ORIGINAL PAPER

Crystal Structure Analysis of Two Chloro(2,20:60,200-terpyridine)gold(III) Complexes

Vivian Gomez • Mark C. Hardwick •

Christine Hahn

Received: 7 November 2011 / Accepted: 6 June 2012 / Published online: 19 June 2012

� Springer Science+Business Media, LLC 2012

Abstract The X-ray crystal structure analysis of [AuCl-

(terpy)](BF4)2 and [AuCl(terpy)](SO3CF3)2 show with the

counter anions BF4- and SO3CF3

- an expanded, more or

less distorted octahedral coordination geometry. These

secondary bonding interactions of the counter anions

with the square planar complex cation [AuCl(terpy)]2? are

discussed and compared with those found in related

gold(III) terpyridine complexes. In [AuCl(terpy)](SO3

CF3)2 a very short non-bonding Au–O distance of

2.7641(4)A of one of the triflate ions was found. The tet-

rafluoroborate complex is monoclinic with space group P21/

c and cell parameters a = 8.7587(12)A, b = 13.2623(19)A,

c = 15.537(2)A, b = 90.362(2)�, V = 1804.7(4)A3, Z = 4.

The triflate complex is triclinic with space group P �1

and cell parameters a = 7.4198(15)A, b = 12.069(2)A,

c = 13.583(3)A, a = 101.414(3)�, b = 101.922(3)�, c =

94.838(4)�, V = 1156.6(4)A3, Z = 2.

Keywords Crystal structure � Gold(III) complexes �Expanded coordination geometry � Short contacts �Non-coordinating anions

Introduction

During the last decades terpyridine gold(III) complexes

have gained increasing interest as potential anti-tumor

agent. The first synthesis and structural characterization of

[AuCl(terpy)]Cl2�3H2O was reported by Hollis et al. [1].

The structure was recently re-determined at 173 K by

Friedrich et al. [2]. All structural parameters were found to

be practically identical compared to those reported by

Hollis et al. with exception of one of the outer-sphere, non-

coordinating chloride, which is slightly differently located.

More accurate data were obtained by Friedrich et al. since

the measurement was performed at lower temperature.

In view of physiological relevant conditions Pitteri and

co-workers undertook equilibrium and kinetic studies of

the chloro(terpyridine)gold(III) complex in aqueous solu-

tion [3]. Substitution of the chloro ligand by water and

subsequent proton dissociation of the aqua ligand gave the

hydroxo complex [Au(OH)(terpy)](ClO4)2 which was

characterized by X-ray single crystal structure analysis.

A series of studies on interaction of the terpyridine

gold(III) complex with DNA and proteins followed by

Messori et al. [4–9] and de Paula [10]. The 3? oxidation

state of gold in the complex cation [AuCl(terpy)]2? seems

to be sufficiently stabilized under physiologically condi-

tions due to the chelate effect of the terpyridine ligand. The

studies showed very promising anti-proliferative and

cytotoxic properties of [AuCl(terpy)]Cl2�3H2O for various

human tumor cells. Spectroscopic investigations suggest

that the binding affinity of the terpyridine gold complex to

the DNA is mainly based on electrostatic interaction rather

than covalent bonding. The nature of the DNA binding

was found to be reversible. Liu et al. [11] and Sampath

et al. [12] synthesized modified terpyridine gold(III)

complexes at 40 position and the X-ray structures of

V. Gomez � M. C. Hardwick

Department of Physical Sciences, University of Texas

of the Permian Basin, 4901 East University Blvd., Odessa,

TX 79762, USA

C. Hahn (&)

Department of Chemistry, Texas A&M University Kingsville,

700 University Blvd., Kingsville, TX 78363, USA

e-mail: christhahn@gmx.net

123

J Chem Crystallogr (2012) 42:824–831

DOI 10.1007/s10870-012-0320-y

[AuCl{40-R(terpy)}](SO3CF3)2 (R = p-CH3OC6H4, CH3S)

were reported. These structurally modified complexes

exhibit interesting bifunctional substrates for DNA binding

studies [13].

It should be noted that besides the DNA binding prop-

erties the expanded coordination chemistry of terpyridine

gold(III) complexes may be also further studied in the

context of other fields of application such as homogeneous

catalysis. For example Hashmi et al. [14] mentioned the

use of [AuCl(terpy)]Cl2�3H2O as catalyst for the phenol

synthesis from furans.

