Spectroscopic characterization of Schiff base coordinating monomolecular trinuclear complexes prepared through tailored synthesis

Article abstract of DOI:10.1080/00958972.2011.645814

A new bis-N,N′-bidentate Schiff base has been synthesized, characterized, and used in the synthesis of Ru^II and Rh^II complexes, which were further applied as precursors in the preparation of trinuclear complexes. These complexes were characterized by elemental analyses, molar conductance measurements, magnetic susceptibility, FTIR, TGA, FAB-mass, ESI-MS,¹H-NMR,¹³C{¹H}-NMR,¹H- ¹H COSY 2D-NMR, and electronic spectral studies. In complexes, one metal center is coordinated through azomethine nitrogen of bis-N,N′- bidentate Schiff base and the other two metal ions are coordinated through nitrogen of pyridine.

Full text of DOI:10.1080/00958972.2011.645814

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Spectroscopic characterization of Schiff
base coordinating monomolecular
trinuclear complexes prepared through
tailored synthesis
Ripul Mehrotra a , Satyendra N. Shukla b & Pratiksha Gaur b
a Department of Engineering Chemistry , ITM University ,
Gwalior , MP , India
b Coordination Chemistry Research Lab, Department of
Chemistry , Government Model Science College , Jabalpur , MP
482001 , India
Published online: 09 Jan 2012.
To cite this article: Ripul Mehrotra , Satyendra N. Shukla & Pratiksha Gaur (2012) Spectroscopic
characterization of Schiff base coordinating monomolecular trinuclear complexes prepared
through tailored synthesis, Journal of Coordination Chemistry, 65:1, 176-190, DOI:
10.1080/00958972.2011.645814
To link to this article: http://dx.doi.org/10.1080/00958972.2011.645814
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Journal of Coordination Chemistry
Vol. 65, No. 1, 10 January 2012, 176–190
Spectroscopic characterization of Schiff base coordinating
monomolecular trinuclear complexes prepared through
tailored synthesis
RIPUL MEHROTRA*y, SATYENDRA N. SHUKLAz and PRATIKSHA GAURz
yDepartment of Engineering Chemistry, ITM University, Gwalior, MP, India
zCoordination Chemistry Research Lab, Department of Chemistry,
Government Model Science College, Jabalpur, MP 482001, India
(Received 19 June 2011; in final form 11 November 2011)
A new bis-N,N0-bidentate Schiff base has been synthesized, characterized, and used in the
synthesis of RuII and RhII complexes, which were further applied as precursors in the
preparation of trinuclear complexes. These complexes were characterized by elemental analyses,
molar conductance measurements, magnetic susceptibility, FTIR, TGA, FAB-mass, ESI-MS,
1H-NMR, 13C{1H}-NMR, 1H-1H COSY 2D-NMR, and electronic spectral studies. In
complexes, one metal center is coordinated through azomethine nitrogen of bis-N,N0-bidentate
Schiff base and the other two metal ions are coordinated through nitrogen of pyridine.
Keywords: Monomolecular complexes; Rhodium; Ruthenium; Schiff base; Tailored synthesis
1. Introduction
The rational design and synthesis of new solids with organized molecular frameworks
and desirable structural and functional features is a major goal [1]. Metal-containing
supramolecules and coordination polymers have attracted interest because there are
many promising metal fragments available for construction of supramolecular
materials [2]. The homo and hetero coordinated multi-centered metal complexes are
known for magnetic, electronic, electrochemical, photo-optical, and catalytic
properties [3].
Several ruthenium compounds with coordinated dimethylsulfoxide have been shown
to possess good antitumor and antimetastatic properties against animal models. Among
these a Ru(III) complex, NAMI-A, is well-known for its good antimetastatic activity
[4–12]. [Rh(phen)2(phi)]3þ and [Ru(bpy)2(dppz)]3þ were accepted as probes and are
proposed to be metallo-intercalators for mismatch recognition in DNA base pairs
during DNA replication [13, 14].
*Corresponding author. Email: ripul.mehrotra@gmail.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2011.645814

Trinuclear ruthenium and rhodium complexes
177
We were interested to prepare Ru/Rh-containing trinuclear monomolecular
complexes based on quasi-octahedral geometries bearing Schiff-base ligands; Schiff
bases represent one of the most widely utilized classes of ligand in metal coordination
chemistry, finding importance in catalytic applications [15], and various biological
systems [16–18]. Development of a simple synthetic method to assemble commercially
available starting material is also important to extend the range of coordinating
structures in solution. From this synthetic strategy we have focused on a bis-N,N0-
bidentate Schiff base of isoniazid and synthesized 12 ruthenium- and rhodium-
containing complexes.
2. Experimental
RuCl3 ꢀ 3H2O (E. Merck), RhCl3 ꢀ 3H2O (E. Merck), tetramethylenesulfoxide
(Lancaster, UK), and o-phenylenediamine (E. Merck) were used as received.
Analytical grade dimethyl sulfoxide (E. Merck) and routine solvents were used without
purification for synthetic purposes.
Electronic absorption spectra were recorded with a Shimadzu-1700 UV-Vis spectro-
photometer equipped with a PC. Conductivity measurements were carried out at 25ꢁC
on an EI-181 conductivity bridge with a dipping type cell. FTIR spectra were recorded
1
in KBr pellets on a Shimadzu-8400 PC FTIR spectrophotometer. H-NMR, 13C{1H}-
NMR, and 2D-NMR (1H-1H COSY) spectra were recorded in acetone on a Bruker
DRX-300 NMR spectrometer. Gouy’s method was employed for measurement of
magnetic susceptibility; Hg[Co(NCS)4] was used as standard. Diamagnetic correction
was made using Pascal’s constants. Elemental analyses (C, H, N) were performed on an
Elementar Vario EL III Elemental analyzer. FAB-mass spectra were recorded on a Jeol
SX-102 mass spectrometer using NBA as matrix. Thermogravimetric data were in air at
10ꢁC minꢂ1 from 25ꢁC to 750ꢁC using a Shimadzu TGA-50H analyzer. An ESI-MS
spectrum was recorded on an Agilent 6520 Q-Tof mass spectrometer in acetonitrile.
2.1. Synthesis of Schiff base ligand
Ligand was synthesized by Schiff base condensation between isoniazid (INH) and
benzaldehyde with 1 : 1 ratio using standard procedure [19]. Schiff base of INH
(1.3908 g, 6.2 mmol) was dissolved in 25 mL absolute EtOH; to this solution
o-phenylenediamine (0.3352 g, 3.1 mmol) in EtOH (10 mL) was added and the reaction
mixture was kept under reflux for 5 h in an inert atmosphere. Color of the reaction
mixture changed from golden yellow to blood red. Dirty yellow solid was precipitated,
on transfer of blood red transparent solution (drop by drop) into ice cold water, which
was filtered off, washed with cold EtOH, and dried under vacuum. It was recrystallized
from ethanol/water/acetone, 3 : 1 : 2, v/v, to obtain dirty yellow shining crystals. Yield:
4.6548 g (64.7%). Found: C, 73.28; H, 5.06; N, 21.68; C32H26N8 (Mꢀ ¼ 522). Requires:
C, 73.54; H, 5.01; N, 21.44. Selected infrared absorption (KBr, cmꢂ1): ꢁ(N–H),
3436(w); ꢁ(CH¼N), 1635(s); ꢁ(C¼N), 1598(s). 1H-NMR (300 MHz, ꢂ, acetone):
11.18(s, 2H, ¼N–NH); 8.84(s, 2H, CH¼N); 8.62–6.97(m, 22H, Ar–H). 13C{1H}-NMR

