Complexes of Ag(i), Hg(i) and Hg(ii) with multidentate pyrazolyl-pyridine ligands: From mononuclear complexes to coordination polymers via helicates, a mesocate, a cage and a catenate

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Complexes of Ag(I), Hg(I) and Hg(II) with multidentate pyrazolyl-pyridine

ligands: from mononuclear complexes to coordination polymers via helicates,

a mesocate, a cage and a catenate

Stephen P. Argent,^aHarry Adams,^aThomas Riis-Johannessen,^bJohn C. Jeffery,^bLindsay P. Harding,^c

William Clegg,^d,eRoss W. Harrington^dand Michael D. Ward*^a

Received 30th May 2006, Accepted 15th August 2006

First published as an Advance Article on the web 7th September 2006

DOI: 10.1039/b607541j

The coordination chemistry of a series of di- and tri-nucleating ligands with Ag(I), Hg(I) and Hg(II) has

been investigated. Most of the ligands contain two or three N,N^ꢀ-bidentate chelating

pyrazolyl-pyridine units pendant from a central aromatic spacer; one contains three binding sites (2 +

3 + 2-dentate) in a linear sequence. A series of thirteen complexes has been structurally characterised

displaying a wide range of structural types. Bis-bidentate bridging ligands react with Ag(I) to give

complexes in which Ag(I) is four-coordinate from two bidentate donors, but the complexes can take the

form of one-dimensional coordination polymers, or dinuclear complexes (mesocate or helicate). A

tris-bidentate triangular ligand forms a complicated two-dimensional coordination network with Ag(I)

in which Ag · · · Ag contacts, as well as metal–ligand coordination bonds, play a signiﬁcant role. Three

dinuclear Hg(I) complexes were isolated which contain an {Hg₂}²⁺metal–metal bonded core bound to a

single bis-bidentate ligand which can span both metal ions. Also characterised were a series of Hg(II)

complexes comprising a simple mononuclear four-coordinate Hg(II) complex, a tetrahedral Hg^IIcage

4

which incorporates a counter-ion in its central cavity, a trinuclear double helicate, and a trinuclear

catenated structure in which two long ligands have spontaneously formed interlocked

metallomacrocyclic rings thanks to cyclometallation of two of the Hg(II) centres.

aromatic spacers.⁵On reaction with ﬁrst-row transition metal

Introduction

dications, having a preference for pseudo-octahedral coordination

It is a well understood principle in metallosupramolecular chem-

geometry, these have afforded a range of polyhedral coordination

istry that the structures of complexes based on the combination

cages varying in complexity from tetrahedra containing four

of multidentate bridging ligands with labile metal ions is a

metal ions and six bridging ligands to tetra-capped-truncated

compromise between the geometric properties of the ligands

tetrahedra containing 16 metal ions and 24 bridging ligands. In all

(number and arrangement of binding sites; ﬂexibility) and the

cases, the preference of the metal ion for six-coordinate geometry

stereoelectronic properties of the metal ion.^1–5In many cases the

has provided an essential piece of geometric information which

careful exploitation of these principles has allowed rational design

plays an important role in the assembly of the cage complexes.

of elaborate polynuclear assemblies such as helicates,²grids³and

The ligands relevant to this paper are shown in Scheme 1. The

cages⁴from relatively simple components. In other cases, the

complexity of the metal complex assemblies—whilst conforming

to the basic principles outlined—is nonetheless remarkable given

the simplicity of the component parts.^1,5

We have described recently a series of dinucleating and trinucle-

ating bridging ligands in which two or three bidentate, chelating,

pyrazolyl-pyridine units are connected via methylene spacers to

‘2 + 3 + 2’-dentate ligand L²³²is constituted slightly differently,

with a linear sequence of three binding sites which are either

bidentate (pyrazolyl-pyridine) or terdentate [2,6-bis(pyrazol-3-

yl)pyridine]; this ligand was used to prepared trinuclear double

helicates with a range of metal ions, including a mixed-metal

[FeAg₂(L²³²)₂]⁴⁺containing two four-coordinate Ag(I) ions at

the terminal sites and a six-coordinate Fe(II) ion at the central

site.^5j

In this paper we describe the coordination chemistry of this

series of ligands with Ag(I), Hg(I) and Hg(II), which have quite

different stereo-electronic properties and may be expected to

generate quite different metal/ligand assemblies. In particular the

‘soft’ nature of Ag(I) and Hg(I) means that they tend to adopt

coordination numbers lower than six, and are also subject to strong

metal–metal bonding interactions^6,7which are absent for ﬁrst-row

transition metal dications.

^aDepartment of Chemistry, University of Shefﬁeld, Shefﬁeld, UK S3 7HF.

E-mail: m.d.ward@shefﬁeld.ac.uk

^bSchool of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK

BS8 1TS

^cDepartment of Chemical and Biological Sciences, University of Hudders-

ﬁeld, Huddersﬁeld, UK HD1 3DH

^dSchool of Natural Sciences (Chemistry), University of Newcastle, Newcas-

tle upon Tyne, UK NE1 7RU

^eCCLRC Daresbury Laboratory, Warrington, UK WA4 4AD

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Scheme 1

into this solution gave colourless crystals whose elemental analysis

indicates a 1 : 1 stochiometry Ag(L^mPh)(BF₄). The crystal structure

(Fig. 1, Table 1) shows the solid state arrangement to be an inﬁnite

one-dimensional helical coordination polymer with the formula

[Ag(L^mPh)(BF₄)(ⁱPr₂O)]_∞. The asymmetric unit of the crystals

contains one formula unit. Each Ag(I) ion is four-coordinate,

Results and discussion

Ligands

The ligands used for the work in this paper are illustrated in

Scheme 1; the majority have been reported before, but L^mTolis

new. Like the others,⁵it was prepared by reaction of 3(2-pyridyl)-

pyrazole with the appropriate bis(bromomethyl)-substituted or-

ganic spacer, in this case 1-methyl-3,5-bis(bromomethyl)benzene,

in the presence of aqueous NaOH under phase-transfer con-

ditions. Satisfactory characterisation data were obtained (see

Experimental).

◦

Table 1 Selected bond lengths (A) and angles ( ) for [Ag(L^mPh)BF₄)-

˚

(ⁱPr₂O)]_∞

Ag(1)–N(41)

Ag(1)–N(11)

Ag(1)–N(21)

Ag(1)–N(51)

2.228(3)

2.252(3)

2.385(3)

2.425(4)

N(41)–Ag(1)–N(11)

N(41)–Ag(1)–N(21)

N(11)–Ag(1)–N(21)

N(41)–Ag(1)–N(51)

N(11)–Ag(1)–N(51)

N(21)–Ag(1)–N(51)

153.60(11)

125.03(11)

73.28(11)

71.48(11)

122.75(12)

111.80(11)

Complexes of Ag(I) with L^mPh, L^mToland L^pPh

. The reaction

of L^mPhwith [Ag(MeCN)₄][BF₄] in a 1 : 1 ratio in acetonitrile

gave a colourless solution. Slow diffusion of diisopropyl ether

Fig. 1 The one-dimensional helical chain structure of [Ag(L^mPh)(BF₄)(ⁱPr₂O)]_∞(anions and solvent molecules not shown). Ligands are shown with

alternating red and blue colours for clarity, but are all crystallographically equivalent. The Ag(I) ions are in black.

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◦

Table 2 Selected bond lengths (A) and angles ( ) for [Ag₂(L^mTol)₂][ClO₄]₂

˚

chelated by pyrazolyl-pyridine units from two separate ligands.

Each ligand bridges between two metal ions and is related to

the next by a two-fold rotation and translation giving the helix a

periodicity of two Ag(I) ions. The Ag(I) ions follow a zig-zag path

with an Ag–Ag–Ag internal angle of 88.9^◦and Ag–Ag separations

Ag(1)–N(41A)

Ag(1)–N(11)

Ag(1)–N(51A)

Ag(1)–N(21)

2.423(2)

2.310(2)

2.248(2)

2.311(2)

N(41A)–Ag(1)–N(11)

N(41A)–Ag(1)–N(51A)

N(11)–Ag(1)–N(51A)

N(41A)–Ag(1)–N(21)

N(11)–Ag(1)–N(21)

N(51A)–Ag(1)–N(21)

110.75(8)

72.10(8)

154.79(8)

130.80(8)

72.45(8)

125.82(8)

˚

of 8.06 A. Equal numbers of each enantiomer of helix are packed

together as parallel chains.

The Ag(I) ion is coordinated in a distorted four-coordinate

environment with two shorter bonds to the pyridyl donors (average

Symmetry operations used to generate equivalent atoms: A, −x, 2 − y, −z

˚

2.24 A) and two longer bonds to the pyrazolyl donors (average

˚

2.41 A) with a twist angle between the Ag(NN) planes of

88.6^◦. Within the chains, interligand p–p stacking interactions

˚

(separation 3.2–3.5 A) are observed between phenyl spacers of

one ligand and the pyrazolyl-pyridine unit of an adjacent ligand.

Stacking interactions like these are a common feature of one-

dimensional coordination polymers with aromatic ligands.⁸The

arrangement of the helical polymer is such that only one of the

pyrazolyl-pyridyl arms is involved in these stacking interactions.

There are no stacking interactions between the ligands of adjacent

−

parallel chains. BF₄counterions and (disordered) diisopropyl

ether molecules are located in channels running parallel to the

polymeric chains.

In CD₃CN solution the ¹H NMR spectrum of [Ag(L^mPh)(BF₄)]_∞

shows that the ligand has characteristic chemical shifts for metal

coordination at the pyrazolyl-pyridine donors, and has two-fold

symmetry. The ES mass spectrum shows strong peaks at m/z

Fig. 2 The dinuclear cation of [Ag₂(L^mTol)₂][ClO₄]₂. Ligands are shown

with different colours for clarity but are crystallographically equivalent.

+

499.1 {Ag(L^mPh)} and 1087.2 {Ag₂(L^mPh)₂(BF₄)} and a series

of much smaller peaks for higher oligomers of the formula

{Ag_n(L^mPh)_n(BF₄)_n−2

}

²⁺(n = 6–10). This suggests that the dinuclear

helicates.¹¹The complex cation lies on an inversion centre such

that the asymmetric unit contains one complete ligand, one

Ag(I) ion and a perchlorate counterion. Each Ag(I) ion is four-

coordinate, chelated by pyrazolyl-pyridine units from two separate

ligands. The donor units of each ligand approach both Ag(I) ions

from the same direction without the twist observed in ligands

which form helicates. The separation between the Ag(I) ions is

2+

entity {Ag₂(L^mPh)₂} exists to a signiﬁcant extent in solution,

1

consistent with the observation by H NMR of symmetrically

coordinated ligand. The only obvious reason why this should

dominate in solution is if it is in fact a discrete dinuclear complex

with two ligand bridging two metal ions (e.g. a double helicate),

rather just a fragment from the coordination polymer breaking up.

The polymer observed in the solid state may therefore be a kinetic

crystallisation product nucleated by the small concentration of

higher oligomers in solution observed in the mass spectrum.⁹We

note that other examples of helical coordination polymers with

Ag(I) have been described recently.^8,10

˚

8.23 A, marginally larger than that observed in the polymer

[Ag(L^mPh)(BF₄)(ⁱPr₂O)]_∞.

