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Inorganica Chimica Acta 360 (2007) 2009–2015

Synthesis and characterization of some oxovanadium(V) complexeswith internally functionalized oximes: Crystal and molecular

structures of heptacoordinated [VO{ON@C(CH3)(C4H3O-2)}3]and [VO{ON@C(CH3)(C4H3S-2)}3] Æ 0.5C6H6

Vineet Sharma a, Vinita Sharma a, Rakesh Bohra a,*, John E. Drake b,Michael B. Hursthouse c, Mark E. Light c

a Department of Chemistry, University of Rajasthan, Jaipur 302 004, Rajasthan, Indiab Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ont., Canada N9B 3P4

c Department of Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

Received 3 August 2006; received in revised form 18 October 2006; accepted 20 October 2006Available online 27 October 2006

Abstract

New oxovanadium(V) complexes with internally functionalized oximes of the type VO{OPri}3�n{ON@C(CH3)(Ar)}n] (whereAr = C4H3O-2, C4H3S-2 and C5H4N-2 and n = 1–3) have been prepared in quantitative yields by the reaction of VO(OPri)3 with thecorresponding oximes in various stoichiometric ratios in refluxing anhydrous benzene. The products have been characterized by elemen-tal analyses and spectroscopic (FT IR, 1H, 13C{1H} and 51V NMR) studies. FAB mass spectral analysis of [VO{O-Pri}{ON@C(CH3)C4H3S}2] indicates the monomeric nature of the complex. 51V NMR values for these complexes suggest theformation of tetra-coordinate species in solution. However, the single crystal X-ray diffraction studies of [VO{ON@C(CH3)(C4H3O-2)}3] and [VO{ON@C(CH3)(C4H3S-2)}3] Æ 0.5C6H6 exhibit the presence of vanadium(V) atoms in a unique hepta-coordination state withdistorted pentagonal bipyramidal geometry in the solid state. The oxo- atom occupies the axial position while the oximato ligands arebonded in a dihapto (g2-N,O) manner with the formation of three membered rings.� 2006 Elsevier B.V. All rights reserved.

Keywords: Oxovanadium(V) complexes; Internally functionalized oximes; 51V NMR; Hepta-coordination; Dihapto bonding

1. Introduction

Coordination chemistry of oxovanadium(V) complexeshas attracted considerable research interest due to theirimportance in biological [1] as well as in catalytic processes[2]. They also find applications in the field of material sci-ences [3]. A wide range of structural variations associatedwith their diverse reactivity are also making them the cen-ter of continuous research activities [4].

0020-1693/$ - see front matter � 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.ica.2006.10.017

* Corresponding author. Tel./fax: +91 141 2700364.E-mail address: rkbohra@sifymail.com (R. Bohra).

Biological importance of oximes and their complexes isvery well known [5]. Our previous studies on some maingroup and early transition metal complexes with internallyfunctionalized oximes have shown that among variousmultidentate organic ligands, oximes are an importantclass of N/O donor ligands having different coordinatingabilities with the metal centers [6].

Here, we report the reactions of VO(OPri)3 with theinternally functionalized oximes along with the crystaland molecular structures of hepta-coordinated [VO{ON@C(CH3)(C4H3O-2)}3] and [VO{ON@C(CH3)(C4H3S-2)}3] Æ0.5C6H6.

Tab

le1

Ph

ysic

al,

anal

ytic

alan

dso

me

imp

ort

ant

IRd

ata

(cm�

1)

of

oxo

van

adiu

m(V

)co

mp

lexe

sw

ith

inte

rnal

lyfu

nct

ion

aliz

edo

xim

es

Co

mp

lexe

sC

olo

ur

Mel

tin

gp

oin

t(�

C)

OP

ri(%

)o

bse

rved

(cal

cula

ted

)E

lem

enta

lan

alys

es(%

)o

bse

rved

(cal

cula

ted

)IR

dat

a(c

m�

1)

VN

m(V

@O

)m(

V–O

)m(

C@

N)

[VO

{OP

ri } 2{O

N@

C(C

H3)C

4H

3O

}](1

)o

ran

geb

row

n12

938

.19

(38.

