Synthesis, characterization and structure of the first rhenium compound of di-2-pyridyl ketone thiophene-2-carboxylic acid hydrazone (dpktah), fac-[Re(CO)3(N,N-K2-dpktah)Cl]

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Synthesis, characterization and structure of the first rhenium compoundof di-2-pyridyl ketone thiophene-2-carboxylic acid hydrazone (dpktah),fac-[Re(CO)3(N,N-j2-dpktah)Cl]

Mohammed Bakir *, Colin Gyles 1

Department of Chemistry, The University of the West Indies – Mona Campus, Kingston 7, Jamaica

a r t i c l e i n f o

Article history:Received 17 June 2008Received in revised form 21 July 2008Accepted 25 July 2008Available online 6 August 2008

Keywords:RheniumCarbonylDi-2-pyridyl ketoneHydrazoneX-ray structureSpectroscopy

a b s t r a c t

fac-[Re(CO)3(j2-N,N -dpktah)Cl], isolated from the reaction between [Re(CO)5Cl] and di-2-pyridyl ketonethiophene-2-carboxylic acid hydrazone (dpktah) in refluxing toluene, exhibits rich physico-chemicalproperties. The formulation of fac-[Re(CO)3(j2-N,N -dpktah)Cl] was established from the results of its ele-mental analysis and spectroscopic measurements, and confirmed using X-ray crystallography. The 1HNMR spectrum of fac-[Re(CO)3(j2-N,N-dpktah)Cl] revealed the coordination of dpktah and exchange ofthe amide proton. Electronic absorption measurements show two intra-ligand charge transfer transitions(ILCT) and established inter-conversion between fac-[Re(CO)3(j2-N,N-dpktah)Cl] and its conjugate base.Thermo-optical studies confirmed the facile inter-conversion between fac-[Re(CO)3(j2-N,N-dpktah)Cl]and its conjugate base. Optosensing measurements show [MCl2] (M = Zn, Cd or Hg) in concentrationsas low as 1.00 � 10�7 M can be detected and determined using protophilic solutions of fac-[Re(CO)3(j2-N,N-dpktah)Cl]. X-ray structural analysis done on a single crystal of fac-[Re(CO)3(j2-N,N-dpktah)Cl] confirmed its identity and divulge two symmetry-independent molecules in the asymmetricunit. The supramolecular structure of fac-[Re(CO)3(j2-N,N-dpktah)Cl] disclosed anti-parallel chainslocked via a network of hydrogen bonds. Non-classic hydrogen bonds of the type C–H. . .Cl connect mol-ecules in the chain and classic hydrogen bonds of the type N–H. . .O connect adjacent chains.

� 2008 Elsevier B.V. All rights reserved.

1. Introduction

Di-2-pyridyl ketone (dpk) and a range of its derivatives (seeScheme 1) are of current interest because of their physical proper-ties, reactivity patterns, and applications in several areas [1–44].We have been interested in the chemistry of di-2-pyridyl ketonederivatives and reported on the synthesis, structure, and electro-chemical and spectroscopic properties of a variety of their com-pounds including fac-[M(CO)3(j2-N,N-L-L)X] (M = Re or Mn;X = Cl or Br and L-L = dpk, dpkoxime and dpkhydrazone), fac-[Re(CO)3(j3-N,O,N-dpkO,OH)], and [MCl2(j3-N,N,O-dpkhydrazone)](M = Zn or Cd) [7,12,35–44]. Spectroscopic measurements ondpk-hydrazones and their metal complexes in non-aqueoussolvents show two intra-ligand charge transfer transitions (ILCT)that are sensitive to their surroundings [37,39,41,42,44]. Althoughthere has been a growing interest in the chemistry of di-2-pyridylketone derivatives, the coordination chemistry of di-2-pyridylketone hydrazones is scarce and centered around the reactions

between first-row metal salts and dpk-hydrazones to form com-plexes of the type [M(j3-N,N,O-dpkhydrazone)2] for analytical ortherapeutic applications [1–44]. In continuation of our efforts toexploit the coordination chemistry of dpk-derivatives, herein, wewish to report on the synthesis and characterization of the firstrhenium compound of di-2-pyridyl ketone thiophene 2-carboxylichydrazone (dpktah), fac-[Re(CO)3(j2-N,N-dpktah)Cl], wheredpktah binds to the metal center through the nitrogen atoms ofits pyridyl groups. In previous reports we described the synthesis,characterization and structure of [CdCl2(j3-N,N,O-dpktah)], wheredpktah binds to cadmium using one nitrogen atom of its pyridylgroup, a hydrazone nitrogen atom, and the carbonyl oxygen ofthe hydrazone backbone [12].