In this paper the X-ray single crystal structure analysis

of the chloro(terpyridine)gold(III) tetrafluoroborate 1 and

trifluoromethanesulfonate (triflate) 2 are discussed and

compared with those of the terpyridine gold(III) complexes

reported by Hollis (I, [1]), Pitteri (II, [3]), and Sampath

(III, [12]).

N

N

NAu

Cl

SO

OO

OSO

OCF3

F3C

2

N

N

NAu

Cl

BF

FF

FBF

FF

F

1

N

N

NAu

Cl

SO

OO

OSO

OCF3

F3C

CH3S

N

N

NAu

Cl

Cl

OH H

Cl- N

N

NAu

OH

OClO

OO

OClO

OO

I II III

Experimental

Synthesis of Complexes 1 and 2

The starting complex [AuCl(terpy)]Cl2�3H2O was prepared

according to the procedure reported by Pitteri et al. [3].

[AuCl(terpy)](BF4)2 (1): To a solution of 300 mg

(0.509 mmol) of [AuCl(terpy)]Cl2�3H2O in 50 mL of

water an excess AgBF4 (302 mg, 1.55 mmol) was added.

The reaction mixture was warmed up to 80 �C in a water

bath and stirred for 30 min. White precipitate was formed

and filtered off. An excess NaBF4 was added to the filtrate.

The volume of the solution was reduced to about 10 mL

under vacuum. After letting the solution sit over night

yellow crystals were formed. Yield: 297 mg (0.465 mmol,

83 %). M.p. 251 �C. 1H NMR (250 MHz, D2O): d 9.20

(2H, d, JH–H = 6 Hz), 8.70 (7H, m), and 8.07 (2H, m).

[AuCl(terpy)](SO3CF3)2 (2): To a solution of 600 mg

(1.02 mmol) of [AuCl(terpy)]Cl3�3H2O in 50 mL water an

excess AgSO3CF3 (804 mg, 3.13 mmol) was added. The

reaction mixture was warmed up to 80 �C in a water bath

and stirred for 30 min. After stirring overnight at room

temperature the solution turned yellow, and a white pre-

cipitate was formed which was filtered off. To the filtrate

an excess NaSO3CF3 was added. The volume of the solu-

tion was reduced to about 10 ml under vacuum. Yellow

crystals were formed after letting the solution sit overnight.

Yield: 698 mg (0.914 mmol, 90 %). M.p. 269 �C. Analysis

Calcd. for C17H11AuClF6N3O6S2: C, 26.73; H, 1.45; N,

5.50; Found C, 26.84; H, 1.53; N, 5.49. 1H NMR

(250 MHz, D2O): d 9.19 (2H, d, JH–H = 5.7 Hz), 8.71 (7H,

m) and 8.06 (2H, m).

X-Ray Structure Determination of Complexes 1 and 2

Details of the X-ray data collection and reduction, and final

structure refinement calculation for complex 1 and 2 are

summarized in Table 1. Suitable crystals of complex 1 and

2 were respectively selected, coated in a cryogenic pro-

tectant (paratone), and were then fixed to a loop which in

turn was fashioned to a copper mounting pin. The mounted

crystal was then placed in a cold nitrogen stream (Oxford)

maintained at 110 K.

BRUKER SMART APEX II and SMART 1000 CCD

X-ray three-circle diffractometers were employed for

crystal screening, unit cell determination and data collec-

tion. The respective goniometer was controlled using the

APEX II or smart1000 software suites (Microsoft operating

system) [15, 16]. The X-ray radiation employed was gen-

erated from a Mo sealed X-ray tube (Ka = 0.71073 A with

a potential of 50 kV and a current of 40 mA) and filtered

with a graphite monochromator in the parallel mode

(175 mm collimator with 0.5 or 0.8 mm pinholes).

Dark currents were obtained for the appropriate expo-

sure time of 10 s and a rotation exposure was taken to

determine crystal quality and the X-ray beam intersection

with the detector. The beam intersection coordinates were

compared to the configured coordinates and changes were

made accordingly. The rotation exposure indicated

acceptable crystal quality and the unit cell determination

was undertaken. Forty data frames were taken at widths of

0.5� with an exposure time of 10 s. Over 200 reflections

were centered and their positions were determined. These

reflections were used in the auto-indexing procedure to

determine the unit cell. A suitable cell was found and

refined by nonlinear least squares and Bravais lattice pro-

cedures and reported in Table 1. The unit cell was verified

J Chem Crystallogr (2012) 42:824–831 825

123

by examination of the hkl overlays on several frames of

data, including zone photographs. No super-cell or erro-

neous reflections were observed.

