspa = 3-(phenyl)-2-sulfanylpropenoic acid] and shows that the Cl-substituent on the phenyl ring does not create an alternative hydrogen bond. Such a bond could substantially affect the supramolecular organization, which again remains based on the N
H 3 3 3 O hydrogen bond. However, the two structures are slightly different because in the pspa derivative 5372

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Figure 1. (a) The molecular structure of the anion [Hg(Clpspa)2]2
in [HQ]2[Hg(Clpspa)2]; (b) a view of the polymeric structure of [HQ]2[Hg(Clpspa)2].

Figure 2. [HP][Hg(Clpspa)(HClpspa)] (a) numbering scheme; (b) a view of the polymeric structure of the compound showing the hydrogen bonds present in the solid.

Table 2. Selected Bond Lengths (Å) and Angles (°) in [HQ]2[Hg(Clpspa)2] (1)

Table 3. Selected Bond Distances (Å) and Angles (°) in [HP][Hg(Clpspa)(HClpspa)] (2) (a) Hg Environment

(a) Hg Environment Hg(1)
O(11)

2.550(6)

Hg(1)
S(1)

2.342(2)

Hg(1)
S(2)

2.3383(15)

S(2)
Hg(1)
S(1)

174.65(6)

Hg(1)
O(21)

2.608(5)

Hg(1)
S(2)

2.324(2)

Hg(1)
S(1)

2.3454(14)

S(2)
Hg(1)
O(11)

106.87(10) 77.09(9)

S(1)
Hg(1)
O(11)

77.46(14)

S(2)
Hg(1)
O(11)

110.04(15)

Hg(1)
O(11)

2.545(4)

S(1)
Hg(1)
O(11)

S(1)
Hg(1)
O(21)

105.44(13)

S(2)
Hg(1)
O(21)

76.84(14)

Hg(1)
O(21)

2.671(5)

S(2)
Hg(1)
O(21)

75.13(10)

S(2)
Hg(1)
S(1)

170.85(10)

O(11)
Hg(1)
O(21) 113.2(2)

S(1)
Hg(1)
O(21)

106.67(10)

O(11)
Hg(1)
O(21)

115.39(18)

(b) Ligand S(1)
C(12)

1.763(9)

S(2)
C(22)

1.737(7)

O(11)
C(11)

1.250(8)

O(22)
C(21)

1.232(8)

Cl(1)
C(15)

1.734(8)

C(21)
C(22)
S(2)

118.0(4)

O(12)
C(11)

1.249(9)

C(21)
O(21)

1.257(8)

S(1)
C(12)

1.768(6)

O(12)
C(11)
O(11)

122.0(6)

C(11)
C(12)

1.522(10) C(21)
C(22)

1.492(10)

C(12)
C(13)

1.316(9)

1.349(9)

C(22)
C(23)

O(12)
C(11)
O(11) 123.0(8)

O(22)
C(21)
O(21) 121.7(8)

O(12)
C(11)
C(12)

118.4(8)

O(21)
C(21)
C(22)

119.4(8)

O(11)
C(11)
C(12)

118.6(9)

O(22)
C(21)
C(22)

119.0(8)

C(13)
C(12)
S(1)

122.5(6)

C(23)
C(22)
S(2)

122.0(6)

C(11)
C(12)
S(1)

119.9(7)

C(21)
C(22)
S(2)

121.3(6)

there is a secondary Hg 3 3 3 S interaction [Hg
S: 3.4272(16) Å] between chains and this is not present in the case of compound 1; intermolecular Hg
S bond distances shorter than 4 Å were not found. The crystal of [HP][Hg(Clpspa)(HClpspa)] (2) consists of triethylammonium cations and [Hg(Clpspa)(HClpspa)]
anions. The numbering scheme is shown in Figure 2a, and selected bond

(b) Ligands

S(2)
C(22)

1.763(6)

O(12)
C(11)
C(12)

118.9(5)

O(11)
C(11)

1.251(6)

O(11)
C(11)
C(12)

119.1(5)

C(11)
O(12)

1.251(6)

C(13)
C(12)
S(1)

121.9(4)

C(11)
C(12)

1.525(8)

C(11)
C(12)
S(1)

119.9(4)

C(12)
C(13)

1.340(7)

O(21)
C(21)
O(22)

121.2(6)

O(21)
C(21) C(21)
O(22)

1.202(7) 1.321(7)

O(21)
C(21)
C(22) O(22)
C(21)
C(22)

124.8(6) 113.9(5)

C(21)
C(22)

1.493(8)

C(23)
C(22)
S(2)

122.5(5)

C(22)
C(23)