2. Experimental

2.1. Reagents and reaction procedures

The free ligand, dpktah, was prepared using a standard proce-dure as described for the synthesis of di-2-pyridyl ketonep-nitrophenyl hydrazone (dpknph) [37]. All other reagents wereobtained from commercial sources and used without furtherpurification.

0022-2860/$ - see front matter � 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.molstruc.2008.07.026

* Corresponding author. Tel.: +1 876 935 8164; fax: +1 876 977 1835.E-mail address: [email protected] (M. Bakir).

1 Present address: Department of Science and Mathematics, University of Tech-nology-Jamaica, 237 Old Hope Road, Kingston 6, Jamaica.

Journal of Molecular Structure 918 (2009) 138–145

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2.2. Preparation of fac-[Re(j2-N,N-dpktah)(CO)3Cl]

A mixture of [Re(CO)5Cl] (200 mg, 0.55 mmol), dpktah (0.22 mg,0.70 mmol) and toluene (50 mLs) was refluxed for 20 h. The result-ing reaction mixture was allowed to cool to room temperature andreduced in volume to �25 mL. An off-yellow solid was filtered off,washed with hexane and diethyl ether, and dried; yield 230 mg(68%) (Found: C, 37.78; H, 2.18; N, 8.71. C19H12ClN4O4SRe requiresC, 37.16; H, 1.97; N, 9.12%). Infrared data (KBr disk, cm�1): m(C„O)2020, 1910, 1873, m(C@O) 1644 and m(N–H) 3148 cm�1. 1H NMR (dppm): in dmso-d6 12.06 (s, 0.8H, NH), 9.04 (d, 1H, dpk), 8.93 (d, 1H,dpk), 8.30 (t, 1H dpk), 8.23 (t, 1H, dpk), 8.9 (broad d, 1.4H, thio-phene), 8.02 (d, 1H, dpk), 7.99 (d, 1H, dpk), 7.76 (t, 1H, dpk), 7.75(t, 1H, dpk) and 7.25 (t, 1H, thiophene). UV–vis (CH2Cl2, nm):326 (20,600.00); 287 (28,200.00); dmso: 440 (23,614.00), 324(18,745.00); dmf: 440 (32,246.00), 324 (16,850.00).

2.3. Physical measurements

Electronic absorption spectra were recorded on a Perkin-ElmerLambda 19 UV/VIS/NIR spectrometer. Solution 1H NMR spectra

were recorded on a Bruker ACE 500 MHz Fourier-transform spec-trometer and referenced to the residual protons in the incom-pletely deuterated solvent. Infrared spectra were recorded as KBrpellets on a Perkin-Elmer Spectrum 1000 FT-IR Spectrometer.

Table 1Crystal data and structure refinement for fac-[Re(CO)3(j2-N,N-dpktah)Cl]

Empirical formula C19H12ClN4O4ReSFormula weight 614.04Temperature (K) 298(2) KWavelength (Å) 0.71073Crystal system, space group Triclinic, P�1Unit cell dimensionsa (Å) 10.854(4)b (Å) 14.078(2)c (Å) 14.3861(13)a (�) 68.705(6)b (�) 89.874(12)c (�) 89.70(2)Volume (Å3) 2048.1(8)Z, calculated density (Mg/m3) 4, 1.991Absorption coefficient (mm�1) 6.200F(000) 1176Theta range for data collection (�) 2.41 to 19.99Limiting indices �16h610, �126k612, �136 l613Reflections collected/unique 4523/3740 [R(int) = 0.0269]Completeness to h = 19.99� 98.0%Refinement method Full-matrix least-squares on F2