The Ag(I) ions are in a distorted tetrahedral environment with

˚

Ag–N bond lengths in the range 2.28–2.42 A and a twist angle

between the Ag(NN) planes of 59.8^◦. A p–p stacking interaction is

Examination of the crystal structure of [Ag(L^mPh)(BF₄)(ⁱPr₂O)]_∞

suggested that a substituent attached to the vacant meta position

of the central phenylene unit would hinder formation of this coor-

dination polymer by generating an unfavourable steric interaction

with the next ligand in the sequence. Accordingly we prepared the

new ligand L^mTol, reaction of which with [Ag(MeCN)₄][X] (X =

BF₄or ClO₄) in a 1 : 1 ratio in acetonitrile gave a colourless

solution. Slow diffusion of diisopropyl ether into this solution

gave colourless crystals in each case whose elemental analysis

indicates a 1 : 1 stoichiometry of Ag(L^mTol)X. The crystal structures

showed an essentially identical structure in each case, but the

data for the structure of the ﬂuoroborate salt were poor so we

describe here only the structure of the perchlorate salt. X-Ray

analysis shows the solid state structure of the complex to be a

dinuclear ‘mesocate’ with formula [Ag₂(L^mTol)₂][ClO₄]₂, in which

both ligands span both metal ions but in an achiral arrangement

such that the complex is not a helicate (Fig. 2, Table 2). Mesocates

frequently occur when ligand geometry and metal stereochemical

preferences disfavour the twist which imparts chirality into related

observed between the two phenyl spacer rings (separation 3.70 A).

˚

The rings are offset across the inversion centre such that each

methyl group [C(39)] is located above the centre of the other ring.

Within the unit cell, individual mesocate cations are stacked in

columns with the phenyl spacers of adjacent cations facing each

other. Each cation is rotated by 120^◦with respect to the one

above it in order to allow intermolecular p–p stacking interactions

˚

between the phenyl spacer rings (separation 3.4–3.7 A). These

stacking interactions, combined with the intramolecular stacking

previously described, give rise to inﬁnite arrays of stacked phenyl

rings along the axis of the columns. Further stacking interactions

are observed between the pyrazolyl-pyridine rings of cations in

˚

adjacent columns (separation 3.3–3.4 A). Counterions are located

in channels between the columns.

In CD₃CN solution the ¹H NMR spectrum of

[Ag₂(L^mTol)₂][BF₄]₂in acetonitrile is consistent with a two-fold

symmetric ligand coordinated to metal ions at the pyrazolyl-

pyridine binding sites, as also observed for [Ag(L^mPh)(BF₄)]_∞. An

upﬁeld shift of 0.85 ppm for the protons of the methyl group

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(1.42 ppm) compared to the free ligand (2.27 ppm) is observed due

to the shielding effect of the adjacent phenyl ring. The ES mass

spectrum is also similar to that of [Ag(L^mPh)(BF₄)]_∞, with strong

+

peaks at m/z 513.1 {Ag(L^mTol)} and 1115.2 {Ag₂(L^mTol)₂(BF₄)}

and a series of much smaller peaks for higher oligomers of the

2+

formula {Ag_n(L^mTol)_n(BF₄)_n−2

}

(n = 6–10). These observations

indicate similar solution behaviour to that of [Ag(L^mPh)(BF₄)]_∞,

with the predominant species being a dimer {Ag₂(L^mTol)₂} with

2+

two-fold symmetry. The upﬁeld shift of the methyl protons arising

from a ring current effect association with p-stacking of the

tolyl rings is also consistent with the retention of the solid state

structure in solution. Again, minor traces of higher oligomers are

still detected in the mass spectrum, though in this case it seems

the methyl groups inhibit the crystallisation of the polymeric

species and only the dimer crystallises.

Fig. 3 The dinuclear cation of [Ag₂(L^pPh)₂][BF₄]₂. Ligands are shown with

different colours for clarity.

The ligand L^pPhfeatures a more divergent para-phenylene spacer

with a greater separation between the donor groups. The reaction

of L^pPhwith [Ag(MeCN)₄](BF₄) in a 1 : 1 ratio in acetonitrile

gave a colourless solution. Slow diffusion of diisopropyl ether into

this solution gave colourless crystals whose elemental analysis

indicates a 1 : 1 stoichiometry of Ag(L^pPh)(BF₄). The crystal

structure shows this complex to be a dinuclear double helicate

[Ag₂(L^pPh)₂][BF₄]₂with two ligands spanning both Ag(I) ions,

˚

ligand A. The closest contacts are 2.84 A [H(83) · · · C(52)] and

˚

2.71 A [H(86) · · · N(11)]. Thus, the solid-state structure of this

double helicate shows a mixture of face-to-face and edge-to-face

interactions of aromatic rings between the two ligands which in

the solid are in quite different environments.

In solution the ES mass spectrum indicates retention of a

˚

which are separated by 8.40 A (Fig. 2, Table 3). Each Ag(I) ion

1+

dimer structure with peaks at 1085.2 {Ag₂(L^pPh)₂(BF₄)} and

is four coordinate, bound to an N,N-chelating unit from each of

the two ligands; the geometry is highly distorted from tetrahedral.

Equal numbers of opposite enantiomers of helicate are present in

the unit cell.

2+

500.1 {Ag₂(L^pPh)₂} . The number and location of the peaks in

the ¹H NMR spectrum in acetonitrile is consistent with a two-fold

symmetric ligand coordinated to Ag(I) at the pyrazolyl-pyridine

groups. The two-fold ligand symmetry indicates that the two

distinct ligand environments observed in the crystal structure are

exchanging with each other on the NMR timescale, most likely

by rotation of the phenyl rings around the axis between the CH₂

groups. The signal for the four protons of the phenyl ring is shifted

up-ﬁeld to 6.02 ppm (from 7.22 ppm in the free ligand), consistent

with retention of the aromatic stacking observed for this ring in_◦the

crystal structure. The spectrum remained unchanged at −40 C,

notably with no splitting of the signal for the CH₂protons into

different environments, indicating that the energetic barrier to this

ﬂuxional process is low.

Although the Ag(I) ions are four-coordinate, two shorter con-

˚

tacts (2.26–2.30 A) from the pyridyl donors describe a nearly linear

geometry (N–Ag–N angles of 164.3 and 167.9^◦). The two longer

˚

contacts (2.41–2.47 A) from the pyrazolyl donors are pinched

closer together by the conformation of the helicate (N–Ag–N

angles of 118.6 and 115.6^◦). The twist angles between the Ag(NN)

planes of 68.0 and 69.1^◦underline the large distortion from ideal

tetrahedral geometry around the metal ions. The two ligands are

in different environments, distinguished by the orientations of the

phenyl rings of the spacer units. In the case of ligand A (white in

Fig. 3) the phenyl ring is orientated approximately parallel to, and

sandwiched between, the two pyrazolyl-pyridine units of ligand

B (black in Fig. 3) generating a three-component p-stack with

Complexes of Ag(I) with L^biph: a pair of one-dimensional coordi-

nation polymers. Ligand L^biphhas a larger biphenyl spacer unit

which positions the donor groups even further apart. It has

previously been used for the synthesis of large M₄L₆tetrahedral

cages with six-coordinate Co(II); the large size of the cages

allowed exchange of internal and external counter-ions which

could be monitored by NMR spectroscopy.^5eReaction of L^biph

with [Ag(MeCN)₄](BF₄) in a 1 : 1 ratio in either nitromethane or

dmf gave a colourless solution from which in each case colourless

crystals could be isolated whose elemental analysis indicates a 1 :

1 stoichiometry of Ag(L^biph)(BF₄). Structural analysis revealed in

each case one-dimensional coordination polymers with different

conformations according to whether or not the uncoordinated

solvent molecules could be encapsulated in a channel along the

core of the chain.

˚

separations between components of 3.4–3.5 A. In contrast, the

phenyl ring of ligand B is rotated such that it is perpendicular to

the pyrazolyl-pyridine units of ligand A, resulting in edge-to-face

stacking in which the H atoms H(83) and H(86) of the central

phenyl ring of ligand B are directed towards the pyridyl rings of

◦

Table 3 Selected bond lengths (A) and angles ( ) for [Ag₂(L^pPh)₂][BF₄]₂

˚

Ag(1)–N(11)

Ag(1)–N(61)

Ag(1)–N(71)

Ag(1)–N(21)

2.264(3)

2.302(3)

2.403(3)

2.472(3)

Ag(2)–N(51)

Ag(2)–N(101)

Ag(2)–N(91)

Ag(2)–N(41)

2.255(3)

2.278(3)

2.406(3)

2.456(3)

N(11)–Ag(1)–N(61) 164.33(11)

N(11)–Ag(1)–N(71) 124.26(10)

N(51)–Ag(2)–N(101) 167.89(11)

Crystals of [Ag(L^biph)(BF₄)(MeNO₂)]_∞diffracted very weakly,

resulting in large atomic displacement parameters and standard

uncertainties for the resulting structural determination. Despite

this, the gross structure is clear and shows that the complex is

an inﬁnite one-dimensional helical coordination polymer with

N(51)–Ag(2)–N(91)

N(101)–Ag(2)–N(91)

N(51)–Ag(2)–N(41)

119.51(10)

72.48(10)

72.38(10)

N(61)–Ag(1)–N(71)

N(11)–Ag(1)–N(21)

71.40(10)

71.22(10)

N(61)–Ag(1)–N(21) 102.86(9)

N(71)–Ag(1)–N(21) 118.63(11)

N(101)–Ag(2)–N(41) 101.56(10)

N(91)–Ag(2)–N(41) 115.62(10)

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Table 4 Selected bond lengths (A) and angles (^◦) for [Ag(L^biph)-

˚

(BF₄)(MeNO₂)]_∞

Ag(1)–N(11)

Ag(1)–N(21)

2.380(14) Ag(2)–N(51)

2.327(12) Ag(2)–N(61)

2.271(13)

2.417(19)

N(21)–Ag(1)–N(21A) 126.9(6)

N(21)–Ag(1)–N(11A) 130.5(4)

N(51)–Ag(2)–N(51B)

N(51)–Ag(2)–N(61B)

N(51)–Ag(2)–N(61)

N(61B)–Ag(2)–N(61)

139.3(8)

133.7(6)

71.2(7)

N(21)–Ag(1)–N(11)

71.2(5)

N(11A)–Ag(1)–N(11) 137.1(6)

115.9(12)

Symmetry transformations used to generate equivalent atoms: A: −x +

9/4, y, −z + 5/4 B: −x + 7/4, −y + 3/4, z

the asymmetric unit containing one formula unit comprising one

complete ligand and two half-occupancy metal ions on special

positions. Each Ag(I) ion is four-coordinate, bound by N,N-

chelating units from the pyrazolyl-pyridyl units of two separate

ligands; each ligand bridges two Ag(I) ions (Fig. 4 and 5, Table 4).

The polymer is generated by a four-fold rotation and translation

+

of the crystallographically unique {Ag(L^biph)} units, giving the

helix a periodicity of four Ag(I) ions with an alternating sequence

˚

of Ag(1) and Ag(2) centres and an Ag · · · Ag separation of 8.52 A

between every adjacent pair of Ag(I) ions. The Ag(I) ions four units

apart (directly above each other along the helical axis) are

˚

separated by 16.61 A; this deﬁnes the pitch of the helix. Looking

down the helical axis the four Ag(I) ions deﬁne the corners of a

square with the ligands bridging between them. A narrow channel,

˚

ca. 3 A across, is enclosed within this square and contains the

MeNO₂solvent molecules (Fig. 5b); in this end-on view the ‘cross-

˚

section’ of the chain is approximately 17 × 17 A. The two Ag(I)

Fig. 5 Two views of the helical chain in the structure of [Ag(L^biph)-

(BF₄)(MeNO₂)]_∞. (a) A side-on view of a chain; all ligands are crystal-

lographically equivalent but are coloured differently for clarity. (b) A view

along a helical chain (looking along the crystallographic b axis) showing

how MeNO₂solvent molecules lie in the channel within the helical chain.

ions are in typical pseudo-tetrahedral coordination environments

˚

with Ag–N bond lengths of 2.27–2.42 A and dihedral angles

between the two Ag(NN) planes of 89^◦at Ag(1) and 74^◦at Ag(2).