After careful examination of the unit cell, a standard

data collection procedure was initiated. This procedure

consists of collection of one hemisphere of data collected

using omega scans, involving the collection over 1400 0.5�frames at fixed angles for /, 2h, and v (2h = -28�,

v = 54.73�), while varying x. Each frame was exposed for

20 s and contrasted against a 20 s dark current exposure.

The total data collection was performed for duration of

approximately 12 h at 110 K. No significant intensity

fluctuations of equivalent reflections were observed. All

non-hydrogen atoms of the asymmetric unit were refined

with anisotropic displacement parameters, while all

hydrogen atoms were calculated in ideal positions [17].

Results and Discussion

ORTEP views [18] of the complexes 1 and 2 are shown in

Figs. 1 and 2, respectively. The atomic coordinates and

equivalent isotopic thermal parameters are listed in

Tables 2 and 3. The chloro(terpyridine)gold(III) complexes

1 and 2 show in both cases the same, approximately square

planar coordination geometry as was also found for

Table 1 Crystal data and structure refinement for complexes 1 and 2

1 2

Deposit number CCDC 852873a CCDC 852874a

Empirical formula C15H11AuB2F8N3 C17H11AuClF6N3O6S2

Formula weight 639.30 763.82

Temperature (K) 110(2) 110(2)

Wavelength (A) 0.71073 0.71073

Crystal system Monoclinic Triclinic

Space group P21/c P�1

a(A) 8.7587(12) 7.4198(15)

b(A) 13.2623(19) 12.069(2)

c(A) 15.537(2) 13.583(3)

a(�) 90 101.414(3)

b(�) 90.362(2) 101.922(3)

c(�) 90 94.838(4)

V(A3) 1804.7(4) 1156.6(4)

Z 4 2

qcalcd (g cm-3) 2.353 2.193

l (mm-1) 8.387 6.745

F000 1200 728

Crystal size (mm) 0.18 9 0.08 9 0.07 0.30 9 0.10 9 0.10

h range for data collection (�) 2.33–25.00 2.83–24.99

Index ranges (h, k, l) h, ±10; k, ±15; l, ±18 -8 B h B ? 7; -11 B k B ? 14; l, ±26

Reflections collected 15144 7524

Independent reflections/Rint 2945/0.0447 3707/0.0370

Completeness % to h (�) 92.6/25.00 91.2/24.99

Absorption correction Semi-empirical from equivalents

Max/min transmission 0.5874/0.3105 0.5519/0.2368

Refinement method Full-matrix least-squares on F2

Data/restraints/parameters 2945/0/271 3707/12/325

Goodness of fit on F2 1.004 1.003

R1 (obsd, I [ 2r(I)/all) 0.0199/0.0265 0.0305/0.0330

wR2 (obsd, I [ 2r(I)/all) 0.0408/0.0434 0.0740/0.0760

Max/min Dq e�A-3 0.911/–0.674 1.210/–1.926

a CCDC 852873 and CCDC 852874 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via

www.ccd.cam.ac.uk/data_request/cif, by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre,

12, Union Road, Cambridge CB2 1EZ, UK, fax: ?44 1223 336033

826 J Chem Crystallogr (2012) 42:824–831

123

complexes I–III. The gold atom lies practically in plane

with the coordination plane which is defined by the best

plane of the three nitrogen atoms and the chlorine atom in

complexes 1 and 2 (DAu = 0.010(3)A, 1; 0.039(4)A, 2)

[19]. The terpyridine ligand is slightly bent with C13 lying

0.297(5)A out of the coordination plane in complex 1 and

C8 by 0.243(7)A in complex 2. All other bond lengths and

angles for complexes 1 and 2 are very similar to those

observed in the other terpyridine complexes I–III. Selected

bond lengths and angles of complexes 1 and 2 are listed in

Table 4. The common structural features of all gold(III)

terpyridine complexes are the relatively small angles N1–

Au–N2 and N2–Au–N3 of about 81� and short Au–N2

distances (\2.00 A) [3]. These characteristic parameters

are also found in complexes 1 and 2 respectively [1:

80.88(16)�, 81.53(16)�; 2: 81.69(13)�, 81.36(13)�, and 1:

1.947(3)A, 2: 1.954(4)A]. Constraints in the two five-

membered rings formed by the coordinated terpyridine

ligand and the gold center forces a shortened Au–N2 bond

length combined with a reduced N1–Au–N3 angle

(* 162�), which deviates considerably from linearity.