Data/restraints/parameters 3740/0/542Goodness-of-fit on F2 1.045Final R indices [I > 2r(I)]a,b R1 = 0.0444, wR2 = 0.1184R indices (all data) R1 = 0.0517, wR2 = 0.1236Extinction coefficient 0.0016(3)Largest diff. peak and hole (e Å3) 1.787 and �1.254

a R1 =P

||Fo| � |Fc||/P

|Fo|.b wR2 = {

P[wðF2

o � F2c Þ

2]/P

wðF2oÞ

2]}1/2; where w = [r2ðF2oÞ + (0.0957P)2 + 1.84P]�1

and P = ðF2o þ 2F2

c Þ=3.

Scheme 2. dpktah and fac-[Re(CO)3(j2-N,N-dpktah)Cl].

Scheme 1. Selected di-2-pyridyl ketone derivatives.

500.001000.001500.002000.00

Wavenumber, cm-1

1

2

Fig. 1. Infrared spectra of dpktah (1) and fac-[Re(CO)3(j2-N,N-dpktahCl](2) measured in KBr.

M. Bakir, C. Gyles / Journal of Molecular Structure 918 (2009) 138–145 139


2.4. X-ray crystallography

Brown crystals of fac-[Re(CO)3(j2-N,N-dpktah)Cl] were ob-tained from an acetonitrile solution of fac-[Re(CO)3(j2-N,N-dpk-tah)Cl] when allowed to stand for several days. A single crystalwas selected and mounted on a glass fiber with epoxy cement. ABruker AXS with a Mo-Ka radiation and a graphite monochromatorwas used for data collection, and the SHELXTL software packageversion 5.1 was used for structure solution [45,46]. Cell parametersand other crystallographic information are given in Table 1. Allnon-hydrogen atoms were refined with anisotropic thermalparameters.

2.5. Analytical procedures

Elemental microanalyses were performed by MEDAC Ltd.,Department of Chemistry, Brunel University, Uxbridge, UnitedKingdom.

3. Results and discussion

The reaction between [Re(CO)5Cl] and dpktah in refluxing tol-uene gave fac-[Re(CO)3(j2-N,N-dpktah)Cl] (see Scheme 2) in goodyield. This reaction is similar to those reported for the synthesisof a variety of rhenium compounds of the type fac-[Re(CO)3

(L-L)Cl] where L-L = j2-N,N-bidentate ligand [35–39,47,48]. TheIR spectrum of fac-[Re(CO)3(j2-N,N-dpktah)Cl] (see Fig. 1) showspeaks consistent with the presence of coordinated carbonyl

(C„O) groups, and dpktah. In the carbonyl m(C„O) region, threestrong peaks appeared at 2020, 1920 and 1880 cm�1, similar to

0.00

0.10

0.20

0.30

0.40

300.00 400.00 500.00 600.00

Wavelength, nm

Abs

orba

nce

1

2

3

2

3

1

Fig. 2. Electronic absorption of fac-[Re(CO)3(j2-N,N-dpktah)Cl] in dmf (1), dmso(2) and CH2Cl2 (3).

0.00

0.10

0.20

0.30

0.40

0.50

300 400 500 600

Wavelength, nm

Abs

orba

nce

1

2

3

1

2

3

Fig. 3. Electronic absorption spectra of 2.00 � 10�5 M fac-[Re(CO)3(j2-N,N-dpk-tah)Cl] in dmf (1), in the presence of 1.00 � 10�3 NaBF4 (2) and in the presence of1.00 � 10�3 M NaBH4 (3).

-2.25

-2.00

-1.75

-1.50

-1.25

-1.00

-0.75

-0.50

2.70 2.90 3.10 3.30 3.50

1/Tx103, K-1

Ln(

A44

0/A

324)

1

2

Fig. 4. A plot of ln(A440/A324) versus 1/T � 103 K�1 of 2.00 � 10�5 M fac-[Re(CO)3(j2-N,N-dpktah)Cl] in dmso (1) and dmf (2).