Intramolecular aromatic p-stacking interactions occur between

every pyridine ring and phenyl spacer ring of its neighbouring

˚

ligand (separations ≈ 3.5 A). The crystal packing shows equal

The crystals isolated from dmf–diisopropyl ether proved to be

[Ag(L^biph)(BF₄)(ⁱPr₂O)_0.5(dmf)_0.25

]

(Fig. 6 and 7, Table 5). The

∞

numbers of opposite-handed helices aligned parallel to each other.

Inter-chain aromatic stacking interactions occur between the

pyridine rings at the corners deﬁned by Ag(1) where opposite-

handed chains interpenetrate. The BF₄counterions are located

in the cavities at the corners of the spirals between the Ag(I) ions

gross structure of this is similar to that of the nitromethane

solvate, being a one-dimensional chain with a periodicity of

four Ag(I) ions (Fig. 7a), two of which are crystallographically

independent. The different metal cations do not alternate, but form

the sequence {Ag(1)–Ag(1)–Ag(2)–Ag(2)–}_∞such that there are

−

that lie four units (i.e. one helical period) apart.

˚

different Ag · · · Ag separations; these are 9.61 A [Ag(1) · · · Ag(1)];

Fig. 4 Asymmetric unit of [Ag(L^biph)(BF₄)(MeNO₂)]_∞showing the

labelling scheme (H atoms, anions and solvent molecules omitted for

clarity). The pyrazolyl-pyridine units with hollow bonds are from adjacent

asymmetric units and are included to illustrate the coordination sphere

around Ag(1) and Ag(2).

Fig. 6 Asymmetric unit of [Ag(L^biph)(BF₄)(ⁱPr₂O)_0.5(dmf)_0.25

the labelling scheme (H atoms, anions and solvent molecules omitted for

clarity).

]

showing

∞

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of [Ag(L^biph)(BF₄)(ⁱPr₂O)_0.5(dmf)_0.25

]

covers an area of ca. 14 ×

Table 5 Selected bond lengths (A) and angles (^◦) for [Ag(L^biph)-

˚

∞

(BF₄)(ⁱPr₂O)_0.5(dmf)_0.25

]

˚

∞

10 A, compared to ca. 17 × 17 A for the nitromethane solvate in

which the chain has a more open arrangement to allow solvent

molecules to occupy a central channel. In addition, Fig. 8 shows

the arrangement of Ag(I) ions along the axis of the chain in each

structure. Whereas in [Ag(L^biph)(BF₄)(MeNO₂)]_∞the sequence of

Ag(I) ions forms an obvious helix with every Ag · · · Ag vector

involving a rotational movement in the same sense about the axis of

Ag(1)–N(61B)

Ag(1)–N(61A)

Ag(1)–N(51B)

Ag(1)–N(51A)

2.306(8) Ag(2)–N(21B)

2.309(8) Ag(2)–N(21A)

2.332(8) Ag(2)–N(11A)

2.335(7) Ag(2)–N(11B)

2.271(7)

2.288(7)

2.344(7)

2.369(8)

N(61B)–Ag(1)–N(61A) 127.4(3) N(21B)–Ag(2)–N(21A) 131.7(2)

N(61B)–Ag(1)–N(51B) 72.5(3) N(21B)–Ag(2)–N(11A) 140.8(2)

N(61A)–Ag(1)–N(51B) 129.9(3) N(21A)–Ag(2)–N(11A)

N(61B)–Ag(1)–N(51A) 146.9(3) N(21B)–Ag(2)–N(11B)

71.9(3) N(21A)–Ag(2)–N(11B) 133.1(2)

N(51B)–Ag(1)–N(51A) 118.4(3) N(11A)–Ag(2)–N(11B) 117.6(3)

the chain, in [Ag(L^biph)(BF₄)(ⁱPr₂O)_0.5(dmf)_0.25

]_∞this is not the case

72.2(2)

71.8(3)

with alternate Ag · · · Ag vectors changing direction. Accordingly

N(61A)–Ag(1)–N(51A)

this latter chain is still chiral but is not helical.

Fig. 8 The arrangement of Ag(I) ions in [Ag(L^biph)(BF₄)(MeNO₂)]_∞

(top) and [Ag(L^biph)(BF₄)(ⁱPr₂O)_0.5(dmf)_0.25

]

(bottom), emphasising the

∞

more compact arrangement and the non-helical arrangement in the latter

compared to the former.

The electrospray mass spectrum in each case indicates that the

predominant species in solution is a dimer with peaks at 1239.2

+

2+

{Ag₂(L^biph)₂(BF₄)} and 500.1 {Ag₂(L^biph)₂} . A weaker peak at

1903.4 {Ag₆(L^biph)₆(BF₄)₄} suggests a small concentration of a

2+

higher oligomer, possibly a linear or cyclic polymer fragment.

The H NMR spectrum of {Ag(L^biph)(BF₄)(MeNO₂)}_∞in ace-

1

Fig. 7 Two views of the chain in the structure of [Ag(L^biph)(BF₄)-

(ⁱPr₂O)_0.5(dmf)_0.25]_∞. (a) A side-on view of the chain with crystallographi-

cally equivalent ligands coloured the same (red, dark blue, light blue). The

ligands coloured red have no internal symmetry. The dark blue ligands (at

the top of the picture) and the light blue ligands (bottom) each have twofold

internal symmetry; thus the asymmetric unit contains two Ag(I) ions, one

complete red ligand, and half of each of the light blue and dark blue ligands.

(b) A view along a chain showing the relatively compact arrangement of

the chain with no internal channel [cf. Fig 5(b)]; the dark red and light

red ligands are crystallographically equivalent but are shaded differently

for clarity. The light blue and dark blue ligands are crystallographically

inequivalent, as before.

tonitrile shows peaks consistent with a two-fold symmetric ligand

coordinated to Ag(I) at the pyrazolyl-pyridine groups. We suggest

therefore that the solution species are likely to either be a ﬂuxional

dinuclear double helicate or a dinuclear mesocate. The ¹H NMR

spectrum showed no changes on reducing the temperature to

−40 ^◦C.

Complex of Ag(I) with L^mes

.

The triangular ligand L^meshas been

of particular interest in assembly of polyhedral cages with ﬁrst-row

transition metal dications because it caps a face of a metal cage,

rather than spanning an edge; this recently allowed, for example,

preparation of a cuboctahedral cage in which L^mescapped four

of the eight triangular faces.^5gWe expected that reaction with

Ag(I) might, given the preference of Ag(I) for four-coordinate

geometries, result in a trinuclear complex [Ag₃(L^mes)₂]³⁺in which

two ligands would cap opposite faces of an Ag₃triangle; such M₃L₂

capsules based on other combinations of metal ions and triply-

bridging ligands are well known.¹²

The material isolated from reaction of L^meswith AgBF₄gave

an ES mass spectrum showing peaks corresponding to Ag : L^mes

assemblies with 1 : 1, 2 : 2, 3 : 2, 2 : 3, 3 : 3 and 4 : 3 stoichiometries,

suggesting a structure more complex than an [Ag₃(L^mes)₂]³⁺cage.

Recrystallisation afforded single crystals of coordination network

{[Ag₄(L^mes)₃](BF₄)₄}_∞with a slightly different ratio of components

˚

8.53 A [Ag(1) · · · Ag(2)]; and 7.67 A [Ag(2) · · · Ag(2)]. Although

superﬁcially similar to the structure of [Ag(L^biph)(BF₄)(MeNO₂)]_∞,

the structure of [Ag(L^biph)(BF₄)(ⁱPr₂O)_0.5(dmf)_0.25

] has an impor-

∞

tant difference which is most apparent in the end-on view (Fig. 7b);

there is no channel running along the centre of the chain because

the conformation of the bridging ligands is such that the central

space is occupied by the biphenyl spacers of the bridging ligands.

The larger size of dmf molecules compared to nitromethane

means that dmf molecules would be too big to occupy a channel

like the one in [Ag(L^biph)(BF₄)(MeNO₂)]_∞, with the result that

a more compact chain forms with the solvent molecules now

in the spaces between the chains. The rectangular cross-section

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Fig. 9 Asymmetric unit of {[Ag₄(L^mes)₃](BF₄)₄}_∞showing the labelling scheme (H atoms and anions omitted for clarity). One of the three independent

ligands is shown with hollow bonds for clarity.

(Ag : L^mes= 1.33 : 1, rather than 1.5 : 1 which would occur in the

cage) and in which Ag · · · Ag interactions play an important role. It

is likely that the high lability of Ag(I) permits a range of complexes

with slightly different stoichiometries to be accessible, as others

have noticed,¹³and this network is the one that preferentially

crystallises.

Crystals of {[Ag₄(L^mes)₃](BF₄)₄}_∞were small and scattered very

weakly, and required a synchrotron X-ray source to give a data set

leading to a structure with R₁= 14.1%. The asymmetric unit

contains four independent Ag(I) ions and three independent

bridging ligands (Fig. 9 and 10, Table 6). Four Ag(I) ions require

eight bidentate pyrazolyl-pyridine units, and the three ligands

provide nine, so one pyrazolyl-pyridine unit is not involved in

metal coordination. The Ag–L^mesassembly consists of a one-

◦

Table 6 Selected bond lengths (A) and angles ( ) for {[Ag₄(L^mes)₃]-

˚

(BF₄)₄}_∞

Ag(1)–N(51A)

Ag(1)–N(11C)

Ag(2)–N(11B)

Ag(2)–N(51B^a)

Ag(3)–N(11A)

Ag(3)–N(31A^b)

Ag(4)–N(31B)

Ag(4)–N(31C)

2.306(8) Ag(1)–N(61A)

2.348(8) Ag(1)–N(21C)

2.301(9) Ag(2)–N(21B)

2.350(9) Ag(2)–N(61B^a)

2.337(8) Ag(3)–N(21A)

2.364(8) Ag(3)–N(41A^b)

2.311(9) Ag(4)–N(41B)

2.345(9) Ag(4)–N(41C)

2.280(8)

2.238(7)

2.378(9)

2.286(9)

2.317(8)

2.287(8)

2.269(10)

2.221(7)

N(51A)–Ag(1)–N(61A)

72.7(3) N(51A)–Ag(1)–N(11C)

120.2(4)

128.8(4)

72.8(3)

118.0(3)

112.4(3)

N(51A)–Ag(1)–N(21C) 137.4(4) N(61A)–Ag(1)–N(11C)

N(61A)–Ag(1)–N(21C) 134.0(4) N(11C)–Ag(1)–N(21C)

Ag(3^c)–Ag(2)–N(11B)

Ag(3^c)–Ag(2)–N(51B^a)

N(11B)–Ag(2)–N(21B)

81.0(3) Ag(3^c)–Ag(2)–N(21B)

74.1(3) Ag(3^c)–Ag(2)–N(61B^a)

71.2(4) N(11B)–Ag(2)–N(51B^a) 153.8(4)

N(11B)–Ag(2)–N(61B^a) 125.6(4) N(21B)–Ag(2)–N(51B^a) 113.5(4)

N(21B)–Ag(2)–N(61B^a) 129.0(4) N(51B^a)–Ag(2)–N(61B^a)

73.1(4)

115.3(3)

113.4(3)

Ag(2^d)–Ag(3)–N(11A)

Ag(2^d)–Ag(3)–N(31A^a)

N(11A)–Ag(3)–N(21A)

76.6(2) Ag(2^d)–Ag(3)–N(21A)

77.0(2) Ag(2^d)–Ag(3)–N(41A^b)

Fig. 10 Two views of the structure of {[Ag₄(L^mes)₃](BF₄)₄}_∞. (a) A view

showing the chain structure, with crystallographically equivalent ligands

coloured the same as each other; underneath is a sketch illustrating the

connectivity. (b) A view showing the 2-D sheet formed by Ag · · · Ag

interactions between the chains; in this picture each chain has all of its

ligands coloured the same (Ag atoms are in black).