Compared to the Au–N1 and Au–N3 bond lengths ranging

from 2.014(3) to 2.028(3)A, the Au–N2 bond lengths are

significantly shorter. In general Au–N bond lengths are

found to be typically between 2.00 and 2.08 A [19]. Very

short Au–N bond lengths have been also reported for some

other gold compounds of nitrogen, for example 1.93(2)A in

[(Ph3PAu)4N]BF4 [20] and 1.93(1)A in tris[l-3,5-bis(flu-

oromethyl)pyrazolato-N,N0]trigold(I) [21].

The Au–Cl bond lengths in complexes 1 and 2 are not

significantly different [1: 2.2574(10)A, 2: 2.2711(12)A].

Very similar Au–Cl distances were also found in com-

plexes I and III [I: 2.269(2)A, III: 2.259(3)A].

The most interesting feature of the square planar ter-

pyridine gold(III) complexes I–III is the expanded geom-

etry by loose coordination of the counter anions or a water

molecule. The terpyridine complexes [AuCl(terpy)]X2

(X = BF4, 1; SO3CF3, 2) show with the counter anions a

quite similar expanded, more or less distorted octahedral

coordination geometry (cf. Figs. 1, 2). In each of the

complexes one counter anion has a short contact to the gold

atom (\3.00 A), which is considerably shorter than the

calculated van der Waals bond lengths [22], while the other

anion has a slightly longer distance ([3.00 A) to the gold

atom, which is, however, not longer than the van der Waals

bond length. For complex 1 the contacts of the two tetra-

fluoroborate ions with the gold atom are found to be

Au���F4 2.915(3)A and Au���F5 3.130(2)A. A similar short

Au���F contact [2.969(9)A] was observed for the square

planar gold(III) complex [AuCl(BPMA-H)]BF4 (BPMA-

H = bis[2-pyridylmethyl]amide) [23]. Whereas in [Au(bi-

py)Cl2]BF4 the Au���F contacts with 3.165 and 3.213 A are

somewhat longer than those in complex 1 [3].

Fig. 1 ORTEP view of 1 showing the extended coordination

geometry of the square planar [AuCl(terpy)]2? complex dication

with the two BF4- counter anions. Displacement ellipsoids are drawn

at the 50 % probability level

Fig. 2 ORTEP view of 2 showing the extended coordination

geometry of the square planar [AuCl(terpy)]2? complex dication

with the two SO3CF3- counter anions. Displacement ellipsoids are

drawn at the 50 % probability level. Symmetry code: (i) 1 - x, 1 - y,

1 - z; (ii) -x, -y, 1 - z

J Chem Crystallogr (2012) 42:824–831 827

123

In complex 2 one oxygen atom of each triflate ion has a

contact to the gold center [Au���O3A 2.7641(4)A and

Au���O3B 3.1799(5)A)]. Au���O3A represents the shortest

gold–oxygen contact with the gold(III) center compared to

those in complexes I–III. The triflate ions in the terpyridine

complex III have gold–oxygen distances of 2.938(9)A and

3.08(1)A [12] and the perchlorate ions in complex II have

Au���O distances of 3.023(8)A and 3.069(8)A [3]. In

complex I the water molecule has a Au���O distance of

3.022 A [1], which is similar to those in the perchlorate

complex II. The Au���Cl distance of one of the non-coor-

dinating chloride ions in complex I was found to be

3.049(2)A [1]. While the two Au���O contacts in complex 2

are considerably different (D = 0.416 A), in complexes II

and III these contacts are rather similar (II: D = 0.142 A,

III: D = 0.046 A) and lie more closely around 3.00 A.

Notable, in the bis(2-pyridinyl)amine (BPMA) complex

[AuCl(BPMA)](SO3CF3)2 the Au���O contacts of two tri-

flate ions were found to be both significantly shorter than

3.00 A [2.786(8) and 2.842(7)A] [23] and are only slightly

longer by 0.02 and 0.08 A than Au���O3A in complex 2.

