Organoantimony(V) cyanoximates: Synthesis, spectra and crystal structures

Article abstract of DOI:10.1021/ic9906048

A series of 25 new organoantimony(V) cyanoximates has been synthesized and studied using IR, visible, and NMR spectroscopy and X-ray analysis. Crystal structures were determined for compounds (C₆H₅)₄Sb{ONC(CN)C(O)NH₂} (1) and (C₆H₅)₄Sb{ONC(CN)C(O)N(CH₃)₂} (2). Both complexes crystallized in the monoclinic space group P2₁/c (Z = 4) with unit cell parameters (A, grad) of a = 14.921(3), b = 10.165(2), c = 17.571(7), β = 113.26(6) for compound 1, and a = 16.415(4), b = 10.406(3), c = 17.152(3), β = 117.79(2) for compound 2. For 5438 and 5056 independent reflections the refinement yielded R-factors 0.022 and 0.037 for the structures of 1 and 2, respectively. Cyanoxime anions are bound to the antimony(V) atoms in a monodentate fashion via the oxygen atoms of the oxime groups. The ligands adopt trans-anti configuration in these compounds. The coordination polyhedron in both complexes is a distorted trigonal bipyramid with the axial location of the cyanoxime ligand. A similar binding mode of other anions in synthesized organoantimony(V) complexes has been offered on the basis of the similarity of their IR spectra to those of the compounds whose structures were determined crystallographically. The exact assignment of vibrations involving the oxime group was carried out using synthesized ¹⁵N (53%) isotopomers.

Full text of DOI:10.1021/ic9906048

Inorg. Chem. 2000, 39, 1227-1237
1227
Organoantimony(V) Cyanoximates: Synthesis, Spectra and Crystal Structures
Konstantin V. Domasevitch,† Nikolay N. Gerasimchuk,*,‡ and Andrew Mokhir‡
Inorganic Chemistry Division, Department of Chemistry, T. Shevchenko University,
Vladimirskaya 64 St., 252034, Kiev, Ukraine, and Department of Chemistry, Ladd, 104,
North Dakota State University, Fargo, North Dakota 58105
ReceiVed May 25, 1999
A series of 25 new organoantimony(V) cyanoximates has been synthesized and studied using IR, visible, and
NMR spectroscopy and X-ray analysis. Crystal structures were determined for compounds (C6H5)4Sb{ONC-
(CN)C(O)NH2} (1) and (C6H5)4Sb{ONC(CN)C(O)N(CH3)2} (2). Both complexes crystallized in the monoclinic
space group P21/c (Z ) 4) with unit cell parameters (Å, grad) of a ) 14.921(3), b ) 10.165(2), c ) 17.571(7),
â ) 113.26(6) for compound 1, and a ) 16.415(4), b ) 10.406(3), c ) 17.152(3), â ) 117.79(2) for compound
2. For 5438 and 5056 independent reflections the refinement yielded R-factors 0.022 and 0.037 for the structures
of 1 and 2, respectively. Cyanoxime anions are bound to the antimony(V) atoms in a monodentate fashion via the
oxygen atoms of the oxime groups. The ligands adopt trans-anti configuration in these compounds. The coordination
polyhedron in both complexes is a distorted trigonal bipyramid with the axial location of the cyanoxime ligand.
A similar binding mode of other anions in synthesized organoantimony(V) complexes has been offered on the
basis of the similarity of their IR spectra to those of the compounds whose structures were determined
crystallographically. The exact assignment of vibrations involving the oxime group was carried out using synthesized
15N (53%) isotopomers.
Introduction
were reported to demonstrate considerably higher in Vitro anti-
cancer activity than cisplatin, Pt(NH3)2Cl2.6
The treatment of malignant formations with transition metals
complexes has a long and successful history.1,2 The vast majority
of such compounds includes mixed halogen-amine or amino-
carboxylate complexes of platinum(II) and palladium(II). These
substances are active ingredients of traditional metallocomplex
cancer chemotherapy drugs. The most fundamental limitation
of the continuous use of these compounds is their high toxicity,
which leads to kidney and/or liver failure. Therefore, a
significant problem with the use of metal-containing chemo-
therapy agents is keeping the cytostatic activity high, while
simultaneously reducing the toxicity.
Today, in addition to developing platinum compounds with
improved therapeutic characteristics, there is a focus on synthesis
and testing for antitumor properties of a large number of
organometallic and traditional inorganic complexes. So far, most
of the research has been concentrated on inorganic gallium3 and
organometallic tin(IV) derivatives such as R′2Sn{S2PR′′2} (R′
) Ph, n-C4H9; R" ) i-OC3H7, Ph).4,5 Some of these complexes
Over the last several years organoantimony derivatives have
also shown significant antitumor activity. These compounds are
diphenylorganoantimony(V) thiophosphates such as Ph2Sb{S2-
PR2} (Ph ) C6H5, R ) Ph, i-OC3H7)7,8 and methylantimony-
(III) complexes such as (CH3)SbL (L ) derivatives of meta-
substituted salicylic acid).9 The action of these complexes is
associated with cytostatic activity10 similar to that for cisplatin.
In addition, the biological toxicity of organoantimony and
organotin compounds is much less than that for Pt and Pd
anticancer substances. The solubility of some of these complexes
is high enough to maintain their appreciable and effective
intracellular concentration.
It is known that compounds of the main group 5 elements,
such as As and Bi, have extensive pharmacological applica-
(7) Silvestru, C.; Silaghi-Dumitrescu, L.; Haiduc, I.; Begley, M. J.; Nunn,
M.; Sowerby, D. B. J. Chem. Soc., Dalton Trans. 1986, 1031.
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Willem, P.; Gielen, M. Appl. Organomet. Chem. 1995, 9, 597-607.
(10) Silvestru, C.; Socaciu, C.; Haiduc, I. Anticancer Res. 1990, 10, 803-
804.
* Corresponding author at present address: Pharmacyclics, Inc., 995 E.
Arques Avenue, Sunnyvale, CA 94086-4521.
‡ North Dakota State University.
† T. Shevchenko University.
(11) (a) Inorganic Biochemistry; Eihgorn, Ed.; Academic Press: New York,
1981. (b) Baxter, G. F. Chem. Ber. 1992, 445-448. (c) Burford, N.;
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G. B.; Curtis, J. M. Gastroenterology 1994, 106, A59. (d) LeBlanc,
R.; Veldhuysen, van Zanten; Burford, N.; Agosc, L.; Leddin, D. J.
Gastroenterology 1995, 108, A860. (e) Agosc, L.; Burford, N.;
Cameron, T. S.; Curtis, J. M.; Richardson, J. F.; Robertson, K. N.;
Yhard, G. B. J. Am. Chem. Soc. 1996, 118, 3225-3232. (f) Agosc,
L.; Briand, G. G.; Burford, N.; Cameron, T. S.; Kwiatkowski, W.;
Robertson, K. N. Inorg. Chem. 1997, 36, 2855-2860.
(12) (a) Silvestru, C.; Haiduc, I. Main Group Elements and Their
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A.; Sushma, I.; Singh, R. V.; Tandon, J. P. Main Group Chem. 1997,
20 (10), 663-667. (c) Phor, A. Synth. React. Inorg. Met-Org. Chem.
1995, 25, 1685-1697.
(1) (a) Rosenberg, B.; Van Camp, L.; Trosko, J. E.; Mansour, V. H. Nature
1969, 222, 385. (b) Nikolini, M., Ed. Platinum and Other Coordination
Compounds in Cancer Chemotherapy; Martinus-Nijhoff Publishing:
Boston, 1988. (c) Gibson, D.; Gean, K.-F.; Ben-Shoshan, R.; Ramu,
A.; Ringel, I.; Katzhendler, J. J. Med. Chem. 1991, 34, 414-420.
(2) Gielen, M. Metal Based Antitumor Drugs; Freud, London, 1988.
(3) Haiduc, I.; Silvestru, C. Organometallics in Cancer Therapy; CRC
Press: Boca Raton, FL, 1989 and 1990; Vols. 1 and 2.
(4) Silvestru, C.; Ilies, F.; Haiduc, I.; Gielen, M.; Zuckerman, J. J. J.
Organomet. Chem. 1987, 330, 315.
(5) Lefferts, J. L.; Molloy, K. C.; Zuckerman, J. J.; Haiduc, I.; Curtui,
M.; Guta, C.; Ruse, D. Inorg. Chem. 1980, 19, 2861.
