Double-stranded metal-organic networks for one-dimensional mixed valence coordination polymers

Inorg. Chem. 2005, 44, 8326−8342

Double-Stranded Metal−Organic Networks for One-Dimensional Mixed

Valence Coordination Polymers

Daniel Robertson,^†John F. Cannon,^‡and Nikolay Gerasimchuk*^,†

Department of Chemistry, Southwest Missouri State UniVersity, Temple Hall 456, Springfield,

Missouri 65804, and Department of Chemistry and Biochemistry, Brigham Young UniVersity,

Benson Science Building 100, ProVo, Utah 84602

Received March 29, 2005

The design of new types of metal−organic networks and the search for unusual crystal architecture represents an

important task for modern inorganic and materials chemistry research. A group of new monosubstituted

phenylcyanoximes, containing F, Cl, and Br atoms at the 2, 3, or 4 positions, were synthesized using the high yield

nitrosation reaction with CH₃

spectrometry) and structurally characterized. Results of X-ray analysis revealed nonplanar trans

2-chlorophenyl(oximino)acetonitrile, H(2Cl PhCO); a nonplanar anti configuration for 4-chlorophenyl(oximino)-

acetonitrile, H(4Cl PhCO); and planar cis syn geometry for 3-fluorophenyl(oximino)acetonitrile, H(3F PhCO). All

−

ONO and were spectroscopically (¹H NMR, ¹³C NMR, UV

−visible, IR, mass

−anti geometry for

−

arylcyanoximes undergo deprotonation in solutions with the formation of colored anions exhibiting pronounced

negative solvatochromism in a series of polar protic and aprotic solvents. Nine thallium(I) cyanoximates were obtained

using the reaction between hot (

arylcyanoximes HL. Crystal structures of two Tl(I) cyanoximates [Tl(2Cl

∼

95

°

C) aqueous solutions of Tl₂CO₃and solid powdery monohalogenated

PhCO) and Tl(4Br PhCO)] contained

−

centrosymmetric dimeric units (TlL)₂that are connected to a coordination polymer by means of an oxygen atom of

the oxime group of the neighboring molecule. Cyanoxime anions act as bridging ligands in both structures where

the polymeric motif consists of double-stranded Tl

planar rhombes. Thallium atoms form infinite linear arrays with close intermetallic separations. The nearest Tl(I)

‚‚Tl(I) distances are 3.838 and 4.058 Å in the Tl(2Cl PhCO) and Tl(4Br PhCO) structures, respectively, close to

that in metallic thallium (3.456 Å). Monosubstituted phenyl groups are well aligned in -stacking columns that are

−O chains interconnected with the formation of zigzagging Tl₂O₂

‚

−

π

perpendicular to the array of Tl(I) atoms and stabilize formed structures. Coordination polyhedrons of thallium(I) in

these complexes represent distorted trigonal pyramids with stereoactive lone pair.

Introduction

conductive nonmetallic substances and reliable supercon-

ducting material promises great reduction in future energy

and materials consumption for transportation and the use of

electricity. So far, ceramics, containing various transition-

metal oxides, were found to be high-temperature supercon-

ductors above the boiling point of nitrogen.³These com-

pounds, however, encounter serious problems such as the

instability of crystal lattices associated with the loss of

superconductivity over time and after a reiterated strong

Delocalized mixed-valence compounds^1,2have great po-

tential as electric conductors. The discovery of highly

* Author to whom correspondence should be addressed. Phone: (417)

836-5165. Fax: (417) 833-5829. E-mail: nig434f@smsu.edu.

^†Southwest Missouri State University.

^‡Brigham Young University.

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8326 Inorganic Chemistry, Vol. 44, No. 23, 2005

10.1021/ic050465w CCC: $30.25

Published on Web 10/13/2005

Double-Stranded Metal-Organic Networks

Scheme 1

magnetic field has been applied. Conductive coordination

polymers based on an organic ligand network promise certain

advantages over ceramics. An electron transfer (hopping)

between different oxidation states is a key phenomenon in

the electric conductivity of mixed-valence compounds.⁴

There are ongoing investigations in classical one-electron-

transfer compounds based on copper(I/II),⁵ruthenium(II/III),⁶

iron(II/III),⁷manganese(II/III or III/IV),⁸and other (Cr,⁹Co¹⁰)

redox pairs. There also is a growing interest in the two-

electron-transfer mixed-valence compounds based on gold-

(I/III),¹¹nickel(II/IV),¹²and thallium(I/III)¹³and the con-

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systems.¹⁴Both systems represent classical one-dimensional

solids that possess significant electrical conductivity (Scheme

1).

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Inorganic Chemistry, Vol. 44, No. 23, 2005 8327

Robertson et al.

Scheme 2

OH)-R, where R is an electron-withdrawing group such as

CN,²³amide,²⁴thioamide,²⁵keto,²⁶carboxylic esters,²⁷hy-

drazide,²⁸or 2-heteroaryl.²⁹Since cyanoximes show an

unprecedented variety of different binding modes to metal

ions,³⁰these molecules are far better ligands than conven-

tional monoximes and dioximes. Also, the cyanoximes

possess higher acidity than the latter and, therefore, more

easily undergo deprotonation to form anionic species that

readily interact as nucleophiles (bases) with metal cations.

Thus, the cyanoximes’ pK_avalues^22arange from 4.5 to 7.5

and are 2-4 orders of magnitude lower than those for

acetone-oxime (10.8), acetophenone-oxime (9.2), and dim-

ethylglyoxime (10.2).^49,61There are about three dozen

cyanoximes known and studied up to date. The vast majority

cm^-1), making a formation of mixed-valence thallium-based

coordination polymers that exhibit electron hopping achiev-

able. Interesting examples of heterometallic Tl-Pt and

polymeric chain Tl-Au compounds were recently reported.¹⁹

A generation of mixed-valence species can be achieved

through the cocrystallization of two homovalent coordination

compounds^14a,dor through the controlled partial oxidation

of the low-valent metal complexes using halogen vapors or

an electric current.²⁰

There are three important factors that guide the search for

mixed-valence coordination polymers that may exhibit an

electrical conductivity and even lead to high-temperature

superconductivity. These are (1) the formation of a well-

organized one-dimensional polymeric motifs such as col-

umns, chains, or narrow sheets connected by nonbonding

interactions; (2) a close spatial location of metal ions in the

crystal lattice due to appropriate bridging atoms/groups or

direct metal-metal interactions; and (3) similar coordination

geometries and bonding properties for metal centers in

different oxidation states. The latter property leads to a low

energy barrier between two different oxidation states and

creates the condition for electron transport (hopping),⁴

induced by light or temperature.

One of the key conditions for success in the search for

conducting mixed-valence compounds and materials is the

discovery and exploration of new bridging ligand systems

that can ensure formation of the one-dimensional polymeric

structures of complexes (Scheme 2).

Our attention turned to oximes, a versatile group of stable

organic molecules. The oximes form numerous coordination

compounds²¹with a majority of metal ions including those

existing in two or more different oxidation states. Cyan-

oximes,²²in particular, represent a new and interesting class

of excellent ligands with the general formula NC-C(dN-

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8328 Inorganic Chemistry, Vol. 44, No. 23, 2005

Double-Stranded Metal-Organic Networks

Scheme 3

of these ligands act as chelators in metal complexes, but the

bridging function of the ligands is known as well. Cyanoxi-

companied by the formation of five-membered chelate rings

as a result of the participation of donor atoms (O, N, or S)

present on different R group.^25,30,45

42

mate anions, as superior ampolydentate organic ligands,^31,32

are a good choice for the design of metal-organic networks

that support one-dimensional polymeric motifs in the struc-

tures. Thus, cyanoximes exhibit an extensive bridging

function via donor atoms of the NC-C(NO)- fragment in

numerous complexes (Scheme 3). Often, bridging is ac-

Anionic bridging ligands may facilitate an electric con-

ductivity in formed mixed-valence coordination polymers

with closely located metal centers (Scheme 2). Presented in

Scheme 4, monosubstituted halogenated arylcyanoximes and

their metal complexes were largely unknown prior to this

investigation. These molecules, however, represent an in-

teresting set of organic flexible ligands that cannot form

chelate metallocycles and may not only act as bridging

groups to form coordination polymers but also feature

π-stacking interactions. Therefore, we selected nine arylcy-

anoximes, shown in Scheme 4, for our studies.

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Inorganic Chemistry, Vol. 44, No. 23, 2005 8329

Robertson et al.