The interaction of the counter anions is not limited to

one donor atom per ion and the gold center. Moreover,

Table 2 Atomic coordinates (A 9 104) and equivalent isotropic

displacement parameters (A2 9 103) for complex 1

x y z U(eq)

Au 3539(1) 1937(1) 1364(1) 16(1)

Cl 1765(1) 750(1) 1650(1) 26(1)

F(1) 7844(3) 2202(2) 2586(2) 43(1)

F(2) 6278(4) 3515(2) 2704(2) 53(1)

F(3) 6944(4) 2648(3) 3902(2) 60(1)

F(4) 5414(3) 1914(2) 2921(2) 45(1)

F(5) 2966(2) 3131(2) -345(2) 28(1)

F(6) 595(3) 3821(2) -355(2) 36(1)

F(7) 889(3) 2163(2) -80(2) 33(1)

F(8) 1317(3) 2761(2) -1424(2) 48(1)

N(1) 2312(4) 3181(2) 1631(2) 16(1)

N(2) 5063(4) 2943(2) 1061(2) 18(1)

N(3) 5267(3) 993(2) 1044(2) 17(1)

C(1) 3098(4) 4063(3) 1464(2) 15(1)

C(2) 893(4) 3211(3) 1932(2) 18(1)

C(3) 182(4) 4120(3) 2075(2) 21(1)

C(4) 918(4) 5016(3) 1893(2) 24(1)

C(5) 2417(4) 4967(3) 1588(2) 22(1)

C(6) 4671(4) 3919(3) 1144(2) 17(1)

C(7) 6425(4) 2606(3) 788(2) 17(1)

C(8) 7497(4) 3319(3) 557(2) 20(1)

C(9) 7152(4) 4332(3) 642(2) 22(1)

C(10) 5724(4) 4648(3) 947(2) 19(1)

C(11) 6560(4) 1505(3) 797(2) 19(1)

C(12) 5266(4) -4(3) 1121(2) 22(1)

C(13) 6550(5) -558(3) 956(3) 27(1)

C(14) 7861(5) -59(3) 680(3) 27(1)

C(15) 7853(4) 984(3) 607(3) 24(1)

B(1) 6632(6) 2570(4) 3048(3) 30(1)

B(2) 1421(5) 2971(3) -568(3) 21(1)

U(eq) is defined as one-third of the trace of the orthogonalized Uij

tensor

Table 3 Atomic coordinates (A 9 104) and equivalent isotropic

displacement parameters (A2 9 103) for complex 2

x y z U(eq)

Au 2025(1) 1549(1) 7275(1) 18(1)

Cl 3459(2) 721(1) 6049(1) 30(1)

N(1) 3867(6) 1395(4) 8541(3) 22(1)

N(2) 856(6) 2328(4) 8333(3) 21(1)

N(3) -170(6) 1982(4) 6336(3) 20(1)

C(1) 3458(7) 1922(4) 9447(4) 20(1)

C(2) 4602(7) 1931(4) 10381(4) 24(1)

C(3) 6247(7) 1449(5) 10415(4) 28(1)

C(4) 6649(7) 908(5) 9495(4) 28(1)

C(5) 5442(7) 896(4) 8573(4) 25(1)

C(6) 1719(7) 2458(4) 9326(4) 20(1)

C(7) 979(7) 3059(4) 10069(4) 21(1)

C(8) -646(7) 3522(4) 9785(4) 25(1)

C(9) -1485(7) 3395(5) 8739(4) 24(1)

C(10) -683(7) 2801(4) 8004(4) 22(1)

C(11) -1272(7) 2594(4) 6876(4) 22(1)

C(12) -2769(8) 2982(5) 6367(4) 28(1)

C(13) -3179(8) 2765(5) 5280(4) 30(1)

C(14) -2065(8) 2149(5) 4760(4) 33(1)

C(15) -564(7) 1755(4) 5306(4) 24(1)

S(1A) 6223(2) 5174(1) 2028(1) 26(1)

F(1A) 7482(6) 3723(4) 3103(5) 86(2)

F(2A) 8685(7) 5455(5) 3758(4) 99(2)

F(3A) 5881(7) 4886(5) 3824(4) 78(2)

O(1A) 7717(7) 5056(4) 1503(4) 62(2)