(6) Bonalam, M.; Biesemans, M.; Meunier, J.; Piret, R.; Willem, R.;
Gielen, M. Appl. Organomet. Chem. 1992, 6, 197.
10.1021/ic9906048 CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/02/2000

1228 Inorganic Chemistry, Vol. 39, No. 6, 2000
Domasevitch et al.
Scheme 1
*An anion; respective acid HOsNdC(CN)2 is unknown.
tions,11 as pioneered with the famous phenylarsenic derivative
salVarsan by Paul Ehrlich. Interestingly enough, several orga-
noantimony compounds have also exhibited antimicrobial
properties.12
It was interesting to obtain a series of organometallic
antimony cyanoximates that were previously unknown. In these
cases there may be an opportunity to combine useful properties
both from the organometallic side of the molecule and from
the acido-ligand as well. This is important for the design of a
new group of organoantimony compounds with potentially
useful anticancer properties. Therefore, summarizing the above,
systematic studies which involve syntheses, spectroscopic, and
structural characterization of the R4SbL and R3Sb(Hal)L (R )
Ph; L ) monoxime anion; Hal ) F-, Cl-, Br-) represent the
main topic of the current paper.
On the other hand, there is a group of multidentate organic
ligands, namely, oximes, which have known biological activity
such as growth regulatory, antimicrobial, and fungicidal. For
example, oxime groups are present in molecules of the family
of Althiomycin antibiotics.13 Many oximes are weak organic
acids that can easily form numerous salts and complex
compounds. Some oximes, namely cyanoximes (compounds
having the general formula HOsNdC(CN)sR, where R is an
electron withdrawing group: Scheme 1 and ref 14), demonstrate
a variety of properties as biologically active molecules with low
toxicity. For instance, amide-cyanoxime HOsNdC(CN)s
C(O)NH2 exhibits growth regulation in plants,15 and N,N-
dimethylamide-cyanoxime, HOsNdC(CN)sC(O)N(CH3)2
shows antidote properties against agricultural organophosphorus
pesticides.16 The sulfur-containing thioamide-cyanoxime, HOs
NdC(CN)sC(S)NH2 and its Na+, K+, Cu2+, and Ni2+ salts
demonstrated antimicrobial and fungicidal activity,17 etc.
Experimental Part
Synthesis of Ligands. In general, R-substituted acetonitriles that
have the formula NC-CH2-R (R ) electronwithdrawing group) are
the most convenient precursors for the preparation of cyanoximes,
shown with their commonly used abbreviations in Scheme 1. Meyer’s
reaction18 allows the desired cyanoximes to be obtained with good yields
from the above acetonitriles:
-T, +N2
NCsCH2sR + KNO2(CH3COOH)
8 HOsNdC(CN)-R
(1)
(13) (a) Kists, H. A.; Szymanski, E. F.; Dorman, D. E. J. Antibiotics 1975,
28 (4), 286-291. (b) Nakamura, H.; Iitaka, Y.; Sakakibara, H.;
Umezawa, H. J. Antibiotics 1974, 27 (11), 894-896.
(14) (a) Gerasimchuk, N. N.; Kuzmann, E.; Buki, A.; Vertes, A.; Nagy,
L.; Burger, K. Inorg. Chim. Acta 1991, 188 (11), 45-50. (b)
Domasevich, K. V.; Gerasimchuk, N. N. Russ. J. Inorg. Chem. 1992,
37 (10), 3207-3212. (c) Ponomareva, V. V.; Dalley, N. K.; Xiaolan
Kou; Gerasimchuk, N. N.; Domasevich, K. V. J. Chem. Soc., Dalton
Trans. 1996, 2351-2359.
(15) (a) Hubele, A.; Kuhne, M. Patent of the USA #4063921, 1977. (b)
Davidson, S. H. Patent of the USA #3780085, 1974.
(16) (a) Ciba-Geigy A. G. Patent of Austria #367268, 1982. (b) Ciba-Geigy
AG. Patent of Poland #127786, 1985.
(17) (a) Paliy, G. K.; Skopenko, V. V.; Gerasimchuk, N. N.; Doma-
shevskaya, O. A.; Makats, E. F.; Rakovskaya, R. V. Patent of the
USSR #1405281, 1988. (b) Paliy, G. K.; Skopenko, V. V.; Gerasim-
chuk, N. N.; Makats, E. F.; Domashevskaya, O. A.; Rakovskaya, R.
V. Patent of the USSR #1405282, 1988.
Therefore, compounds such as H(ECO),19 H(ACO),20 H(TCO),21
H(PiCO),22 H(BCO),14c and H(PCO)23 were synthesized according to
reaction 1 and published procedures. These cyanoximes were then
extracted by ether or CHCl3 from acidified to pH ) 4 aqueous solutions.
(18) (a) Meyer, M. Chem. Chem. Ber. 1873, 3, 1492. (b) Kolbe, A.; Kohler,
H. Z. Z. Anorg. Allg. Chem. 1970, 373, 230.
(19) Zhmurko, O. A.; Skopenko, V. V.; Gerasimchuk, N. N. Dokl. Akad.
Nauk UkSSR 1989, B(7), 37-41.
(20) Konrad, M.; Shulze, A. Chem. Ber. 1909, 42, 735-742.
(21) Skopenko, V. V.; Domashevskaya, O. A.; Gerasimchuk, N. N.;
Tyukhtenko, S. I. Ukr. Khim. Zhurn. 1986, 52 (7), 686-691.
(22) Fedorenko, D. A.; Gerasimchuk, N. N.; Domasevich, K. V. Russ. J.
Inorg. Chem. 1993, 38 (9), 1535-1539.
(23) Gerasimchuk, N. N.; Zhmurko, O. A.; Tyuhtenko, S. I. Russ. J. Inorg.
Chem. 1993, 38 (2), 301-306.

Organoantimony(V) Cyanoximates
Inorganic Chemistry, Vol. 39, No. 6, 2000 1229
Scheme 2
The potassium salt of the malonodinitrile oxime, K(CCO), is the only
source of CCO- anion available since the respective H-oxime is
unknown.24
Less trivial preparation of H(DCO), its thio analogue H(TDCO),
and 2-hetarylcyanoximes such as H(TNCO) and H(QCO) is shown in
Scheme 2 and described below.
The following procedure describes the preparation of 2-cyano-N,N-
dimethylacetamide, which is a precursor for the synthesis of ligands
such as H(DCO) and H(TDCO) (Scheme 2).
2-Cyano-N,N-dimethylacetamide, NC-CH2-C(O)N(CH3)2. A 30
mL aliquot of cyanoacetic ester, NC-CH2-C(O)OC2H5, was added
dropwise to a 7 M solution of dimethylamine in isopropyl alcohol (200
mL). This solution was obtained by condensation of boiling dimethyl-
amine, which was produced by reaction of NH2(CH3)2+Cl- with KOH,
into i-PrOH. A 14 g quantity of colorless crystalline 2-cyano-N,N-
dimethylacetamide precipitated from the above mixture after 12 h at
-10 °C. A new portion of 30 mL of cyanoacetic ester at the same
conditions gives 20.5 g more of crystalline amide. The combined
precipitate was washed with cold i-PrOH and dried under vacuum. The
compound is well soluble in H2O and acetone; mp ) 64 °C. 1H NMR
(200 MHz, in DMSO-d6 (ppm)): 3.99 (2H, s, methylene), 2.93 (3H, s,
methyl), 2.85 (3H, s, methyl). 13C{1H} NMR (400 MHz, in DMSO-d6
(ppm)): 24.83 (CH3), 35.20 (CH3), 47.04 (CH2), 115.61 (CN), 162.80
(amide).
2-(Oximido)(N,N-dimethylamido)acetonitrile, H(DCO). A 20 g
sample of the above 2-cyano-N,N-dimethylacetamide was dissolved in
100 mL of an aqueous solution of 26.5 g of KNO2. Then 21.8 mL of
glacial acetic acid was added dropwise under stirring and inert gas
protection over 3 h and the reaction mixture was cooled to -5 °C. A
white precipitate of 2-(oximido)(N,N-dimethylamido)acetonitrile, 16.5
g (65%), formed after keeping the resulting solution overnight in a
refrigerator at -5 °C. The microcrystalline precipitate of H(DCO) was
filtered off, washed with icy water, and dried in a vacuum. The extra
amount (∼6 g) of cyanoxime can be obtained from the above mother
liquor by extraction of H(DCO) with ether, although the organic layer
is contaminated with acetic acid. 2-(Oximido)(N,N-dimethylamido)-
acetonitrile is poorly soluble in cold water but nicely soluble in ether,
acetic acid, and acetone; mp ) 138 °C. Anal. found (calculated) for
C5H7N3O2, %: N, 31.76 (32.02); C, 44.59 (44.24); H, 5.64 (5.58).