Scheme 4

cyanoximates, those that contain (a) a nonplanar bridging

anion in the oxime form and those that contain (b) a planar

conjugated anion in the nitroso form in cases where the

ligands can form chelate complexes. These complexes are

reflected in binding modes 2 and 4-6, respectively (Scheme

3). Careful analysis of the known structures of complexes

has necessitated a search for new ligands for metal-organic

networks, ligands that are able to form stable one-

dimensional coordination polymers with spatially close linear

arrays of metal ions.

Halogenated arylcyanoximes could provide interesting

examples of crystal lattice architecture due to the involvement

of halogen atoms in the coordination to the metal center.

The affinity of Tl(I) toward halogenides has been well-

established and resembles that for Ag(I) cations.³³The

presence of halogen atoms at the 2, 3, or 4 positions on the

phenyl group of these cyanoximes may provide additional

support for the coordination of ligands to the monovalent

thallium centers. Ortho-assistancessupport upon coordina-

tion of the ligands containing halogen atoms (Cl, Br, or I)

in aromatic compounds to the metal centershas been

established for numerous organometallic complexes of

transition metals.³⁴The Ln-F dative interactions were

recently reported for several lanthanide fluorinated thiolate

complexes.³⁵A rare extra-coordination of fluorine atoms

leading to the formation of a planar five-membered chelate

ring in Zn(II) 2,6-difluorophenol complexes was found as

well.³⁶Also, the weak extra-coordination of halogen atoms

from neighboring molecules in the samples of solid Ag(I)

and Tl(I) halomethanesulfonates was recently discussed.³⁷

Some results of the first part of our investigation dealing

with the synthesis and characterization of Tl(I) monosub-

stituted arylcyanoximates are reported here.

In general, Tl(I) forms coordination compounds of several

structural types: distorted Tl₄O₄cubes in tetramers or

cages;^64,66planar Tl₂O₂or nonplanar [Tl₂X₂]^2-(X ) S, Se,

Te) rhombic units in molecular complexes;^63,67isolated or

polymeric Tl-Pt, Tl-Au, or Tl-Cu clusters;⁶⁵and zigzag

polymers. A very interesting polymeric staircase structure

consisting of Tl₂O₂skewed rhombes in thallium(I) ortho-

nitrophenolate was reported recently.⁶²Planar conjugated

anionic cyanoximes were found in ionic alkali metal salts^42b,59

and chelate complexes of transition metals.^24a,30a,60In both

of these types of compounds, cyanoximes exist as nitroso

anions. In some cases, alkali metals such as sodium,

potassium,⁴³and cesium^42boften form stable ionic “acid salts”

of monoprotic cyanoximes of MHL₂composition (L )

amidecyanoximes and 2-heteroaryl-cyanoximes). Contrary

to those salts, thallium(I) forms cyanoximates of TlL with

1:1 stoichiometry with a significant degree of covalent

bonding between the metal center and ligand. Previously,

we discussed the synthesis and crystal structures of several

thallium(I) cyanoximates.⁴⁵The results of these studies are

summarized in Table 1. There are two different types of Tl

Results and Discussion

1. Ligands Characterization. With the exception of

2-chlorophenyl(oximino)acetonitrile H(2Cl-PhCO),⁵⁸none

of the monosubstituted arylcyanoximes shown in Scheme 4

were known prior to this study. These compounds undergo

deprotonation with the formation of yellow anions; the color

originates from low-intensity n f π* transitions (ꢀ ) 20-

200 M^-1cm^-1) of the nitroso chromophore in the visible

region of the spectrum. Anionic cyanoximates possess, in

alkali metal salts, conjugated planar structures^22,30-32in which

the negative charge is delocalized throughout the anion, and

they may be described using several resonance forms, as

shown in Scheme 5. This behavior is consistent with that

observed earlier for other cyanoxime ligands²²where the

majority of resonance structures of cyanoxime anions

represent nitroso forms. Indeed, in ionic alkali metal or

ammonium salts, there are nitroso anions, judging from the

shorter N-O distances versus the C-N bond length in the

fragment.

(62) (a) Harrowfield, J. M.; Sharma, R. P.; Shand, T. M.; Skelton, B. W.;

White, A. H. Austr. J. Chem. 1998, 51(8), 707-722. (b) Harrowfield,

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1998, 51 (8), 735-745.

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Chem. 1989, 28 (20), 3829-3830. (b) El-Hadad, A. A.; Kickham, J.

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D. P.; Scott, B. L. Inorg. Chem. 2001, 40 (9), 2177-2184.

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Chem. Soc. 2001, 123, 173-174. (b) Crespo, O.; Fernandez, E. J.;

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Catalano, V. J.; Bennett, B. L.; Yson, R. L.; Noll, B. C. J. Am. Chem.

Soc. 2000, 122, 10056-10062.

Figure 1 shows typical spectral changes, such as the bands’

batochromic shift, indicating charge delocalization during the

deprotonation of cyanoximes. Traditionally, the solvent effect

on absorption in the UV and visible regions of spectra has

been used for the characterization of new chromophores and

(66) Campbell, J.; Mercier, H. P. A.; Santry, D. P.; Suontamo, R. J.;

Borrmann, H.; Schrobigen, G. J. Inorg. Chem. 2001, 40 (2), 233-

254.

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A. M.; Schrobilgen, G. J. Inorg. Chem. 1998, 37 (8), 1929-1943.

8330 Inorganic Chemistry, Vol. 44, No. 23, 2005

Double-Stranded Metal-Organic Networks

Table 1. Results of the Structural Investigation of Some Tl(I) Cyanoximates

Tl‚‚‚Tl distance,

metal center

coordination number

complex^a

Tl(ACO)

Å

structure, motif, comments

ref

45c

4.47

4.41

5

3

ruffled, regular Tl₂O₂rhombes

isolated Tl₂O₂rhombes

Tl(BCO)

45d

Tl(CCO)

4.26

7

very complicated 3D network

56

Tl(2PCO)

Tl(4Br-PhCO)

Tl(TDCO)

Tl(PiCO)

Tl(2Cl-PhCO)

Tl(TLCO)

Tl metal

4.13

4.06

4.05

4.03, 4.06

3.84

4

3

7

4,5

3

well-organized Tl‚‚‚O chains

33a

this work

45b

45i

this work

45k

well-organized, irregular Tl₂O₂sheet

well-organized Tl‚‚‚S and Tl‚‚‚O chains

isolated, very complex TlL trimers

well-organized irregular Tl₂O₂sheets

isolated dimers TlL; NO group disordered

face-centerd cubic lattice

3.65

3.45

4

8

54

^a1:1 stoichiometry compounds with abbreviated ligand structures, which are shown below:

Scheme 5

better understanding their electronic structures. It is interest-

is the highest among other solvents. Again, this is evidence

for negative solvatochromism, at which the value of the

dipole moment of a molecule or ion in the excited state is

smaller than that in a ground state,³⁸reflecting a charge

transfer from the terminal oxygen atom of the NO group

into nitrogen or carbon atoms of the oxime fragment in the

excited state.

In some cases, the ¹³C NMR spectra of the synthesized

monosubstituted arylcyanoximes contained only one set of

signals, indicating the presence of only one geometrical

isomer,⁴¹syn or anti, in solutions at room temperature. These

compounds are H(2F-PhCO), H(2Cl-PhCO), H(2Br-

PhCO), H(3Br-PhCO), and H(4F-PhCO). An anti isomer

is considered to be more favorable. The ¹³C NMR spectra

of other cyanoximes, such as H(4Br-PhCO), H(4Cl-PhCO),

H(3Cl-PhCO), and H(3F-PhCO), contain two sets of

signals due to the presence of two isomers in the DMSO-d₆

solutions at room temperature. The ¹H NMR spectra of these

mixtures also displayed a double set of lines strongly

overlapped in the aromatic region.

ing to note that deprotonated monosubstituted arylcyan-

oximes (cyanoximate anions) exhibit a pronounced negative

solvatochromic effect³⁸(Figure 2). There is a substantial

difference between the λ_maxvalues of the n f π* transition

in the visible region of the spectra of cyanoximate anions in

the protic solvents ROH (R ) H, CH₃, C₂H₅, n-C₃H₇, and

t-C₄H₉) and those of aprotic solvents such as acetone, CH₃-

CN, DMF, and DMSO. The energy gap, for example,

between absorbances in CH₃OH (at 392 nm) and DMSO (at

443 nm) for solutions of tetrabutylammonium (4Br-PhCO)^-

is 35.1 kJ/mol, which is consistent with a hydrogen bond of

medium strength.