178
R. Mehrotra et al.
(300 MHz, ꢂ, acetone): 168.6(CH¼N), 169.3(C¼N); 133.6–122.8(Ar–C). FAB-MS
[C32H26N8 þ H]þ m/z ¼ 523.
2.2. Synthesis of complexes
2.2.1. Preparation of Schiff base ruthenium precursors (1). A hot ethanolic (20 mL)
solution of the Schiff base (0.5226 g, 0.1 mmol) and a hot ethanolic (20 mL) solution of
RuCl3 ꢀ 3H2O (0.0261 g, 0.1 mmol) were mixed together with constant stirring. The
reaction mixture was refluxed for 12 h at ꢃ75ꢁC. On cooling, dark brown product
formed which was filtered off, washed with cold ethanol, and dried under vacuum over
fused calcium chloride. Purity of product was checked by TLC. Yield: 0.2054 g (77.3%);
m.p. 4 220ꢁC; Found: C, 55.52; H, 3.71; N, 16.20; C32H26N8Cl2Ru (Mꢀ ¼ 694).
Requires: C, 55.34; H, 3.77; N, 16.13. Selected infrared absorption (KBr, cmꢂ1):
ꢁ(N–H), 3438(w); ꢁ(CH¼N), 1621(s); ꢁ(C¼N), 1578(s); ꢁ(M–Cl), 335(s); ꢁ(M–N),
278(s). Electronic spectra (ꢃmax, nm (" in (mol Lꢂ1) cmꢂꢂ11)) in acetonitrile: 678(72),
530(216), 414(569), 340(948), 296(1098). Dm at 25ꢁC (ꢀ in (mol Lꢂ1) cmꢂ1): 52 in
DMSO, 98 in acetonitrile, 138 in acetone. 1H-NMR (300 MHz, ꢂ, acetone): 11.13(s, 2H,
¼N–NH); 9.02(s, 2H, CH¼N); 8.96-6.88(m, 22H, Ar–H). 13C{1H}-NMR (300 MHz, ꢂ,
acetone): 170.2(CH¼N), 170.8(C¼N); 134.0–121.2(Ar–C). FAB-MS (m/z):
[C32H26N8Cl2Ru104]þ ¼ 697, [C32H26N8Cl2Ru þ H]þ ¼ 695, [C32H26N8Cl2Ru96]þ ¼ 689,
[C32H26N8Cl2Ru–Cl]þ ¼ 659, [C32H26N8 þ H]þ ¼ 523, [RuCl2]þ ¼ 172.
2.2.1.1. Preparation of 2. Complex 1 (0.0695 g, 0.1 mmol) dissolved in acetone 15 mL
was added to precursor complex [cis, fac-RuCl2(S-dmso)3(O-dmso)] [20], (0.2 mmol) in
20 mL acetone and refluxed for 4–6 h. After cooling the precipitate was filtered off and
washed with water. Color: Black, Yield: 0.1245 g (79.9%); m.p. 4 220ꢁC; Found:
C, 35.11; H, 4.18; N, 7.52; S, 12.82; C44H62N8S6O6Cl6Ru3 (Mꢀ ¼ 1507). Requires: C,
35.06; H, 4.15; N, 7.43; S, 12.76. Selected infrared absorption (KBr, cmꢂ1): ꢁ(N–H),
3442(w); ꢁ(CH¼N), 1613(s); ꢁ(C¼N), 1581(s); ꢁ(SO), 1101(s); ꢁ(M–S), 407(m);
ꢁ(M–Cl), 333(s); ꢁ(M–N), 283(s). Electronic spectra (ꢃmax, nm (" in (mol Lꢂ1) cmꢂ1))
in acetonitrile: 663(58), 532(298), 402(582), 302(963). Dm at 25ꢁC (ꢀꢂ1 in
(mol Lꢂ1) cmꢂ1): 46 in DMSO, 101 in acetonitrile, 142 in acetone. 1H-NMR
(300 MHz, ꢂ, acetone): 11.17(s, 2H, ¼N–NH); 9.13(s, 2H, CH¼N); 8.84–6.93(m, 22H,
Ar–H); 3.52(s, 12H, CH3); 3.49(s, 12H, CH3); 3.42(s, 12H, CH3). 13C{1H}-NMR
(300 MHz, ꢂ, acetone): 170.0(CH¼N), 170.4(C¼N); 133.1–120.3(Ar–C); 45.8
(S–C); 44.9(S–C); 43.6þ(S–C). FAB-MS (m/z): [C44H62N8S6O6Cl367Ru3]þ ¼ 1519,
[C44H62N8S6O6Cl6Ru1304] ¼ 1516, [C44H62N8S6O6Cl6Ru3 þ H]þ ¼ 1508, [C44H62N8S6
O6Cl6Ru936]þ ¼ 1492, [C32 H26N8 þ H]þ ¼ 523.
2.2.1.2. Preparation of 3. Complex 3 was obtained from [trans-RuCl2(S-dmso)4] [21],
(0.2 mmol) in a manner similar to that used for synthesis of 2. Color: Black, Yield:
0.1068 g (68.6%); m.p. 4 220ꢁC; Found: C, 35.09; H, 4.12; N, 7.45; S, 12.78;
C44H62N8S6O6Cl6Ru3 (Mꢀ ¼ 1507). Requires: C, 35.06; H, 4.15; N, 7.43; S, 12.76.
Selected infrared absorption (KBr, cmꢂ1): ꢁ(N–H), 3430(w); ꢁ(CH¼N), 1622(s);
ꢁ(C¼N), 1588(s); ꢁ(SO), 1099(s); ꢁ(M–S), 406(m); ꢁ(M–Cl), 334(s); ꢁ(M–N), 278(s).
Electronic spectra (ꢃmax, nm (" in (mol Lꢂ1) cmꢂꢂ11)) in acetonitrile: 669(64), 528(244),
418(602), 328(992), 294(1046). Dm at 25ꢁC (ꢀ in (mol Lꢂ1) cmꢂ1): 68 in DMSO,