20)

16.4

5(1

6.47

)4.

44(4

.53)

992,

s56

2,57

0,m

1571

,m

[VO

{OP

ri }{O

N@

C(C

H3)C

4H

3O

} 2]

(2)

yell

ow

bro

wn

168

15.7

8(1

5.78

)13

.54

(13.

61)

7.39

(7.4

8)98

4,m

562,

572,

m15

72,

w[V

O{O

N@

C(C

H3)C

4H

3O

} 3]

(3)

bro

wn

160

11.5

8(1

1.60

)9.

49(9

.56)

999,

s59

2,m

1571

,m

[VO

{OP

ri } 2{O

N@

C(C

H3)C

4H

3S

}](4

)o

ran

geb

row

n11

436

.28

(36.

33)

15.6

2(1

5.66

)4.

28(4

.31)

984,

s56

0,57

8,w

1620

,w

[VO

{OP

ri }{O

N@

C(C

H3)C

4H

3S

} 2]

(5)

bro

wn

ora

nge

130

14.1

7(1

4.53

)12

.52

(12.

53)

6.77

(6.8

9)98

4,s

562,

570,

m16

15,

w[V

O{O

N@

C(C

H3)C

4H

3S

} 3]

(6)

ora

nge

158

10.4

2(1

0.45

)8.

57(8

.62)

984,

m56

2,m

1630

,w

[VO

{OP

ri } 2{O

N@

C(C

H3)C

5H

4N

}](7

)d

ark

bro

wn

159

36.7

0(3

6.88

)15

.63

(15.

91)

4.34

a(8

.75)

920,

s55

7,56

5,m

1590

,w

[VO

{OP

ri }{O

N@

C(C

H3)C

5H

4N

} 2]

(8)

dar

kb

row

n14

214

.79

(14.

90)

12.8

5(1

2.85

)6.

99a

(14.

14)

953,

s55

0,56

0,m

1594

,m

[VO

{ON

@C

(CH

3)C

5H

4N

} 3]

(9)

bro

wn

124

10.7

7(1

0.78

)8.

86a

(17.

79)

974,

s54

4,m

1598

,s

w,

wea

k;

m,

med

ium

;s,

stro

ng.

aA

rom

atic

rin

gn

itro

gen

can

no

tb

ees

tim

ated

by

Kje

ldh

alm

eth

od

asco

nfi

rmed

by

bla

nk

exp

erim

ent

wit

hp

yrid

ine.

2010 V. Sharma et al. / Inorganica Chimica Acta 360 (2007) 2009–2015

2. Experimental

2.1. Materials, methods and instrumentation

All manipulations were carried out under strictly anhy-drous conditions. Due precautions were taken in handlingthe hazardous chemicals like benzene. The solvents andreagents were dried and purified prior to use by conven-tional methods. VO(OPri)3 [7] and the oximes [8] were pre-pared by literature methods. Vanadium was estimated asV2O5 and nitrogen was estimated by Kjeldhal’s method[9]. Isopropanol and isopropoxy groups were estimatedoxidimetrically as described in the literature [10]. IR spec-tra (4000–400 cm�1) were recorded as Nujol mullsbetween CsI plates or as dry KBr pellets on Nicolet-Magna-550 or Perkin–Elmer-377 FT IR Spectrophotom-eters. 1H (in CDCl3), 13C{1H} (in CDCl3/D6-DMSO)and 51V (in Benzene) NMR spectra were recorded on a300 MHz Jeol FX Spectrometer. TMS was used as aninternal standard for 1H and 13C{1H}. 51V chemical shiftswere referenced to the external standard VOCl3 withupfield shift being considered as negative. The FAB massspectra were recorded on a Jeol SX 102/DA-6000 MassSpectrometer using m-nitrobenzyl alcohol (NBA) as thematrix.