71.7(3) N(11A)–Ag(3)–N(31A^b) 152.5(3)

N(11A)–Ag(3)–N(41A^a) 127.2(3) N(21A)–Ag(3)–N(31A^b) 113.9(3)

N(21A)–Ag(3)–N(41A^a) 130.8(4) N(31A^b)–Ag(3)–N(41A^b) 71.1(3)

N(31B)–Ag(4)–N(41B)

N(31B)–Ag(4)–N(41C) 137.0(5) N(41B)–Ag(4)–N(31C)

N(41B)–Ag(4)–N(41C) 135.8(4) N(31C)–Ag(4)–N(41C)

73.3(4) N(31B)–Ag(4)–N(31C)

114.1(4)

131.9(4)

72.7(3)

Symmetry operations used to generate equivalent atoms^a−x + 3, −y, −z.

dimensional chain whose basic connectivity is illustrated in

Fig. 10(a), with symmetry-equivalent ligands in the same colour.

b

−x + 1, −y + 1, −z + 1. ^cx + 1, y − 1, z. ^dx − 1, y + 1, z.

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Thus the ligand repeat sequence is ABC–CBA–ABC–CBA etc.

with the metal ions occurring along the chain either singly

[Ag(1), Ag(4)] or in adjacent symmetry-equivalent pairs [Ag(2),

Ag(3)]. The ligands depicted in red and green both use all three

bidentate arms for coordination; the ligand depicted in blue

has one of its three arms not coordinated to a metal ion. All

four Ag(I) ions are accordingly coordinated by two bidentate

N-donor units. These chains are further associated into two-

dimensional sheets via Ag · · · Ag interactions involving Ag(2) and

pyridyl donors subtend an angle of 140^◦at the Hg(II) centre. An N₄

pseudo-tetrahedral coordination environment is quite common in

Hg(II) complexes.¹⁴Oxygen atoms of one of the perchlorate anions

are involved in weak pseudo-axial interactions to the metal ion

˚

[Hg(1) · · · O(11), 2.80 A; Hg(1) · · · O(13), 2.90 A; Hg(1) · · · O(12)

˚

and Hg(1) · · · O(14) are both > 3 A] such that this perchlorate

anion acts as a bridge linking chains of monomeric Hg(II) units

(Fig. 11b).

On slower recrystallisation (weeks), however, we noticed that

crystals of a different habit also formed; elemental analysis

and mass spectrometry indicated the unexpected formulation

Hg₂(L)(ClO₄)₂, consistent with formation of an Hg(I) species.

The structure of [Hg₂(L^oPh)(MeNO₂)₂][ClO₄]₂(Fig. 12, Table 8)

˚

Ag(3) atoms in adjacent chains (separation 3.333 A). The two

pyrazolyl-pyridine units attached to each of these metal ions are

also p-stacked with those from the other metal ion (see Fig. 10b); it

will be apparent from this ﬁgure that columns of aromatic stacking

between ligands run through the crystal structure.

shows that a single ligand L^oPhcan coordinate to an Hg₂dimer

2+

with each pyrazolyl-pyridine group chelating one of the metal

ions in a bidentate fashion, with the N₂Hg–HgN₂core nearly

planar: the two HgN₂planes have an angle of 12^◦between

Complexes of Hg(I) with L^oPh, L^mPh, L^pPh

.

Reaction of L^oPhwith

Hg(ClO₄)₂in a 1 : 1 ratio in MeNO₂afforded a clear solution from

which a microcrystalline product deposited following diffusion

of diethyl ether vapour into the solution. Given that other six-

˚

them, and Hg(1) and Hg(2) are respectively 0.15 and 0.25 A

out of the mean plane of N(11), N(21), N(41) and N(51). The

bridging phenylene unit is nearly perpendicular to the N₂Hg–

HgN₂core, making an angle of 81^◦with the N(11)–N(21)–N(41)–

N(51) mean plane. The two Hg(I) centres are three-coordinate,

with one bidentate N-donor chelating ligand [Hg–N distances

coordinate metal dications (Co²⁺and Zn²⁺) form tetrahedral

5a,5b

[M₄(L^oPh)₆]⁸⁺cages with L^oPh

,

formation of an analogous

cage seemed a likely possibility. However, the initially-formed

crystalline material proved to be the simple mononuclear complex

[Hg(L^oPh)](ClO₄)₂in which L^oPhacts as a tetradentate chelate to

a single four-coordinate Hg(II) centre (Fig. 11, Table 7). The two

HgN₂planes make an angle of 46^◦to one another, and—as we have

noted with other structures (see below)—the Hg–N(pyridyl) bonds

are much shorter than the Hg–N(pyrazolyl) bonds, and the two

˚

2.25–2.42 A, with the Hg–N(pyridyl) bonds being shorter than

˚

the Hg–N(pyrazolyl)bonds] and an Hg · · · Hg bond (2.518 A),

although there are weak axial interactions with perchlorate oxygen

˚

atoms [Hg(1) · · · O(14), 2.89 A; Hg(2) · · · O(13), 2.96 A]. It is clear

that the structure of L^oPhis ideally suited to holding a pair of

2+

Hg(I) ions together in an {Hg₂} unit, and this has facilitated

slow reduction of Hg(II) to Hg(I) during the crystallisation.

Fig. 12 Structure of the dinuclear complex cation of [Hg₂(L^oPh)-

(MeNO₂)₂][ClO₄]₂(H atoms omitted for clarity).

Reaction of L^mPhor L^pPhwith Hg(ClO₄)₂afforded, in the

ﬁrst instance, products assumed to be Hg(II) complexes. Mass

spectroscopic analysis showed peaks corresponding to a wide

range of Hg : L combinations and it seems likely that the initially-

formed materials are either poorly-soluble coordination networks

Fig. 11 Structure of the mononuclear complex [Hg(L^oPh)][ClO₄]₂(H

atoms and one anion omitted for clarity).

Table 8 Selected bond lengths (A) and angles (^◦) for

˚

◦

Table 7 Selected bond lengths (A) and angles ( ) for [Hg(L^oPh)](ClO₄)₂

[Hg₂(L^oPh)(MeNO₂)₂][ClO₄]₂

˚

Hg(1)–N(51)

Hg(1)–N(11)

2.157(4)

2.196(4)

Hg(1)–N(21)

Hg(1)–N(41)

2.342(4)

2.458(4)

Hg(1)–N(11)

Hg(1)–N(21)

Hg(1)–Hg(2)

Hg(2)–N(51)

Hg(2)–N(41)

2.28(2)

2.42(2)

2.518(2)

2.25(2)

2.39(2)

N(11)–Hg(1)–N(21)

N(11)–Hg(1)–Hg(2)

N(21)–Hg(1)–Hg(2)

N(51)–Hg(2)–N(41)

N(51)–Hg(2)–Hg(1)

N(41)–Hg(2)–Hg(1)

70.6(8)

155.7(5)

133.5(5)

71.1(8)

159.5(6)

126.7(5)

N(51)–Hg(1)–N(11) 139.96(15) N(51)–Hg(1)–N(41)

N(51)–Hg(1)–N(21) 145.48(15) N(11)–Hg(1)–N(41) 136.97(14)

N(11)–Hg(1)–N(21)

72.95(14)

72.75(16) N(21)–Hg(1)–N(41)

87.40(14)

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◦

Table 9 Selected bond lengths (A) and angles ( ) for [Hg₂(L^mPh)-

Table 10 Selected bond lengths (A) and angles ( ) for [Hg₂(L^pPh)][ClO₄]₂

˚

(DMF)₂][ClO₄]₂

Hg(1)–Hg(2)

2.5227(7) N(21A)–Hg(1)–N(11A)

70.9(3)

158.43(19)

130.7(2)

70.8(3)

143.5(2)

137.3(2)

71.1(3)

148.9(2)

138.6(2)

70.9(3)

150.7(2)

137.79(19)

Hg(1)–Hg(2)

Hg(1)–N(21)

Hg(1)–N(11)

Hg(2)–N(51)

Hg(2)–N(41)

Hg(2)–O(61)

2.5237(6)

2.340(5)

2.354(6)

2.310(6)

2.373(6)

2.579(6)

N(21)–Hg(1)–N(11)

N(21)–Hg(1)–Hg(2)

N(11)–Hg(1)–Hg(2)

N(51)–Hg(2)–N(41)

N(51)–Hg(2)–Hg(1)

N(41)–Hg(2)–Hg(1)

N(51)–Hg(2)–O(61)

N(41)–Hg(2)–O(61)

Hg(1)–Hg(2)–O(61)

70.09(19)

148.19(15)

138.43(14)

70.5(2)

149.56(15)

137.28(14)

79.56(19)

90.7(2)

Hg(1)–N(21A) 2.259(8)

Hg(1)–N(11A) 2.398(8)

Hg(2)–N(51A) 2.322(8)

Hg(2)–N(41A) 2.390(8)

N(21A)–Hg(1)–Hg(2)

N(11A)–Hg(1)–Hg(2)

N(51A)–Hg(2)–N(41A)

N(51A)–Hg(2)–Hg(1)

N(41A)–Hg(2)–Hg(1)

Hg(3)–Hg(4)

Hg(3)–N(11B)

Hg(3)–N(21B)

Hg(4)–N(41B)

Hg(4)–N(51B)

2.5149(8) N(11B)–Hg(3)–N(21B)

2.279(8)

2.421(8)

2.295(8)

2.340(8)

N(11B)–Hg(3)–Hg(4)

N(21B)–Hg(3)–Hg(4)

N(41B)–Hg(4)–N(51B)

N(41B)–Hg(4)–Hg(3)

N(51B)–Hg(4)–Hg(3)

107.16(13)

or mixtures of products. NMR spectra of these materials showed

them clearly to be complicated mixtures. If the Hg(II) ions are

four-coordinate, one-dimensional coordination chains are likely

products (cf. some of the Ag(I) complexes described earlier); if

they are six-coordinate, cage complexes are the likely result.^5g,5h

However, slow recrystallisation (weeks) again afforded in each

case, in modest yield, a crop of X-ray quality single crystals for

which elemental analysis indicated the formulation Hg₂(L)(ClO₄)₂;

this was conﬁrmed crystallographically. As before we assume that

very slow reduction of Hg(II) to Hg(I) allows good quality crystals

to be formed.

[Hg₂(L^mPh)(dmf)₂][ClO₄]₂displays essentially the same core

structure as [Hg₂(L^oPh)]²⁺, with the two Hg(I) ions in distorted

trigonal planar coordination environments having Hg–N bond

˚

lengths in the slightly narrower range 2.31–2.37 A, and an Hg–

˚

Hg separation of 2.524 A (Fig. 13, Table 9). The N₂Hg–HgN₂

Fig. 14 Structure of the two independent dinuclear complex units of

[Hg₂(L^pPh)][ClO₄]₂(H atoms omitted for clarity).

core is considerably more distorted from planarity, with a twist

of 18^◦between the two HgN₂planes. Whereas Hg(1) is three

coordinate, Hg(2) has an additional axial interaction with a dmf

solvent molecule [Hg(2) · · · O(61), 2.579 A].

molecule is even more distorted with a twist between the two HgN₂

planes of 45^◦; again there are weak axial interactions with per-

˚

chlorate ions [Hg(3) · · · O(32), 2.830 A; Hg(4) · · · O(42), 2.818 A].

The two independent complex cations are associated by a p-

stacking interaction involving one pyrazolyl-pyridine unit of each

˚

cation. The Hg · · · Hg separations are 2.523 A [Hg(1) · · · Hg(2)]

˚

and 2.515 A [Hg(3) · · · Hg(4)].

This set of Hg(I) complexes with L^oPh, L^mPhor L^pPhforms an

2+

interesting homologous series. Whilst other examples of Hg₂

dimers with N₂Hg–HgN₂donor sets are known,¹⁵they are very

much rarer than Hg(II) complexes.^7,16It is suggested that the

driving force for these cation–cation interactions is the large

increase in solvation energy on moving from a mono- to di-cation

arising from a quadratic dependence on the charge of the species.¹⁷

It is noticeable how L^oPhappears to have an optimal separation

2+

between the two bidentate groups to accommodate an Hg₂unit

Fig. 13 Structure of the dinuclear complex cation of [Hg₂(L^mPh)(dmf)₂]-

with the ligand in a near-planar conformation; as the ligands get

longer, due to the meta and then para substitution pattern of the

bridging ligand, greater degrees of distortion are required to bring

the two bidentate termini close enough together to accommodate

[ClO₄]₂(H atoms omitted for clarity).