Trinuclear ruthenium and rhodium complexes
179
104 in acetonitrile, 152 in acetone. 1H-NMR (300 MHz, ꢂ, acetone): 11.14(s, 2H,
¼N–NH); 9.18(s, 2H, CH¼N); 8.98–7.06(m, 22H, Ar–H); 3.43(s, 12H, CH3); 3.32(s, 24H,
CH3). 13C{1H}-NMR (300 MHz, ꢂ, acetone): 169.8(CH¼N), 170.1(C¼N); 134.8–
120.9(Ar–C); 45.3(S–C); 44.6(S–C). FAB-MS (m/z): [C44H62N8S6O6Cl367Ru3]þ ¼ 1519,
[C44H62N8S6O6Cl6Ru1304]þ ¼ 1516,
[C44H62N8S6O6Cl6Ru3 þ H]þ ¼ 1508,
[C44H62N8S6O6Cl6Ru936]þ ¼ 1492, [C32H26N8 þ H]þ ¼ 523.
2.2.1.3. Preparation of 4. Complex 4 was obtained from [cis-RuCl2(S-tmso)4] [22],
(0.2 mmol) in a manner similar to that used for the synthesis of 2. Color: Black,
Yield: 0.0989 g (70.0%); m.p. 4 220ꢁC; Found: C, 40.51; H, 4.40; N, 6.70; S,
11.66; C56H74N8S6O6Cl6Ru3 (Mꢀ ¼ 1663). Requires: C, 40.43; H, 4.48; N, 6.74; S,
11.56. Selected infrared absorption (KBr, cmꢂ1): ꢁ(N–H), 3445(w); ꢁ(CH¼N),
1624(s); ꢁ(C¼N), 1582(s); ꢁ(SO), 1122(s); ꢁ(M–S), 398(m); ꢁ(M–Cl), 336(s); ꢁ(M–N),
275(s). Electronic spectra (ꢃmax, nm (" in (mol Lꢂ1) cmꢂ1)) in acetonitrile: 687(82),
546(276), 413(548), 304(1006). Dm at 25ꢁC (ꢀꢂ1 in (mol Lꢂ1) cmꢂ1): 56 in DMSO, 102 in
1
acetonitrile, 134 in acetone. H-NMR (300 MHz, ꢂ, acetone): 11.20(s, 2H, ¼N–NH);
9.14(s, 2H, CH¼N); 8.80–6.98(m, 22H, Ar–H); 4.06(m, 8H, S–CH2); 4.01(m, 8H,
S–CH2); 3.51(m, 8H, S–CH2); 2.31(m, 24H, S–C–CH2). 13C{1H}-NMR (300 MHz,
ꢂ, acetone): 169.3(CH¼N), 169.9(C¼N); 133.4–121.0(Ar–C); 57.8 (S–C); 57.4(S–C);
55.9(S–C);
27.3(S–C–C);
26.8(S–C–C);
25.1(S–C–C).þ FAB-MS
(m/z):
[C56H74N8
[C56H74N8S6O6Cl367Ru3]þ ¼ 1675,
[C56H74N8S6O6Cl6Ru1304] ¼ 1672,
S6O6Cl6Ru396]þ ¼ 1648, [C56H74N8S6O6Cl6Ru3 þ H]þ ¼ 1664, [C32H26N8 þ H]þ ¼ 523.
2.2.1.4. Preparation of 5. Complex 5 was obtained from [trans-RuCl2(S-tmso)4] [22],
(0.2 mmol) in a manner similar to that used for 2. Color: Black, Yield: 0.0964 g (68.2%);
m.p. 4 220ꢁC; Found: C, 40.38; H, 4.51; N, 6.78; S, 11.60; C56H74N8S6O6Cl6Ru3
(Mꢀ ¼ 1663). Requires: C, 40.43; H, 4.48; N, 6.74; S, 11.56. Selected infrared absorption
(KBr, cmꢂ1): ꢁ(N–H), 3435(w); ꢁ(CH¼N), 1617(s); ꢁ(C¼N), 1586(s); ꢁ(SO), 1128(s);
ꢁ(M–S), 401(m); ꢁ(M–Cl), 332(s); ꢁ(M–N), 274(s). Electronic spectra (ꢃmax, nm (" in
(mol Lꢂ1) cmꢂ1)) in acetonitrile: 686(86), 534(268), 420(596), 336(1044), 299(1123). Dm at
25ꢁC (ꢀꢂ1 in (mol Lꢂ1) cmꢂ1): 73 in DMSO, 109 in acetonitrile, 154 in acetone. 1H-NMR
(300 MHz, ꢂ, acetone): 11.15(s, 2H, ¼N–NH); 9.10(s, 2H, CH¼N); 8.94–6.83(m, 22H,
Ar–H); 3.98(m, 8H, S–CH2); 3.53(m, 16H, S–CH2); 3.36(m, 24H, S–C–CH2). 13C{1H}-
NMR (300 MHz, ꢂ, acetone): 170.1(CH¼N), 170.7(C¼N); 134.7–119.8(Ar–C); 57.2(S–
C);
55.8(S–C);
27.0(S–C–C);
25.4(S–C–C).
FAB-MS
(m/z):
[C56H74N8S6O6Cl367Ru3]þ ¼ 1675, [C56H74N8S6O6Cl6Ru3104]þ ¼ 1672, [C56H74N8S6
O6Cl6Ru3 þ H]þ ¼ 1664, [C56H74N8S6O6Cl6Ru936]þ ¼ 1648, [C32H26N8 þ H]þ ¼ 523.
2.2.1.5. Preparation of 6. Complex 6 was obtained from [mer-RhCl3(S-dmso)2(O-
dmso)] [23], (0.2 mmol) in a manner similar to that used for synthesis of 2. Color:
Blackish-brown, Yield: 0.0898 g (55.9%); m.p. 4 220ꢁC; Found: C, 33.78; H, 3.56;
N, 7.80; S, 9.08; C40H50N8S4O4Cl8RuRh2 (Mꢀ ¼ 1425). Requires: C, 33.70; H, 3.54; N,
7.86; S, 8.99. Selected infrared absorption (KBr, cmꢂ1): ꢁ(N–H), 3428(w); ꢁ(CH¼N),
1614(s); ꢁ(C¼N), 1583(s); ꢁ(SO), 1096(s); ꢁ(M–S), 402(m); ꢁ(M–Cl), 352(s), 330(s);
ꢁ(M–N), 282(s). Electronic spectra (ꢃmax, nm (" in (mol Lꢂ1) cmꢂ1)) in acetonitrile:
675(66), 541(258), 407(609), 298(1128). Dm at 25ꢁC (ꢀꢂ1 in (mol Lꢂ1) cmꢂ1): 58 in
DMSO, 111 in acetonitrile, 124 in acetone. 1H-NMR (300 MHz, ꢂ, acetone): 11.22(s, 2H,
¼N–NH); 9.08(s, 2H, CH¼N); 8.83–6.85(m, 22H, Ar–H); 3.48(s, 12H, CH3);