140 M. Bakir, C. Gyles / Journal of Molecular Structure 918 (2009) 138–145


those reported for a variety of rhenium compounds of the typefac-[Re(CO)3(L-L)Cl], thus confirming the assigned fac-geometry[35,47,48]. The m(C@O) of the hydrazone moiety appeared at1644 cm�1 and the combined m(C@C) and m(C@N) of the pyridinevibrations appeared at 1602, 1590 and 1570 cm�1. In the spec-trum of free dpktah, the carbonyl stretching vibration m(C@O) ap-peared at 1660 cm�1 and the combined m(C@C) and m(C@N) ofthe pyridine vibrations appeared at 1586, 1578, and 1568 cm�1

[43]. These results confirm the coordination of dpktah and show

delocalization of the electron density of the carbonyl (C@O)group of dpktch upon coordination to rhenium moiety. A singleabsorption peak appeared in the m(NH) stretching mode at3148 cm�1, signaling a free N–H bond in the solid state [49].The 1H NMR spectrum of fac-[Re(CO)3(j2-N,N-dpktah)Cl] indmso-d6 shows resonances consistent with the binding of dpk-tah. Integration of the amide proton observed at 12.05 ppm tothe aromatic one proton observed at 9.04 ppm at 303.15 K gavea ratio of 0.80 consistent the partial exchange of the amide pro-ton with solvent protons. No evidence of paramagnetic linebroadening or unusual shifts of resonances appeared in the spec-tra of this compound, confirming its diamagnetic character.

The electronic absorption spectra of fac-[Re(CO)3(j2-N,N-dpk-tah)Cl] measured in non-aqueous solvents are sensitive to theirsurroundings. Fig. 2 shows the electronic absorption spectra offac-[Re(CO)3(j2-N,N-dpktah)Cl] in CH2Cl2, dmso, and dmf andFig. 3 shows the electronic absorption spectra of fac-[Re(CO)3(j2-N,N-dpktah)Cl] in dmf in the presence and absence of NaBH4 andNaBF4. In CH2Cl2, a strong absorption band appeared at 326 nm,and in dmso and dmf, two electronic transitions appeared between

Scheme 3. Acid–base inter-conversion of fac-[Re(CO)3(j2-N,N-dpktah)Cl].

Table 2Extinction coefficientsa and thermodynamic parameters of fac-[Re(CO)3(j2-N,N-dpktah)Cl] in dmf and dmso at 298.15 K

e440

(M�1 cm�1)e324

(M�1 cm�1)DH£

(kJ mol�1)DS£

(J mol�1)DG£

(kJ mol�1)K

dmf 32,246.00 16,850.00 �11.90 �41.38 +0.39 +0.12dmso 23,614.00 18,745.00 +12.70 +24.95 +5.27 +0.85

a Calculated using 2.00 � 10�5 M fac-[Re(CO)3(j2-N,N-dpktah)Cl] solution in thepresence and absence of 1 � 10�3 M NaBF4.

0.00

0.10

0.20

0.30

0.40

0.50

300.00 400.00 500.00 600.00

Wavelength, nm

Abs

orba

nce

[ZnCl2][ZnCl2]

1

2

3

4

5

6

7

1

2

3

Fig. 5. Electronic absorption spectra of 2.00 � 10�5 M fac-[Re(CO)3(j2-N,N-dpk-tah)Cl] in dmso (1) in the presence of 2.00 � 10�7 (2), 5.00 � 10�7 (3), 1.00 � 10�6

(4), 2.00 � 10�6 (5), 4.00 � 10�6 and 1.00 � 10�5 M [ZnCl2].

0.00

0.10

0.20

0.30

0.40

0.50

0.00 20.00 40.00 60.00 80.00 100.00 120.00

Concentration x 107, M

Abs

orba

nce

123

45

6

Fig. 6. A plot of the absorbance of fac-[Re(CO)3(j2-N,N-dpktah)Cl] 2.00 � 10�5 M indmso (1, 2 and 3) and its conjugate base (4, 5 and 6) versus concentration of [ZnCl2](1 and 6), [CdCl2] (2 and 5), [HgCl2] (3 and 4).