The crystal structure of [Hg₂(L^pPh)][ClO₄]₂contains in the asym-

metric unit two independent but similar [Hg₂(L^pPh)][ClO₄]₂units,

each having the same basic dinuclear structure as in the previous

examples but with a slightly different conformation from each

other (Fig. 14, Table10). All four Hg(I) ions are in a distorted trig-

onal planar coordination environment with Hg–N bond lengths

2+

the Hg₂unit. It is also apparent that the Hg · · · Hg separation

˚

does not have much scope for variation, being ≈ 2.52 A in every

case.

For all three complexes, ES mass spectra in dmf solution conﬁrm

retention of the dinuclear complex with its Hg · · · Hg interaction,

˚

in the range 2.26–2.42 A and Hg–Hg separations of 2.52 A. In the

molecule containing Hg(1) and Hg(2) the two HgN₂planes have

a twist of 30^◦between them, and both metal ions have weak axial

interactions with perchlorate ions which are on opposite faces of

the N₂Hg–HgN₂unit to minimise steric interference between them

+

2+

with peaks at m/z 893.1 {Hg₂(L)(ClO₄)} and 397.1 {Hg₂(L)}

(where L = L^oPh, L^mPhor L^pPh) in each case. A number of other peaks

in the mass spectrum suggest the presence of several other species

including [Hg(L)₂][ClO₄], [Hg₂(L)₂][ClO₄]₂and [Hg₄(L)₂][ClO₄]₄.

It is therefore likely that the structure observed in the solid state

˚

[Hg(1) · · · O(11), 2.729 A; Hg(2) · · · O(23), 2.656 A]. The second

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Table 11 Selected bond lengths (A) for [Hg₄(L^biph)₆⊂ClO₄][ClO₄]₇·

˚

is in each case a kinetic crystallisation product of a mixture of

several species in solution.

(MeNO₂)₃

Hg(1)–N(21C)

Hg(1)–N(21A)

Hg(1)–N(11B)

Hg(1)–N(11A)

Hg(1)–N(21B)

Hg(1)–N(11C)

Hg(2)–N(61F)

Hg(2)–N(11D)

Hg(2)–N(21D)

Hg(2)–N(51A)

Hg(2)–N(51F)

Hg(2)–N(61A)

2.306(15)

2.327(12)

2.340(15)

2.375(14)

2.432(13)

2.487(12)

2.268(12)

2.272(13)

2.390(12)

2.442(11)

2.449(11)

2.477(13)

Hg(3)–N(11E)

Hg(3)–N(61D)

Hg(3)–N(51D)

Hg(3)–N(51B)

Hg(3)–N(21E)

Hg(3)–N(61B)

Hg(4)–N(11F)

Hg(4)–N(61E)

Hg(4)–N(21F)

Hg(4)–N(61C)

Hg(4)–N(51C)

Hg(4)–N(51E)

2.196(12)

2.308(12)

2.398(12)

2.485(12)

2.495(13)

2.512(14)

2.262(14)

2.301(13)

2.438(14)

2.451(11)

2.471(12)

2.476(14)

Tetrahedral cage complex of Hg(II) with L^biph

. The formation of

the dinuclear Hg(I) complexes described above is clearly facilitated

by the fact that the ligands L^mPhand L^pPhare sufﬁciently short

to be able to coordinate one bidentate terminus to each Hg(I)

2+

centre of the {Hg₂} unit. We were therefore interested to

see what would happen using a much longer bridging ligand,

such as L^biph, where this cannot happen as the two pyrazolyl-

pyridine units are too far apart. The reaction of L^biphwith

Hg(ClO₄)₂in a 1 : 1 ratio in nitromethane gave a colourless

solution from which crystals were grown by the slow diffusion

of diisopropyl ether. Elemental analysis of the crystals suggested

the empirical formula Hg₂(L^biph)₃(ClO₄)₄, indicating that in this

case the metal ions have remained in the +2 oxidation state. The

crystal structure shows the complex to be the tetrahedral cage

[Hg₄(L^biph)₆⊂ClO₄][ClO₄]₇·(MeNO₂)₃(Fig. 15, Table 11). Four six-

coordinate Hg(II) ions lie at the corners of the tetrahedron and

are each coordinated by a bidentate terminus from three of the

six ligands which span each of the edges of the cage. One of the

−

eight ClO₄anions is encapsulated inside the cage. The topology

of the cage is similar to that of the previously described series

of Co(II) cages [Co₄(L^biph)₆⊂A][A]₇(A⁻= BF₄⁻, ClO₄⁻, PF₆and

−

I⁻).^5eClearly, the fact that L^biphis too long to coordinate both

bidentate termini to the same metal centre precludes formation of

either simple mononuclear complexes {cf. [Hg(L^oPh)](ClO₄)₂} or

the dinuclear Hg(I) complexes.

˚

The Hg–N bond lengths are in the range 2.20–2.50 A, slightly

longer than those for HgN₄donor sets and similar to other

examples of HgN₆coordination.¹⁸The tetrahedron is more

regular than those observed for cages with Co(II);^5ethe Hg · · · Hg

separations along the edges of the tetrahedron span the narrower

˚

range 11.64–12.23 A. There are two types of metal coordination

geometry present in the cage; Hg(1) has fac tris-chelate geometry,

whereas the remaining three Hg(II) ions have mer tris-chelate

geometry. This results in the cage having a (non-crystallographic)

C₃symmetry axis through Hg(1) and the centre of the triangular

face deﬁned by Hg(2)–Hg(3)–Hg(4), such that all three ligands in

the basal plane are equivalent, and the three ligands connecting the

base to the apex are equivalent, with neither type of ligand having

any internal symmetry. All the metal centres in each cage have the

same optical conﬁguration, all D or all K with both enantiomers

present in the unit cell.

−

As observed for the Co(II) analogues, the encapsulated ClO₄

˚

anion is closer to ‘apical’ Hg(1) (Hg · · · Cl: 5.85 A) than the three

˚

‘basal’ Hg(II) ions (Hg · · · Cl separations in the range 7.81–7.95 A).

−

This displacement allows the oxygen atoms of the ClO₄to make

several contacts with the CH₂linker units short enough to be C–

˚

H · · · O hydrogen bonds (O · · · C distances 3.09–3.24 A). Three

more anions outside the cage sit in cavities in the three faces of

the tetrahedron which meet at Hg(1), and make similar C–H · · · O

hydrogen bonds with CH₂groups from the ligands.

Intramolecular p–p stacking interactions are an important

feature of the complex; every single pyrazolyl-pyridine group is

p-stacked to the phenyl ring of a neighbouring ligand’s spacer unit

˚

(separations 3.2–3.7 A). Twists between the rings of the biphenyl

spacers allow each phenyl ring to optimise these interactions by

aligning itself better with the adjacent pyrazolyl-pyridine units.

These twist angles between phenyl rings are larger for the ligands

connected to ‘apical’ Hg(1) (42.6–52.7^◦) than for the ligands

spanning the ‘basal’ Hg(II) ions (26.2–30.6^◦). Outside the cage

the remaining four perchlorate anions, and solvent molecule, were

Fig. 15 Two views of the complex cation of the cage complex

[Hg₄(L^biph)₆⊂ClO₄][ClO₄]₇·(MeNO₂)₃(H atoms and all anions except

the encapsulated one omitted for clarity). (a) A view emphasising the

tetrahedral architecture, showing two ligands and part of the numbering

scheme. (b) A view showing the whole cage with each ligand coloured

separately.

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Fig. 16 500 MHz ¹H NMR spectrum of [Hg₄(L^biph)₆⊂ClO₄][ClO₄]₇showing the presence of two independent ligand environments (as observed in the

crystal structure); the eight protons of the four CH₂groups were matched into pairs (labelled a–d) with a COSY spectrum.

difﬁcult to locate with only limited data from weakly scattering

crystals. They are distributed over several disordered sites with

fractional occupancies, though the approximate overall total of

eight anions, which conﬁrms the oxidation state of the Hg(II)

˚

Hg–N separations in the range from 2.277–2.614 A with the

shortest two being to the pair of pyridyl donors which are mutually

trans; the Hg–N(pyrazolyl) donors are all considerably longer, and

the average Hg–N distance is 2.42 A. In contrast the terminal

ions Hg(1) and Hg(3) both have four-coordinate environments

in which the N(pyridyl)–Hg–N(pyridyl) angle is close to linear

[174^◦at Hg(1) and 158^◦at Hg(3)] and these bonds are relatively

short, with the Hg–N(pyrazolyl) bonds again being much longer.

˚

1

ions, is clear. The H NMR spectrum of the complex (Fig. 16)

is exactly consistent with the cage structure observed in the solid

state being retained in solution, with signals in the aromatic region

totalling 48 protons (from two inequivalent ligands which have no

internal symmetry). Although many of the signals are overlapping,

enough of them are distinct to allow accurate integration; of

particular note are the eight doublets with the lowest chemical

shift which correspond to the protons of the four inequivalent CH₂

groups (conﬁrmed by a two-dimensional COSY spectrum). The

fact that this NMR spectrum is clean, with no indication of minor

additional components or traces of free ligand, indicates that the

cage complex is a robust structure which completely retains its

integrity in solution—an important point from the view of future

studies into its host–guest chemistry.

Table 12 Selected bond lengths (A) for [Hg₃(L²³²)₂](ClO₄)₆·6MeCN

˚

Hg(1)–N(11B)

Hg(1)–N(11A)

Hg(1)–N(21A)

Hg(1)–N(21B)

Hg(2)–N(51A)

Hg(2)–N(51B)

Hg(2)–N(61B)

2.151(4)

2.162(4)

2.404(4)

2.488(4)

2.277(3)

2.286(3)

2.373(3)

Hg(3)–N(91A)

Hg(3)–N(91B)

Hg(3)–N(81B)

Hg(3)–N(81A)

Hg(2)–N(41A)

Hg(2)–N(41B)

Hg(2)–N(61A)

2.155(3)

2.238(4)

2.307(4)

2.442(4)

2.412(3)

2.531(3)

2.614(3)

N(11B)–Hg(1)–N(11A) 174.46(15) N(91A)–Hg(3)–N(91B) 157.94(13)

N(11B)–Hg(1)–N(21A) 110.19(13) N(91A)–Hg(3)–N(81B) 125.46(13)

N(11A)–Hg(1)–N(21A) 73.91(13) N(91B)–Hg(3)–N(81B) 73.66(13)

N(11B)–Hg(1)–N(21B) 73.34(13) N(91A)–Hg(3)–N(81A) 74.34(13)

N(11A)–Hg(1)–N(21B) 108.52(13) N(91B)–Hg(3)–N(81A) 105.15(13)

N(21A)–Hg(1)–N(21B) 116.35(12) N(81B)–Hg(3)–N(81A) 124.30(12)

N(51A)–Hg(2)–N(51B) 159.61(12) N(61B)–Hg(2)–N(41B) 139.83(12)

N(51A)–Hg(2)–N(61B) 124.77(12) N(41A)–Hg(2)–N(41B) 114.62(11)

N(51B)–Hg(2)–N(61B) 70.68(12) N(51A)–Hg(2)–N(61A) 69.48(12)

N(51A)–Hg(2)–N(41A) 71.23(12) N(51B)–Hg(2)–N(61A) 93.89(11)

N(51B)–Hg(2)–N(41A) 126.80(12) N(61B)–Hg(2)–N(61A) 108.24(11)

N(61B)–Hg(2)–N(41A) 85.45(12) N(41A)–Hg(2)–N(61A) 139.18(11)

N(51A)–Hg(2)–N(41B) 95.17(11) N(41B)–Hg(2)–N(61A) 79.76(11)

N(51B)–Hg(2)–N(41B) 69.52(12)

Helical and catenated trinuclear complexes of Hg(II) with L²³²

.