180
R. Mehrotra et al.
3.36(s, 12H, CH3). 13C{1H}-NMR (300 MHz, ꢂ, acetone): 169.8(CH¼N), 170.3(C¼N);
132.9–117.3(Ar–C); 45.7 (S–C); 44.8(S–C). FAB-MS (m/z): [C40H50N8S4O4
Cl387RuRh2]þ ¼ 1441,
[C40H50N8S4O4Cl8RuRh1203]þ ¼ 1429,
[C40H50N8S4O4Cl8
RuRh2 þ H]þ ¼ 1426, [C40H50N8S4O4Cl8Ru96Rh2]þ ¼ 1420, [C32H26N8 þ H]þ ¼ 523.
2.2.1.6. Preparation of 7. Complex 7 was obtained from [mer-RhCl3(S-tmso)2(O-
tmso)] [23], (0.2 mmol) in a manner similar to that used for 2. Color: Blackish-brown,
Yield: 0.1144 g (78.0%); m.p. 4 220ꢁC; Found: C, 37.74; H, 3.84; N, 7.40; S, 8.44;
C48H58N8S4O4Cl8RuRh2 (Mꢀ ¼ 1529). Requires: C, 37.69; H, 3.82; N, 7.32; S, 8.38.
Selected infrared absorption (KBr, cmꢂ1): ꢁ(N–H), 3440(w); ꢁ(CH¼N), 1619(s);
ꢁ(C¼N), 1581(s); ꢁ(SO), 1118(s); ꢁ(M–S), 400(m); ꢁ(M–Cl), 354(s), 338(s); ꢁ(M–N),
275(s). Electronic spectra (ꢃmax, nm (" in (mol Lꢂ1) cmꢂ1)) in acetonitrile: 682(78),
548(232), 404(561), 307(1093). Dm at 25ꢁC (ꢀꢂ1 in (mol Lꢂ1) cmꢂ1): 64 in DMSO, 113
in acetonitrile, 140 in acetone. 1H-NMR (300 MHz, ꢂ, acetone): 11.16(s, 2H, ¼N–NH);
9.12(s, 2H, CH¼N); 8.95–7.02(m, 22H, Ar–H); 3.96(m, 8H, S–CH2); 3.68(m, 8H,
S–CH2); 2.48(m, 16H, S–C–CH2). 13C{1H}-NMR (300 MHz, ꢂ, acetone): 170.1
(CH¼N), 170.9(C¼N); 134.6–121.1(Ar–C); 57.6 (S–C); 56.2(S–C); 26.9(S–C–C);
25.3(S–C–C). FAB-MS (m/z): [C40H58N8S4O4Cl387RuRh2]þ ¼ 1545, [C48H58N8S4O4Cl8
RuRh1203]þ ¼ 1533,
[C48H58N8S4O4Cl8RuRh2 þ H]þ ¼ 1530,
[C48H58N8S4O4Cl8
Ru96Rh2]þ ¼ 1524, [C32H26N8 þ H]þ ¼ 523.
2.2.2. Preparation of Schiff base rhodium precursor (8). A hot ethanolic (20 mL)
solution of the Schiff base (0.5226 g, 0.1 mmol) and a hot ethanolic (20 mL) solution of
RhCl3ꢀ3H2O (0.0263 g, 0.1 mmol) were mixed together with constant stirring. The
reaction mixture was refluxed for 8 h at ꢃ75ꢁC. On cooling, dark brown red product
formed, was filtered off, washed with cold ethanol, and dried under vacuum over fused
calcium chloride. Purity of product was checked by TLC. Yield: 0.2189 g (82.8%);
m.p. 4 220ꢁC; Found: C, 55.22; H, 3.80; N, 16.14; C32H26N8Cl2Rh (Mꢀ ¼ 696).
Requires: C, 55.19; H, 3.76; N, 16.09. Selected infrared absorption (KBr, cmꢂ1): ꢁ(N–
H), 3446(w); ꢁ(CH¼N), 1623(s); ꢁ(C¼N), 1587(s); ꢁ(M–Cl), 356(s); ꢁ(M–N), 280(s).
Electronic spectra (ꢃmax, nm (" in (mol Lꢂ1) cmꢂ1)) in acetonitrile: 478(126), 406(302),
332(763), 302(984). ꢄeff ¼ 1.87 mB; Dm at 25ꢁC (ꢀꢂ1 in (mol Lꢂ1) cmꢂ1): 12 in DMSO,
53 in acetonitrile, 12 in acetone. FAB-MS (m/z): [C32H26N8Cl327Rh]þ ¼ 700,
[C32H26N8Cl2Rh þ H]þ ¼ 697, [C32H26N8Cl2Rh-Cl]þ ¼ 661, [C32H26N8 þ H]þ ¼ 523,
[RhCl2]þ ¼ 173.
2.2.2.1. Preparation of 9. Complex 8 (0.0696 g, 0.1 mmol) dissolved in acetone
15 mL was added to [(dmso)2H]þ[trans-RuCl4(dmso)2]ꢂ [24], (0.2 mmol) in 20 mL
acetone and refluxed for 4–5 h. After cooling the precipitate was filtered off and washed
with water. Color: Blackish-brown, Yield: 0.1165 g (78.4%); m.p. 4 220ꢁC; Found:
C, 31.90; H, 3.92; N, 6.81; S, 11.72; C44H64N8S6O6Cl10Ru2Rh (Mꢀ ¼ 1653). Requires:
C, 31.97; H, 3.90; N, 6.78; S, 11.64. Selected infrared absorption (KBr, cmꢂ1):
ꢁ(N–H), 3441(w); ꢁ(CH¼N), 1625(s); ꢁ(C¼N), 1579(s); ꢁ(SO), 1098(s), 1054(s);
ꢁ[(dmso)2H]þ, 728(br s); ꢁ(M–S), 397(m); ꢁ(M–Cl), 352(s), 335(s); ꢁ(M–N), 288(s).
Electronic spectra (ꢃmax, nm (" in (mol Lꢂ1) cmꢂ1)) in acetonitrile: 483(148),
410(284), 335(782), 300(1002). ꢄeff ¼ 1.72 mB; Dm at 25ꢁC (ꢀꢂ1 in (mol Lꢂ1) cmꢂ1):
126
in
DMSO.
FAB-MS
(m/z):
[C44H64N8S6O6Cl3107Ru2Rh]þ ¼ 1673,