2-Cyano-N,N-dimethylthioacetamide, NC-CH2-C(S)N(CH3)2. A
22.4 g sample of 2-cyano-N,N-dimethylacetamide, NC-CH2-C(O)N-
(CH3)2, were refluxed with 28.8 g of P4S10 in 200 mL of anhydrous
ethyl acetate during 3 h. Control for the reaction completion was
achieved by monitoring of disappearance of the starting oxo-amide on
TLC. Solution was evaporated to dryness after filtration through Celite.
Solid residue was twice recrystallized from iso-propyl alcohol. Yield:
14.1 g (55%). Compound represents colorless needles, poorly soluble
in water, but readily dissolves in acetone, ether and n-PrOH; mp ) 85
(24) (a) Kohler, H.; Seifert, B. Z. Anorg. Allg. Chem. 1970, 379, 1-8. (b)
Chow, J. M.; Britton, D. Acta Crystallogr., Sect. B 1974, 30 (5), 1117-
1118.
1
°C. H NMR (200 MHz, DMSO-d6 (ppm)): 3.98 (methylene, s, 2H),

1230 Inorganic Chemistry, Vol. 39, No. 6, 2000
Domasevitch et al.
3.30 (methyl, s, 3H), 3.38 (methyl, s, 3H). Pos. FABMS (m/z): 128.1.
Anal. For C5H8N2S found (calculated), %: N 21.3 (21.8), C 46.2 (46.8).
Scheme 3
2-(Oximido)-N,N-dimethylthioamidoacetonitrile, H(TDCO). A
12.8 g sample of 2-cyano-N,N-dimethylthioacetamide and 8.3 g of
NaNO2 were dissolved in 800 mL of H2O at 45 °C, and then the solution
was slowly cooled to 5 °C. Hydrochloric acid (1 M, 120 mL) was
dropwise added over 2 h and under inert gas protection. The reaction
mixture was kept overnight at 0 °C and then filtered. Cyanoxime
H(DTCO) then was extracted using three portions (50, 100, and 200
mL) of diethyl ether. The extract was dried over Na2SO4 and then
concentrated to give an orange oil that slowly crystallized. Yield: 15.4
g (97%). The compound appears as yellow-orange crystalline material,
soluble in acetone and ether and poorly soluble in water; mp ) 97-99
°C. Anal. found (calculated) for C5H7N3OS, %: N, 26.2 (26.7); S, 20.1
(20.4); C, 37.9 (38.2). Positive FABMS (m/z): 157.1.
2-(Cyanomethyl)-∆2-thiazolin, NC-CH2-C3H4NS. The following
procedure describes the preparation of 2-(cyanmethyl)-∆2-thiazolin,
which is a precursor for the synthesis of the thiazolin-cyanoxime
H(TNCO). A 23.2 g sample of 2-aminoethanethiol was added in small
portions over a period 2 h to a solution prepared by dissolving 20.4 g
of freshly distilled CH2(CN)2 and 17.7 mL of CH3COOH in 150 mL
of anhydrous C2H5OH at room temperature. The volume of the reaction
mixture was reduced to a third of the original volume by slow
evaporation of the solvent, which required about 5 h. The oil obtained
was mixed with 150 mL of water. NC-CH2-C3H4NS was extracted
using three 100 mL portions of chloroform. The extract was dried over
Na2SO4, and the solvent was removed under reduced pressure to give
a red oil. This oil was quickly distilled at 80-85 °C/0.001 Hg mm to
give a yellow oily product that was unstable at room temperature.
Yield: 40%. The product should be stored in the refrigerator under an
inert gas atmosphere. Anal. found (calculated) for C5H6N2S, %: N,
22.43 (22.20); S, 25.08 (25.36).
NMR spectra (1H and other nuclei) for all shown in Scheme 1
cyanoxime ligands are presented in S1-S3 of the Supporting Informa-
tion.
Coordination Compounds. All cyanoximes presented in Scheme
1 easily undergo deprotonation upon addition of base, forming yellow
anions:14b,25
-
+
HOsNdC(CN)sR + base )
[OsNsC(CN)sR] + baseH
colorless
yellow
(2)
2-(Oximidocyanmethyl)-∆2-thiazolin, H(TNCO). A 2.29 g sample
of C5H6N2S, the synthesis of which is described above, and 1.85 g of
KNO2 were dissolved in a mixture of 30 mL of water and 20 mL of
ethanol. After the mixture was cooled to -3° C, 2.1 mL of concentrated
HCl (∼35%) in 10 mL of H2O was added dropwise over a period 30
min. After 3 h the resulting cyanoxime precipitate was filtered off,
washed with ice water (∼5 mL), and dried. Yield: 81%. The cyanoxime
obtained crystallizes as a monohydrate that is soluble in ether, methanol,
and ethanol. Anal. found (calculated) for H(TNCO)‚H2O, C5H7N3O2S,
%: N, 24.51 (24.27); S, 18.38 (18.49).
This is because of the several orders of magnitude increased acidity of
cyanoximes in comparison with other monoximes14c,26 or dioximes.27
Moreover, reaction 2 is the best way of obtaining the fast crystallizable
and pure Tl(I) cyanoximates if Tl2CO3 is used in such preparations.14c,28
Potassium salts of the above ligands were synthesized upon reaction
of K2CO3 with 2 equiv of cyanoximes in warm ethanol. Removal of
solvent under vacuum yielded bright-yellow solid compounds that have
KL formulae, as shown by elemental analyses. Potassium salts of all
cyanoximates except H(TCO) and H(TDCO) have been used in the
ion exchange reactions with equimolar amounts of AgNO3 in aqueous
solutions to form insoluble silver(I) cyanoximates. Quantitatively
precipitated AgL (L ) anions of ligands in Scheme 1) complexes were
filtered, washed with icy water, and dried under vacuum. These silver-
(I) complexes then were employed for the syntheses of organoantimony-
(V) cyanoximates, as shown in Scheme 3. Thus, heterogeneous
exchange reactions in anhydrous CH3CN between equimolar amounts
of fine powdered solid AgL and solutions of respective Sb(V)
derivatives at room temperature in the dark within ∼20 min lead to a
high-yield formation of organoantimony complexes.
2-(Oximido)-2-quinolylacetonitrile, H(QCO). The chlorination of
quinaldine was carried out in CCl4 using gaseous Cl2, and the
disappearance of the starting compound on TLC was used as a control
for the reaction completion. The introduction of a cyano group was
done in hot DMF according to standard procedure. The yellowish-white
waxy solid obtained was distilled in high vacuum to give pure, low
melting, white crystalline 2-quinolylacetonitrile. Synthesis of the oxime
was accomplished in a manner essentially the same as for the
preparation of HPCO. For the oxime preparation, 1.68 g (0.01 mol) of
2-quinolyl-acetonitrile was mixed with 0.66 g (0.011 mol) of glacial
acetic acid and the mixture was cooled to -50 °C. To this mixture
was rapidly added 0.85 g (0.01 mol) of solid KNO2 in an inert
atmosphere. After ∼5 h of slowly warming to room temperature, the
white flaky cyanoxime precipitate was filtered off, washed with 20
mL of water, and dried in a vacuum desiccator over KOH. Yield: 87%.
Mp ) 184 °C (H2O), decomposition temperature ) 217 °C. Anal. found
(calculated) for C11H9N3O2, %: C, 61.25 (61.39); N, 19.11 (19.53); H,
4.22 (4.19). Pure H(QCO) is a white microcrystalline precipitate and
is insoluble in water, hexane, and benzene but is soluble in acetone
and alcohols.
Silver(I) complexes of thioamide-containing cyanoximes H(TCO)
and H(TDCO) cannot be obtained because of their fast decomposition
reactions and formation of black Ag2S. These ligands, however, form
stable and light-insensitive orange Tl{TDCO} and Tl{TCO} complexes,
which have been used in a way similar to the above exchange reactions
during the preparation of Sb(V) derivatives with other cyanoximates.
Thallium(I) halogenides (e.g., TlBr, TlCl) are sparingly soluble in CH3-
CN, and these salts at 0 °C can be quantitatively separated from
solutions of organoantimony(V) cyanoximates.