O(2A) 4559(7) 4405(4) 1588(4) 56(1)

O(3A) 5894(5) 6337(3) 2338(3) 36(1)

C(1A) 7114(10) 4797(7) 3257(6) 54(2)

S(1B) 649(2) 901(1) 2282(1) 23(1)

F(1B) 1484(7) 3116(3) 2721(3) 64(1)

F(2B) 3848(5) 2184(4) 2850(3) 57(1)

F(3B) 2272(5) 2345(4) 4018(3) 57(1)

O(1B) 614(5) 956(4) 1225(3) 33(1)

O(2B) 1587(5) 13(4) 2638(4) 42(1)

O(3B) -1089(5) 1028(3) 2586(3) 33(1)

C(1B) 2150(8) 2193(6) 3015(4) 37(1)

U(eq) is defined as one-third of the trace of the orthogonalized Uij

tensor

828 J Chem Crystallogr (2012) 42:824–831

123

further short contacts are observed between each of the

tetrafluoroborate ions and [AuCl(terpy)]2? in complex 1

below and above the coordination plane, which are listed in

Table 5. The F2 atom of the tetrafluoroborate ion above the

plane shows short contacts to three atoms of the central

pyridine ring (N2, C6, and C10). The F1 atom has short

distances to the adjacent ipso carbon atoms of the central

and one terminal pyridine ring (C7 and C11). This allows

the boron atom B1 to have short contacts with N2 and C7

which both are significantly shorter than the van der Waals

distances. The fluorine atom F5 of the tetrafluoroborate ion

below the coordination plane has—except the contact to

the gold center—further three short contacts to the atoms

N2, C6 and C1. The F5���C6 distance is ca. 0.23 A shorter

than the van der Waals bond length. Similar additional

F���C and F���N contacts (2.90–3.13 A) are also found in

[AuCl(BPMA-H)]BF4, which are formed by the tetrafluo-

roborate ion and the bis(2-pyridylmethyl)amide ligand

[23]. They are of the same magnitude as those in complex

1, cf. Table 5.

In contrast, in complex 2 only one triflate ion does show

an additional short contact between one oxygen atom and

one carbon atom [O1A���C10 3.119(5)A]. A similar feature

is observed for the triflate ions in [AuCl(BPMA)]

(SO3CF3)2, however each one has a short O���C contact of

3.20(1) and 3.16(1)A [23].

The [AuCl(terpy)]2? moieties of complexes 1 and 2 are

furthermore connected through several hydrogen bridging

bonds (see Figs. 3, 4) forming more complex associates

with each other and the counter anions in both structures.

These structural studies show that BF4- and SO3CF3

-

form distorted pseudo-octahedral coordination geometries

with [AuCl(terpy)]2? which are very similar to those of

complexes I–III. This type of expanded coordination

occurs preferably in cationic AuIII complexes containing

a planar ligand sphere [3]. However, in some cases

p-stacking of planar ligands of two neighboring complex

cations can prevent the contact of the counter-anion with

the gold center as found for example in the tetrafluorobo-

rate complexes 5,7,12,14-tetramethyl-1,4,8,11-tetraazocy-

lotetradeca-4,6,9,11,13-pentaenato gold(III) [24] and [Au

(dmp)(NC9H6O)]? (dmp = 2-(dimethylaminomethyl)phenyl,

NC9H6O = 8-hydroxyquinoline) [25]. For square planar

gold(III) complexes with more spatial ligands such as PPh3

the interaction of the counter-anion with the gold center is

sterically hindered as in [AuCl(CH3)(tpy)]SO3CF3 (tpy =

2-p-tolylpyridine) [26].

It is interesting to observe these multiple contacts of the

polyatomic counter anions BF4- and SO3CF3

- with the

terpyridine ligand of the complex cation [AuCl(terpy)]2? in

1 and 2, which were not reported for complexes II and III

[3, 12]. Comparing complexes 1 and 2, short contacts are

more numerous for the smaller counter-anion in complex 1,

where the higher charge/size ratio of the tetrafluoroborate

ion may afford a stronger electrostatic interaction to the

complex cation than the triflate in complex 2. In addition

crystal packing forces as well as hydrogen bridging bonds

could be responsible for the formation those close contacts.