Trinuclear ruthenium and rhodium complexes
181
[C44H64N8S6O6Cl10Ru1204Rh]þ ¼ 1659, [C44H64N8S6O6Cl10Ru2Rh103]þ ¼ 1655, [C44H64
N8S6O6Cl10Ru2Rh þ H]þ ¼ 1654,
N8 þ H]þ ¼ 523.
[C44H64N8S6O6Cl10Ru926Rh]þ ¼ 1643,
[C32H26
2.2.2.2. Preparation of 10. Complex 10 was obtained from [Na]þ[trans-
RuCl4(dmso)2]ꢂ [24], (0.2 mmol) in a manner similar to that used for 9. Color:
Blackish-brown, Yield: 0.1345 g (82.1%); m.p. 4 220ꢁC; Found: C, 31.30; H, 2.75;
N, 8.15; S, 4.71; C36H38N8S2O2Cl10Na2Ru2Rh (Mꢀ ¼ 1384). Requires: C, 31.23; H,
2.77; N, 8.09; S, 4.63. Selected infrared absorption (KBr, cmꢂ1): ꢁ(N–H), 3447(w);
ꢁ(CH¼N), 1615(s); ꢁ(C¼N), 1577(s); ꢁ(SO), 1108(s); ꢁ(M–S), 399(m); ꢁ(M–Cl), 356(s),
333(s); ꢁ(M–N), 281(s). Electronic spectra (ꢃmax, nm (" in (mol Lꢂ1) cmꢂ1)) in
acetonitrile: 472(139), 397(296), 340(744), 303(963). ꢄeff ¼ 1.78 mB; Dm at 25ꢁC (ꢀꢂ1
in (mol Lꢂ1) cmꢂ1): 118 in DMSO. FAB-MS (m/z): [C36H38N8S2O2Cl10
Na2Ru2Rh þ Na]þ ¼ 1407,
S2O2Cl10Na2Ru926Rh]þ ¼ 1374, [C32H26N8 þ H]þ ¼ 523.
[C36H38N8S2O2Cl3107Na2Ru2Rh]þ ¼ 1404,
[C36H38N8S2
O2Cl10Na2Ru2104Rh]þ ¼ 1390, [C36H38N8S2O2Cl10Na2Ru2Rh103]þ ¼ 1385, [C36H38N8
2.2.2.3. Preparation of 11. Complex 11 was obtained from [(tmso)H]þ[trans-
RuCl4(tmso)2]ꢂ [22], (0.2 mmol) in a manner similar to that used in synthesis of 9.
Color: Blackish-brown, Yield: 0.0987 g (68.6%); m.p. 4 220ꢁC; Found: C, 31.10; H,
3.80; N, 6.89; S, 8.06; C48H60N8S4O4Cl10Ru2Rh (Mꢀ ¼ 1600). Requires: C, 31.01; H,
3.78; N, 6.99; S, 8.01. Selected infrared absorption (KBr, cmꢂ1): ꢁ(N–H), 3433(w);
ꢁ(CH¼N), 1620(s); ꢁ(C¼N), 1582(s); ꢁ(SO), 1126(s), 1028(s); ꢁ[(tmso)H]þ, 724(brs);
ꢁ(M–S), 403(m); ꢁ(M–Cl), 351(s), 337(s); ꢁ(M–N), 280(s). Electronic spectra (ꢃmax, nm
(" in (mol Lꢂ1) cmꢂ1)) in acetonitrile: 486(142), 399(278), 344(792), 299(998).
ꢄeff ¼ 1.67 mB; Dm at 25ꢁC (ꢀꢂ1 in (mol Lꢂ1) cmꢂ1): 138 in DMSO. FAB-MS
(m/z): [C48H60N8S4O4Cl3170Ru2Rh]þ ¼ 1620, [C48H60N8S4O4Cl10Ru1204Rh]þ ¼ 1606,
[C48H60N8S4O4Cl10Ru2Rh103]þ ¼ 1602,
[C48H60N8S4O4Cl10Ru2Rh þ H]þ ¼ 1601,
[C48H60 N8S4O4Cl10Ru926Rh] þ ¼ 1590, [C32H26N8 þ H]þ ¼ 523.
2.2.2.4. Preparation of 12. Complex 12 was obtained from [(dmso)2H]þ
[trans-RhCl4(dmso)2]ꢂ [25], (0.2 mmol) in a manner similar to that used for synthesis
of 9. Color: Blackish-brown, Yield: 0.1244 g (83.8%); m.p. 4 220ꢁC; Found: C, 31.89;
H, 3.85; N, 6.81; S, 11.70; C44H64N8S6O6Cl10Rh3 (Mꢀ ¼ 1656). Requires: C, 31.90;
H, 3.89; N, 6.76; S, 11.61. Selected infrared absorption (KBr, cmꢂ1): ꢁ(N–H), 3439(w);
ꢁ(CH¼N), 1618(s); ꢁ(C¼N), 1584(s); ꢁ(SO), 1103(s), 1056(s); ꢁ[(dmso)2H]þ, 726(brs);
ꢁ(M–S), 406(m); ꢁ(M–Cl), 358(s); ꢁ(M–N), 276(s). Electronic spectra (ꢃmax, nm (" in
(mol Lꢂ1) cmꢂ1)) in acetonitrile: 484(128), 408(298), 346(801), 297(1004). ꢄeff ¼ 1.82 mB;
Dm at 25ꢁC (ꢀꢂ1 in (mol Lꢂ1) cmꢂ1): 132 in DMSO. FAB-MS (m/z):
[C44H64N8S6O6Cl3107Rh3]þ ¼ 1676, [C44H64N8S6O6Cl10Rh1303]þ ¼ 1662, [C44H64N8S6
O6Cl10Rh3 þ H]þ ¼ 1657, [C32H26N8 þ H]þ ¼ 523.
3. Results and discussion
Empirical formulae of Schiff base (Schiff base ligand, SBL) and 1–12 were in
conformity with elemental analyses. Molecular weights were determined by mass