2.2. Preparation of [VO{OPri}2{ON@C(CH3)-

(C4H3O-2)}]

A benzene solution of 2-acetyl furyl oxime (680 mg,5.4 mmol) was added slowly to the benzene solution ofVO(OPri)3 (1.33 g, 5.4 mmol). The colour of the solutioninstantly changed to orange-brown. The contents wererefluxed and the progress of the reaction was monitoredby estimating liberated isopropanol in the azeotropicfractions. On completion of the reaction (�4 h), excesssolvent was removed in vacuo and an orange brown col-oured solid was obtained. Yield: 1.67 g (99.4%), m.p.129 �C.

All other alkoxy and tris-derivatives were prepared bythe above procedure. The physical and analytical data ofthe derivatives are summarized in Table 1.

2.3. X-ray diffraction analyses

Orange block crystals of [VO{ON@C(CH3)(C4H3O-2)}3] (3) and of [VO{ON@C(CH3)(C4H3S-2)}3] Æ 0.5C6H6

(6) were mounted on glass fibres. Data were collected ona Bruker-Nonius Kappa CCD area detector diffractome-ter (/ and x scans chosen to give a complete asymmetricunit) at the University of Southampton EPSRC NationalCrystallography Service. Data collection and cell refine-ment [11] gave cell constants corresponding to monocliniccells whose dimensions are given in Table 2 along withother experimental parameters. The crystal of 3 wastwinned and treated as two components using EVALCCD

[12]. However, the presence of additional minor twin

Table 2Crystal data and structure refinement for [VO{ON@C(CH3)(C4H3O-2)}3] (3) and [VO{ON@C(CH3)(C4H3S-2)}3] Æ 0.5C6H6 (6)

Compound 3 6

Molecular formula C18H18O7N3V C21H21O4N3S3VM 439.29 526.53Crystal system monoclinic monoclinicSpace group P21/c P21/na (A) 17.553(2) 8.8204(3)b (A) 16.391(3) 30.9999(6)c (A) 27.68(1) 9.6627(3)b (�) 101.37(2) 115.927(1).V (A3) 7809(4) 2376.2(1)Z 16 4T (K) 120(2) 120(2)l (mm�1) 0.554 0.714F(000) 3616 1084Measured reflections 13393 12776Independent reflections [Rint] 13393 [0.0000] (8264 for F2 > 4r(F2)) 5186 [0.0322] (4201 for F2 > 4r(F2))Final R indices [F2 > 4r(F2)] R1 = 0.1042, wR2 = 0.1948 R1 = 0.0474, wR2 = 0.1311R indices (all data) R1 = 0.1891, wR2 = 0.2536 R1 = 0.0620, wR2 = 0.1404Goodness-of-fit on F2 1.064 1.038

V. Sharma et al. / Inorganica Chimica Acta 360 (2007) 2009–2015 2011

domains compromised the data quality leading to slightlyhigh R-factors. In both compounds (3 and 6), an absorp-tion correction was applied [13].

Table 3Selected bond lengths (A) and angles (�) for [VO{ON@C(CH3)(C4H3O-2)}3] (

Compound 3 V(1) V(2)

V(1)–O(1) 1.571(6) 1.581(6)V(1)–O(2) 1.915(6) 1.914(6)V(1)–O(3) 1.926(6) 1.932(6)V(1)–O(4) 1.886(6) 1.894(6)V(1)–N(1) 1.989(8) 1.978(8)V(1)–N(2) 1.975(7) 2.011(8)V(1)–N(3) 2.275(7) 2.259(7)