Linear correlations between the positions of bands in

the spectra of ionic tetrabutylammonium cyanoximates,

N(C₄H₉)₄L^-, and between solvent parameters such as pK_a

+

and Kosower’s specific solvation energy^39,40Z were found

for several of the alcohols ROH used (Figure 3). The highest

energy for optical transitions in UV-visible spectra of

cyanoximate anions was observed for aqueous solutions and

is typical of negative solvatochromism.

The solvation by aprotic solvents such as DMF and DMSO

significantly lowers the energy of the n f π* transition in

the visible region of the spectra [Figure 2; Supporting

Information, S1 (S1, S2, S3, etc. refer to sections in the PDF

Supporting Information file; refer to the key given in the

Supporting Information section at the end of this paper for

details)].

The most intense signals in the ¹H NMR spectra of

synthesized HL (L ) monosubstituted arylcyanoxime;

Scheme 4) in DMSO-d₆solutions were tentatively assigned

Hydrogen bonding with solvent molecules is strongest in

aqueous solutions, and the energy of this transition in spectra

1

to the most sterically preferable anti configuration. The H

Inorganic Chemistry, Vol. 44, No. 23, 2005 8331

Robertson et al.

Figure 1. UV spectra of solutions of protonated (blue) and deprotonated

cyanoxime (red, as tetrabutylammonium salt) showing a batochromic shift

of π f π* transition bands due to conjugation in an anion. Solution in

EtOH at 5 × 10^-4M concentration in a 1 mm quartz cuvette; T ) 296 K.

Figure 3. Correlations between absorbance maximum of conjugated aryl-

oxime band (π f π* transition) in UV spectra of NBu₄⁺(3F-PhCO)^-and

solvent ROH parameters such as pK_a(red) and specific solvation energy Z

(blue). Red: linear fit for y ) A + Bx, with A ) -386.8, B ) 0.0145; R

) 0.981. Blue: linear fit for y ) A + Bx, with A ) 74.10, B ) -0.001 82;

R ) -0.90.

Figure 2. Solvatochromic series for solutions of NBu₄⁺(4Br-PhCO)^-in

different solvents. Isomolar solutions (5 mM) in 1 cm quartz cuvette; T )

296 K.

NMR spectra of all compounds contained broadened signals

of the oxime hydrogen around 14 ppm. Unfortunately, no

separate OH signals for syn and anti isomers were found,

indicating a fast proton exchange between the two isomers.

H(3F-PhCO) in the solid state exists as a mixture of cis-

syn and cis-anti isomers with a planar structure. However,

according to the X-ray analysis data discussed below, the

majority of arylcyanoximes studied up to date adopt only

one particular configuration in the solid state.⁶⁹The exact

assignment of a particular syn or anti configuration in a

solution by the NMR method was beyond the scope of this

research because it requires special 2D NOE experiments.

Data of room temperature ¹³C NMR spectroscopy for all

synthesized monosubstituted arylcyanoximes are available

in the Supporting Information, S2 and S3.

Figure 4. Molecular structure and numbering scheme for nonplanar

arylcyanoximes H(2Cl-PhCO) (A) and H(4Cl-PhCO) (B) drawn at the

50% thermal ellipsoids probability level. Hydrogen atoms, with the exception

of H1, are omitted for clarity.

orless substances that can be crystallized to form single

crystals suitable for X-ray analysis using slow evaporation

of solutions in CCl₄or water. All of the crystallized

compounds do not contain solvent molecules, contrary to

some heterocyclic cyanoximes.^30b,42Crystallographic data for

structures of three protonated arylcyanoximes HL are shown

in Table 2.

1.2. Structure of H(2Cl-PhCO). The molecular structure

of H(2Cl-PhCO) is shown in Figure 4A. Bond lengths and

valence angles in the structure are summarized in Table 3.

The cyanoxime is nonplanar and adopts a trans-anti

configuration^30bin the solid state. Thus, the oxime fragment

and chlorine atom are on opposite sides of the molecule along

the C2-C7 direction. There are two planar fragments in the

structure of the molecule: the cyanoxime fragment C8-C7-

1.1. Crystal Structures of Synthesized Cyanoximes. The

halogenated monosubstituted arylcyanoximes represent col-

(68) Arulsami, N.; Bohle, S. J. Org. Chem. 2000, 65 (4), 1139-1143.

(69) Goeden, L. The Synthesis, Characterization and Biological Activity

Studies of Pt(II) and Pd(II) Disubstituted Arylcyanoximes. MS thesis,

Southwest Missouri State University, Springfield, MO, May 2005.

8332 Inorganic Chemistry, Vol. 44, No. 23, 2005

Double-Stranded Metal-Organic Networks

Table 2. Crystallographic Data for Several Synthesized Monosubstituted Arylcyanoximes and Their Tl(I) Complexes

parameter

empirical formula

fw

H(2Cl-PhCO)

C₈H₅ClN₂O

180.59

H(3F-PhCO)

C₈H₅FN₂O

164.14

H(4Cl-PhCO)

C₈H₅ClN₂O

180.59

Tl(4Br-PhCO)

C₈H₄BrN₂OTl

428.41

Tl(2Cl-PhCO)

C₈H₄ClN₂OTl

383.95

cryst syst

space group

monoclinic

P2_1/c

monoclinic

P2_1/c

monoclinic

P2_1/c

monoclinic

P2_1/n

monoclinic

P2_1/n

a, Å

b, Å

c, Å

9.5477(5)

12.1061(7)

7.6112(5)

90

111.26(4)

90

8.8628(18)

12.533(3)

7.1450(11)

90

106.577(15)

90

11.8836(9)

6.8572(4)

11.3390(7)

90

115.39(5)

90

13.1112(13)

4.0577(4)

17.0940(17)

90

92.140(2)

90

3.8382(7)

11.0065(18)

20.901(4)

90

92.447(3)

90

R

â

γ

vol, Å³

819.9(8)

4

760.2(2)

4

834.7(9)

4

908.8(16)

4

882.2(3)

4

Z

T, K

296(2)

293(2)

100(2)

193(2)

λ, A

0.710 73

1.463

0.412

0.710 73

1.433

0.115

0.710 73

1.437

0.405

0.710 73

3.131

22.124

0.710 73

2.891

18.565

D (calcd), Mg/m³

µ, mm^-1

F(000)

368

336

368

760

688

reflns collected

(independent)

R (all data)

wR²(all data)

1954 (1436)

1834 (1339)

2003 (1465)

14118 (3213)

5699 (1899)

0.0424

0.0891

0.0651

0.1301

0.0411

0.0961

0.0338

0.0693

0.0689

0.1650

Table 3. Selected^aBond Lengths (Å) and Valence Angles (deg) in the Structures of Three Monosubstituted Arylcyanoximes

H(2Cl-PhCO) H(4Cl-PhCO)

angle angle

bond

Cl(1)-C(1)

O(1)-N(1)

N(1)-C(7)

N(2)-C(8)

C(1)-C(2)

C(2)-C(3)

C(2)-C(7)

C(7)-C(8)

1.374(2)

1.377(19)

1.287(2)

1.134(2)

1.398(2)

1.392(3)

1.477(2)

1.448(3)

C(2)-C(1)-Cl(1)

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

C(3)-C(2)-C(7)

C(1)-C(2)-C(7)

C(7)-N(1)-O(1)

N(1)-O(1)-H(1)

N(1)-C(7)-C(8)

N(1)-C(7)-C(2)

C(8)-C(7)-C(2)

N(2)-C(8)-C(7)

120.75(14)

117.86(16)

118.81(16)

123.33(18)

111.59(14)

109.5(14)

121.17(15)

118.03(15)

120.71(14)

178.5(2)

C(1)-C(6)

C(1)-C(2)

C(1)-Cl(1)

C(4)-C(7)

C(7)-N(1)

C(7)-C(8)

C(8)-N(2)

N(1)-O(1)

1.374(2)

1.379(3)

1.738(2)

1.467(2)

1.289(2)

1.449(2)

1.134(2)

1.378(2)

C(6)-C(1)-Cl(1)

C(5)-C(4)-C(3)

C(5)-C(4)-C(7)

C(3)-C(4)-C(7)

N(1)-C(7)-C(8)

N(1)-C(7)-C(4)

C(8)-C(7)-C(4)

N(2)-C(8)-C(7)

119.14(14)

118.46(16)

120.51(15)

121.01(15)

120.21(15)

121.18(14)

118.55(13)

177.23(18)

H(3F-PhCO)^b

bond

angle

bond

angle

C(2)-F(1)

C(3)-C(4)

C(4)-C(5)

C(4)-C(7)

C(8)-N(1)

1.357(7)

1.387(8)

1.376(8)

1.467(8)

1.118(8)

F(1)-C(2)-C(3)

C(5)-C(4)-C(3)

C(5)-C(4)-C(7)

C(3)-C(4)-C(7)

C(8)-C(7)-C(4)

116.6(7)

119.3(6)

118.7(6)

122.0(6)

119.4(6)

C(7)-N(2b)

C(7)-N(2a)

N(2a)-O(1a)

N(2b)-O(1b)

1.27(2)

N(1)-C(8)-C(7)

C(7)-N(2a)-O(1a)

C(7)-N(2b)-O(1b)

179.0(9)

108.3(8)

104.8(11)

1.334(11)

1.366(13)

1.384(15)

^aThe geometry of phenyl group is normal and not shown. ^bContains a mixture of syn and anti isomers in the same crystal (see Figure 5).