Antimony trichloride (Fluka) and bromobenzene (Aldrich) were
reagent grade quality and used without additional purification. SbCl3
was the only precursor used for the preparation of starting materials
for organoantimony(V) cyanoximates. Syntheses of Sb(C6H5)3, (C6H5)2-
SbCl3, (C6H5)4SbBr, and (C6H5)3Sb(halogen)2 were carried out accord-
ing to published procedures.29 Certainly, it is clear that any other
substituted aryl derivatives of antimony(V) can be obtained in a similar
manner if these functional groups do not interfere with Grignard
reaction. For example, the presence of the poly(ethylene glycol)
(25) Mokhir, A.; Domasevich, K. V.; Dalley, N. K.; Kou, X.; Gerasimchuk,
N. N.; Gerasimchuk, O. A. Inorg. Chim. Acta 1999, 284 (1), 85-98.
(26) CRC. Handbook of Chemistry and Physics, 49th ed.; Chemical Rubber
Co.: Cleveland, OH, 1968.
(27) Lange’s Handbook of Chemistry; Dean, J. A., Ed.; McGraw-Hill: New
York, 1985.
(28) Skopenko, V. V.; Ponomareva, V. V.; Simonov, Yu. A.; Domasevich,
K. V. Russ. J. Inorg. Chem. 1994, 39, 1332.

Organoantimony(V) Cyanoximates
Inorganic Chemistry, Vol. 39, No. 6, 2000 1231
fragments in the phenylantimony units will provide necessary water
solubility for prospective pharmacologically interesting compounds.52
Typical preparations of organoantimony(V) cyanoximates is de-
scribed only for two compounds and shown below.
Sb(C6H5)3{PiCO}Br. To a solution of 0.513 g of triphenylantimony-
(V) dibromide, Sb(C6H5)3Br2, in 25 mL of dry acetonitrile was added
0.262 g of solid powdery Ag{PiCO} in small portions at 40 °C over
∼20 min and with intensive stirring. Flaky AgBr precipitate that formed
was filtered off and then, after washing with 5 mL of dry CH3CN,
discarded. Solute containing triphenylantimony(V) cyanoximate was
concentrated at ambient temperature under vacuum to give a colorless
microcrystalline complex.
Sb(C6H5)4{ECO}. Powdered silver(I) salt, Ag{ECO}, in an amount
of 0.249 g was added in small portions to a solution of tetraphenyl-
antimony(V) bromide in 25 mL of dry CH3CN. The reaction was carried
out under stirring at room temperature within ∼20 min. A colorless
solution of Sb(C6H5)4{ECO} was carefully filtered from AgBr and then
concentrated on a rotavap at room temperature to yield white micro-
crystalline solid organoantimony(V) cyanoximate.
Some important properties of synthesized Sb(V) complexes such as
analytical data and IR spectra are shown in Table 1 and S4 and S5
(Supporting Information). All these compounds are colorless crystalline
materials with relatively low melting points.
Physical Methods. Elemental analysis for N, C, H, and S were
carried out using a Carlo Erba Strumentazione C1600 apparatus. Melting
points are presented without correction. Molecular weights of a series
of organoantimony(V) cyanoximates were determined by cryoscopic
method in benzene. This approach was used to characterize the
speciation of complexes in bulk solutions since high molecular weight
aggregates are rarely seen during mass-spectrometric studies. Spectro-
scopic and analytical data have confirmed suggested formulas for the
synthesized both cyanoxime ligands and their Sb(V) complexes (Table
1 and S4 and S5).
(29) (a) Kocheshkov, K. V.; Skoldinov, A. P.; Zemlyanskii, N. N. Metody
Elementorganicheskoi Khimii: Sur′ma, Vismut (Methods of Organo-
element Chemistry: Antimony and Bismuth); Nauka: Moscow, 1976.
(b) Shen, K. W.; McEwen, W. E.; La Placa, S. J. J. Am. Chem. Soc.
1969, 90, 1718. (c) Beauchamp, A. L.; Bennett, M. J.; Cotton, F. A.
J. Am. Chem. Soc. 1969, 91, 297.
(30) (a) Domashevskaya, O. A.; Mazus, M. D.; Gerasimchuk, N. N.;
Dvorkin, A. A.; Simonov, Yu. A. Russ. J. Inorg. Chem. 1989, 34 (7),
936-939. (b) Domasevich, K. V.; Gerasimchuk, N. N.; Rusanov, E.
B.; Gerasimchuk, O. A. Russ. J. Gen. Chem. 1996, 66 (4), 652-657.
(31) (a) Domasevich, K. V.; Skopenko, V. V.; Gelbrish, T.; Sieler, J.; Hoyer,
E. Russ. J. Gen. Chem. 1996, 66 (6), 989-993. (b) Domasevich, K.
V. Isonitrosomethanides and Coordination Compounds on Their Base.
Autoreferat on D. Sci. Thesis, Chemistry Department of Kiev
Shevchenko University, Kiev, Ukraine, 1998; p 13.
(32) Domasevich, K. V. Synthesis and Investigations of the Donor
Properties of New Cyanoxime Type Acidoligands. Ph.D. Thesis,
Chemistry Department of Kiev, Shevchenko University, Kiev, Ukraine,
1993; p 205.
(33) Domasevich, K. V.; Mokhir, A.; Rusanov, E. B. Russ. J. Gen. Chem.
1966, 66 (9), 1501-1505.
(34) (a) Domasevich, K. V.; Ponomareva, V. V.; Rusanov, E. B. J. Coord.
Chem. 1995, 34, 259. (b) Domasevich, K. V.; Skopenko, V. V.; Sieler,
J. Inorg. Chim. Acta 1996, 249, 151-155. (c) Skopenko, V. V.; Zub,
Yu. L. Ukr. Khim. Zhurn. 1978, 4 (12), 1235-1241.
(35) (a) Simonov, Yu. A.; Domashevskaya, O. A.; Skopenko, V. V.;
Dvorkin, A. A.; Gerasimchuk, N. N.; Malinovskii, T. I. Russ. J. Coord.
Chem. 1991, 17 (5), 702-706. (b) Domashevskaya, O. A.; Simonov,
Yu. A.; Gerasimchuk, N. N.; Dvorkin, A. A.; Mazus, M. D. Russ. J.
Coord. Chem. 1990, 16 (11), 1544-1548. (c) Domasevich, K. V.;
Ponomareva, V. V.; Skopenko, V. V.; Tsan, G.; Sieler, J. Russ. J.
Inorg. Chem. 1997, 42 (7), 1128-1133. (d) Domasevich, K. V.;
Lindeman, S. V.; Struchkov, Yu. T.; Gerasimchuk, N. N.; Zhmurko,
O. A. Russ. J. Inorg. Chem. 1993, 38 (1), 98-103.
(36) (a) Gerasimchuk, N. N.; Nagy, L.; Schmidt, H.-G.; Noltemeyer, M.;
Bohra, R.; Roesky, H. Z. Naturforsch. 1992, 47b, 1741-1745. (b)
Skopenko, V. V.; Ponomareva, V. V.; Domasevich, K. V.; Sieler, J.;
Kempe, R.; Rusanov, E. B. Russ. J. Gen. Chem. 1997, 67 (6), 893-
902. (c) Domasevich, K. V.; Skopenko, V. V.; Mokhir, A. Russ. J.
Inorg. Chem. 1995, 40 (5), 781-786.
Spectroscopy. The compounds obtained were studied by IR (400-
4000 cm-1) spectroscopy in KBr pellets using UR-20 (Karl Zeiss, Jena)
and FT-IR Nikolet Impact 440 spectrometers. Assignments of vibrations
that include the oxime group have been made using 53% enriched 15
N
(NO group) cyanoximes and their Sb(V) complexes. IR spectroscopy
data for studied organoantimony compounds are summarized in Table
1. Spectra for thallium(I) and silver(I) complexes were recorded on a
Mattson 2020 Galaxy FT-IR spectrometer in Nujol mulls.
1H, 13C, and 14N NMR spectra for cyanoximes and their alkali metal
salts were obtained on the FT Bruker CXP-200 spectrometer using a
10 mm probe. Proton and carbon-13 spectra for organoantimony(V)
cyanoximates were recorded by operating a JEOL GSX400 FT
spectrometer. The same instrument has been used for variable-
1
temperature H experiments in DMSO-d6 and CDBr3.