O(1)–V(1)–O(2) 105.3(3) 103.3(3)O(1)–V(1)–O(3) 104.4(3) 106.1(3)O(1)–V(1)–O(4) 103.9(3) 103.7(3)O(2)–V(1)–O(3) 84.8(3) 84.4(3)O(2)–V(1)–O(4) 127.4(3) 129.4(3)O(3)–V(1)–O(4) 127.9(3) 126.7(3)O(1)–V(1)–N(1) 100.3(3) 101.0(3)O(1)–V(1)–N(2) 100.1(3) 99.3(3)O(1)–V(1)–N(3) 141.5(3) 141.6(3)O(2)–V(1)–N(1) 40.2(3) 40.4(3)O(3)–V(1)–N(2) 40.4(3) 40.5(3)O(4)–V(1)–N(3) 37.6(2) 37.9(3)N(1)–V(1)–N(2) 157.6(3) 157.5(3)N(1)–V(1)–N(3) 84.5(3) 85.3(3)N(2)–V(1)–N(3) 85.3(3) 84.8(3)N(1)–V(1)–O(4) 92.0(3) 92.6(3)N(2)–V(1)–O(4) 92.0(3) 91.9(3)O(3)–V(1)–N(1) 124.2(3) 123.0(3)O(2)–V(1)–N(2) 124.0(3) 124.5(3)N(3)–V(1)–O(2) 102.7(3) 105.4(3)N(3)–V(1)–O(3) 104.0(3) 101.5(3)V(1)–O(2)–N(1) 72.8(4) 72.3(4)V(1)–O(3)–N(2) 71.7(4) 72.9(4)V(1)–O(4)–N(1) 86.5(4) 85.4(4)O(2)–N(1)–V(1) 66.9(4) 67.3(4)O(3)–N(2)–V(1) 67.9(4) 66.6(4)O(4)–N(3)–V(1) 55.9(3) 56.7(3)

The structures were solved by direct methods [14] andwere refined using the WINGX version [15] of SHELX-97[16]. For 3, the reflections were merged in the twin process-

3) and [VO{ON@C(CH3)(C4H3S-2)}3] Æ 0.5C6H6 (6)

V(3) V(4) Compound 6

1.579(6) 1.575(6) 1.597(2)1.920(6) 1.916(7) 1.924(2)1.938(6) 1.933(6) 1.935(2 )1.895(6) 1.888(6) 1.908(2)1.994(8) 1.998(8) 2.020(2)1.969(7) 1.982(7) 1.991(3)2.287(7) 2.249(7) 2.196(3)

103.5(3) 103.2(3) 104.5(1)105.9(3) 104.9(3) 105.7(1)103.4(3) 103.2(3) 105.89(9)84.7(3) 84.9(3) 85.54(9)

128.7(3) 129.7(3) 127.31(8)127.3(3) 127.5(3) 124.80(9)99.7(3) 100.8(3) 99.5(1)99.6(3) 98.9(3) 99.0(1)

140.6(3) 141.4(3) 144.12(9)40.4(3) 40.6(3) 40.40(8)40.4(3) 40.4(3) 40.55(9)37.3(2) 38.3(2) 38.71(8)

158.4(3) 158.2(3) 159.6(1)83.5(3) 83.7(3) 80.84(9)87.7(3) 86.7(3) 89.07(9)92.4(3) 92.6(3) 92.53(9)92.4(3) 92.0(3) 90.51(9)

123.7(3) 123.9(3) 124.82(9)124.6(3) 124.8(3) 125.48(9)103.7(3) 104.6(3) 98.65(9)104.5(3) 103.8(3) 103.04(9)72.8(4) 72.9(4) 73.6(1)71.0(4) 71.7(4) 71.9(1)86.9(4) 85.0(4) 81.9(1)66.8(4) 66.5(4) 66.0(1)68.6(4) 67.9(4) 67.5(1)55.8(3) 56.8(3) 59.4(1)

Fig. 1. ORTEP plot of the asymmetric unit of [VO{ON@C(CH3)(C4H3O-2)}3](3). The non-hydrogen atoms are drawn with 50% probability ellipsoids.General labelling is omitted for clarity.