We described earlier how L²³²formed trinuclear double helicates

with a range of metal ions, including a mixed-metal Ag(I)–Fe(II)–

Ag(I) complex exploiting the four-coordinate and six-coordinate

nature of the terminal and central binding sites in the helicate.^5jRe-

action of L²³²with Hg(ClO₄)₂afforded a mixture of two crystalline

products which could be separated manually. The major product

is the trinuclear helicate [Hg₃(L²³²)₂](ClO₄)₆·6MeCN in which all

three metal centres are in the same Hg(II) oxidation state despite

their different coordination environments (Fig. 17, Table 12). The

central ion Hg(2), although nominally six-coordinate, displays

Fig. 17 Structure of the complex cation of the trinuclear double helicate [Hg₃(L²³²)₂](ClO₄)₆·6MeCN (H atoms omitted for clarity).

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˚

each ligand interact with a different metal ion. An additional and

unexpected feature of this is that each of the terminal Hg(II) ions

is coordinated to a pyrazolyl ring in a cyclometallating C-donor

coordination mode; cyclometallating coordination of aromatic

ligands to Hg(II) is well known.¹⁹Thus the central metal ion

Hg(1) is in an N₆coordination environment with, again, the two

shortest bonds being those to the pyridyl donors. The terminal

metal ions Hg(2) and Hg(3) are however each coordinated by

one pyrazolyl-pyridine unit from the terminus of one ligand, and

a cyclometallating pyrazolyl donor from the other terminus of

The average Hg–N distances are 2.30 A for Hg(1) and 2.29 A

at Hg(3), with the shorter average bond length [compared to

Hg(1)] reﬂecting the lower coordination number. The intertwining

of the two ligands results in inter-ligand p-stacking, with each

ligand having one of its phenylene spacers stacked between two

pyrazolyl/pyridine units of the other ligand. This phenylene spacer

also has two of its C–H bonds directed towards the face of

a phenylene spacer from the other ligand to which it is near-

perpendicular [87^◦between rings C(72A)–C(77A) and C(72B)–

C(77B); and 83^◦between rings C(32A)–C(37A) and C(32B)–

C(37B)], resulting in a combination of face-to-face and edge-to-

face stacking involving these phenylene spacers. Despite the fact

that, in the crystal structure, the two phenylene spacers of each

ligand are in quite distinct environments (one in the helical ‘core’

involved in p-stacking, and one on the periphery of the helix),

◦

Table 13 Selected bond lengths (A) and angles ( ) for [Hg₃(L²³²–_H)₂]-

(ClO₄)₄·3MeNO₂

˚

Hg(1)–N(51A)

Hg(1)–N(51B)

Hg(1)–N(41B)

Hg(1)–N(41A)

Hg(1)–N(61B)

Hg(1)–N(61A)

2.294(8) Hg(2)–C(84A)

2.315(8) Hg(2)–N(11A)

2.348(8) Hg(2)–N(21A)

2.363(8) Hg(3)–C(84B)

2.486(8) Hg(3)–N(11B)

2.526(8) Hg(3)–N(21B)

2.024(11)

2.130(10)

2.680(9)

2.040(11)

2.124(10)

2.642(9)

1

the H NMR spectrum in solution shows a symmetric structure

with each ligand having twofold symmetry (see Experimental).

The Hg(1) · · · Hg(2) and Hg(2) · · · Hg(3) separations are 7.89 and

˚

7.63 A respectively.

N(51A)–Hg(1)–N(51B) 155.1(3) N(51B)–Hg(1)–N(61A)

N(51A)–Hg(1)–N(41B) 126.1(3) N(41B)–Hg(1)–N(61A)

91.5(3)

98.8(3)

The minor product from this reaction proved to be something

of a surprise and is shown in Fig. 18, Table 13; it is a catenate

[Hg₃(L²³²_–H)₂](ClO₄)₄·3MeNO₂in which each mono-deprotonated

ligand forms an independent macrocyclic ring by coordination

of its termini to the same Hg(II) ion, with the two metallo-

macrocyclic rings connected by a third Hg(II) ion bound to the

terdentate unit of each ligand. This assembly therefore achieves

the same 3 : 2 metal : ligand stoichiometry but in a different way

from that found in the helicate in which all three binding sites of

N(51B)–Hg(1)–N(41B)

N(51A)–Hg(1)–N(41A)

70.7(3) N(41A)–Hg(1)–N(61A) 139.0(3)

70.5(3) N(61B)–Hg(1)–N(61A) 96.1(3)

N(51B)–Hg(1)–N(41A) 129.4(3) C(84A)–Hg(2)–N(11A) 171.6(5)

N(41B)–Hg(1)–N(41A)

N(51A)–Hg(1)–N(61B)

N(51B)–Hg(1)–N(61B)

N(41B)–Hg(1)–N(61B) 136.8(3) C(84B)–Hg(3)–N(21B)

N(41A)–Hg(1)–N(61B)

N(51A)–Hg(1)–N(61A)

98.4(3) C(84A)–Hg(2)–N(21A) 116.5(4)

97.1(3) N(11A)–Hg(2)–N(21A)

68.6(3) C(84B)–Hg(3)–N(11B)

70.2(4)

174.0(4)

113.7(4)

70.7(3)

96.3(3) N(11B)–Hg(3)–N(21B)

69.2(3)

Fig. 18 Two views of the complex cation of the trinuclear cyclometallated catenate [Hg₃(L²³²_–H)₂](ClO₄)₄·3MeNO₂(H atoms omitted for clarity). (a) A

view showing the atom labelling scheme, with one ligand depicted with hollow bonds for clarity; (b) a view emphasising the aromatic stacking around the

central Hg(II) ion.

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the same ligand. The coordination geometry around Hg(2) and

Hg(3) is in fact nearly linear two-coordinate [from pyridyl N

and pyrazolyl C donors subtending an angle of 172^◦at Hg(2)

and 174^◦at Hg(3)] with the Hg–N(pyrazolyl) distances being

crystallisation affords a complex two-dimensional coordination

polymer in which Ag · · · Ag interactions play an important role in

cross-linking adjacent one-dimensional chains.

The coordination chemistry of these ligands with mercury is

complicated by the availability of two oxidation states: L^oPh, L^mPh

˚

much longer (2.68 and 2.64 A respectively). A signiﬁcant feature

2+

of the structures is aromatic p-stacking, with the terdentate

bis(pyrazolyl)-pyridine unit of each ligand sandwiched between

the two para-phenylene groups of the other with separations of ≈

and L^pPhall afford [Hg₂L]²⁺based on an {Hg^I₂} metal–metal

bonded core with one end of the bridging ligand attached to

each metal ion. Where reduction to Hg(I) did not occur, the

Hg(II) centres could be either four-coordinate {as in mononu-

clear [Hg(L^oPh)]²⁺} or six-coordinate {as in the tetranuclear cage

[Hg₄(L^biph)₆⊂ClO₄]⁷⁺which contains an anion in the central

cavity}. Both four- and six-coordinate Hg(II) centres occur in

the trinuclear double helicate [Hg₃(L²³²)₂]⁶⁺. Finally, a surprise

by-product in the preparation of [Hg₃(L²³²)₂]⁶⁺was the catenate

[Hg₃(L²³²_–H)₂]⁴⁺whose formation is made possible by the facility

with which Hg(II) forms cyclometallated complexes having low

coordination numbers. For the Hg compounds in particular, the

possibility of Hg^I–Hg^Imetal–metal bonded species forming, and

the possibility of cyclometallation of a pyazolyl ring, result in

highly unpredictable coordination chemistry.

˚

3.4–3.5 A between the near-parallel planes. ES mass spectra of a

redissolved crystal conﬁrmed retention of the structure in solution,

with peaks apparent at m/z 1105.2, 703.5 and 502.6 corresponding

(4−n)+

to {Hg₃(L²³²_–H)₂(ClO₄)_n}

(n = 2, 1, 0 respectively). We were

unable to isolate enough crystals for a good ¹H NMR spectrum.

We could not convert the helicate [Hg₃(L²³²)₂](ClO₄)₆to the

catenate [Hg₃(L²³²_–H)₂](ClO₄)₄by treatment with base, even under

vigorous conditions (prolonged reﬂux in MeNO₂), presumably the

catenate forms by an alternative pathway and once the helicate has

formed it is kinetically quite stable.

Preparation of catenates based on metal-ion template effects

is a popular theme in supramolecular coordination chemistry,²⁰

and several rational syntheses have been reported since the ﬁrst

examples from Sauvage et al. based on the Cu(I)/phen skeleton.²¹

The formation of a catenated structure here, albeit as a minor com-

ponent during formation of the trinuclear helicate, likely occurs

only because for Hg(II) a cyclometallated coordination mode is

possible. (We note that Sauvage et al. reported a mononuclear

catenate based on unexpected C–H activation of an aromatic

ring by Pd(II), giving a cyclometallated structure, in 1989).²²

Examination of the structure of [Hg₃(L²³²_–H)₂](ClO₄)₄suggests

that conventional N,N-bidentate coordination of the two terminal

pyrazolyl-pyridine units of each ligand to the same terminal metal

centre would be difﬁcult in a catenated structure, as the two

arms of each ligand cannot stretch far enough to converge to

the necessary extent to provide an N₄coordination environment.

In fact only one pyrazolyl N-donor interacts with each terminal

Hg(II) centre and those are weak, long-range interactions; the

principal coordination to these Hg(II) centres is the near-linear

N,C (pyridine and cyclometallated pyrazolyl) donors. Cyclometal-

lation to Hg(II) is favoured when the coordination number is low, as

here, because of the electroneutrality principle;¹⁹anionic C-donor

ligands would make the metal centre too electron rich if there

were too many other ligands. Accordingly with metal ions such

as ﬁrst-row transition metals and Ag(I), where cyclometallation

as a coordination mode is rarer, only the conventional trinuclear

helicates were observed on reaction with L²³²with no evidence for

alternative cyclometallated products.^5j

Experimental

General details

5h

5g

The ligands L^mPh

,

L^pPh

,

and L^biph(ref. 5e) were prepared as

described previously. Other organic starting materials and metal

salts were purchased from Aldrich and used as received. ¹H

NMR spectra were recorded on Bruker AC-250, AMX2–400

or DRX-500 spectrometers. Electron impact mass spectra were

recorded on a VG-Autospec magnetic sector instrument at the

University of Shefﬁeld. Electrospray mass spectra were recorded

on a VG Quattro II triple-quadrupole instrument or a Bruker

MicroTOF mass spectrometer in electrospray positive ion mode,

at the University of Huddersﬁeld.