300 and 600 nm (see experimental section). The observed transi-tions are intra-ligand charge transfer (ILCT) due to p–p* of dpk fol-

lowed by dpk to thiophene charge transfer mixed with metal toligand charge transfer (MLCT). The intensity of the low energy elec-tronic transition increases as the solvent basicity increases, andpoints to protonation of the solvent by the amide proton of fac-[Re(CO)3(j2-N,N-dpktah)Cl] (see Scheme 3). This is consistent withthe 1H NMR results that show exchange of the amide proton of fac-[Re(CO)3(j2-N,N-dpktah)Cl] in dmso-d6 protons and completedeprotonation of fac-[Re(CO)3(j2-N,N-dpktah)Cl] using excessNaBH4. The reverse was obtained when NaBF4 was used in placeof NaBH4. A comparison of these spectra with those reported forthe free ligand show the low energy electronic transition of fac-[Re(CO)3(j2-N,N-dpktah)Cl] shifts to lower energy, and the highenergy electronic transition shifts to higher energy compared tothe free ligand, thus corroborating the mixed MLCT and ILCT char-acter of the electronic transitions of fac-[Re(CO)3(j2-N,N-dpk-tah)Cl] [43].

Variable temperature studies on a dmf solution of fac-[Re(-CO)3(j2-N,N-dpktah)Cl] show that as the temperature increases,the intensity of the low energy electronic transition decreasesand the intensity of the high energy electronic transition increases.The reverse was obtained when the temperature was allowed todecrease or when dmso was used in place of dmf. A plot ofln(A440/A324) of fac-[Re(CO)3(j2-N,N-dpktah)Cl] versus 1/T �103 K�1 in dmf and dmso gave straight lines that allowed for calcu-lation of the thermodynamic parameters (see Fig. 4 and Table 2) forthe inter-conversion between fac-[Re(CO)3(j2-N,N-dpktah)Cl] andits conjugate base.2 A comparison of these values with those re-ported for the free ligand suggests that the inter-conversion be-tween fac-[Re(CO)3(j2-N,N-dpktah)Cl] and its conjugate base ismore facile than that between dpktah and its conjugate base [44].

When fac-[Re(CO)3(j2-N,N-dpktah)Cl] was allowed to interactwith stoichiometric amounts of [MCl2] (M = Zn, Cd or Hg) in dmso,a progressive increase in the intensity of the low energy electronictransition and decrease in the intensity of high energy electronic

Scheme 4. Acid–base conversion of fac-Re(CO)3(j2-N,N-dpktah.MCl2)Cl.

Fig. 7. A view of the solid structure of fac-[Re(CO)3(j2-N,N-dpktah)Cl]. The thermalellipsoids are drawn at the 30% probability level.

Table 3Bond lengths (Å) and angles (�) for fac-[Re(CO)3(j2-N,N-dpktah)Cl]

Re–C(1) 1.912(15) Re0–C(10) 1.903(14)Re–C(2) 1.921(14) Re0–C(20) 1.888(14)Re–C(3) 1.899(14) Re0–C(30) 1.930(13)Re–N(1) 2.202(9) Re0–N(10) 2.193(8)Re–N(2) 2.222(8) Re0–N(20) 2.222(9)Re–Cl 2.456(3) Re0–Cl0 2.467(3)C(00)–N(3) 1.296(13) C(000)–N(30) 1.297(12)N(4)–C(4) 1.377(15) N(40)–C(40) 1.407(14)N(4)–N(3) 1.347(11) N(40)–N(30) 1.355(11)O(4)–C(4) 1.231(13) O(40)–C(40) 1.222(13)O(1)–C(1) 1.162(14) O(10)–C(10) 1.149(14)O(2)–C(2) 1.158(13) O(20)–C(20) 1.157(14)O(3)–C(3) 1.128(13)