Fig. 2. ORTEP plot of one of the molecules in the asymmetric unit of[VO{ON@C(CH3)(C4H3O-2)}3] (3) as a representative example. The non-hydrogen atoms are drawn with 50% probability ellipsoids.

2012 V. Sharma et al. / Inorganica Chimica Acta 360 (2007) 2009–2015

ing software before refinement with the result that SHELX

gives the merging R as zero. All of the non-hydrogen atomswere treated anisotropically. All of the hydrogen atoms

Fig. 3. ORTEP plot of VO[ON@C(CH3)(C4H3S)]3 Æ 0.5C6H6 (6). Thenon-hydrogen atoms are drawn with 50% probability ellipsoids and thebenzene molecule is omitted for clarity.

were included in idealized positions with isotropic thermalparameters set at 1.2 times that of the carbon atom towhich they were attached.

Selected distances and bond angles are given in Table 3and the molecules are displayed as ORTEP diagrams inFigs. 1–3. Additional material available from the Cam-bridge Crystallographic Data Centre comprises the finalatomic coordinates and thermal parameters for all atomsand a complete listing of bond distances and angles.

3. Results and discussion

Substitution of the isopropoxy groups in VO(OPri)3 byinternally functionalized oximes in different molar ratiosin refluxing anhydrous benzene yields products as depictedbelow:

VOðOPriÞ3 þ nfHON@CðMeÞðArÞg! ½VOfOPrig3�nfON@CðMeÞðArÞgn� þ nPriOH "

[where Ar = (C4H3O-2), (C4H3S-2) and (C5H4N-2) andn = 1–3].

All these reactions are quite facile and quantitative. Theproducts obtained are coloured solids with sharp meltingpoints. Initially the reaction mixture of all these derivativesis soluble in benzene but after complete drying the solidproducts became insoluble. Elemental analyses corre-sponded to the expected formulae (Table 1). FAB massspectral analysis of the complex [VO{OPri}{ON@C(CH3)C4H3S}2] (5) indicates the presence of monomericspecies.

Fragmented ion/(m/e)+: [VO{OCH(CH3)2}{ONC(C4H3S)}{ONC(CH3)(C4H3S)}]/391; [VO{OCH(CH3)2}{ONC(CH3S)}{ONC(CH3)(C4H3S)}]/355; [VO{OCH(CH3)2}{OC(CH3S)}{ONC(CH3)(C4H3S)}]/341; [VO{OC(CH2-

S)}{ONC(CH3)(C4H3S)}]/281; [VO{CO}{OC(CH3)(C4H3-S)}]/221; [VO{CO}{OC(H)(C4H3S)}]/207; [VO{C}{OC(H)(C4H3S)}]/191; [VO{C}{OC4H3S}]/178; [VO{C}{OC3-H2S}]/165; [VO{CO}{C2H3S}]/154; [VO{C}{C3S}]/147.

The IR spectra of all these complexes (Table 1) wereinterpreted by comparing with those of the free oximesand other related complexes [4o,17]. Absence of anyabsorption in the region 3400–3200 cm�1 due to the –OHgroup of the free oximes indicates deprotonation of the –OH group and formation of V–O bond. This is further sup-ported by the appearance of bands in the region 550–592cm�1 assignable to mV–O. In all these derivatives, the pres-ence of strong to medium intensity bands in the region920–999 cm�1 due to mV@O vibrations indicates non-involvement of the V@O oxygen in the coordination withanother vanadium atom. However, appearance of mV@Oband at the lower energy region (920 cm�1) in complex 7

as compared to that of the other complexes (Table 1) sug-gests the presence of some polymeric interactions in thesolid state [2e]. Further, in the IR spectra of all the com-plexes there is only a slight shift in the mC@N band oncomplexation.