Preparation of L^mTol

N-Bromo-succinimide (42 g, 233.2 mmol) and AIBN (ca. 5

mg) were added to a stirred solution of mesitylene (10.0 g,

83.3 mmol) in dry CCl₄(200 cm³); the mixture was heated to

reﬂux for 3 h. The orange solution was allowed to cool and

the resulting white precipitate was removed by ﬁltration. The

solution was then concentrated to an orange oil which was puriﬁed

by column chromatography on alumina, eluting with hexane,

yielding the mixture of inseparable isomers 1,3-bis(bromomethyl)-

5-methyl-benzene (the desired product) and 1-(dibromomethyl)-

3,5-dimethyl-benzene (undesired by-product) as a white solid (R_f

0.55, 10% DCM–hexane). This mixture of isomers (6.4 g, 23.0

mmol), 3-(2-pyridyl)pyrazole (7.5 g, 51.7 mmol), aqueous NaOH

(10 M, 25 cm³), toluene (100 cm³) and Bu₄NOH (40% aqueous

solution, 3 drops) was stirred vigorously at 60^◦for 3 h. The

mixture was diluted with H₂O (100 cm³) and the organic layer

separated, dried over MgSO₄and concentrated before puriﬁcation

by alumina column (CH₂Cl₂: thf, 19 : 1) to give L^mTol(R_f0.26) as a

white powder (Yield: 5.24 g, 25%). ¹H NMR (250 MHz, CDCl₃):

d 8.62 (2H, ddd, J 4.9, 1.8, 0.9; pyridyl H⁶), 7.92 (2H, dt, J 7.9,

0.9; pyridyl H³), 7.70 (2H, td, J 7.9, 1.8; pyridyl H⁴), 7.39 (2H, d,

J 2.4; pyrazolyl H⁵), 7.19 (2H, ddd, J 7.3, 4.9, 1.2; pyridyl H⁵),

Conclusions

This set of ligands has afforded an interesting range of structural

types in the complexes with Ag(I), Hg(I) and Hg(II). Four-

coordinate bis-bidentate coordination around Ag(I) can afford a

dinuclear double helicate, a dinuclear mesocate or an inﬁnite one-

dimensional chain from a set of three very similar bridging ligands

(L^mPh, L^mToland L^pPh). With the more extended bridging ligand L^biph

one-dimensional chains result whose conformation depends on

whether or not solvent molecules can be accommodated in a

channel along the core of the chain. The triply-bridging ligand L^mes

appears to afford the simple cage [Ag₃(L^mes)₂]²⁺in solution, but

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6.97 (2H, s; phenyl H^4/6), 6.95 (1H, s; phenyl H²), 6.89 (2H, d, J

2.1; pyrazolyl H⁴), 5.32 (4H, s; CH₂), 2.27 (3H, s; CH₃). EI-MS

m/z 406 (M⁺). Found: C, 73.1; H, 5.4; N, 20.3%. Required for

C₂₅H₂₂N₆·(H₂O)_0.25: C, 73.1; H, 5.5; N, 20.5%.

+

14.8%. ESMS: m/z 700.2 {Ag(L^mes)} , 1485.4 {Ag₂(L^mes)₂(BF₄)} ,

1680.3 {Ag₃(L^mes)₂(BF₄)₂} , 2074.4 {Ag₂(L^mes)₃(BF₄)} , 2271.6

+

{Ag₃(L^mes)₃(BF₄)₂} , 2466.6 {Ag₄(L^mes)₃(BF₄)₃} .

+

Complexes with Hg(I) and Hg(II)

Complexes with Ag(I)

Complexes with Hg(I) or Hg(II) were prepared by mixing

equimolar quantities of ligand and Hg(ClO₄)₂in nitromethane

(for L^oPh, L^pPhand L^biph) or dimethylformamide (for L^mPh). Single

crystals suitable for X-ray crystallographic and other analyses were

grown by slow diffusion of diisopropyl ether into these solutions.

Characterisation data for the complexes were as follows:

Complexes of the ligands with Ag(I) were prepared by combining

equimolar quantities of Ag(MeCN)₄BF₄or Ag(ClO₄) with the

appropriate ligand in distilled acetonitrile. Single crystals suitable

for X-ray crystallographic and other analyses were grown by slow

diffusion of diisopropyl ether into these solutions. Characterisa-

tion data for the complexes were as follows:

[Hg(L^oPh)][ClO₄]₂. ¹H NMR (400 MHz, CD₃NO₂): d 8.85 (2H,

ddd, J 5.3, 0.9, 0.6; pyridyl H⁶), 8.41 (2H, td, J 7.8, 1.6; pyridyl

H⁴), 8.35 (2H, ddd, J 7.9, 1.6, 0.9; pyridyl H³), 7.94 (2H, ddd, J

7.3, 5.6, 1.8, pyridyl H⁵), 7.87 (2H, d, J 2.6; pyrazolyl), 7.69–7.64

(2H, m; phenyl), 7.61–7.56 (2H, m; phenyl), 7.28 (2H, d, J 2.4;

pyrazolyl), 5.44 (4H, s, CH₂). Found: C, 35.3; H, 2.4; N, 8.7%.

Required for Hg(C₂₄H₂₀N₆)(ClO₄)₂·H₂O: C, 35.6; H, 2.7; N, 8.8%.

[Ag(L^mPh)(BF₄)]_∞. ¹H NMR (250 MHz, CD₃CN): d 8.19 (2H,

ddd, J 4.9, 1.5, 0.9; pyridyl H⁶), 7.93 (2H, dd, J 7.0, 1.5; pyridyl

H⁴), 7.89 (2H, ddd, J 7.9, 1.8, 0.9; pyridyl H³), 7.85 (2H, d, J

2.4; pyrazolyl H⁵), 7.36 (2H, ddd, J 7.0, 5.2, 1.8; pyridyl H⁵),

7.32 (1H, s; phenyl H⁵), 7.09 (1H, s; phenyl H²), 7.08 (2H, s;

phenyl H^4/6), 6.94 (2H, d, J 2.4; pyrazolyl H⁴), 5.17 (4H, s; CH₂).

Found: C, 49.3; H, 3.5; N, 14.5%. Required for AgC₂₄H₂₀N₆BF₄:

2+

ESMS: m/z 297.1 {Hg(C₂₄H₂₀N₆)} , 493.2 {Hg(C₂₄H₂₀N₆)₂} ,

C, 49.1; H, 3.4; N, 14.3%. ESMS: m/z 499.1 {Ag(L^mPh)} ,

+

693.1 {Hg(C₂₄H₂₀N₆) (ClO₄)} , 1085.3 {Hg(C₂₄H₂₀N₆)₂(ClO₄)} ,

1087.2 {Ag₂(L^mPh)₂(BF₄)} , 1675.3 {Ag₆(L^mPh)₆(BF₄)₄} , 1968.3

+

2+

+

1484.1 {Hg₂(C₂₄H₂₀N₆)₂(ClO₄)₃} .

2+

{Ag₇(L^mPh)₇(BF₄)₅} , 2261.4 {Ag₈(L^mPh)₈(BF₄)₆} , 2555.4

2+

[Hg₂(L^oPh)(MeNO₂)₂][ClO₄]₂. Crystals of this were isolated in

small amounts mixed in with crystals of [Hg(L^oPh)][ClO₄]₂when

the recrystallisation was carried out slowly (weeks). ESMS: m/z

{Ag₉(L^mPh)₉(BF₄)₇} , 2848.4 {Ag₁₀(L^mPh)₁₀(BF₄)₈} .

[Ag₂(L^mTol)₂][BF₄]₂. ¹H NMR (250 MHz, CD₃CN): d 8.30

(2H, ddd, J 4.9, 1.8, 0.9; pyridyl H⁶), 7.93 (2H, dd, J 6.7, 1.5;

pyridyl H⁴), 7.90 (2H, ddd, J 7.9, 1.8, 0.9; pyridyl H³), 7.86 (2H,

d, J 2.4; pyrazolyl H⁵), 7.38 (2H, ddd, J 7.0, 4.9, 1.8; pyridyl H⁵),

7.08 (1H, s; phenyl H²), 6.96 (2H, d, J 2.4; pyrazolyl H⁴), 6.74

(2H, s; phenyl H^4/6), 5.02 (4H, s; CH₂), 1.42 (3H, s; CH₃). Found:

C, 49.8; H, 3.5; N, 13.9%. Required for Ag₂(C₂₅H₂₂N₆)₂(BF₄)₂:

+

693.1 {Hg(C₂₄H₂₀N₆)(ClO₄)} , 1285.2 {Hg₂(C₂₄H₂₀N₆)₂(ClO₄)} .

[Hg₂(L^mPh)(dmf)₂][ClO₄]₂. ¹H NMR (400 MHz, CD₃NO₂): d

8.69 (2H, d, J 4.4; pyridyl H⁶), 8.28–8.20 (6H, m), 7.89 (1H, s;

phenyl H²), 7.81 (2H, pseudo-t, J 5.5; pyridyl H⁴or H⁵) 7.48 (1H,

t, J 7.9, phenyl H⁵), 7.25–7.21 (4H, m), 5.70 (4H, s, CH₂). Found:

C, 31.2; H, 2.6; N, 9.1%. Required for C₃₀H₃₄N₈Cl₂Hg₂O₁₀: C,

C, 50.0; H, 3.7; N, 14.0%. ESMS: m/z 513.1 {Ag(L^mTol)} ,

+

2+

31.6; H, 3.0; N, 9.8%. ESMS: m/z 397.1 {Hg₂(L^mPh)} , 592.1

1115.2 {Ag₂(L^mTol)₂(BF₄)₁} , 1717.3 {Ag₆(L^mTol)₆(BF₄)₄} , 2016.9

+

2+

+

{Hg₂(L^mPh)₂} , 893.1 {Hg₂(L^mPh)(ClO₄)} , 985.3 {Hg(L^mPh)₂} ,

2+

{Ag₇(L^mTol)₇(BF₄)₅} , 2317.4 {Ag₈(L^mTol)₈(BF₄)₆} , 2618.5

1283.2 {Hg₂(L^mPh)₂(ClO₄)} , 1885.1 {Hg₄(L^mPh)₂(ClO₄)₃} .

+

2+

{Ag₉(L^mTol)₉(BF₄)₇} , 2918.6 {Ag₁₀(L^mTol)₁₀(BF₄)₈} .

[Hg₂(L^pPh)][ClO₄]₂. ESMS m/z 397.1 {Hg₂(L^pPh)} , 593.1

2+

[Ag₂(L^pPh)₂][BF₄]₂. ¹H NMR (250 MHz, CD₃CN): d 8.38 (2H,

d, J 5.2; pyridyl H⁶), 7.97–7.86 (4H, m; pyridyl H³and H⁴), 7.78

(2H, d, J 2.4; pyrazolyl H⁵), 7.38 (2H, ddd, J 7.0, 4.9, 1.8; pyridyl

H⁵), 6.99 (2H, d, J 2.4; pyrazolyl H⁴), 6.02 (4H, s; phenyl), 4.85

(4H, s; CH₂). Found: C, 48.2; H, 3.4; N, 14.1%. Required for

Ag₂(C₂₄H₂₀N₆)₂(BF₄)₂·(H₂O): C, 48.4; H, 3.6; N, 14.1%. ESMS:

2+

+

{Hg₂(L^pPh)₂} , 893.1 {Hg₂(L^pPh)(ClO₄)} , 985.3 {Hg(L^pPh)₂} ,

1285.2 {Hg₂(L^pPh)₂(ClO₄)} , 1377.5 {Hg(L^pPh)₃} , 1885.1

+

{Hg₄(L^pPh)₂(ClO₄)₃} . Found: C, 29.4; H, 2.2; N, 8.7%. Required

+

for C₂₄H₂₀N₆Cl₂Hg₂O₈: C, 29.0; H, 2.0; N, 8.5%. The crystals were

not sufﬁciently soluble to obtain a ¹H NMR spectrum.

m/z 500.1 {Ag₂(L^pPh)₂} , 1085.2 {Ag₂(L^pPh)₂(BF₄)} .

2+

+

[Hg₄(L^biph)₆][ClO₄]₈·(MeNO₂)₃. ESMS:

m/z

335.1

2+

+

{Hg(L^biph)} , 569.2 {Hg(L^biph)₂} , 769.1 {Hg(L^biph)(ClO₄)} ,

[Ag(L^biph)(BF₄)(MeNO₂)]_∞. ¹H NMR (250 MHz, CD₃CN): d

8.03 (2H, d, J 4.9; pyridyl H⁶), 7.92 (2H, d, J 2.4; pyrazolyl H⁵),

7.57 (2H, td, J 7.8, 1.8; pyridyl H⁴), 7.69 (2H, d, J 7.9; pyridyl

H³), 7.26 (2H, ddd, J 7.6, 4.9, 1.5; pyridyl H⁵), 7.05–6.90 (6H, m;

phenyl), 6.87 (2H, br s; phenyl), 6.75 (2H, d, J 2.4; pyrazolyl H⁴),

5.03 (4H, s; CH₂). Found: C, 50.0; H, 4.0; N, 11.6%. Required for

Ag(C₃₀H₂₄N₆)(BF₄)·3(H₂O): C, 50.2; H, 4.2; N, 11.7%. ESMS:

4+

3+

1002.7 {Hg₄(L^biph)₆(ClO₄)₄} , 1370.3 {Hg₄(L^biph)₆(ClO₄)₅} ,

2+

2105.4 {Hg₄(L^biph)₆(ClO₄)₆} . Found: C, 29.8; H, 2.0; N, 8.8%.