N1-O1 and the 2-chlorophenyl group. The dihedral angle

between these planes is ∼43°. Distances C7-N1 ) 1.287-

(2) Å and N1-O1 ) 1.3769(19) Å and valence angles at

C7 in the oxime fragment are normal for cyanoximes.^22,30,31

The shortest distance between the Cl1 and N2 atoms is 3.440

Å. Molecules of H(2Cl-PhCO) are packed into the crystal

by means of π-π-stacking interactions and hydrogen bond-

ing between the nitrogen atom N2 of the cyano group (A)

and the hydrogen atom attached to the oxygen atom (D) of

the oxime group. The parameters for H bonding in the crystal

are O1-H1‚‚‚N2 ) 2.904(2) Å, H1‚‚‚N2 ) 2.09 Å, and

(DHA) ) 173.9°. H-bound molecules of H(2Cl-PhCO)

form chains that are connected by “slipped” π-stacking

interactions.

cyanoxime fragment, no further cis or trans assignment of

geometry can be made. Two planar fragments can be seen

in the structure of H(4Cl-PhCO), the aryl group and the

cyanoxime group. There are several dihedral angles that

describe deviation of the whole molecule from planarity, for

example, C3-C4-C7-N1 ) 17° and C8-C7-N1-O1 )

-1.1°. The distances C7-N1 and N1-O1 are equal to 1.289-

(2) and 1.3784(18) Å, respectively; these values are normal

for cyanoximes.^22,30,31Hydrogen bonding between H1 of the

oxime group and N1(#1) in the cyano group of the neighbor-

ing molecule and π-π stacking interactions are responsible

for the packing of H(4Cl-PhCO) molecules into a crystal.

This H bond has the following parameters: O1-H1‚‚‚N2-

(#1) ) 2.8388(19) Å and H1‚‚‚N2(#1) ) 2.03 Å with the

angle (DHA) ) 171.1°.

1.3. Structure of H(4Cl-PhCO). The molecular structure

of H(4Cl-PhCO) is shown in Figure 4B, while valence

angles and bond distances for the molecule are presented in

Table 3. This cyanoxime also adopts an anti configuration.

Since the chlorine atom is at the para position to the

1.4. Structure of H(3F-PhCO). The molecular structure

of H(3F-PhCO) is shown in Figure 5A. The oxygen and

nitrogen atoms of the oxime group in this compound are

disordered by two positions, indicating coexistence of the

Inorganic Chemistry, Vol. 44, No. 23, 2005 8333

Robertson et al.

Na⁺and Tl⁺derivatives are presented in the Supporting

Information, S4. Sodium salts of the ligands were obtained

as alternative precursors for monovalent thallium complexes

and also for IR-spectroscopic studies of uncoordinated

cyanoximates in ionic salts. According to established IR

criteria for cyanoxime coordination,^23,45a,ia low-frequency

shift of ν(NO) and ν(CNO) vibrations⁴⁵ⁱcompared to those

in ionic NaL are evidenced in the bridging binding mode 2

of the oxime fragment (Scheme 3).

2.1. Crystal Growth and Structures of Thallium(I)

Cyanoximates. Monovalent thallium easily forms crystals

with cyanoxime ligands. However, obtaining quality single

crystals of Tl(I) cyanoximates, suitable for X-ray analysis,

represents a challenging problem. For example, there is a

tendency for Tl⁺organometallic compounds⁴⁶to form fibrous

microcrystals of poor quality. There are two major obstacles

that affect crystallization of thallium complexes: (a) the fast,

within several seconds, formation of very thin fibers or plate-

looking crystals upon cooling of hot aqueous solutions of

TlL (L ) monosubstituted arylcyanoximes) and (b) twinning

of the crystals formed. The difference in solubility of TlL

in hot and room-temperature aqueous solutions is significant.

Therefore, obtaining the second or third crop of crystals from

the mother liquors can take weeks. The most successful

method of growing suitable quality crystals of TlL is a hot

filtration of the reaction mixture into a large mouse test tube,

immersed into 4-5 L of water preheated to ∼96 °C in a

large Dewar flask equipped with an insulating cap. Cooling

of the obtained solution to room temperature takes several

days and usually affords X-ray quality crystals of monovalent

thallium cyanoximates. Photographs of crystalline samples

of some of the obtained thallium(I) cyanoximates are shown

in the Supporting Information, S5 and S6. The crystal-

lographic data for the two TlL complexes reported in this

work are summarized in Table 2.

Figure 5. (A) Molecular structure and numbering scheme for planar

H(3F-PhCO) that represents a mixture of the syn (60%) and anti (40%)

isomers: view of superimposed molecules. (B) H-bonding in the crystal.

two geometrical isomers in the crystal. A detailed analysis

of the experimental data set converged to R ) 0.065 for the

structure having 60% of its molecules as syn and 40% of its

molecules as anti isomers. The disorder in the CNO fragment

in some of the cyanoxime complexes was documented

earlier.^31e,45kBond lengths and valence angles are presented

in Table 3. 3-Fluorophenyl(oximino) acetonitrile, H(3F-

PhCO), adopts a planar configuration in the solid-state, being

the second documented case of such geometry for protonated

cyanoximes after NC-C(NOH)-C(O)NH₂(ACO).⁶⁸All

bond lengths and angles at the oxime carbon atom C7 and

nitrogen atoms N2A and N2B are normal for these geometric

isomers. The distance H3-O1 ) 2.300 Å in the syn isomer

can be considered as a long hydrogen bond. The distance

F1-H3 is 2.499 Å and is slightly smaller than the distance

between fluorine and the closest hydrogen atom H1: F1-

H1 ) 2.512 Å. This slight tilt toward the H3 atom reflects

an attractive interaction between the two atoms. The torsion

angles in the skeleton of the molecule around the C4 and

C7 atoms are close to 0° (or 180°), reflecting an unexpected

planarity of the fluorinated cyanoxime. The values of these

angles are C5-C4-C3-C7 ) -0.3°, O1-N2-C7-C4 )

-179°, and O1-N2-C7-C8 ) 179.5°. There is hydrogen

bonding in the structure between the H1a atom of the oxime

group and the N1 atom of the CN group neighboring

molecule, resulting in the formation of a zigzag chain along

the y direction. Interestingly, the presence of the two isomers

does not affect the packing mode of the cyanoxime into a

crystal (Figure 5B).

2.2. Tl(2Cl-PhCO). The molecular structure of Tl(2Cl-

PhCO) represents an interesting centrosymmetric dimer and

is shown in Figure 6A, while bond lengths and valence angles

in the structure of the complex are summarized in Table 5.

The anion in the structure is in the oxime form and adopts

a nonplanar trans-anti configuration similar to that in

H(2Cl-PhCO). There are two planar fragments in the

structure: the 2-chlorophenyl group and the cyanoxime

fragment. The value of the torsion angle at the C3-C7 bond

in the thallium(I) complex (48.3°) is close to that for the

protonated cyanoxime ligand (43°). There are small changes

in bond lengths and angles in the oxime fragment in the Tl-

(I) complex as compared to those in the protonated cyan-

oxime. It is interesting to compare bond lengths N-O and

C-N in the oxime group in the uncoordinated ligand and in

its metal complex. Thus, O1-N1 ) 1.377 Å and N1-C7 )

1.287 Å for H(2Cl-PhCO), while the same distances are

1.364 Å and 1.310 Å, respectively, in the structure of Tl-

(2Cl-PhCO) (Tables 3 and 5). The sum of these bond

lengths for both compounds is almost identical: 2.664 Å in

the ligand itself and 2.674 Å in its thallium(I) complex. This

evidences redistribution and decreasing of the electron

Peculiarities of the stereochemistry for other known

cyanoximes are summarized in Table 4.