Table 41H, 13C and 51V NMR data (d ppm) of oxovanadium(V) complexes with internally functionalized oximes

Name of the complexes 1H NMR in d ppm 13C{1H} NMR in d ppm 51V NMR ind ppm

[VO{OPri}2{ON@C(CH3)C4H3O}] (1) 1.21 (d, 6.0 Hz, CH3–OPri), 2.20 (s, CH3–oxime), 4.03 (sept, 6.1 Hz,CH–OPri), 6.54 (dd, 3.5 Hz d, 1.8 Hz d, H-4), 6.72 (m, H-3), 7.59 (br, H-5)

11.0 (CH3–oxime), 25.5 (CH3–OPri), 62.1 (CH–OPri), 109.0(C-4), 111.5 (C-3), 143.5 (C-5), 145.7 (C-2), 150.8 (C@N)a

�627.0b

[VO{OPri}{ON@C(CH3)C4H3O}2] (2) 1.25 (d, CH3–OPri), 2.20 (s, CH3–oxime), 4.39 (m, CH–OPri), 6.45(m, H-4), 6.64 (m, H-3), 7.46 (m, H-5)

15.2 (CH3–oxime), 28.5 (CH3–OPri), 62.4 (CH–OPri), 109.7(C-4), 112.4 (C-3), 142.6 (C-5), 145.1 (C-2), 151.5 (C@N)

[VO{ON@C(CH3)C4H3O}3] (3) 2.21 (s, CH3–oxime), 6.45 (dd, 1.83 Hz, H-4), 6.54 (d, 3.30 Hz, H-3),7.47 (m, H-5)

14.3 (CH3–oxime), 111.2 (C-4), 112.2 (C-3), 139.0 (C-5),144.0 (C-2), 149.0 (C@N)

[VO{OPri}2{ON@C(CH3)C4H3S}] (4) 1.22 (d, 6.01 Hz, CH3–OPri), 2.50 (s, CH3–oxime), 4.03(m, CH–OPri), 7.03 (br, H-4), 7.39 (m, H-3), 7.43 (m, H-5)

11.8 (CH3–oxime), 25.5 (CH3–OPri), 62.1 (CH–OPri), 125.6(C-4), 126.7 (C-3), 130.6 (C-5), 140.9 (C-2), 149.5 (C@N)a

�625.7b

[VO{OPri}{ON@C(CH3)C4H3S}2] (5) 1.21 (d, 6.0 Hz, CH3–OPri), 2.50 (s, CH3–oxime) 4.05 (m, CH–OPri),7.03 (m, H-4), 7.32 (m, H-3), 7.38 (m, H-5)

11.9 (CH3–oxime), 30.7 (CH3–OPri), 62.8 (CH–OPri), 126.3(C-4), 127.3 (C-3), 130.6 (C-5), 141.0 (C-2), 149.6(C@N)a

[VO{ON@C(CH3)C4H3S}3] (6) 2.49 (s, CH3–oxime), 7.02 (m, H-4), 7.28 (m, H-3), 7.38(m, H-5) 11.9 (CH3–oxime), 127.2 (C-4), 129.1 (C-3), 131.7 (C-5),140.9 (C-2), 151.2 (C@N)

�812.4b

[VO{OPri}2{ON@C(CH3)C5H4N}] (7) 1.05 (d, 6.01, CH3-OPri), 2.22 (s, CH3–oxime), 3.78 (m, CH–OPri),7.29 (br, H-4), 7.83 (m, H-5), 7.95 (m, H-3), 8.59 (s, H-6)a

11.8 (CH3–oxime), 25.8 (CH3–OPri), 62.1 (CH–OPri),121.2 (C-5), 127.8 (C-3), 137.6 (C-4), 149.3 (C-6), 153.0 (C-2), 156.6 (C@N)a

[VO{OPri}{ON@C(CH3)C5H4N}2] (8) highly insoluble in CDCl3 and D6-DMSO[VO{ON@C(CH3)C5H4N}3] (9) 2.42 (s, CH3–oxime), 7.29 (dt, 1.1 Hz, H-4), 7.71 (dt, 1.65 Hz, H-5),

7.85 (d, 8.06 Hz, H-3), 8.66 (d, H-6)10.8 (CH3–oxime), 120.6 (C-5), 123.7 (C-3), 136.5 (C-4),148.9 (C-6), 154.3 (C-2), 156.6 (C@N)

s, singlet; d, doublet; m, multiplet; br, broad signal.a Spectra have been recorded in D6-DMSO.b Spectra have been recorded in benzene.