1.342(7)

distances and angles are listed in Table 3. In the anion, the Hg atom is tetracoordinated in an HgO2S2 environment created by the two different ligands, Clpspa and HClpspa, both of which are S,O-bidentate. The two Hg
S bond lengths [2.3383(15), 2.3454(14) Å] are similar and are slightly shorter than the sum of 5373

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Table 4. Selected Bond Distances (Å) and Angles (°) in [Hg(HClpspa)2] 3 4H2O (3 3 4H2O)a (a) Hg Environment Hg(1)
S(1)

2.360(2)

S(1)#1
Hg(1)
S(1)

180.00(11)

Hg(1)
O(1)

2.650(8)

S(1)
Hg(1)
O(1)#1

104.59(18)

S(1)
Hg(1)
O(1) O(1)#1
Hg(1)
O(1)

75.41(18) 180.0(3)

(b) Ligands Cl(1)
C(5)

1.746(9)

C(3)
C(2)
S(1)

123.7(7)

S(1)
C(2)

1.767(9)

C(1)
C(2)
S(1)

117.7(7)

C(2)
C(3) C(2)
C(1)

1.350(12) 1.499(13)

O(1)
C(1)
O(2) O(1)
C(1)
C(2)

122.9(10) 124.7(10)

O(1)
C(1)

1.212(12)

O(2)
C(1)
C(2)

112.4(9)

O(2)
C(1)

1.326(13)

Symmetry transformations used to generate equivalent atoms: #1
x + 1,
y + 2,
z. a

Figure 3. (a) The molecular structure of [Hg(HClpspa)2] 3 4H2O (3 3 4H2O); (b) a view of the polymeric structure of the compound (water molecules occluded in the lattice are not shown).

the covalent radii (2.37 Å).26 The Hg
O bond length is shorter for the di-deprotonated ligand [2.545(4) Å] than for the corresponding monoprotonated ligand [2.671(5) Å] as a consequence of the lower donor character of the protonated carboxylate group; the S
Hg
S angle is 174.65(6)°. Regarding the ligands, the main structural difference between Clpspa and HClpspa concerns the COO group, which is involved in the protonation. In the carboxylate group both C
O bond lengths are very similar, but the difference between the two C
O bonds in the COOH group, as in the free acid,29 is more significant, showing the presence of a CdO double bond and a C
OH single bond.30 The planarities of the L2
and HL
fragments are also different. The two chelate HgSCCO rings, which in this case make an angle between planes of 75.5(1)°, have a different planarity [HgS(1)C(12)C(11)O(11) (rms: 0.148) and HgS(2)C(22)C(21)O(21) (rms: 0.077)] and the angles with the corresponding Cl
C6H4 plane are also different: 59.6(2)° in L2
and 25.2(2)° in HL
. In the crystal, the triethylammonium cation, which has unremarkable parameters,31 is hydrogen bonded to the O atom of the carboxylate group through an N
H 3 3 3 O hydrogen bond [N(1)
H(1) 3 3 3 O(11): 0.91, 1.81. 2.718(7) Å, 177.8°], but this bond does not support the association, which is supported by an O
H 3 3 3 O hydrogen bond [O(22)
H(22) 3 3 3 O(12)#1: 0.82, 1.79, 2.597(6) Å, 169.4°; #1 =
x + 1/2, y + 1/2,
z + 1/2] between the COOH group of an [Hg(L)(HL)] anion and the COO
group of a neighbor. This bond creates the helical supramolecular association depicted in Figure 2b; an alternative view from the b axis is given in Figure S2, Supporting Information, and this clearly shows the empty internal core of the helix.