N(1)–Re–N(2) 82.0(3) N(10)–Re0–N(20) 82.0(3)C(1)–Re–N(1) 174.5(4) C(10)–Re0–N(10) 176.3(4)C(2)–Re–N(1) 96.5(5) C(20)–Re0–N(10) 96.2(4)C(3)–Re–N(2) 91.0(4) C(30)–Re0–N(20) 92.3(4)C(2)–Re–N(2) 177.7(4) C(20)–Re0–N(20) 176.5(4)C(1)–Re–Cl 91.9(4) C(10)–Re0–Cl0 93.6(4)C(3)–Re–Cl 176.6(3) C(30)–Re0–Cl0 177.4(3)C(1)–Re–C(2) 87.4(5) C(20)–Re0–C(10) 86.8(6)C(3)–Re–C(1) 90.1(5) C(10)–Re0–C(30) 88.4(5)C(3)–Re–C(2) 90.9(5) C(20)–Re0–C(30) 90.8(5)O(1)–C(1)–Re 178.9(12) O(10)–C(10)–Re0 175.1(12)O(2)–C(2)–Re 176.1(11) O(20)–C(20)–Re0 178.1(11)O(3)–C(3)–Re 178.9(11) O(30)–C(30)–Re0 178.0(9)N(3)–N(4)–C(4) 120.6(9) N(30)–N(40)–C(40) 119.3(8)O(4)–C(4)–N(4) 119.2(10) O(40)–C(40)–N(40) 118.2(10)C(00)–N(3)–N(4) 121.2(8) C(000)–N(30)–N(40) 119.8(8)

2 For the following interconversion:

fac-½ReðCOÞ3ðj2-N;N-dpktahÞCl�¢ fac-½ReðCOÞ3ðj2-N;N-dpktah-HÞCl� ð1Þ

Application of Beer’s Law gives:

A440=A324 ¼ e440c440=e324c324 ð2Þand lnðA440=A324Þ ¼ lnðe440=e324Þ þ ln K ð3Þ

The equilibrium constant is related to the thermodynamic parameters as shown inEq. (4):

ln K ¼ DS;=R� DH;=RT ð4Þ

and the substitution of (4) into (3) gives:

lnðA440=A324Þ ¼ lnðe440Þ=e324 þ DS;=R� DH;=RT ð5Þ

A plot of lnðA440=A324Þ versus 1/T gives a straight line with a gradient of �DH;=R andan intercept of flnðe440=e324Þ þ DS;=Rg.



transition was observed. Fig. 5 shows the electronic absorptionspectra of fac-[Re(CO)3(j2-N,N-dpktah)Cl] in the presence and ab-sence of [ZnCl2] in dmso. A plot of absorbance of fac-[Re(CO)3

(j2-N,N-dpktah)Cl] and its conjugate base versus concentration of[MCl2] is shown in Fig. 6 and shows that [MCl2] in concentrationsas low as 1.00 � 10�7 M can be detected and determined, and that

Fig. 8. A view of the extended structure of fac-[Re(CO)3(j2-N,N-dpktah)Cl]. Non-covalent bonds are donated by dashed line.

Table 4Hydrogen bonds lengths (Å) and angles (�) for for fac-[Re(CO)3(j2-N,N-dpktah)Cl]

D–H...A d(D–H) d(H...A) d(D...A) <(DHA)

N(40)–H(40)...O(40)1 0.86 2.09 2.902(11) 156.0N(4)–H(4)...O(4)2 0.86 2.10 2.905(10) 156.4C(12)–H(12)...O(2)3 0.93 2.58 3.293(15) 133.6C(220)–H(220)...O(1)4 0.93 2.60 3.077(14) 112.4C(24)–H(24)...Cl05 0.93 2.81 3.586(11) 141.7C(240)–H(240)...Cl6 0.93 2.81 3.571(11) 139.7

Symmetry transformations used to generate equivalent atoms: 1 �x+1,�y, �z; 2 �x,�y+1, �z; 3 �x, �y+2, �z; 4 �x+1, �y+1, �z+1; 5 x�1, y, z; 6 x+1, y�1, z.

Fig. 9. Views of the hydrogen bonds in extended structure of fac-[Re(CO)3(j2-N,N-dpktah)Cl].



[MCl2] with high charge density (charge/size ratio) exhibits thehighest sensitivity. Although the nature of the interaction between[MCl2] and fac-[Re(CO)3(j2-N,N-dpktah)Cl] remains to be investi-gated, a plausible interaction may involve the coordination of[MCl2] to the hydrazone nitrogen and sulfur atoms of coordinateddpktah (see Scheme 4). The proposed mode of interaction increasesthe acidity of the amide proton, thus promoting facile acid–base in-ter-conversion between fac-[Re(CO)3(j2-N,N-dpktah.MCl2)Cl] andits conjugate base. The proposed mode of interaction is consistentwith the absence of any change in the energy of electronic transi-tions upon the addition of increasing amounts of [MCl2] and the in-crease in acidity of fac-[Re(CO)3(j2-N,N-dpktah)Cl] upon binding to[MCl2].