V.

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2014 V. Sharma et al. / Inorganica Chimica Acta 360 (2007) 2009–2015

NMR spectra of all these derivatives (except complex 8

which is insoluble) have been recorded in CDCl3/D6-DMSO and the data are summarized in Table 4. In the1H NMR spectra, the absence of hydroxy proton reso-nances of the free ligands (d 8.58–9.23 ppm) indicatesdeprotonation of the oxime and concomitant formationof V–O bond. In the oxovanadium(V) isopropoxo-oximatoderivatives, the proton and carbon resonances of isoprop-oxy groups appeared in the expected region with theexpected multiplicities [CH3 (d 1.05–1.25) ppm and CH (d3.78–4.39) ppm in the 1H NMR; CH3 (d 25.5–30.7) ppmand CH (d 62.1–62.8) ppm in the 13C{1H}NMR].Methyl-oxime proton resonances of all the derivatives arealmost unchanged or slightly shielded on complexation incomparison with the free ligand. However, the methyl-oxime carbon resonances are deshielded. Ring protonand carbon resonances of the oxime moiety exhibit a shiftof (�) ±1 and �3 ppm in the 1H and 13C{1H} NMR spec-tra, respectively. Again C@N carbon in these derivatives isalmost unchanged (a shift of ±2 ppm on complexation),suggesting that this nitrogen atom is not taking part incoordination in solution. However, in the solid state thisnitrogen atom is apparently involved in coordination withthe central vanadium atom as revealed by the X-ray diffrac-tion studies of two of the derivatives [VO{ON@C(CH3)(C4H3O-2)}3] (3) and [VO{ON@C(CH3)(C4H3S-2)}3] Æ0.5C6H6 (6).

In the 51V NMR spectra of some of the derivatives, thepresence of a single 51V NMR resonance in the region [d�(625.7–627.0) ppm] suggests the existence of tetra-coordi-nated species in the solution [18]. However, due to poorsolubilities of other complexes in CDCl3/C6H6 solutionthe 51V NMR spectra could not be recorded. The appear-ance of 51V NMR chemical shift at d �812.4 ppm for thecomplex [VO{ON@C(CH3)(C4H3S-2)}3] (6) reveals highshielding effect on vanadium atom.

Among all of the compounds, only for[VO{ON@C(CH3)(C4H3O-2)}3] (3) were X-ray qualitycrystals obtained in this instance by simply cooling thereaction mixture to room temperature. Orange block crys-tals, similar in appearance to those of 3, were obtained of[VO{ON@C(CH3)(C4H3S-2)}3] Æ 0.5C6H6 (6) as a resultof attempts to recrystallize [VO{OPri}{ON@C(CH3)(C4H3S-2)}2] (5) from benzene indicating that the tris-spe-cies is thermodynamically more stable.

The single-crystal X-ray diffraction studies of[VO{ON@C(CH3)(C4H3O-2)}3] (3) and [VO{ON@C(CH3)(C4H3S-2)}3] Æ 0.5C6H6 (6) show that all the oximatoligands are bonded in a dihapto (g2-N,O) manner [6d] withthe formation of a three membered ring. All four moleculesin the asymmetric unit of 3 are displayed in Fig. 1 and oneof these, labeled as V(1), is displayed in Fig. 2. The benzenemolecule is not displayed in the Ortep diagram of 6 (Fig. 3).In Table 3, selected bond lengths and angles are given withthose of the molecule that is labeled as V(1) in the first col-umn and correspondingly those of the other molecules in

the columns headed V(2), V(3) and V(4), followed by thosefor 6.