182
R. Mehrotra et al.
spectral study. In mass spectra of 1–12 isotopic patterns clearly identify Ru- and
Rh-containing ions, because there are few relevant ions in spectrum. Only six important
ions appear in each spectrum contain ruthenium, although there may be more than
one kind of each of these ions due to the presence of different kinds of ligands in
the analyte. Since ruthenium has six isotopes with significant natural abundance
(415%) from 96 to 104 amu, rhodium has one 103 amu and Cl has two (35 and
37 amu). Metal complexes never give the parent ion in FAB-MS spectrum, as molecular
ion (figure 1). Thus, the ion of highest mass observed in spectrum is the complex
cation [26].
The molar conductivities for 1–7 were between 46 and 73 in DMSO, 98 and 113 in
acetonitrile, and 138and 154 in acetone, within the ranges suggested for 1 : 1 electrolytes
[27]. In solution one chloride is replaced by solvent, leading to the 1 : 1 electrolyte; the
second chloride must not undergo exchange by another solvent molecule, or we would
observe a 2 : 1 electrolyte.
To obtain qualitative information in relation to the type of species present in
solution, 1 was analyzed by ESI-MS in acetonitrile. The ESI-MS method was chosen
because ions formed upon ESI under soft ionization conditions correlate with species
that exist in solution [28, 29]. The ESI-MS spectrum of 1 was recorded in different time
intervals (initially to 48 h). The main peaks observed in ESI spectra were according to
ion masses and their isotopic patterns Ru(II) gaseous mono-cations
[RuCl(SBL)(ACN)]þ (m/z ¼ 700) (figure 2). These findings are fully consistent with
conductivity data, that during dissolution in solution, one chloride is replaced by
solvent (reaction 1). However no further exchange with the second chloride is observed
(reaction 2). Molar conductance for 8 was low, indicating its nonelectrolytic nature in
solutions, confirming Clꢂ remains coordinated. This feature also supports that rhodium
derivatives, unlike the ruthenium complexes [30], are stable in solutions and have no
Figure 1. FAB-MS of 1.

Trinuclear ruthenium and rhodium complexes
183
Figure 2. ESI-MS of 1 in acetonitrile.
tendency to form polymeric aggregates. Molar conductances for 9–12 were 118–138
indicating their ionic nature [24, 31].
½RuCl2ðSBLÞꢄ þ Solvent ! ½RuCl ðSBLÞðSolventÞꢄþ þ Clꢂ,
½RuClðSBLÞðSolventÞꢄþ þ Solvent ! No exchange:
ð1Þ
ð2Þ
3.1. Infrared spectral analysis
In FTIR spectra of INH Schiff base, a band at 1690 cmꢂ1, corresponding to free (C¼O)
amide stretch [32], vanished in spectra of Schiff base chelate, suggesting complete
condensation of amide C¼O with primary amine. A new strong absorption at
1598 cmꢂ1 is attributable to characteristic stretching frequencies of the imino linkage
ꢁ(C¼N). The band for free ꢁ(CH¼N) in INH Schiff base, ꢃ1635 cmꢂ1, is found at
almost the same position in FTIR spectra of synthesized SBL. In complexes both bands
were shifted to lower wavenumber by ꢃ10–22 cmꢂ1 indicating coordination takes place
through the nitrogen of (C¼N) group [33]. This was also confirmed by appearance of
ꢁ(M–N) at ꢃ280 cmꢂ1. A weak band in the range ꢃ3440 cmꢂ1 in synthesized Schiff base
is assigned for secondary –NH.
Pyridine ring vibrations are affected by nitrogen coordination with a metal. Most
affected are pyridine ring deformation, in plane ring deformation, and out-of-plane
deformation [34], which appear at 1580–1585, 620–640, and 410–420 cmꢂ1, respectively,
in free ligands. In-plane ring deformation and out-of-plane deformation on coordina-
tion to metal show positive shifts by ꢃ25–30 cmꢂ1 [35, 36]. The pyridine ring
deformation is less sensitive to coordination, in spectra of 2–7 and 9–12; this band is
superimposed or masked out. The ꢁ(M–Npy) at ꢃ280 cmꢂ1 also verified coordination of
pyridine nitrogen with metal in these complexes [31].
In 2–7 and 9–12, one or two bands at 1096–1128 cmꢂ1 were assigned for ꢁ(SO). This
band at 1054 cmꢂ1 for free dmso and 1028 cmꢂ1 for free tmso shows a positive shift in
ꢁ(SO), indicating coordination of sulfur to metal. In all complexes a band near 400 cmꢂ1
was assigned for ꢁ(M–S). Sharp bands between 360 and 330 cmꢂ1 were assigned for