The solid state structure of fac-[Re(CO)3(j2-N,N-dpktah)Cl] wasdetermined using single crystal X-ray crystallography. A view ofthe molecular structure of fac-[Re(CO)3(j2-N,N-dpktah)Cl] isshown in Fig. 7 and reveals two symmetry-independent moleculesin the asymmetric unit. Each molecule in the asymmetric unitadopts distorted octahedral geometry with two nitrogen atomsfrom the pyridine rings of dpktah and two carbon atoms of coordi-nated carbonyl groups occupying the equatorial positions; the ax-ial positions are occupied by a chlorine atom and a carbon atom ofa coordinated carbonyl group. The carbonyl groups are in facialposition with an average [C–Re–C] angle of 89.06(4)� for bothenantiomers. The pyridine N,N-chelating dpktah forms a six mem-bered (Re–N–C–C–C–N) metallocyclic ring with the pyridine ringsin a butterfly formation. The hydrazone C@N–N–C backbone is co-planar, pointing in the same direction as the axial carbonyl group.The thiophene ring is not co-planar with the hydrazone backbone.The N–N bite angle [N(1)-Rex-N(2)] of 82.0(3)� in both enantio-mers is in the range reported for a variety of rhenium compoundscontaining a six membered Re–N–C–C–C–N metallocyclic ring, andis larger than those reported for a variety of rhenium compoundsthe type fac-[Re(CO)3(j2-N,N-L-L)Cl] that contain five-memberedRe–N–C–C–N metallocyclic ring [38,39,50–54]. The amide hydro-gen atom and carbonyl oxygen atom are in the cis position. Thebond distances and angles of the coordinated atoms (see Table 3)are normal and similar to those reported for a variety of rheniumcompounds of the type fac-[Re(CO)3(N-N)X] where N–N = a-dii-mine ligand and X = anion [38,39,51–54].

A view of the extended structure of fac-[Re(CO)3(j2-N,N-dpk-tah)Cl] is shown in Fig. 8 and reveals anti-parallel chains of fac-[Re(CO)3(j2-N,N-dpktah)Cl] linked via a network of hydrogenbonds (see Table 4 and Fig. 9). Non-classic hydrogen bonds ofthe type Cl. . .H–C link adjacent molecules in the chain (seeFig. 9a) while classic hydrogen bonds of the type O. . .H–N be-tween the carbonyl oxygen atom and amide proton of the hydra-zone backbone connect adjacent chains (see Fig. 9b). The bonddistances and angles of hydrogen bonds are normal and similarto those reported for a variety of compounds containing suchbonds [38,39].

Due to their diverse coordination modes, physical properties,reactivity patterns, and potential applications in several areas,work is in progress in our laboratory to further exploit the chemis-try of polypyridyl-like ligands and their metal compounds.

4. Conclusion

The first rhenium compound of dpktah, fac-[Re(CO)3(j2-N,N-dpktah)Cl], has been isolated and characterized. Spectroscopicmeasurements established facile inter-conversion between fac-[Re(CO)3(j2-N,N-dpktah)Cl] and its conjugate base, and show that[MCl2] in concentrations as low as 1.00 � 10�7 M can be detectedand determined using protophilic solutions of fac-[Re(CO)3

(j2-N,N-dpktah)Cl]. Single crystal X-ray structural determination

of fac-[Re(CO)3(j2-N,N-dpktah)Cl] shows two symmetry-indepen-dent molecules in the asymmetric unit and that the extendedstructure exhibits chains interlocked via a network of hydrogenbonds.

Acknowledgment

We acknowledge Ms. Tony Johnson for NMR measurements.

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Documents

Synthesis, characterization and structure of the first rhenium compound of di-2-pyridyl ketone thiophene-2-carboxylic acid hydrazone (dpktah), fac-[Re(CO)3(N,N-K2-dpktah)Cl]