UV-visible spectra for solutions of synthesized cyanoximes and
their Sb(V) complexes were recorded on a Shimadzu SPC 2100
spectrophotometer in the range of 350-850 nm using 10 mm quartz
cells. Variable-temperature experiments in a circulating thermostat were
carried out for selected complexes from 291 to 358 K.
Mass spectra for several synthesized compounds were obtained using
Autospec Q and ZAB spectrometers from VG-Analytical Ltd., of
Manchester (England). Positive FAB technique with m-nitrobenzylic
alcohol (NBA) as the matrix was used for characterization of different
cyanoxime derivatives.
X-ray Crystallography. Single crystals suitable for X-ray diffraction
experiments were obtained upon slow evaporation of acetonitrile
solutions of organoantimony(V) cyanoximates at room temperature in
the dark. Another successful way of growing single crystals of these
complexes was found to be in slow cooling of saturated at 348 K
solutions of the compounds in 50% aqueous ethanol to room temper-
ature in a thermostat (∼2 days). For the X-ray diffraction experiment,
colorless crystals of prismatic habit with linear dimensions not
exceeding 0.5 mm were selected. The X-ray experiment for a
monocrystal of Ph4Sb{ACO} was carried out on an Enraf Nonius
CAD-4 diffractometer, while for a monocrystal of Ph4Sb{DCO} a
Syntex P21 apparatus was used for data collection. In both cases Mo
KR (λ ) 0.710 73 Å) radiation and a graphite monochromator have
been used for the diffraction experiment. The crystal structure of Ph4-
Sb{ACO} was solved by the heavy atom technique and refined by the
least-squares method in the full matrix anisotropic approximation. The
reflections with I > 3σ(I) have been used in the refinement procedure.
Solution of the structure of Ph4Sb{DCO} was carried out using the
direct method and refined in the full matrix anisotropic approximation
by the least-squares mode. The reflections with I > 5σ(I) were allowed
(37) Simonov, Yu. A.; Dvorkin, A. A.; Gerasimchuk, N. N.; Mazus, M.
D.; Domasevich, K. V. Kristallografiya 1990, 35 (3), 766.
(38) Skopenko, V. V.; Lampeka, R. D. Russ. J. Inorg. Chem. 1982, 27
(12), 3117-3119.
(39) Lampeka, R. D.; Zubenko, A. I.; Skopenko, V. V. Teor. Exp. Chem.
1984, 20 (5), 519-525.
(40) Gerasimchuk, N. N.; Nagy, L.; Schmidt, H.-G.; Roesky, H. Russ. J.
Inorg. Chem. 1992, 37 (4), 818-824.
(41) Domasevich, K. V. Russ. J. Gen. Chem. 1997, 67 (12), 1937-1943.
(42) Gunter, H. NMR Spectroscopy: An Introduction; John Wiley &
Sons: New York, 1983.
(43) Gillespie, R. J.; White, R. In Nuclear Magnetic Resonance and Its
Application to Stereochemistry; Klyne, W., de la Mar, P. B. D., Eds.;
Progress in Stereochemistry; Academic Press: New York, 1962; Vol.
3.
(44) Gordon, A. J.; Ford, R. A. The Chemist’s Companion; John Wiley &
Sons: New York, 1972.
(45) Gerasimchuk, N. N.; Domasevich, K. V.; Zhmurko, O. A. Plenar
Lecture at VI Conference on Crystallochemistry of Inorganic and
Coordination Compounds, Lvov, Ukraine; Sept 22-26, 1992; Pro-
ceedings p 19.
(46) Skopenko, V. V.; Zub, Yu. L.; Lampeka, R. D.; Bel’skii, V. DopoVidi
AN UkSSR 1983, B(4), 60-62.
(47) Gerasimchuk, N. N.; Simonov, Yu. A.; Dvorkin, A. A.; Rebrova, O.
N. Russ. J. Inorg. Chem. 1993, 38 (2), 266-271.
(48) Gerasimchuk, N. N.; Domasevich, K. V.; Kapshuk, A. A. Russ. J.
Inorg. Chem. 1993, 38 (9), 1530-1534.
(49) Domasevich, K. V.; Skopenko, V. V.; Rusanov, E. B. Z. Naturfosch.
1996, 51b, 832-837.
(50) Mokhir, A. A.; Gerasimchuk, N. N.; Pol’shin, E. V.; Domasevich, K.
V. Russ. J. Inorg. Chem. 1994, 39 (2), 289-293.
(51) Khavryuchenko, V. D.; Domashevskaya, O. A.; Gerasimchuk, N. N.;
Skopenko, V. V. Theor. Exp. Chem. 1988, 24 (3), 303-309.
(52) (a) Sessler, J. L.; Mody, T. D.; Hemmi, G. W.; Lynch, V. Inorg. Chem.
1993, 32, 3175-3187. (b) Dr. Mody Tarak, private communication.

1232 Inorganic Chemistry, Vol. 39, No. 6, 2000
Domasevitch et al.
Table 1. Most Important Vibrational Frequencies in IR Spectra of the Synthesized Organoantimony(V)-Oxime Derivatives
vibrations in cyanoxime group
C6H5- group and Sb-Ph vibrations
compound
ν(CtN)
ν(CdX)a
ν(CdN)b
ν(ΝsÃ)b
F(NH2)
νas(CsH)
y(ν′19)
v(ν8)
Ph2Sb{ACO}Cl2
Ph2Sb{DCO}Cl2
Ph3Sb{ACO}Fc
Ph3Sb{DCO}Fc
Ph3Sb{ACO}Cl
Ph3Sb{DCO}Cl
Ph3Sb{BCO}Cl
Ph3Sb{PiCO}Cl
Ph3Sb{TCO}Cl
Ph3Sb{TNCO}Cl
Ph3Sb{ACO}Br
Ph3Sb{DCO}Br
Ph3Sb{ECO}Br
Ph3Sb{PiCO}Br
Ph3Sb{ACO}J
Ph4Sb{CCO}
2230
2230
2235
2225
2225
2220
2220
2222
2227
2225
2227
2220
2225
2222
2225
2220
2217
2218
2210
2212
2210
2210
2212
2215
1668
1625
1675
1627
1680
1638
1640
1680
882
1605
1680
1642
1710
1662
1700
1575
1585
1577
1585
1515
1570
1565
1572
1595
1520
1520
1570
1505
1505
1535
1565
1480
1567
1475
1475
1480
1520
1480
1485
1067
1035
1062
1020
1030
1015
1055
1029
1045
1050
1027
1015
1028
1025
1045
1170
1095
1050
1065
1130
1132
1060
1020
1035
1595
3180
447
682
682
685
687
682
685
685
687
687
690
682
677
677
675
692
689
695
692
692
3090
447
1580
1575
3065
454
3060
455
3060
452
3050
453
3050
455
3060
445, 456
430, 445, 455
457
1612
1573
3050
3065
3050
452
3055
455
3055
456
3055
452
1585
1580
3060
455
3060
415, 446
443, 452
445, 455
456
Ph4Sb{ACO}
1682
1635
1730
1662
1628
970
3050, 3065
3020, 3055
3060
Ph4Sb{DCO}
Ph4Sb{ECO}
Ph4Sb{PiCO}
Ph4Sb{BCO}
Ph4Sb{TDCO}
Ph4Sb{PCO}
Ph4Sb{QCO}
3060
445
457
444, 452
460, 450
448
3050
690
687
693
694
3050
1580
1595
3060
3060
a X ) sulfur atom (for TCO- and TDCO-), oxygen atom (for ACO-, DCO-, BCO-, PiCO-, ECO-), or nitrogen atom (PCO-, TNCO-, QCO-).
b The exact assignment for these vibrations was carried out using 15N isotopomers and was also based on the force-field calculations.51 c IR spectra
also contained ν(Sb-F) vibrations at 507 (for ACO-) and 509 (for DCO-) cm-1
.