2. Metal Complexes. The most important IR frequencies

for all synthesized protonated arylcyanoximes HL and their

8334 Inorganic Chemistry, Vol. 44, No. 23, 2005

Double-Stranded Metal-Organic Networks

Table 4. Stereochemical Peculiarities of Several Cyanoxime Ligands

Inorganic Chemistry, Vol. 44, No. 23, 2005 8335

Robertson et al.

Table 4. (Continued)

^aX-ray single crystals analysis. ^bData from NMR spectroscopic measurements including, in some cases, variable temperature studies.

density on the N-O bond in the molecule when an anion

coordinates to the metal center.

metal-oxygen distances are ∼0.2 Å shorter than the inter-

dimeric Tl-O contact. Several reference sources provide

slightly different values of ionic radii for oxygen and

thallium(I): 1.40 and 1.54 Å (∑ ) 2.94 Å),^33a1.32 and 1.47

Å (∑ ) 2.79 Å),⁴⁷and 1.38 and 1.50 Å (∑ ) 2.88 Å),⁷⁰

respectively. Nevertheless, all three Tl-O distances in

synthesized Tl(I) arylcyanoximates are shorter than the above

sums of ionic radii^39,47for these elements and, therefore, are

considered as bonds. There are two slightly different

rhombes, 1 and 2, in the structure of the complex. The

dihedral angle and other geometrical parameters in these

rhombes are shown in Figure 9. Thallium(I) ions in the

Centrosymmetric dimeric Tl₂L₂units (L ) 2Cl-PhCO)

that consist of planar Tl₂O₂rhombes are connected to the

one-dimensional staircase structure by means of the oxygen

atom of the oxime group of the neighboring unit, forming

infinite columns (Figures 7 and 8). The cyanoxime anion in

the structure of Tl(2Cl-PhCO) acts as a bridging ligand and

forms a one-dimensional coordination polymer (binding

mode 2, Scheme 3). There are two short and almost equal

Tl(1)-O(1) bonds (2.587 and 2.594 Å) inside the rhomb in

a dimeric unit and one slightly longer Tl(1)-O(1*) bond

(2.803 Å) between the adjacent, at 90.7°, rhombs in the

structure of Tl(2Cl-PhCO). Thus, the two intradimeric

(70) Shannon, R. D. Acta Crystallogr., Sect A 1976, 32, 751-767.

8336 Inorganic Chemistry, Vol. 44, No. 23, 2005

Double-Stranded Metal-Organic Networks

and the aryl group is 9.4°. Interestingly, the configuration

and degree of planarity of the cyanoxime in an anion and is

almost the same in the structures of H(4Cl-PhCO) and Tl-

(4Br-PhCO). H(4Cl-PhCO), certainly, is a structurally

analogous ligand to H(4Br-PhCO). Bond lengths O1-N2

and N2-C7 of the oxime fragment in the Tl(I) complex are

1.346 and 1.309 Å, respectively, while the same bond lengths

in the structure of uncomplexed H(4Cl-PhCO) are 1.378

and 1.289 Å. It is remarkable, however, that the sum of both

bond lengths is practically identical: 2.655 Å for Tl(4Br-

PhCO) and 2.667 Å for H(4Cl-PhCO) (Tables 3 and 5).

Again, differences in bond distances in the oxime group

between the ligand and the metal complex reflect a redis-

tribution of the electron density in the C-N-O fragment

during complexation to the metal center.

The crystal structure of Tl(4Br-PhCO) is similar to that

of Tl(2Cl-PhCO) described above. Thus, the centrosym-

metric dimers [Tl(4Br-PhCO)]₂are joined together by

oxygen atoms of bridging cyanoxime anions into columns

(Figure 10), oriented along the y axis. The cyanoxime anion

acts as the bridging ligand (binding mode 2, Scheme 3) using

an oxygen atom of the NO group to form Tl₂O₂rhombes

(Figure 6B). The Tl₂O₂rhombes are connected with a

formation of ruffled or zigzag sheets; the dihedral angle

between the Tl₂O₂planar fragments is equal to 99.2°. Two

rhombes, 1 and 2, in the structure have slightly different

geometry (Figure 11). All three Tl-O bonds in the structure

have very close values, 2.640, 2.640, and 2.687 Å, where

the interdimeric distance is ∼0.05 Å longer than the

intradimeric contacts. Again, the sum of ionic^47,70radii for

Tl and O is greater than the above distances, which are

considered as bonds. The shortest Tl‚‚‚Tl distance is 4.058

Å and is ∼0.6 Å greater than that in metallic thallium. The

crystal structure of the complex represents a double-stranded

one-dimensional coordination polymer with infinite, well-

aligned linear arrays of close monovalent Tl cations (Figures

10-12).

The structure of the coordination polyhedron in the

structure of Tl(4Br-PhCO) can be best described as a

distorted trigonal pyramid and is shown in S8 of the

Supporting Information. The lone pair of Tl(I) in the structure

is stereoactive, directed away from the columns of polymeric

Tl(4Br-PhCO) complexes and pointed toward the bromine

atoms of neighboring columns in an open cleft.

The π-π stacking interactions between the 4-bromophenyl

groups of neighboring molecules at a distance of 4.058 Å

stabilize this elegant structure (Figure 12). It should be

mentioned that there are long, additional interactions of an

electrostatic nature between Br2 and N1 atoms (nitrile group)

and thallium(I) centers (Figure 10). These both intra- and

intercolumn interactions provide additional stabilization to

the crystal lattice. Also, it is important to note a short, 3.632

Å, Br‚‚‚Br nonbonding contact in the structure. The Br2-

Br2′-Br2 angle between neighboring columns of Tl(4Br-

PhCO) is 83°, while the closest distance between bromine

atoms in the same π-stack column is 4.058 Å (see the

Supporting Information, S9). This intracolumnar Br‚‚‚Br

distance is significantly larger than the intercolumnar separa-

Figure 6. Molecular structures and numbering schemes for centrosym-

metric dimers [Tl(2Cl-PhCO)]₂(A) and [Tl(4Br-PhCO)]₂(B), an ORTEP

drawing at the 50% probability ellipsoids.

structure form infinite linear arrays aligned along the x axis.

The shortest Tl‚‚‚Tl separation in the structure is 3.838 Å,

which is only slightly longer than that for metallic thallium

(a ) 3.456 Å). Centrosymmetric dimers [Tl(2Cl-PhCO)]₂

pack into a crystal with the formation of a lattice that is

stabilized by π-π stacking interactions between 2-chloroaryl

groups (Figure 7). Organization of the crystal structure is

shown in Figure 8. The structure of a ruffled Tl₂O₂rhombes

displaying a motif of zigzag sheets is shown in Figure 9.

The geometry of the Tl(I) coordination polyhedron in the

structure of the complex is best described as a distorted

trigonal pyramid and is displayed in S7 of the Supporting

Information. The central atom has a stereoactive lone pair

pointed away from the π-π stacking columns of Tl(2Cl-

PhCO) in the open cleft between them. It should be

mentioned that the Tl1‚‚‚N2 contacts have a nonbonding,

electrostatic origin due to the improper orientation of the

CN group and thallium centers. Thus, angles between the

nitrogen atom and the two closest Tl(I) ions are 89.9° and

120°, which is significantly less than expected for the

conventional binding angle, ∼180°, in numerous metal-

cyanide complexes.

Contrary to our expectations, the ortho chlorine atoms of

the aryl group do not support the metal center in the complex

by additional coordination, and they do not participate in

forming a crystal lattice. The nearest distance, Tl‚‚‚Cl )

4.186 Å, is beyond any reasonable interaction considered

between these two atoms. The closest distance between the

chlorine atom and another atom of a neighboring molecule

is Cl1‚‚‚H4 ) 3.017 Å, which is the same as the sum of

their van der Waals radii (3.00 Å)⁴⁷and may indicate weak

interaction between columns of TlL complexes.

2.3. Tl(4Br-PhCO). The molecular structure of this

complex is shown in Figure 6B, while bond lengths and

valence angles in the structure of Tl(4Br-PhCO) are

presented in Table 5. The cyanoximate anion in Tl(4Br-

PhCO) is nearly planar and adopts an anti configuration of

the oxime group with respect to the 4-bromophenyl group;

the dihedral angle between the planar cyanoxime fragment

Inorganic Chemistry, Vol. 44, No. 23, 2005 8337

Robertson et al.