184
R. Mehrotra et al.
ꢁ(M–Cl) stretch. In 9, 11, and 12 a broad band at ꢃ725 cmꢂ1 along with a sharp band at
ꢃ1054 cmꢂ1 for dmso analog and at 1028 cmꢂ1 in tmso analog indicates the presence of
hydrogen bonded dmso/tmso [20, 21, 24, 31].
3.2. Electronic spectral analysis and magnetic moment
Complexes 1–7 are diamagnetic (low spin d6, s ¼ 0), as expected for low spin Ru(II) and
Rh(III) complexes. These complexes show four or five bands in electronic spectra. In 6
and 7, three broad absorptions with low extinction coefficient were observed at
1
3
682–675 nm, 548–541 nm, and 407–404 nm, which may be assigned for A1g ! T1g,
1
1
1
1
1
1A1g ! T1g, and A1g ! T2g of Rh(III) [37] and which may include A1g ! T1g and
1
1A1g ! T2g transition assigned for Ru(II) complexes. In 1–5, higher energy absorption
at 420–402 nm was probably due to MLCT transition. However higher energy
absorption bands below 340 nm were attributed to ꢅ ! ꢅ* intraligand transition in the
coordinated ꢅ–acidic imine [38–41].
Low spin Ru(III) complexes are (d5) and Rh(II) are (d7) system. In electronic spectra
of 9–11, four bands were observed between 486 and 472 nm, 410 and 397 nm, 344 and
335 nm, and 303 and 299 nm. The intense absorption at ꢃ406 nm coupled with a less
intense transition at 480 nm was ascribed to charge transfer from chloride to Ru(III), a
typical identification for RuClꢂ4 [42]. The lowest energy absorptions in 8–12 may
4
4
4
4
4
4
correspond to T1g(F) ! T2g(F), T1g ! A2g, and T1g(F) ! T1g(P) transitions of
Rh(II). These bands are characteristic of an octahedral environment around Rh2þ [43].
In 9, 11, and 12 a weak absorption at 300 nm was due to the presence of protonated
sulfoxide cation [38–41].
Complex 8 is paramagnetic with magnetic moment 1.87 BM. For 9–12, magnetic
moments range between 1.67 and 1.82 BM at room temperature, lower than the
predicted values. This lowering may occur due to the presence of low symmetry ligand
fields, metal–metal interactions, or extensive electron delocalization between the species
linking paramagnetic centers [44]. This spin–spin alternation leads to antiferromagnetic
coupling which depends on the number of atoms located between the interacting
ions [45].
3.3. NMR spectral analysis
1
In H-NMR spectrum of Schiff base, a sharp signal for two ¼N–NH groups was
observed at ꢂ 11.18 ppm [46], not much shifted after complexation, indicating
noninvolvement of ¼N–NH in coordination. Nonappearance of signal for –NH2
near ꢂ 5.00 ppm indicates its involvement during condensation with (C¼O) amide
carbonyl. The singlet at ꢂ 8.84 ppm was assigned for two azomethine protons. This
signal shifts downfield between ꢂ 9.18 and 9.02 ppm after complexation, probably due
to lone pair donation from azomethine (CH¼N) nitrogen to metal [47]. Signals for
22 aromatic and hetero aromatic protons were between ꢂ 8.62 and 6.97 ppm.
In 1H-1H COSY NMR spectrum of Schiff base (Supplementary material), cross-peaks
were observed in the aromatic region due to proton–proton coupling between connected
carbons [20]. A signal for hetero aromatic proton at ꢂ 8.62 ppm for Hpy-ortho is connected
by cross-peak to the signal at ꢂ 8.21 ppm assigned for Hpy-meta. The signal Ar–Hmeta at

Trinuclear ruthenium and rhodium complexes
185
ꢂ 7.96 ppm is connected to two separate signals observed at ꢂ 7.51 ppm for Ar–Hpara and
ꢂ 6.97 ppm for Ar–Hortho by cross-peaks.
In 13C{1H}NMR spectra of Schiff base (Supplementary material), the multiplet
between ꢂ 133.6 and 122.8 ppm is assigned for aromatic carbons. Signal for (C¼O)
amide at ꢂ 163.2 ppm in INH Schiff base spectra completely disappeared and a new
signal was observed at ꢂ 169.3 ppm, assigned for ꢂ(C¼N), confirming involvement of
(C¼O) amide in condensation. Signal for ꢂ(CH¼N) was observed at ꢂ 168.6 ppm. Both
signals were shifted downfield in all complexes, confirming binding of metal with imine
nitrogen [47]. Thus on the basis of above discussion the most plausible structure for the
ligand is suggested in figure 3.
1
In H-NMR spectra of 1–7, signals for aromatic protons were between ꢂ 8.98 and
6.83 ppm and in 13C{1H}-NMR spectra aromatic carbons were between ꢂ 134.8 and
117.3 ppm.
In 1H-NMR spectra of 2, three singlets were observed with intensity 1 : 1 : 1,
indicating three different methyl protons of dmso. Signals at ꢂ 3.52 and ꢂ 3.49 ppm
(for 12 protons each) were assigned for CH3 protons of dmso trans to Cl, which are
diastereotopic; signal at ꢂ 3.42 ppm was assigned for 12 methyl protons of dmso trans to
pyridine of the chelate [20, 31, 48]. Similar structure is derived from 13C{1H}-NMR
spectra where three signals at ꢂ 45.8, ꢂ 44.9, and ꢂ 43.6 ppm confirm the presence of three
environments for methyl carbons.
In 1H-NMR spectra of 3, two singlets with intensity ratio 1 : 2 were observed,
indicating two types of CH3 protons. The singlet at ꢂ 3.43 ppm for 12 protons was
assigned for dmso trans to pyridine and the singlet at ꢂ 3.32 ppm for 24 protons to
dmso’s trans to each other. In 13C{1H}-NMR spectra two signals for (S–C) carbon of
1
dmso at ꢂ 45.3 and ꢂ 44.6 ppm confirms the H suggestions.
1
However in H-NMR spectra of 4, four signals were observed with relative intensity
of 1 : 1 : 1 : 3, indicating four environments for tmso protons. Multiplets at ꢂ 4.06 and
ꢂ 4.01 ppm (for eight protons each) are assigned for S–CH2 of tmso, trans to Cl,
and probably diastereotopic. The multiplet centered at ꢂ 3.51 ppm, for eight pro-
tons, was assigned for two S–CH2 protons of tmso trans to pyridine of the chelate. The
multiplet at ꢂ 2.31 ppm was assigned for 24 protons of all S–C–CH2 groups [31, 48–50].
N
N
NH
HN
N
N
N
N
Figure 3. 3-D structure of Schiff base.