Required for C₁₈₀H₁₄₄N₃₆Cl₈Hg₄O₃₂·(0.25dmf): C, 29.4; H, 2.0; N,

8.7%. For ¹H NMR data, see main text.

[Hg₃(L²³²)₂](ClO₄)₆·6MeCN. This was isolated in good yield

as the main product from combination of L²³²with Hg(ClO₄)₂

m/z 576.1 {Ag₂(L^biph)₂} , 1239.2 {Ag₂(L^biph)₂(BF₄)} , 1903.4

2+

+

1

in MeCN. H NMR (270 MHz, CDCl₃): d 8.56 (2H, d, J 5.2;

4+

{Ag₆(L^biph)₆(BF₄)₄} .

pyridyl H⁶), 8.30–8.15 (5H, m; pyridyl H⁴all, pyridyl H³terminal

rings), 8.09 (2H, d, J 7.3; pyridyl H³central ring), 8.00 (2H,

d, J 2.4; pyrazolyl), 7.88 (2H, d, J 2.4; pyrazolyl), 7.79 (2H,

td, J 7.0, 5.7; pyridyl H⁵), 7.22–7.19 (4H, m; pyrazolyl), 5.65

(4H, d, J 8.2; phenyl), 5.59 (4H, d, J 8.2; phenyl), 5.13 (2H,

d, J 16.2; CH₂), 4.88 (2H, d, J 16.2; CH₂), 4.58 (2H, d, J

16.2; CH₂), 3.80 (2H, d, J 16.2; CH₂). Found: C, 37.9; H,

{[Ag₄(L^mes)₃](BF₄)₄}_∞. ¹H NMR (250 MHz, CD₃CN): d 7.91

(3H, d, J 4.9; pyridyl H⁶), 7.85–7.77 (6H, m; pyridyl H³/H⁴),

7.69 (3H, d, J 2.4 pyrazolyl), 7.23 (3H, ddd, J 7.3, 5.0,

2.3; pyridyl H⁵), 7.79 (3H, d, J 2.5; pyrazolyl), 5.44 (6H, s;

CH₂), 2.20 (9H, s; methyl). Found: C, 50.3; H, 3.9; N, 14.4%.

Required for Ag₄(C₃₆H₃₃N₉)₃(BF₄)₄·2H₂O: C, 50.8; H, 3.9; N,

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2.8; N, 11.3%. Required for Hg₃(C₄₃H₃₅N₁₁)₂(ClO₄)₆·6H₂O: C,

over two sites with occupation factors of 0.33/0.67 for the anion

containing B(1), and 0.44/0.56 for the anion containing B(2);

these B and F atoms were reﬁned with isotropic displacement

parameters. The dmf molecule is disordered over a twofold axis

which runs through the central C–N bond, such that half of the

molecule lies in the asymmetric unit; these atoms were also reﬁned

isotropically.

Crystals of {[Ag₄(L^mes)₃](BF₄)₄}_∞were tiny (that used had

dimensions of 0.20 × 0.04 × 0.002 mm³) and required synchrotron

radiation to give a ﬁnal R1 value of 14.1%. Within the limits

of the data the gross structure of the coordination network (the

asymmetric unit contains four metal cations and three ligands) is

well deﬁned although, as with the previous case, the esd’s on the

metric parameters are high and bond distances and angles should

not be over-interpreted. It was possible to locate only 1.5 of the

expected four [BF₄]⁻anions; two were located in general positions

but one was reﬁned with a site occupancy of 50% to keep the

thermal displacement parameters reasonable. Similarity restraints

were used extensively during the reﬁnement (e.g. all six-membered

rings were restrained to be similar, as were all ﬁve-membered rings;

all B–F distances were likewise restrained to be similar).

The structural determinations of [Hg(L^oPh)][ClO₄]₂and

[Hg₂(L^mPh)(dmf)₂][ClO₄]₂were straightforward and presented no

problems. Crystals of [Hg₂(L^oPh)(MeNO₂)₂][ClO₄]₂scattered only

very weakly. One of the perchlorate anions was disordered over

two sites and reﬁned with a 50% site occupancy in each; the atoms

involved were reﬁned with isotropic displacement parameters.

In addition, atoms C(12) and C(52) of the ligand needed to

be reﬁned isotropically to prevent them from becoming ‘non-

positive-deﬁnite’ during reﬁnement. In [Hg₂(L^pPh)][ClO₄]₂one of

the four independent perchlorate ions was also disordered, with

the central atom [Cl(2)] ﬁxed but the set of four oxygen atoms

occupying one of three sites with occupancies of 37, 35 and 28%.

These oxygen atoms were reﬁned with isotropic displacement

parameters, restraints were applied to the Cl–O and O · · · O

separations, and to the displacement parameters of the oxygen

atoms.

5+

38.0; H, 3.0; N, 11.3%. ESMS: m/z 422.7 {Hg₃(L²³²)₂(ClO₄)} ,

4+

3+

553.1 {Hg₃(L²³²)₂(ClO₄)₂} , 770.5 {Hg₃(L²³²)₂(ClO₄)₃} , 1205.2

2+

{Hg₃(L²³²)₂(ClO₄)₄} .

[Hg₃(L²³²_–H)₂](ClO₄)₄·3MeNO₂. This was isolated as the mi-

nor component from the above recrystallisation. ESMS: m/z

502.6 {Hg₃(L²³²_−H)₂} , 703.5 {Hg₃(L²³²_−H)₂(ClO₄)} , 1105.2

4+

3+

{Hg₃(L²³²_−H)₂(ClO₄)₂} . Found: C, 41.2; H, 3.1; N, 12.6%. Re-

2+

quired for Hg₃(C₄₃H₃₄N₁₁)₂(ClO₄)₄·5(H₂O): C, 41.3; H, 3.2; N,

12.3%.

X-Ray crystallography

A summary of the details of the crystal data, data collection and

reﬁnement details is given in Table 14. All structural determina-

tions were carried out using Bruker SMART-1000 or APEX-2

CCD diffractometers equipped with Mo–Ka X-radiation at the

University of Shefﬁeld, apart from (i) [Ag₂(L^pPh)₂][BF₄]₂which was

analysed at the University of Bristol on a Bruker PROTEUM CCD

diffractometer equipped with Cu–Ka radiation from a rotating-

anode source, and (ii) {[Ag₄(L^mes)₃](BF₄)₄}_∞for which data were

collected at the Daresbury Synchrotron Radiation Source (station

9.8) using a Bruker SMART-APEX2 diffractometer and Si(111)-

monochromatized synchrotron radiation with a wavelength close

to the Zr absorption edge. In all cases, absorption corrections were

applied using SADABS,²³and structure solution and reﬁnement

was carried out using SHELXS-97 and SHELXL-97 respectively.²⁴

The structures were solved by direct methods or heavy atom Pat-

terson methods and reﬁned by full-matrix least-squares methods

on F². Hydrogen atoms were placed geometrically and reﬁned with

a riding model and with U_isoconstrained to be 1.2 (1.5 for methyl

groups) times U_eqof the carrier atom. All non-hydrogen atoms

were reﬁned anisotropically except where stated otherwise below.

CCDC reference numbers 609491–609503. For crystallographic

data in CIF or other electronic format see DOI: 10.1039/b607541j

i

For [Ag(L^mPh)(BF₄)(ⁱPr₂O)_0.5]_∞the Pr₂O molecule in the sym-

metric unit was in a general position but reﬁned satisfactorily with

a site occupancy of 0.5 for all atoms; geometric restraints were used

to keep the geometry of this molecule reasonable. The structural

determinations of [Ag₂(L^mTol)₂](ClO₄)₂and [Ag₂(L^pPh)₂](BF₄)₂were

straightforward.

Crystals of [Hg₄(L^biph)₆⊂ClO₄][ClO₄]₇·(MeNO₂)₃scattered

weakly and, like other structural determinations of large cages, the

reﬁnement presented several problems. In the cage superstructure

only the Hg atoms could be reﬁned with anisotropic displacement

parameters, and extensive use of geometric restraints helped to

ensure that all aromatic rings were ﬂat with all pyridyl rings

having similar geometries to one another and all pyrazolyl rings

having similar geometries to one another. The eight perchlorate

anions were located in 17 sites with site occupancies of 100%

(two cases, reﬁned anisotropically), 50% (nine cases, reﬁned

isotropically) or 25% (six cases, reﬁned isotropically); for the sites

with occupancies of 50 or 25% extensive use was made of geometric

restraints to keep the structures of the anions reasonable. The three

nitromethane solvent molecules were located at ﬁve sites (one with

100% occupancy and four with 50% occupancy); all were reﬁned

with isotropic displacement parameters and were restrained to

have similar geometries. Given the extensive disorder and weak

scattering the R1 value of 11.8% is very reasonable.

Crystals of [Ag(L^biph)(BF₄)(MeNO₂)]_∞, although of a reasonable

size, scattered very weakly and only data with 2h ≤ 45^◦were

used in the ﬁnal reﬁnement. The asymmetric unit contains two

formula units, i.e. two independent Ag(I) ions and two ligand

molecules. Both of the [BF₄]⁻anions in the asymmetric unit

exhibited disorder; in one case the B atom was ﬁxed but the F atoms

were disordered over two orientations with site occupancies of 50%

in each; in the other case the entire anion was disordered over two

sites with site occupancies of 50% in each. All B and F atoms

were reﬁned with isotropic displacement parameters. Extensive

use of geometric restraints (e.g. all aromatic rings ﬂat; equivalent

atom–atom separations in different aromatic rings restrained to

be similar), and restraints on the displacement parameters, was

required to keep the reﬁnement stable. The esd’s on the metric

parameters are accordingly high for this structure, although the

gross geometry is perfectly clear.

The structural determination of [Hg₃(L²³²)₂](ClO₄)₆·6MeCN

presented no problems. For [Hg₃(L²³²_−H)₂](ClO₄)₄·3MeNO₂one

of the perchlorate anions was disordered over two sites (50% site

occupancy in each); the Cl atoms involved could be reﬁned with

In crystals of [Ag(L^biph)(BF₄)(ⁱPr₂O)_0.5(dmf)_0.25

]

the two in-

∞

dependent anions in the asymmetric unit were each disordered

5010 | Dalton Trans., 2006, 4996–5013

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The Royal Society of Chemistry 2006

©

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This journal is

The Royal Society of Chemistry 2006

Dalton Trans., 2006, 4996–5013 | 5011

©

View Article Online

anisotropic displacement parameters, but the oxygen atoms all

needed to be reﬁned with ﬁxed isotropic displacement parameters.

Two of the three lattice solvent molecules were well-behaved and

reﬁned anisotropically; the third required geometric restraints and

was reﬁned with ﬁxed isotropic displacement parameters to keep

the reﬁnement stable.

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Acknowledgements

We thank the EPSRC and University of Shefﬁeld for ﬁnancial

support. We also thank EPSRC for funding of the UK National

Crystallography Service, and CCLRC (UK) for access to syn-

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Complexes of Ag(i), Hg(i) and Hg(ii) with multidentate pyrazolyl-pyridine ligands: From mononuclear complexes to coordination polymers via helicates, a mesocate, a cage and a catenate

DOI: 10.1039/b607541j

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