Table 2. Crystallographic Data for 1 and 2
Table 3. Selected Bond Lengths and Angles in the Structure of
(C6H5)4Sb{ACO}
1
2
bond
length, Å
valence angles,
grad
formula
C27H22O2N3Sb
542.2
monoclinic
P21/c
14.921(3)
10.165(2)
17.571(7)
90
113.26(6)
90
C29H26N3O2Sb
570.2
monoclinic
P21/c
16.415(4)
10.406(3)
17.152(3)
90
117.79(2)
90
molecular weight
Sb-O(1)
Sb-C(4)
2.259(1)
2.124(3)
2.122(2)
2.163(3)
2.117(3)
1.342(2)
1.218(3)
1.282(3)
1.329(4)
1.134(4)
1.496(3)
1.434(4)
O(1)-Sb-C(4)
O(1)-Sb-C(10)
O(1)-Sb-C(16)
O(1)-Sb-C(22)
C(4)-Sb-C(10)
C(4)-Sb-C(16)
C(4)-Sb-C(22)
C(10)-Sb-C(16)
C(10)-Sb-C(22)
C(16)-Sb-C(22)
Sb-O(1)-N(1)
O(1)-N(1)-C(1)
N(1)-C(1)-C(2)
N(1)-C(1)-C(3)
C(2)-C(1)-C(3)
O(2)-C(2)-N(2)
O(2)-C(2)-C(1)
N(2)-C(2)-C(1)
N(3)-C(3)-C(1)
84.76(7)
80.59(7)
175.92(7)
83.62(7)
119.00(8)
97.98(8)
116.60(8)
95.42(8)
119.97(8)
97.76(9)
110.3(1)
115.9(2)
118.5(3)
121.6(2)
120.0(2)
124.1(3)
121.0(3)
114.9(2)
176.4(3)
crystal system
space group
Sb-C(10)
Sb-C(16)
Sb-C(22)
O(1)-N(1)
O(2)-C(2)
N(1)-C(1)
N(2)-C(2)
N(3)-C(3)
C(1)-C(2)
C(1)-C(3)
a
b
c
R, deg
â, deg
γ, deg
volume, Å3
Z
2339.4(2)
4
2591.9(2)
4
density (calc), g/cm3
exp temp
1.480
1.461
293
190
a
R1
0.022
0.037
b
wR2
0.031
0.043
a For 5972 total reflections, F(000) ) 4250, 386 refined parameters,
and weighting scheme w ) (σ2F + 0.0016F2)-1 b For 5271 total
reflections, F(000) ) 1152, 334 refined parameters and weighting
scheme w ) (σ2F + 99.0000F2)-1
.
.
compounds in the crystal state indicates the oxime character of
coordinated anions. This is opposite to the observed yellow or
orange colors* for nitroso-anions in alkali metal,30 ammonium,31
phosphonium(V)32 and arsonium(V),33 salts of cyanoximes.54
All these compounds form ionic bonds between cations and
anions in the crystal lattice, as was shown by X-ray analysis.
Nevertheless, tetraarylantimony(V) cyanoximates could have
several possible structural motifs, as shown in Figure 1. These
include both ionic and covalent binding of anions to the
antimony atoms in complexes. Lack of the electrical conductivity
of Ph4SbL solutions in CH3CN and the absence of high
molecular weight aggregates in benzene, CH2Cl2 and CHCl3
in the refinement procedure. An empirical absorption correction was
made by the DIFABS program, while the SHELXTL PLUS software
package has been used in all calculations. The positions of hydrogen
atoms were established by calculations and were refined isotropically
using a riding model. Data of the X-ray experiment are shown in Table
2. The final atomic positional and thermal parameters for both structures
are presented in Tables S6-S13 (Supporting Information). Selected
bond lengths and angles for the structures of Ph4Sb{ACO} and Ph4-
Sb{DCO} are shown in Tables 3 and 4, respectively. Packing diagrams
for both crystallographically characterized complexes are exhibited in
S16 and S17 (Supporting Information).
Results and Discussion
Synthesized organoantimony(V) complexes with cyanoxime
ligands represent monomeric species according to molecular
mass measurements by the cryoscopic method (see S4, Sup-
porting Information). Complexes form nonconducting solutions
at room temperature in benzene, acetonitrile, or propanol, which
evidence their molecular nature. Absence of color for these
(53) (a) Sidman, J. W. J. Am. Chem. Soc. 1957, 79, 2669. (b) Kohler, H.;
Lux, J. Inorg. Nucl. Chem. Lett. 1968, 4, 133-136.
(54) The color of ionic cyanoximates originates from the n f dµ transition
in the nitroso chromophore, as was observed and assigned earlier for
-
-
NO2 and ONC(CN)2 anions.53 The value of molar absorptivity ꢀ
for anionic cyanoximes ranges between 80 and 170 M-1 cm-1 (Figures
4 and 5).

Organoantimony(V) Cyanoximates
Inorganic Chemistry, Vol. 39, No. 6, 2000 1233
Figure 1. Possible spatial arrangements for tetraarylantimony(V) cyanoximates: (*) different bidentate coordination modes: chelate (five- or
six-membered rings) and bridging; (**) idealized central atom hybridization states.
Table 4. Selected Bond Lengths and Angles in the Structure of
(C6H5)4Sb{DCO}
bond
length, Å
valence angles,
grad
Sb-O(1)
2.226(4)
2.167(6)
2.112(4)
2.122(4)
2.114(4)
1.339(4)
1.299(7)
1.493(6)
1.430(9)
1.230(7)
1.337(8)
1.151(9)
1.472(10)
1.448(8)
C(11)-Sb-C(21)
C(21)-Sb-C(31)
C(21)-Sb-C(41)
C(11)-Sb-O(1)
C(31)-Sb-O(1)
C(11)-Sb-C(31)
C(11)-Sb-C(31)
C(31)-Sb-C(41)
C(21)-Sb-O(1)
C(41)-Sb-O(1)
Sb-O(1)-N(1)
N(1)-C(1)-C(2)
C(2)-C(1)-C(3)
C(1)-C(2)-N(2)
C(2)-N(2)-C(4)
C(4)-N(2)-C(5)
O(1)-N(1)-C(1)
N(1)-C(1)-C(3)
C(1)-C(2)-O(2)
O(2)-C(2)-N(2)
C(2)-N(2)-C(5)
C(1)-C(3)-N(3)
94.7(2)
118.1(2)
117.7(2)
175.7(2)
82.8(2)
Sb-C(11)
Sb-C(21)
Sb-C(31)
Sb-C(41)
O(1)-N(1)
N(1)-C(1)
C(1)-C(2)
C(1)-C(3)
C(2)-O(2)
C(2)-N(2)
C(3)-N(3)
N(2)-C(4)
N(2)-C(5)
94.7(2)
94.7(2)
121.3(2)
83.4(2)
86.6(2)
104.4(3)
118.9(5)
117.8(5)
118.5(5)
124.1(4)
116.4(5)
116.2(4)
122.8(4)
118.0(5)
123.4(4)
119.0(5)
177.0(5)
Figure 2. Molecular structure of (C6H5)4Sb{ACO} at 30% probability
ellipsoids. Hydrogen atoms of phenyl groups are omitted for clarity.
(according to mass-spectrometric data and temperature depres-
sion measurements), allow us to exclude structures A and D.
However, since cyanoximes themselves represent polydentate
monoanionic ligands with a variety of donor atoms (Scheme
1), neither structure B nor C can be ruled out.
The question of binding modes of cyanoxime anions in
synthesized complexes as well as their stability in different
solvent systems and aqueous solutions is of great importance
because of the possible future pharmacological applications of
these compounds. Stability is particularly important for opti-
mized drug development and biodistribution.
Crystal Structures of Complexes. Although almost all
synthesized organoantimony(V) cyanoximates represent micro-
crystalline compounds, quality single crystals suitable for X-ray
analysis were obtained only for two complexes. Both complexes,
Ph4Sb{ACO} and Ph4Sb{DCO}, have molecular structures that
are displayed in Figures 2 and 3, respectively. Packing diagrams
for both structures are shown in S16 and S17 (Supporting
Information), where molecules of complexes form infinite stacks
held together by van der Waals forces. The antimony atoms in
both complexes are five-coordinate, and their geometries are
represented as distorted trigonal bipyramids (Figures 2 and 3).
Coordination polyhedra in studied organoantimony(V) cyan-
oximates in general are similar to those determined for Ph4-
Figure 3. Molecular structure of (C6H5)4Sb{DCO}: view at 30%
probability ellipsoids. Shown general numbering scheme and only H
atoms at methyl groups in the amide fragment.
SbOCH3 and Ph4SbOH.29 The three equatorial positions are
occupied by phenyl groups. Another phenyl group, which has
slightly elongated Sb-C distances and the oxygen atom of the
oxime group of the acido ligand are located in the axial positions
(Tables 3 and 4). The equatorial phenyl groups adopt the most
sterically favorable propeller-type configuration and are some-
what tilted toward coordinated cyanoxime ligands. Angles Cax-
Sb-Ceq in both structures are in the range between 90° and
100°. The angle Cax-Sb-Oax is 175.9(7)° for Ph4Sb{ACO} and
175.7(2)° for Ph4Sb{DCO} (Tables 3 and 4).