It might be also possible that the distance of the donor atom

of the counter anion to the gold center is a critical factor to

establish additional short contacts to the complex cation. In

complex 2 only the triflate ion with the shorter Au���Ocontact [2.7641(4)A] has also another short O���C contact

(see above), while the second triflate ion with a Au���Ocontact, which is no shorter than the van der Waals bond

Table 4 Selected bond lengths (A) and angles (�) for complexes 1and 2 in comparison with complexes I–III

1 2 I II III

Au–N1 2.014(3) 2.014(4) 2.029(6) 2.009(5) 2.025(8)

Au–N2 1.947(3) 1.954(4) 1.931(7) 1.949(4) 1.945(7)

Au–N3 2.028(3) 2.026(4) 2.081(6) 2.008(4) 2.018(8)

Au–Cl 2.2574(10) 2.2711(12) 2.269(2) – 2.259(3)

N1–Au–

N2

80.88(16) 81.69(13) 81.4(3) 81.2(2) 81.4(3)

N2–Au–

N3

81.53(16) 81.36(13) 81.4(3) 81.5(2) 81.2(3)

N1–Au–

N3

162.94(12) 162.37(17) 162.7(3) 162.6(2) 162.5(3)

N2–Au–

Cl

177.32(9) 177.38(13) 176.9(2) – 178.9(2)

Table 5 Short contacts in A of BF4- and SO3CF3

- to [AuCl(ter-

py)]2? in complexes 1 and 2

1 Length Length-

v.d.Waals

2 Length Length—

v.d.

Waals

Au���F4 2.915(3) -0.215 Au���O3Ai 2.7641(4) -0.416

N2���F2 2.862(4) -0.158 C10���O1Ai 3.119(5) -0.101

N2���B1 3.407(6) -0.143 Au���O3Bii 3.1799(5) -0.000

C6���F2 2.846(4) -0.324

C7���F1 3.097(4) -0.073

C7���B1 3.515(6) -0.185

C10���F2 3.151(4) -0.019

C11���F1 3.132(4) -0.038

Au���F5 3.130(2) -0.000

N1���B2 3.511(6) -0.039

N2���F5 2.856(4) -0.164

C1���F5 3.073(4) -0.097

C6 ���F5 2.938(4) -0.232

Symmetry code: (i) 1 - x, 1 - y, 1 - z; (ii) -x, -y, 1 - z

J Chem Crystallogr (2012) 42:824–831 829

123

length, does not show any further short contacts to the

[AuCl(terpy)]2? complex cation. Notable, in the bis(2-py-

ridinyl)amine (BPMA) complex [AuCl(BPMA)](SO3CF3)2

where the Au���O contacts of the two triflate ions are both

shorter than the van der Waals bond lengths [23], each of

the triflate ions show one further contact between an oxy-

gen and a carbon atom.

These short contacts of the counter anions with the

gold(III) terpyridine complex cation are a very interesting

subject to study further in more detail. Due to their elec-

trostatic nature these anion interactions could be models for

the binding mechanism of gold(III) complexes with the

DNA which is so far not completely understood [8, 11, 13].

It might be suggested that the gold(III) terpyridine complex

cation interacts primarily with the phosphate groups of the

nucleotides in terms of forming a similar expanded octa-

hedral coordination geometry with possibly further short

contacts. Also the reversible nature of the interaction could

be explained by this binding model. As discussed above,

important is the planarity of the ligand sphere combined

with a high positive charge of the gold(III) complex.

Therefore the [AuCl(terpy)]2? complex cation seems to be

an ideal structure to study the intercalation with the DNA.

As it was shown in previous studies, DNA binding prop-

erties of terpyridine gold(III) complexes are very sensitive

to structural modifications [13]. Increasing the positive

charge led to an increased binding affinity, while the

introduction of a more spatial group strongly reduces the

DNA binding affinity. These observations are essentially in

agreement with the conditions for the formation of the

expanded coordination geometry at the square planar

gold(III) complexes (see discussion above).

In conclusion we report two further examples of gold

(III) complexes with close contacts of non-coordinating

anions to the gold center. These secondary bonding phe-

nomena are not only important to gain deeper under-

standing for DNA binding properties but also to study other

substrate activation at the metal center in terms of an

incipient reaction [27, 28]. This type of secondary bonding

at the gold(III) center also plays an important role in other

fields of coordination chemistry such as in the development

of gold containing supramolecular coordination polymers

[29].