The crystal of [Hg(HClpspa)2] 3 4H2O (3 3 4H2O) contains neutral Hg(HClpspa)2 units that are each hydrogen bonded to two water molecules, with the other molecules occluded in the lattice. The numbering scheme is shown in Figure 3a and selected bond distances and angles are listed in Table 4. In each unit the Hg atom is bonded to two S and two O atoms of two HClpspa ligands to give an HgO2S2 kernel. The two Hg
S bonds are identical, and the bond distance [2.360(2) Å] is only slightly shorter than the sum of the covalent radii [2.37 Å].26 The Hg
O bonds are also identical and the bond distance [2.650(8) Å] is longer than the sum of the covalent radii (1.98 Å)26 but shorter than the sum of the van der Waals radii (3.4 Å).27,28 With regard to the angles around the metal, the bite of the ligands, 75.41(18)°, is the minor angle, whereas the S
Hg
S and the O
Hg
O angles are the largest — with values of 180.0° in both cases. Some of the parameters for this kernel, in particular the latter angles, can be influenced by an intermolecular Hg 3 3 3 S interaction between the Hg atom of one unit and the S atom of a neighboring unit. The intermolecular distance (3.241 Å) — even though considerably longer than the sum of the covalent radii (2.37 Å)26 — is also significantly shorter than the sum of the van der Waals radii of the two atoms (3.80 Å),27,28 and, as can be seen in Figure 3b, this creates chains that are parallel to the a axis (The packing of this chains together with the position of the occluded water molecules is shown in Figure S3, Supporting Information). When this interaction is taken into account the Hg coordination kernel can be described as distorted octahedral. In this octahedron, the O
Hg
O and S
Hg
S angles are both 180°, but the Hg
S bond distances are very different [2.360 and 3.243 Å] and the bite of the ligand, 75.41(18)°, is the minor angle. Regarding the ligands, the parameters for the two C
O bonds of the COOH group are close to those found in the free acid29 and are consistent with the presence of CdO and C
OH bonds,30 with the last group hydrogen bonded to a water molecule [O(2)
H(2) 3 3 3 O(1W): 0.82, 1.83, 2.645(13) Å, 172.7°]. The two chelate HgSCCO rings (rms 0.137) are coplanar and make angles of 49.8(1)° with the Cl
C6H4 plane. The data were compared with those for the equivalent neutral examples containing S,O-bidentate ligands available in the literature, including complexes of thiosalicylic acid,14,15 monothioderivatives of 2,2,6, 6-tetramethyl-3,5-heptanedione,32,33 2-dimethylamino-3,4-dioxocyclobut-1-en thiolate,34 and N-(piperidyl-thiocarbonyl)benzamide.35 5374

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Crystal Growth & Design

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Scheme 2

The closest situation for the Hg kernel is that of the thiosalicylic acid complex described in ref 15b, which was isolated as a dioxane solvate. In this example, the Hg
S bond distances are similar, but the Hg 3 3 3 S and the Hg
O (with a nonsignificant interaction) are longer than in the present case. When the three structures (see Scheme 2) are considered jointly, one can visualize the effect of ligand protonation on the structural parameters. In terms of the kernel, the following observations can be made: (i) The Hg
S bond distance does not change significantly when one of the ligands is protonated but the S
Hg
S angle changes from 170.85(10)° in 1 to 174.65(6)° in 2. Recent surveys of Hg(II) thiolate structures36 show values for these Hg
S distances in the range 2.32
2.36 Å for linear [Hg(SR)2] complexes, 2.42
2.45 Å for trigonal [Hg(SR)3]
species and 2.52
2.58 Å for tetrahedral [Hg(SR)4]2
ones. The data for 1 and 2, as well as for other equivalent sulfanylcarboxylates16 (or in other complexes with S,O-donor ligands14,15,32
35), show that the increase in the Hg
S bond length is not significant when the coordination number increases on the basis of the O-donor atom but that the S
Hg
S angle is quasi-linear. A similar situation also occurs when the Hg atom of an [Hg(SR)2] thiolate bonds pyridine to give a tricoordinated T-shaped complex,37 a carboxylate group to give a seesaw-shaped geometry,36b or when, as in 3 3 4H2O, a secondary intermolecular interaction increases the Hg coordination number. However, when the ligand is an S, S0 -bidentate donor, we previously observed38 a more marked influence on the Hg
S bond distance because, in a complex with the diphenyldithiophosphinate, we found values of 2.428(2) and 2.467 Å for the shorter Hg
S bonds in an HgS4 distorted tetrahedral kernel in which the S
Hg
S angles deviate significantly from linearity. (ii) The HL
ligand in 2 gives rise to a longer Hg
O bond distance than the L2
ligand, although in 1, where the two ligands reach the same degree of protonation, the two Hg
O bond distances are also significantly different. (iii) The weak Hg 3 3 3 S interaction found in 3 3 4H2O does not significantly change the intramolecular Hg
S and Hg
O bonds (although they are the longest found in the present complexes), but it significantly changes the O
Hg
O angle, which reaches a value of 180° (see Scheme 3).