Table 5. Selected^aBond Lengths (Å) and Valence Angles (deg) in the Structures of Thallium Complexes

Tl(2Cl-PhCO)

Tl(4Br-PhCO)

valence angle

bond length

valence angle

bond length

Tl(1)-O(1)^b

Tl(1)-O(1)#1

Cl(1)-C(2)

O(1)-N(1)

N(1)-C(7)

N(2)-C(8)

C(1)-C(2)

C(1)-C(6)

C(1)-C(7)

C(7)-C(8)

2.587(13)

2.594(13)

1.770(18)

1.364(18)

1.31(2)

1.17(3)

1.36(3)

1.40(3)

1.49(2)

O(1)-Tl(1)-O(1)#1

N(1)-O(1)-Tl(1)

N(1)-O(1)-Tl(1)#1

Tl(1)-O(1)-Tl(1)#1

C(7)-N(1)-O(1)

C(2)-C(1)-C(7)

C(6)-C(1)-C(7)

C(1)-C(2)-Cl(1)

N(1)-C(7)-C(8)

N(1)-C(7)-C(1)

C(8)-C(7)-C(1)

N(2)-C(8)-C(7)

72.3(5)

102.3(10)

140.0(10)

107.7(5)

114.6(15)

124.1(17)

117.7(16)

119.8(14)

120.2(16)

118.0(16)

121.6(16)

175(2)

Tl(1)-O(1)^c

Tl(1)-O(1)#1

Br(2)-C(4)

O(1)-N(2)

N(2)-C(7)

N(1)-C(8)

C(1)-C(2)

C(1)-C(6)

C(1)-C(7)

C(7)-C(8)

2.641(2)

2.640(3)

1.903(3)

1.346(4)

1.309(4)

1.154(5)

1.396(5)

1.403(5)

1.465(5)

1.453(5)

O(1)-Tl(1)-O(1)#1

N(2)-O(1)-Tl(1)

N(2)-O(1)-Tl(1)#1

Tl(1)-O(1)-Tl(1)#1

C(7)-N(2)-O(1)

C(2)-C(1)-C(7)

C(6)-C(1)-C(7)

C(3)-C(4)-Br(2)

N(2)-C(7)-C(8)

N(2)-C(7)-C(1)

C(8)-C(7)-C(1)

N(2)-C(8)-C(7)

78.23(9)

91.16(17)

123.77(19)

101.77(9)

116.1(3)

120.3(3)

120.8(3)

118.6(2)

118.2(3)

121.3(3)

120.3(3)

178.5(4)

1.42(3)

^aThe geometry of the phenyl group is normal and not shown. ^bThere is also a third contact, Tl(1)-O(1)#2 ) 2.803(7) Å, that is responsible for the

formation of the coordination polymer (Figure 9). ^cThe third contact, Tl(1)-O(1)#3 ) 2.687(2) Å, provides the addition of the oxygen atom to the Tl₂O₂

rhomb in a dimer, leading to a staircase zigzag sheet (Figure 11).

Figure 7. Prospective view of the crystal structure of the Tl(2Cl-PhCO)

Figure 8. Organization of the Tl(2Cl-PhCO) structure showing formation

complex. View along the Tl‚‚‚Tl direction showing the electrostatic

of the polymeric column with a ruffled Tl₂O₂rhombes as a zigzag sheet.

nonbonding Tl1‚‚‚N2 interactions as dashed lines.

Thallium(I) ions are green colored.

tion of 3.632 Å. The shorter than the sum of van der Waals

radii^39,47Br‚‚‚Br distance (3.92 Å) in different compounds

is not unusual and, for example, was reported recently⁴⁸in

the ladder-type bridging structure of the tetrabromocuprate-

(II) anion in its pentylammonium salt.

conductivity and low-temperature superconductivity in crys-

tals was observed in the direction perpendicular to the

π-stacking columns of planar organic molecules.⁵¹In prin-

ciple, electron transport (hopping) between different oxida-

tion states in mixed-valence Tl⁺/Tl³⁺cyanoxime complexes

can be achieved through bridging atoms of an NO- group

of anions, or via aligned π-stacking monosubstituted aryl

groups. To follow the preparation of their mixed-valence

complexes, the next step in our investigation is the synthesis

and study of Tl(III) complexes with the same set of

cyanoxime ligands. In light of the results presented here,

synthesis of the unsubstituted phenylcyanoxime, H(PhCO),

and its thallium complexes is justified with regard to the

closest location of both metal centers and π-stacking aligned

phenyl groups. This investigation is in progress, and results

will be submitted for publication shortly.

It is interesting to compare the distances between π-π-

stacking monosubstituted aryl groups in the structures of both

thallium(I) cyanoximates. Thus, the separation between two

phenyl rings in Tl(2Cl-PhCO) is 3.838 Å, while the same

separation for Tl(4Br-PhCO) is equal 4.058 Å. The differ-

ence is 0.22 Å and is very close to the van der Waals radii

difference between Cl and Br atoms: 0.15 Å. The presence

of π-stacking interactions between haloaryl groups that

provide extra stabilization of the crystal lattice in both

crystallographically characterized thallium(I) complexes is

essential for potential electric conductivity in the crystal.⁵⁰

This situation is similar to that for S or Se tetrafulvalenes

and their metallocomplex derivatives, where an electric

The structures of the two thallium complexes presented

in this paper are similar to the staircase polymeric motif in

8338 Inorganic Chemistry, Vol. 44, No. 23, 2005

Double-Stranded Metal-Organic Networks

Figure 9. Isolated polymeric Tl-O sheets (A) and the geometry of two adjacent planar Tl₂O₂diamonds in the structure (B), an ORTEP representation at

the 50% probability level.

as nitrosating agents. Synthesized monosubstituted cyanoximes with

their commonly used abbreviations are shown in Scheme 4. Melting

points for synthesized protonated cyanoximes and their Na and Tl-

(I) salts were determined in open capillary tubes using the Mel-

Temp apparatus (Thomas-Hoover) without correction. An elemen-

tal analyses on C/H/N content was performed at the Atlantic

Microlab (Norcross, GA) and MicroMass Laboratory at the

University of California (Berkeley).

Spectroscopic Methods. All synthesized organic ligands were

characterized at 296 K using ¹H and ¹³C NMR spectroscopy

(solutions in DMSO-d₆and CDCl₃containing TMS as an internal

standard; Varian Gemini 200 and Bruker Avance DRX-500). UV-

visible spectra were recorded at room temperature on an HP 8354

diode array spectrophotometer in the range 200-1100 nm, using 1

mm and 10 mm quartz cuvettes (from Starna, Inc.). A typical

tabulated optical spectroscopy data set is presented in S1 of the

Supporting Information for H(2Cl-PhCO) as an example. Infrared

spectra were obtained in the range 500-4000 cm^-1using the FT

IR Nicolet Magna 550 spectrophotometer, equipped with OMNIC

software. Spectra of protonated cyanoximes HL and their sodium

salts NaL were recorded using KBr pellets. However, the spectra

of thallium(I) complexes TlL were obtained from fine suspensions

in Nujol because of the solid-state exchange reactions between KBr

and TlL during the pellet preparation. Results of IR spectroscopic

studies of synthesized arylcyanoximates are summarized in S4 of

the Supporting Information. A mass-spectrometric technique (posi-

tive FAB) of the protonated monosubstituted arylcyanoximes was

carried out using Autospec Q and ZAB Finigan spectrometers.

Meta-nitrobenzylic alcohol, NBA, was used as a matrix in all

experiments.

Figure 10. Fragment of the crystal structure of Tl(4Br-PhCO)]. Prospec-

tive view along the y axis showing the electrostatic nonbonding Tl1‚‚‚N1

and Tl1‚‚‚Br2 interactions (dashed lines).

Tl(2-nitrophenolate) reported by Harrowfield et al.^62bIt

appears that weak aromatic organic acids such as phenols

and oximes might support the formation of such double-

stranded one-dimensional polymers stabilized by additional

π-π stacking interactions. Surprisingly, Tl(4-nitrophenolate)

is a tetramer and adopts the shape of a distorted cube.^62b

Further investigations are needed to establish correlations

between the nature of the ligand and the structure of the

obtained Tl(I) complex.

X-ray Crystallography. Crystal and molecular structures were

determined for three protonated arylcyanoximes and two monova-

lent thallium complexes. Suitable single crystals of the obtained

monosubstituted arylcyanoximes H(2Cl-PhCO), H(3F-PhCO),

H(4Cl-PhCO), and Tl(4Br-PhCO) were used for structure deter-

mination using a Siemens R3m/V automated diffractometer. Data

collection for protonated ligands was carried out at room temper-

ature, and a single crystal of the thallium complex Tl(4Br-PhCO)

was cooled to 100 K. Structural studies of Tl(2Cl-PhCO) were

conducted at 193 K on a diffractometer equipped with a Bruker

Smart CCD area detector. The crystal data and some experimental

data for the compounds that were studied are listed in Table 2.