Cyanoxime anions demonstrate the monodentate binding

1234 Inorganic Chemistry, Vol. 39, No. 6, 2000
Domasevitch et al.
Table 5. Summarized Geometrical Features for ACO- and DCO- Cyanoxime Groups in Different Complexes
compound
H(ACO)
ligand conformation and compound’s structural feature
oxime is planar, trans-anti configuration
reference
45
M{ACO} (M ) Rb+, Cs+)
Ni{ACO}2‚2H2O
Pb{ACO}2‚H2O
Tl{ACO}
anion is planar, trans-anti configuration,
nitroso-from
30a
46
anion is planar, cis-anti configuration,
nitroso-form in bidentate chelate trans complex
anion is planar, cis-anti configuration,
nitroso-form in bidentate chelate cis complex
47
nitroso-form of nonplanar anion;
bridging coordination mode
48
Ph6Te3O2{ACO}2
(Ph ) C6H5)
oxime is planar, trans-anti configuration,
monodentate binding via NO-group oxygen atom
49
Ph4Sb{ACO}
(C2H5)3Sn{ACO}
H(DCO)
planar oxime anion, trans-anti configuration,
monodentate coordination via NO-oxygen atom
this work
45, 50
37
anion is planar, oxime form in trans-anti
configuration; bidentate bridging coordination mode
oxime is nonplanar planar,
trans-anti configuration
Ph4Sb{DCO}
nonplanar oxime anion in trans-anti
configuration, monodentate coordination
via NO-oxygen atom
this work
35d
Cu{DCO}2*H2O
planar anion, cis-anti configuration,
nitroso-form in bidentate chelate trans complex
mode via oxygen atoms of NO groups in both structures. This
is a quite rare case of coordination of anions in this class of
ligands.24a,31b,34 The most common is a bidentate chelate14c,35
or bridging mode24b,25,28,36 observed earlier in complexes of
transition metals, and p-metals such as Tl(I), Ag(I), and Sn-
(IV), respectively (Table 5). The distance Sb-Oax is shorter in
the Ph4Sb{DCO} complex (2.226 Å) than for the Ph4Sb{ACO}
complex (2.259 Å). This fact is rather unexpected since the more
bulky cyanoxime anion is closer to the central atom of Sb(V)
than the less sterically hindered ACO- anion. Moreover, the
SbsO(1)sN(1) angle of adjustment of the cyanoxime group
to the tetraphenylantimony fragment is smaller in the structure
of Ph4Sb{DCO} (104.4°) than in the structure of Ph4Sb{ACO}
(110.3°) (Tables 3 and 4). These unusual structural features can
be explained when examining the structures of anions in both
organoantimony(V) cyanoximates. The ACO- anion in Ph4Sb-
{ACO} is planar, while the DCO- ligand in Ph4Sb{DCO} is
not. The latter anion has two planar fragments, O(1)N(1)C(1)C-
(3)N(3) and O(2)C(2)N(2) with a dihedral angle between them
of 47.8(1)° (Table 4). In fact, this angle is larger in Ph4Sb-
{DCO} than in the structure of free oxime H(DCO), where it
was found to be 28.2(3)°.37 The origin of a greater dihedral
angle of the cyanoxime group in the structure of Ph4Sb{DCO}
can be rationalized as the deviation from planarity relaxes a
steric repulsion between the ligand and equatorial phenyl groups
in the complex. Apparently, this also results in differences in
the geometry of SbsO(1)N(1) fragments for the two studied
organoantimony(V) cyanoximates. The C(1)C(3)N(3) nitrile
groups are linear; the corresponding angles equal 176.4° and
177.0° for Ph4Sb{ACO} and Ph4Sb{DCO}, respectively. The
cyanoxime anions in structures of both complexes adopt trans-
anti configuration with respect to mutual orientation of the oxime
and the CdO groups. Some interesting structural peculiarities
of the cyanoxime ligands for crystallographically characterized
compounds are summarized in Table 5. This table contains
examples that practically reflect the HSAB theory by Bassolo
and Pearson. Indeed, complexes of transition metals such as Ni
and Cu include cyanoximate anions that are bound in bidentate
chelate fashion. Similar behavior of the ACO- anion was found
also in the Pb(II) complex (Table 5). Ligands exhibit nitroso
character in the above compounds. In alkali metal ionic salts
all studied to date cyanoximes are planar and also show the
same nitroso character. This fact is reflected in a shorter NsO
bond in comparison with the CsN bond in the CsNsO
fragment. Oxophilic central atoms such as TeIV, SnIV, and SbV
prefer to form bonds with acido ligands via oxygen atoms.
Anions in the later compounds are in the oxime form. Numerous
examples of ampolydentate coordination of cyanoxime anions
(e.g., different coordination modes for different central atoms
and also often bridging function with multiple contacts) were
recently reviewed.14c,25,31b,36a
Spectroscopic Studies. IR Spectra. The assignments of
vibrations with participation of the -CNO group of the
cyanoxime ligand were carried out using 15N isotopomeric
compounds. There were observed splitting and shifts in IR bands
associated with vibrations of the oxime group in comparison
with spectra of nonlabeled compounds. Previously it was found
that the positions of ν(NO) and ν(CNO) vibrations in IR spectra
are dependent to a great extent on the oxime or nitroso character
of this group in a particular compound.24a,36a,38 Moreover, the
coordination mode of the cyanoxime ligand was found to be
reflected in the IR spectrum.39,40 The respective spectral-
structural correlation based on comparison of data of X-ray
analysis and vibrational spectroscopy were well established.41
The most pronounced feature of IR spectra of organoantimony-
(V) cyanoximates is in their very low frequencies of ν(NO)
vibrations in comparison with 3d metal complexes or alkali
metal salts (Table 1). The positions of these bands are close to
those found in IR spectra of free cyanoximes HL. This is
unambiguous evidence of monodentate coordination of cyan-
oxime anions to Sb(V) by means of the oxygen atom of the
oxime group. There were no significant changes observed for
vibrational frequencies of other functional groups of anions in
the IR spectra of organoantimony(V) cyanoximates that might
be associated with additional coordination of these ligands to
Sb(V) atoms. Since all complexes synthesized and discussed

Organoantimony(V) Cyanoximates
Inorganic Chemistry, Vol. 39, No. 6, 2000 1235
Figure 4. UV-visible spectra of fully dissociated As(C6H5)4+(ACO)-
(7.6 × 10-3 M solution, dotted line) and [Sb(C6H5)4{ACO}] in DMF
after heating at 100 °C within 5 min (6.2 × 10-3 M solution, solid
line).
Figure 5. UV-visible spectra of ionic solution of As(C6H5)4+(BCO)-
(5.4 × 10-3 M) in pyridine (dashed line) and molecular solution of
[Sb(C6H5)4{BCO}] (4.8 × 10-3 M) in pyridine (solid line).
Temperature and/or solvent dependent color change could
be used for monitoring of reaction 3 using UV-visible
spectroscopy if such a reaction would occur. Variable-temper-
ature spectroscopic measurements in the above donor solvents
in the range +18° to +85 °C revealed that there are no signifi-
cant changes in absorbance between 350 and 850 nm. After
heating in test tubes to above 100 °C, solutions of several
organoantimony(V) cyanoximates in pure DMF gradually
change color and became slightly yellow, but no quantitative
information was drawn from these observations (Figures 4 and
5; S18 (Supporting Information)). Therefore, at ambient tem-
peratures in solvents of potential biological interest, the Sb(V)
complexes synthesized and discussed in the present paper are
stable.
here demonstrate very similar IR spectra, an assumption about
the analogous structures of tetraarylantimony(V) cyanoximates
to those determined by X-ray analysis has been made (Table
1). This observation means all other Ph4SbL compounds
obtained likely contain monodentate anions bound to the
antimony atoms in a fashion similar to that found in the
structures of Ph4Sb{ACO} and Ph4Sb{DCO}. Therefore, struc-
ture B in Figure 1 clearly reflects this binding mode.
Monohalogenated trisphenylantimony(V) cyanoximates prob-
ably also have a trigonal bipyramidal structural motif where
the phenyl groups are located in the equatorial plane while
monodentate cyanoxime anions and atoms of halogens occupied
axial positions. However, to this date there is no direct structural
confirmation to that suggestion.