Scheme 3

(iv) Besides the aforementioned influence on the kernel, the Hg 3 3 3 S interaction supports the supramolecular interaction of the molecular units in 3 3 4H2O. The COOH group in this compound is hydrogen bonded to a water molecule (Figure 3a) and is not involved in the supramolecular association detected in the crystal. In contrast, in 2 the COOH group of one unit and the COO
group of a neighbor are involved (Figure 2b) in the formation of an O
H 3 3 3 O hydrogen bond that supports the creation of a helix, and in 1 both the COO
groups are O 3 3 3 H
N hydrogen bonded with the diisopropylammonium group to form chains (Figure 1b). Spectroscopy. The IR spectra provide evidence for the deprotonation of the SH group and the S-coordination to the metal in all three complexes [absence of the ν (S
H) band located around 2550 cm
1 in the free ligand] and also confirm the presence of COO
or COOH groups in each case. Furthermore, the vibrations corresponding to the COOH group of the free ligand (1638, 1437, 1259 cm
1) are replaced in the IR spectrum of [HQ]2[Hg(Clpspa)2] (1) by bands typical of a carboxylate group with νasym(COO
) at 1549 and νsymCOO)
at 1346 cm
1, that is, close to the positions previously found16 for other equivalent [HQ]2[Hg(xspa)2] complexes; a strong band at 1621 cm
1 was assigned39 to the δ(NH2) vibration of the diisopropylammonium cation. In the IR spectrum of [HP][Hg(Clpspa)(HClpspa)] (2), two groups of bands were observed that are typical of the deprotonated carboxylate group of the Clpspa ligand, at 1543 and 1345 cm
1 (close to positions found in 1), along with those of the COOH group, at 1664, 1436, and 1280 cm
1, due to the HClpspa ligand. The position of the latter group of bands is similar in the IR spectrum of 3. In complexes 2 and 3, the coordination and the different hydrogen bonds involving the carboxylic acid group is responsible for the shift with respect to the position of the band in the free ligand. 5375

dx.doi.org/10.1021/cg200963g |Cryst. Growth Des. 2011, 11, 5370–5377

Crystal Growth & Design The 1H, 13C, and 199Hg NMR spectra provide information about the ligand protonation in solution. In the 1H NMR spectrum of 1 the low field broad signal assigned in the ligand to the proton of the COOH group is absent, an observation consistent with deprotonation of this group upon coordination. Unfortunately, this signal was not found in the spectrum of 2, probably due its broad nature, as often observed for a protonated ligand. However, this signal was observed as a very broad peak in the spectrum of 3, thus showing the presence of the protonated ligand. In the 13C NMR spectra of the three compounds, the shielding of C(3) and the deshielding of C(2) confirmed the persistence in solution of the S-coordination [ref 16 and refs therein]. With respect to the presence of the undeprotonated or protonated COOH group in the compounds, the C(1) signals for 1 are in positions close to those found before [ref 16 and refs therein] for compounds in which the carboxylate group is present and has a monodentate coordinative behavior, thus suggesting the persistence in solution of the coordination mode found in the solid state. In the spectrum of 2 there are two signals (172.9 and 170.6 ppm) that are attributable to C(1), and these are consistent with the presence of the two different groups in this compound. In the spectrum of 3, only one signal is observed and this is in practically the same position as in the free ligand. The 199Hg chemical shifts are also sensitive to the protonation of the ligand. In the 199Hg spectrum of 1 the chemical shift is in the range accepted for a metal coordination number of four16,40
42 whereas the signal observed for 3 is at higher field (
1030 ppm), which would agree with a lower coordination number for the metal.43
45 However, this difference — bearing in mind the number of factors that can affect the 199Hg chemical shifts44,45 — could also be due to a lower donor ability of the protonated ligand,46 which would also explain why the chemical shift for 2 appears at higher field than for 1.

’ CONCLUSION The mercury(II) complexes [HQ]2[Hg(Clpspa)2], [HP][Hg(Clpspa)(HClpspa)], and [Hg(HClpspa)2] [where HQ = diisopropylammonium and HP = triethylammonium cations and H2Clpspa = 3-(2-chlorophenyl)-2-sulfanylpropenoic acid] were synthesized and structurally characterized, the latter as [Hg(HClpspa)2 ] 3 4H 2 O. These compounds contain the [Hg(Clpspa)2]2
, [Hg(Clpspa)(HClpspa)]
, and [Hg(HClpspa)2] units, a finding that shows the presence of the ligand with different degrees of protonation. The structural characterization of the compounds showed that this protonation, which can be detected by spectroscopic methods and is produced on the carboxylate group, modifies the structural parameters of the Hg-kernel as well as the supramolecular association in the crystal. ’ ASSOCIATED CONTENT

bS

Supporting Information. Alternative views of the structures of [HP][Hg(Clpspa)(HClpspa)], [HQ]2[Hg(Clpspa)2], and [Hg(HClpspa)2] 3 4H2O (3 3 4H2O). CIF files giving X-ray data with details of refinement procedures for compounds 1, 2, and 3 3 4H2O. This information is available free of charge via the Internet at http://pubs.acs.org. The CIF files can also be obtained from the Cambridge Crystallographic Data Centre (CCDC) as CCDC-835889, CCDC-835890, and CCDC835891.

ARTICLE

’ AUTHOR INFORMATION Corresponding Author

*(M. D.C.) E-mail: delfi[email protected]. (J.S.) E-mail: jose.sordo@ usc.es. Tel.: 34-981-528074. Fax: 34-981-547102.

’ ACKNOWLEDGMENT We thank the Direcci
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