More detailed crystallographic information for the analyzed com-

Synthesized Tl(I) cyanoximates all form long needle-type

crystals (Supporting Information, S5 and S6), which repre-

sents a useful property for future electric conductivity studies.

Experimental Section

Materials and Methods. Starting thallium(I) carbonate and

monosubstituted phenylactonitriles R-CH₂-CN were obtained

from Aldrich and were of acceptable quality. Generated in the lab

on the day of the synthesis of cyanoximes, alkylnitrites were used

Inorganic Chemistry, Vol. 44, No. 23, 2005 8339

Robertson et al.

Figure 11. Top and side views of one-dimensional polymeric zigzag sheets in the structure of Tl(4Br-PhCO) (A) and the geometry of two different and

adjacent (Tl1-O1)₂rhombes (B) shown at the 50% thermal ellipsoids probability level.

tuted arylcyanoximes are similar, the synthesis of only one ligand

will be presented in detail.

Preparation of 2-Fluorophenyl(oximino)acetonitrile, H(2F-

PhCO). Metallic sodium in the amount of 0.182 g (7.9 × 10^-3M)

was thinly sliced and then dissolved at room temperature in 20

mL of anhydrous 2-propanol under nitrogen protection. Freshly

prepared neat propylnitrite, n-C₃H₇-ONO (0.916 g, 8.9 × 10^-3

M), was mixed with 1.000 g (7.4 × 10^-3M) of 2-fluorophenyl

acetonitrile in 20 mL of anhydrous 2-propanol at room temperature.

Nitrogen was passed through this solution for ∼10 min. The latter

solution was added dropwise at room temperature within 30 min

to a solution of sodium 2-propoxide. The color of the reaction

mixture immediately turned yellow, and the mixture remained clear

after being stored overnight at 4 °C. The solvent was completely

removed using a rotary evaporator and then an oil pump. The yellow

solid residue was dissolved in 30 mL of water and then acidified

to a pH of ∼5 with the following addition of solid NaCl. This step

resulted in a flaky, slightly pale-yellow precipitate of H(2F-PhCO)

that was filtered, washed with water, and dried in a vacuum

Figure 12. Organization of the one-dimensional coordination polymer in

desiccator over P₄O₁₀. An alternative way of cyanoxime recovery

is extraction with ether (three portions of 25, 50, and 75 mL each).

In this case, ether layers were combined and dried under Na₂SO₄,

and the solvent was completely removed, yielding a pale-white

solid. The yield of H(2F-PhCO) was 74%. mp ) 118 °C. R_f)

0.28 in the 1:4 EtOAc/hexane mobile phase. ¹H NMR (ppm): 14.22

(broad singlet, 1H, OH), 7.68 (m, 1H, Ar H), 7.57 (m, 1H, Ar H),

7.38 (m, 1H, Ar H), 7.32 (m, 1H, Ar H). UV-vis (in EtOH; here

and elsewhere, 1 mm cell, ∼5 × 10^-4M): 228 nm (ꢀ ) 7200),

CN group; 302 nm (ꢀ ) 8900), oximino/aryl fragment. High-

resolution mass spectrometry: calcd for C₈H₅FN₂O, 164.0386;

found, 165.0464 (M + 1).

the structure of Tl(4Br-PhCO)] showing π-stacking interactions between

aligned 4-bromophenyl groups and ruffled Tl₂O₂sheets where spatially close

Tl(I) atoms form an infinite linear array. Metal ions (green) are presented

as balls of the ionic radius size.

pounds is available in the Supporting Information (S11 and

respective CIF files).

Synthesis of Monosubstituted Arylcyanoximes. The prepara-

tion of these compounds was accomplished using route 3 (modified

Meyer reaction⁵²), shown in Scheme 6. The first two, most obvious

routes, 1 and 2, represent nitrosation reactions at acidic conditions

and were successfully used in previous preparations of other

cyanoxime ligands.²²However, these methods did not work for

substituted phenylacetonitriles, which contain a significantly less-

activated methylene group. Nitrosating agents such as alkylnitrites

(n-C₃H₇-ONO and CH₃-ONO) must be prepared fresh before use

to avoid possible and, unfortunately, encountered side reactions.

The commercial productssamylnitrite and butylnitritessfrom Al-

drich were of poor quality. Isolated, spectroscopically and structur-

ally characterized examples of the products of the side reactions

are shown in the Supporting Information, S10. Small quantities (5-

20 g) of methylnitrite or n-propylnitrite were freshly made

(according to published procedures⁵³) each time prior to use in

oxime synthesis reactions. Nitrosation at basic conditions, using

freshly prepared alkylnitrites, leads to desired arylcyanoximes with

70-90% yields. Since all preparations of protonated monosubsti-

The data for other cyanoximes are presented in the following

paragraphs.

H(2Cl-PhCO). Yellow-orange solid, yield 86%. mp ) 112 °C.

1

R_f) 0.27 in 1:4 EtOAc/hexane. H NMR (ppm): 14.15 (singlet,

1H, OH), 7.49 (m, 1H, Ar H), 7.75 (m, 1H, Ar H), 7.66 (m, 2H,

Ar H). UV-vis (in t-BuOH): 220 nm (shoulder), 256 nm (ꢀ )

6500).

H(2Br-PhCO). Light-orange solid, yield 85%. mp ) 83 °C.

1

R_f) 0.25 in 1:4 EtOAc/hexane. H NMR (ppm): 14.52 (singlet,

1H, OH), 7.79 (m, 1H, Ar H), 7.59 (m, 1H, Ar H), 7.54 (m, 1H,

Ar H), 7.49 (m, 1H, Ar H). Mass spectrometry (FAB+): calcd for

C₈H₅BrN₂O, 225.4; found, 226.6 (M + 1).

H(3F-PhCO). White solid, yield 51%. mp ) 115 °C. R_f) 0.14

1

in 1:4 EtOAc/hexane. H NMR (ppm): 14.11 (singlet, 1H, OH),

8340 Inorganic Chemistry, Vol. 44, No. 23, 2005

Double-Stranded Metal-Organic Networks

Scheme 6

Scheme 7

7.79 (doublet, 1H, Ar H), 7.74-7.18 (m, 3H, Ar H). UV-vis (in

methanol): 224 nm (ꢀ ) 8150), CN group; 304 nm (ꢀ ) 7770),

oximino-aryl fragment.

H(3Cl-PhCO). Pale-yellow solid, yield 68%. mp ) 105 °C. R_f

) 0.21 in 1:4 EtOAc/hexane. ¹H NMR (ppm, mixture of two

isomers): 14.05 (broad singlet, 2H, OH), 8.04 (m, 1H, Ar H), 7.85

(m, 1H, Ar H), 7.70-7.56 (m, 6H, Ar H). Mass spectrometry

(FAB+): calcd for C₈H₅ClN₂O, 180.6; found, 181.5 (M + 1).

H(3Br-PhCO). Pale-yellow solid, yield 77%. mp ) 109 °C.

1

R_f) 0.35 in 1:4 EtOAc/hexane. H NMR (ppm): 14.06 (broad

singlet, 1H, OH), 7.79 (s, 1H, Ar H), 7.76-7.36 (m, 3H, Ar H).

Mass-spectrometry (FAB+): calcd for C₈H₅BrN₂O, 225.4; found,

226.6 (M + 1).

H(4F-PhCO). Light-yellow solid, yield 53%. mp ) 89 °C. R_f

) 0.20 in 1:4 EtOAc/hexane. ¹H NMR (ppm): 13.82 (broad singlet,

1H, OH), 8.04 (m, 2H, Ar H), 7.51 (m, 2H, Ar H).

H(4Cl-PhCO). Yellow solid, yield 63%. mp ) 95 °C. R_f)

0.26 in 1:4 EtOAc/hexane. ¹H NMR (ppm, mixture of two

isomers): 14.12 (broad singlet, 2H, OH), 8.05-7.50 (4 doublets,

8H, Ar H).

mixture affords needlelike crystals. Many of these crystals were

not of X-ray analysis quality. While the method of an ion exchange

between NaL (L ) 3-substituted arylcyanoximes) and inorganic

Tl(I) salts (Scheme 7) results in better quality crystals, it takes much

longer. The following preparation of Tl(4Br-PhCO) represents the

typical preparation that was employed during this work.