UV-Visible Stability Studies of Tetraarylantimony(V)
Cyanoximates. Tetraalkylammonium cyanoximates R4N+L-
and compounds with the general formula Ph4EL (E ) P, As; L
) cyanoxime anions) represent ionic substances that readily
dissociate in solutions. Increasing the metallic character of
antimony upon transition in the 5A group down from N to Sb
leads to formation of more stable covalent organoantimony
cyanoximates described in this paper.55 However, it was possible
to suggest that temperature and donor solvents such as pyridine,
ethanol, ethanol/water mixtures, DMF, and DMSO will initiate
the dissociation of tetraarylantimony(V) complexes according
to the equation below.
NMR Spectroscopic Studies of Rotational Barriers in
Some Compounds. Two cyanoxime ligands such as H(ACO)
and H(DCO) and their tetraphenylantimony(V) complexes were
1
examined using variable-temperature H NMR experiments.
Amides contain the C(O)-N group in which bonds have
partially double character due to significant contribution of the
form II into the overall electronic structure:
(4)
This leads to restricted rotation around the C-N bond, which
(3)
requires some activation energy to overcome the barrier. Room-
1
temperature H NMR spectra of both ligands and their com-
plexes consist of well-resolved singlet lines corresponding to
individual signals of protons in the absence of rotation.
Increasing the temperature leads to acceleration of exchange
between two individual states due to rotation around the C-N
bond (Figures 6 and 7). Observation of the coalescence
temperature (tcoal.) is required for estimation of the process
activation energy. Therefore, values of ∆G* were calculated
(55) Generally, it would be interesting to observe the binding mode and
its strength in organobismuth cyanoximates. Comparison of the
organoantimony with similar organobismuth complexes should be
interesting as well. Unfortunately, Bi(III)-cyanoximes have not been
synthesized yet.

1236 Inorganic Chemistry, Vol. 39, No. 6, 2000
Domasevitch et al.
Figure 6. Fragments of selected proton NMR spectra for H(DCO) at
different temperatures. Solution of cyanoxime ligand in DMSO-d6 (CM
) 1.2 × 10-3) and each spectrum obtained after 64 scans.
using the Eyring equation:42
Figure 7. Fragments of selected 1H NMR spectra of (C6H5)4Sb{ACO}
in the region of amide protons at different temperatures. Solution of
the complex in DMSO-d6 (1.7 × 10-3 M). Each spectrum recorded
after 32 scans.
-∆G*
RTc
kBTc
kc ) ø
exp
(5)
(
)
(
)
h
where kc is the exchange rate constant at coalescence temper-
ature Tc (K), kB is Bolzmann’s constant, h is Plank’s constant,
and ø is the transmission coefficient, which in this case equals
1. Since rotation around the amide bond is carried between two
equally populated states, eq 6 was used to determine the rate
constant kc with good approximation.43
Table 6. Data of Dynamic NMR Experiments for
Amide-Containing Cyanoximes and Their Tetraphenylantimony(V)
Complexes
tcoal.
,
kcoal.
,
∆G*, kcal/mol bond length
compound
∆δ, Hza
°C (K)
c-1
(kJ/mol)b
C-N (A)
HACO
Ph4Sb{ACO}
HDCO
32.4
285.9
56.7
50 (323)
57 (330) 635
80 (353) 126
72
16.2 (67.7)
15.1 (63.1)
17.4 (72.6)
18.0 (75.2)
1.331(5)c
1.329(4)d
1.328(6)e
1.337(8)d
x
2
2
Ph4Sb{DCO}
43.2
88 (361)
96
kc ) π (νa - νb)
(6)
a Distance between two signals in the absence of rotation. b Accuracy
of determination is (0.1 kcal/mol. c Data from ref 45. d This work.
e Data from ref 37. Accepted values for CsN single bond: 1.472 Å,
for CdN double bond: 1.320 Å, for CtN triple bond: 1.157 Å (data
from ref 27).
The NMR frequencies for individual states in the absence of
exchange are marked as νa and νb. Fragments of overlaid proton
NMR spectra at different temperatures for the H(ACO) ligand
and graphic determination of tcoal. for Ph4Sb{ACO} are shown
in S14 and S15 (Supporting Information). Experimentally
determined values of ∆ν, tcoal. and therefore calculated values
of ∆G* are presented in Table 6. This table also contains bond
distances C-N in amide group for all compounds examined
here. Commonly observed44 activation energies of amides are
in the range of 12 to 16 kcal/mol. Hence, thermodynamic data
obtained for amides, some ligands, and their organoantimony-
(V) complexes studied in this paper are not significantly different
from those reported previously. Unexpectedly, there was no
correlation observed between values of rotational activation
energy ∆G* and bond lengths C-N in the amide group (Table
6). However, a small difference in ∆G* and tcoal. between Ph4-
Sb{ACO} and Ph4Sb{DCO} complexes can be attributed to the
kinematic factor that is a weight difference between the
hydrogen atom and CH3 group in these ligands.
NMR spectra at room temperature. Two equivalent methyl
groups in Cs{DCO} appeared as a sharp singlet at 3.05 ppm,
while in Cs{TDCO}, they are at 3.42 ppm. Values of chemical
shifts for both salts were measured in DMSO-d6 solutions at
291 K. The bright-yellow color of Cs{DCO} and Cs{TDCO}
indicates the nitroso character of the CNO group in the
compounds (λmax ) 384-455 nm).24a,30 The observation of the
singlet line from two methyl groups in 1H NMR spectra at room
temperature suggests a low rotational barrier in these com-
pounds, which is associated with decreased electron density on
C-N amide bonds. This is contrary to quite significant values
of ∆G* found for both protonated amide-cyanoximes HL and
their organoantimony(V) derivatives described in present paper.
Results of these variable-temperature NMR experiments have
confirmed data of UV-visible spectroscopy that in the studied
temperature region in DMSO organoantimony(V) cyanoximates
are stable compounds. Therefore, monodentate coordination of
Interestingly, the amide-containing cyanoxime anions TDCO-
and DCO- in their Cs+ salts exhibit only one signal in proton

Organoantimony(V) Cyanoximates
Inorganic Chemistry, Vol. 39, No. 6, 2000 1237
anions in complexes as well as their chemical integrity is
unchanged in a variety of different solvents and temperatures.
This is an important factor for prospective pharmacological
applications of new coordination compounds described in this
paper.
Acknowledgment. This work was funded in part by the
Inorganic Chemistry Division of the Chemistry Department of
Kiev University as well as by ALSI Corp. and private founda-
tion. Authors thank Dr. K. Rodgers for his help and encourage-
ment in writing this paper. Authors also thank Dr. S. Lindemann
and Dr. S Tchernega for their help at the beginning of this work,
and Ms. Katherine Dunn for her technical assistance in
preparation of the manuscript.
Conclusion
A total of 25 different organoantimony(V) cyanoximates have
been synthesized and characterized using different spectroscopic
methods. All compounds obtained are monomeric, both in
solution and in the solid state. Crystal structures were determined
for two complexes in which anions demonstrate a monodentate
binding mode to Ph4Sb+ units via the oxygen atom of the oxime
group. Coordination polyhedra of Sb(V) atoms in both com-
pounds are distorted trigonal pyramids with the axial binding
of cyanoxime anions. Analogous IR spectra of other obtained
organoantimony(V) complexes to those characterized by X-ray
analysis suggest a similar coordination mode of anions in these
compounds. All synthesized complexes have shown significant
stability toward dissociation in several solvent systems and at
different temperatures. Values of activation energies for rota-
tional barriers for some amide-cyanoximes and their tetraphen-
ylantimony(V) compounds have been measured.
Supporting Information Available: Data of the NMR spectroscopy
for all synthesized ligands are presented in S1-S3, while analytical
data for all obtained organoantimony(V) cyanoximates are given in
Table S4 and S5. Tables S6-S13 contain crystallographic details such
as thermal displacement parameters and hydrogen atoms coordinates;
Figures S16 and S17 show packing diagrams for Ph4Sb{ACO} and
1
Ph4Sb{DCO}; Figures S14 and S15 exhibit variable temperature H
NMR data for H(ACO) and Ph4Sb{ACO}; Figure S18 contains variable-
temperature UV-visible spectra for a Ph4Sb{ACO} solution in DMF.
This material is available free of charge via the Internet at http:
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