In both 3 and 6, the vanadium(V) atom is heptacoordi-nated with distorted pentagonal bipyramidal geometry(Figs. 2 and 3). The axial V@O bond (1.577(5)ave for 3

and 1.597(2) A for 6) is arranged symmetrically above theapproximate plane relative to the three V–O bonds to giveO@V–O angles ranging from 103.2(3)� to106.1(3)� in bothcompounds. The two V–N bonds that are also in theapproximate plane give O@V–N angles ranging from98.9(3)� to 101.0(3)� for 3 and 99.5(1)� and 99.0(1)� for 6.The similarity of the two oximates in the approximate pen-tagonal plane is further indicated by the similarity of thevalues of the N(1)–V(1)–O(4) and N(2)–V(1)–O(4) anglesin 3 and 6 of 92.1(6)�ave. The V–N bond of the third oximatoligand, that lies at approximately right angles to the othertwo, constitutes the other approximately axial bond withO(1)@V(1)–N(1) 141.1(2)ave for 3 and 144.12(9)� for 6.The V–O bond in this unique oximato ligand is the shortest(V(1)–O(4) 1.891(4) A for 3 and 1.908(2) A for 6) with sim-ilar O(2)–V(1)–O(4) and O(3)–V(1)–O(4) angles of128.8(10)� and 127.4(5)ave� for 3 and 127.31(8)� and124.80(9)� for 6. The O(2)–V(1)–O(3) angle for the ligandsin the approximate plane is 84.7(2)ave� for 3 and 85.54(9)�for 6. The V–O–N angle for the unique oximato ligand islarger (V(1)–O(4)–N(3) 86.0(9)ave� for 3 and 81.9(1) for 6)than those of the similar planar groups (V–O–N angles72.3(7)ave� for 3 and 72.6(10)�ave for 6). The angles withinthe three membered rings are similar, but the acute V–N–O angles average 40.4(2)� for the groups within the planesin 3 and6, while the unique out-of-plane group has a slightlysmaller angle 38.0(6)� ave in 3 and6. The dimensions withinthe three oximato ligands in 3 and 6 are essentially the sameas those found in other coordinated ON@C(CH3)(C4H3O-2) and ON@C(CH3)(C4H3S-2) groups.

4. Conclusion

Nine internally functionalized oxime modified VO(O-Pri)3 derivatives have been prepared and characterized byspectroscopic techniques. Single crystal X-ray diffractionstudies of hepta-coordinated [VO{ON@C(CH3)(C4H3O-2)}3] (3) and [VO{ON@C(CH3)(C4H3S-2)}3] Æ 0.5C6H6 (6)suggest that the oximato ligands are bonded in a dihapto(g2-N,O) manner with the formation of three memberedrings, while the oxo-atom occupies the axial position. Theabove relatively hydrolytically stable modified compoundscould be better potential precursors for material synthesisthan VO(OPri)3.

5. Supplementary material

CCDC 298129 and 298130 contain the supplementarycrystallographic data for VO{ON@C(CH3)(C4H3O-2)}3](3) and VO{ON@C(CH3)(C4H3S-2)}3] Æ 0.5C6H6 (6). Thesedata can be obtained free of charge via http://www.ccdc.

V. Sharma et al. / Inorganica Chimica Acta 360 (2007) 2009–2015 2015

cam.ac.uk/conts/retrieving.html, or from the CambridgeCrystallographic Data Centre, 12 Union Road, CambridgeCB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:deposit@ccdc.cam.ac.uk.

Acknowledgements

We are thankful to DST, UGC and CSIR-New Delhifor financial support. Vinita Sharma is thankful to UGC-New Delhi for Post-doctoral research award. M.B.H.thanks the UK Engineering and Physical Sciences Councilfor support of the X-ray facilities at Southampton. J.E.D.thanks the University of Windsor for financial support.

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