H(4Br-PhCO). Pale-yellow solid, yield 77%. mp ) 135 °C.

1

R_f) 0.27 in 1:4 EtOAc/hexane. H NMR (ppm, mixture of two

Preparation of Thallium(I) 4-Bromophenyl(oximino)aceto-

nitrile, Tl(4Br-PhCO). 0.364 g (0.78 × 10^-3M) of Tl₂CO₃were

dissolved in 10 mL of water at 95 °C. 0.350 g (1.56 × 10^-3M) of

solid H(4Br-PhCO) were added within 5 min, in small portions

under intensive stirring, to a solution of thallium carbonate. The

reaction mixture turned yellow, and carbon dioxide evolved. The

resulting solution was filtered hot into a long glass tube and left

for slow crystallization in a Dewar flask containing 5 L of water at

98 °C. Fibrous yellow crystals were collected by filtration 3 days

later, and the mother liquor was left for further crystallization,

affording X-ray quality single crystals of Tl(4Br-PhCO). The

combined yield was 0.286 g (86%); the complex decomposes at

255 °C. Analogous preparations, as well as the ion-exchange

reactions depicted in Scheme 5, led to all nine thallium(I)

cyanoximates, which represent the yellow/orange/brown crystalline

compounds. The yields, physical properties, and data of the

elemental analysis for synthesized complexes are shown in the

Supporting Information, S12. The most important IR frequencies

for HL, NaL, and TlL (L ) monosubstituted arylcyanoximes) are

also presented in the Supporting Information, S4. Sodium salts are

soluble in cold water, pyridine, DMF, and DMSO. Synthesized

thallium(I) cyanoximates are soluble in pyridine, DMF, DMSO,

and hot water. Both salts are insoluble in acetone, ether, hydro-

carbons and halocarbons, and benzene and its homologues.

isomers): 14.0 (broad singlet, 2H, OH), 7.9-7.65 (4 doublets, 8H,

Ar H). UV-vis (in ethanol): 220 nm (ꢀ ) 8500), CN group; 273

nm (7920), aryl fragment.

Synthesized monohalogenated arylcyanoximes represent white

or pale-yellow crystalline substances soluble in ether, CH₂Cl₂,

CHCl₃, CH₃CN, acetone, ethyl acetate, and alcohols; the compounds

are insoluble in CCl₄, water, benzene, and hexanes. A complete

set of ¹³C NMR spectra for the rest of the synthesized cyanoximes

can be found in the Supporting Information (S1 and S2).

The deprotonation of colorless arylcyanoximes by bases (metal

oxides, hydroxides, and carbonates) in aqueous or alcohol solutions

at room temperature leads to yellow/orange anionic cyanoximates.

A series of sodium salts, NaL, of all monosubstituted halogenated

arylcyanoximes described in this paper was obtained and spectro-

scopically (IR) characterized. A stoichiometric reaction (1:1)

between ethanol solutions of HL and freshly prepared aqueous

NaOH quantitatively affords yellow powdery NaL, which was

filtered and washed with cold EtOH and dried at 40 °C within 24

h using an oil pump.

Synthesis of Monovalent Thallium Complexes. Scheme 7

shows a general approach to the preparation of Tl(I) cyanoximates.

The method that involves using a hot Tl₂CO₃solution is preferred

since, after the CO₂evolution, only pure TlL is left in the reaction

vessel without any other ionic species. Slow cooling of the reaction

Inorganic Chemistry, Vol. 44, No. 23, 2005 8341

Robertson et al.

Safety Note! Although we haVe not encountered any problems

during many years of laboratory work and handling, special care

should be taken during procedures using thallium compounds

because of their toxicity.^54,55

ferent from conventional mixed-valence MX and KCP 1D

solids (Scheme 1) or lattices containing traditional bridging

halogenides, halcogenides atoms, linear anions such as CN^-

-

and N₃, or nonlinear conjugated anions N(CN)₂and

-

C(CN)₃.

Conclusions

The obtained monovalent thallium arylcyanoximates rep-

resent excellent precursors for mixed-valence Tl⁺/Tl³⁺one-

dimensional coordination polymers. Formed rigid Tl₂O₂

zigzag sheets are able to accommodate metal ions in different

oxidation states where mixed-valence complexes may show

electric conductivity via electron hopping between metal

centers in linear arrays of metal ions or through π-stacking

haloaryl groups.

A high-yield synthesis of monohalogen-substituted aryl-

cyanoximes was developed using the respective monosub-

stituted phenylacetonitriles X-Ph-CH₂-CN (X ) F, Cl,

Br at the 2, 3, or 4 positions) and freshly prepared

methylnitrite under basic conditions at room temperature.

Eight out of nine reported cyanoximes were obtained the

first time.

Synthesized cyanoximes were characterized using spec-

troscopic methods (IR, ¹H, ¹³C NMR, UV-visual, and mass

spectrometry) and X-ray analysis. The crystal structures of

three compounds were determined and revealed rare cases

of the coexistence of planar cis-syn and cis-anti isomers

in the same crystal for H(3F-PhCO), nonplanar trans-anti

for H(2Cl-PhCO), and anti configurations for H(4Cl-

PhCO) molecules in the solid state.

All cyanoxime molecules obtained undergo deprotonation

with the formation of yellow/orange conjugated anions with

charge delocalization. Linear correlations between the posi-

tions of a conjugated aryloxime fragment in the UV spectra

of solutions of cyanoximate anions in solvents ROH and

solvent parameters (pK_a, Z) were established. Pronounced

negative solvatochromism in the visible spectra was observed

for cyanoximate anions in eight polar protic and aprotic

solvents.

Future studies include the preparation and characterization

of similar Tl(III) cyanoximates and the synthesis of mixed-

valence Tl(I/III) complexes.

Acknowledgment. The authors thank Dr. C. Barnes for

his valuable help and encouragement at the beginning of this

project and Dr. K. V. Domasevitch for his kind help with

resolving the disorder of the oxime group in the structure of

fluorinated arylcyanoxime. D.R. is thankful to the SMSU

Graduate College and Department of Chemistry for support

during the work on this research project. N.G. is very grateful

to Jackie Hinton for technical assistance, Dr. Eric Bosch for

sharing knowledge of work with the X-Seed program, Dr.

Richard Biagioni for helpful discussions, Dr. Chris Barnhard

for photos of Tl crystals, and the ACS PRF for financial

support (Grant # B-39079-B3).

All synthesized arylcyanoximes readily form Na⁺and Tl⁺

metal salts, where monovalent thallium quantitatively forms

complexes of 1:1 stoichiometry. All nine synthesized Tl(I)

complexes form colored crystals of a needle gabitus. The

crystal and molecular structures of two thallium(I) complexes

were determined and revealed the formation of a double-

stranded coordination polymer comprised of Tl‚‚‚O‚‚‚Tl

zigzag chains making almost orthogonal ruffled Tl₂O₂sheets.

Tl(I) ions in both complexes are aligned into infinite linear

arrays with metal-metal separations close to that in metallic

thallium. Crystal structures of the complexes are additionally

stabilized by π-stacking interactions between haloaryl groups

that are almost perpendicular to the Tl‚‚‚Tl arrays.

Structurally characterized Tl(I) arylcyanoximates form

one-dimensional metal-organic networks completely dif-

Supporting Information Available: Results of UV-visible

spectroscopic studies of H(2Cl-PhCO), S1; ¹³C NMR spectra of

synthesized arylcyanoximes, S2 and S3; IR spectra of HL, NaL,

and TlL (L ) arylcyanoxime), S4; photographs of polycrystalline

and single-crystal samples of TlL, S5 and S6; coordination

polyhedron in Tl(2Cl-PhCO), S7; coordination polyhedron in Tl-

(4Br-PhCO), S8; fragment of crystal packingsthree layerssof Tl-

(4Br-PhCO), S9; encountered side reacted during nitrosation of

the arylcyanoximes, S10; X-ray crystallographic details, S11 and

S12; elemental content for TlL, S13. Detailed crystallographic

information for the analyzed compounds are available in CIF format.

This material is available free of charge via the Internet at

http://pubs.acs.org.

IC050465W

8342 Inorganic Chemistry, Vol. 44, No. 23, 2005

Article Doi

Double-stranded metal-organic networks for one-dimensional mixed valence coordination polymers

DOI: 10.1021/ic050465w

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Article abstract of DOI:10.1021/ic050465w

Full text of DOI:10.1021/ic050465w

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