186
R. Mehrotra et al.
Similarly in 13C{1H}-NMR spectra of this complex signals at ꢂ 57.8 and ꢂ 57.4 ppm
were assigned for S–C of tmso trans to Cl and signal at ꢂ 55.9 ppm for S–C of tmso
trans to pyridine. Signals at ꢂ 27.3, ꢂ 26.8, and ꢂ 25.1 ppm were assigned for (S–C–C)
carbons of tmso.
Similarly, 5 exhibits three sets of multiplets centered at ꢂ 3.98, ꢂ 3.53, and
ꢂ 3.36 ppm. Signals at ꢂ 3.98 and ꢂ 3.53 ppm were assigned for S–CH2 and the signal
at ꢂ 3.36 ppm for S–C–CH2 of tmso. Intensity ratio of these three signals is 1 : 2 : 3.
Thus one tmso is trans to the nitrogen and the other two are trans to each other.
Similar conclusion can be inferred from 13C{1H}-NMR spectra, where signals are
observed at ꢂ 57.2 ppm (S–C trans to pyridine nitrogen) and ꢂ 55.8 ppm (S–C tmso
trans to each other). Signals at ꢂ 27.0 and ꢂ 25.4 ppm are for (S–C–C) carbon of
tmso [31, 48–50].
In 1H-NMR spectra of 6, two singlets with intensity 1 : 1 indicate two different types
of protons; ꢂ 3.48 ppm for 12 protons was assigned for methyl of dmso trans to Cl and
ꢂ 3.36 ppm was assigned for 12 methyl protons of dmso trans to pyridine. In
13C{1H}-NMR spectra two signals were observed for S–C of dmso at ꢂ 45.7 and
ꢂ 44.8 ppm [31, 48].
In 1H-NMR spectra of 7, three multiplets were observed. Signals at ꢂ 3.96
and ꢂ 3.68 ppm were assigned for S–CH2 and at ꢂ 2.48 ppm for S–C–CH2 of tmso [31,
48–50]. In 13C{1H}-NMR spectra, ꢂ 57.6 ppm was assigned for S-C of tmso trans to Cl
and ꢂ 56.2 ppm for S–C of tmso trans to pyridine. Signals at ꢂ 26.9 and ꢂ 25.3 ppm were
assigned for S–C–C of tmso.
3.4. Thermal analysis
Thermal analysis gives information about stability of metal chelates and water
molecules inside or outside the coordination sphere. In 1 and 8, decomposition involved
two steps, the first step loss of two chlorides at 280–300ꢁC and the second loss at 350–
450ꢁC, giving M2O3 [M ¼ Ru(II) and Rh(II)]. The end products of stable metal oxides
such as Ru2O3, Rh2O3 and sometimes even RuO2 were found at 680–720ꢁC as matter
[36, 51]. The absence of an endothermic peak confirmed that the complexes were not
hydrated.
3.5. Structures of 1–7
On the basis of elemental analyses, conductivity experiments, TGA, and spectroscopic
1
studies (FTIR, UV-Vis, FAB-mass, ESI-MS, H-NMR, and 13C{1H}-NMR) the most
plausible structures for 1–7 are suggested in figure 4.
3.6. Structure of paramagnetic complexes 8–12
Signals in NMR spectra of 8–12 were broad and shifted from their original position,
due to paramagnetism [31, 47, 48]. Aqueous solution of 8 does not respond to
qualitative silver nitrate test, confirming that rhodium is þ2 and no Clꢂ ion is coupled
through primary valence to central metal ion. The binding modes of chelate in 8–12 are

Trinuclear ruthenium and rhodium complexes
187
Complex 1
Complex 2/4
Complex 3/5
Complex 6/7
SO = dmso in 2, 3, 6 and tmso in 4, 5, 7
Figure 4. 3-D structure of 1–7.
concluded on the basis of elemental analyses, conductivity experiments, TGA, and
spectroscopic (FTIR, UV-Vis, and FAB-mass) studies as suggested in figure 5.
4. Conclusion
We have prepared and spectroscopically characterized two RuII/RhII complexes with a
new bis-N,N0-bidentate Schiff base. This RuII/RhII Schiff base complex was utilized as
spacer in stepwise synthesis of trinuclear compounds. Participation of passive amide
carbonyl group in Schiff base condensation makes synthesis of the ligand quite
interesting. The imine interactions with metal and lone pair donation from metal
chelate to sulfoxide precursors make syntheses fascinating. Consequently, tailored
synthetic approach plays a significant role in the preparation of multi-nuclear

188
R. Mehrotra et al.
Complex 8
Complex 9/10/11
Complex 12
SO = dmso in 9, 10, 12 and tmso in 11.
[X]+ = [(dmso)2H]+ in 9 and 12; [Na]+ in 10; [(tmso)H]+ in 11.
Figure 5. 3-D structure of 8–12.
compounds. Qualitative examination of RuII/RhII Schiff base chelate complexes in
solutions conclude that on dissolution, in the RuII complex one chloride is substituted
with solvent, resulting in 1 : 1 electrolyte, while RhII chelate complexes are stable in
solutions.
Acknowledgments
The authors are grateful to Prof. Jim Atwood for his valuable comments and
suggestions, which were helpful in preparing the revised version of the manuscript. They
are also grateful to Principal and Head, Chemistry Department, Government Model
Science College, Jabalpur, for providing laboratory facilities and continuous encour-
agement. They thank SAIF, CDRI, Lucknow, for recording spectra and elemental data.
RM is grateful to the CSIR, New Delhi, India for sanctioning the Senior Research
Fellowship (F. No. 08/31(0008)/2009-EMR-I).

Trinuclear ruthenium and rhodium complexes
189
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