Acknowledgments This work has been supported by the donors

of the Petroleum Research Fund, administered by the American

Chemical Society (No. 48223-GB3), the Welch Foundation (No.

AW-0013), and the NSF-LSAMP program of the University of Texas

System. Dr. J. H. Reibenspies (Texas A&M University, College

Station) is acknowledged for the X-Ray single crystal structure

analyses.

References

1. Hollis LS, Lippard SJ (1983) J Am Chem Soc 105:4293

2. Friedrich HB, Maguire GEM, Martincigh BS, McKay MG,

Pietersen LK (2008) Acta Cryst E64:1240

3. Pitteri B, Marangoni G, Visentin F, Bobbo T, Bertolasi V, Gilli P

(1999) J Chem Soc Dalton Trans 677

4. Messori L, Abbate F, Marcon G, Orioli P, Fontani M, Mini E,

Mazzei T, Carottu S, O’Connell T, Zanello P (2000) J Med Chem

43:3541

5. Messori L, Orioli P, Tempi C, Marcon G (2001) Biochem Bio-

phys Res Commun 281:352

6. Messori L, Marcon G, Orioli P (2003) Bioinorg Chem Appl 1:177

7. Marcon G, Messori L, Orioli P, Cinellu MA, Minghetti G (2003)

Eur J Biochem 270:4655

Fig. 3 Short contacts between the complex dications and the

counteranions of complex 1

Fig. 4 Short contacts between the complex dications and the

counteranions of complex 2

830 J Chem Crystallogr (2012) 42:824–831

123

8. Messori L, Marcon G, Innocenti A, Gallori E, Franchi M, Oriolo

P (2005) Bioinorg Chem Appl 3:239

9. Casini A, Kelter G, Gabbiani C, Cinellu MA, Minghetti G,

Fregona D, Fiebig HH, Messori L (2009) J Biol Inorg Chem

14:1139

10. de Paula QA, Mangrum JB, Farell NP (2009) J Inorg Biochem

103:1347

11. Liu HQ, Cheung TC, Peng SM, Che CM (1995) J Chem Soc

Chem Commun 1787

12. Sampath U, Putnam WC, Osiek TA, Touami S, Xie J, Cohen D,

Cagnolini A, Droege P, Klug D, Barnes CL, Modak A, Bashkin

JK, Jurisson SS (1999) J Chem Soc Dalton Trans 2049

13. Shi P, Jiang Q, Zhao Y, Zhang Y, Jun L, Lin L, Ding J, Guo Z

(2006) J Biol Inorg Chem 11:745

14. Hashmi ASK, Rudolph M, Weyrauch JP, Wolfle M, Frey W, Bats

JW (2005) Angew Chem Int Ed 44:2798

15. Bruker (2000) SMART (5.632). Bruker Analytical X-ray Inst.

Inc., Madison

16. Bruker (2003) SAINT (6.45). Bruker Analytical X-ray Inst. Inc.,

Madison

17. Sheldrick GM (2008) Acta Cryst A64:112

18. Farrugia LJ (2008) ORTEP-3 (2.02) for windows. Department of

Chemistry, University of Glascow, Glascow

19. Schmidbaur H (1999) Gold: progress in chemistry, biochemistry

and technology. John Wiley & Sons, Chichester, p 311

20. Slovokhotov YuL, Struchkov YuT (1984) J Organomet Chem

277:143

21. Bovio B, Bonati F, Banditelli G (1984) Inorg Chim Acta 87:25

22. Mercury 2.4 for Windows (2004–2011) Cambridge Crystallo-

graphic Data Centre, Cambridge

23. Cao L, Jennings MC, Puddephatt RJ (2007) Inorg Chem 46:1361

24. Park CH, Lee B, Everett GW (1982) Inorg Chem 21:1681

25. Vicente J, Chicote MT, Bermudez MD, Jones PG, Fitschen C,

Sheldrick GM (1986) J Chem Soc Dalton Trans 2361

26. Venugopal A, Shaw AP, Tornoos KW, Heyn RH, Tilsit M (2011)

Organometallics 30:3250

27. Bent HA (1968) Chem Rev 68:587

28. Alcock NW (1972) Adv Inorg Chem Radiochem 15:1

29. Puddephatt RJ (2008) Chem Soc Rev 37:2012

J Chem Crystallogr (2012) 42:824–831 831

123