Dinuclear species versus zigzag or helical polymers in palladium, zinc, and copper complexes with ditopic bis(pyrazolyl)methane ligands

FULL PAPER

DOI:10.1002/ejic.201300948

Dinuclear Species versus Zigzag or Helical Polymers in

Palladium, Zinc, and Copper Complexes with Ditopic

Bis(pyrazolyl)methane Ligands

Gema Durá,^[a]M. Carmen Carrión,^[a,b]Félix A. Jalón,^[a]

Blanca R. Manzano,*^[a]and Ana M. Rodríguez^[c]

COVER PICTURE

Keywords: N ligands / Noncovalent interactions / Bis(pyrazolyl) ligands / Coordination polymers / Supramolecular

chemistry

Two new all-nitrogen donor ditopic ligands, namely, p-bis-

[bis(pyrazol-1-yl)methyl]biphenyl (L3) and p-bis[bis(3,5-di-

methylpyrazol-1-yl)methyl]biphenyl (L4), have been synthe-

sized. Their coordination chemistry, along with that of the

previously described ligands p-bis[bis(pyrazol-1-yl)methyl]-

benzene (L1) and p-bis[bis(3,5-dimethylpyrazol-1-yl)methyl-

]benzene (L2), has been explored with different metallic

fragments. The reactions of L1–L4 with PdCl₂(PhCN)₂,

Pd(OAc)₂and Zn(NO₃)₂led to the formation of dinuclear spe-

cies with anti orientation of the metallic fragments and

bis(bidentate) chelation of the coordinated ligands. The reac-

tions of L1 or L3 with Cu(OAc)₂produced zigzag polymers

with Cu₂(OAc)₄paddle-wheel units alternating with ligands

that coordinate through one pyrazolyl ring at each end. The

reaction between L3 and [Cu(CH₃CN)₄][BF₄] leads to a heli-

cal racemic coordination polymer. The presence of methyl

groups on the pyrazolyl rings and the geometry of the metal

centres influence the parameters of the metallacycles formed

by chelate coordination of the ligands. The discrete mole-

cules and the polymers organize to give three-dimensional

structures through different noncovalent interactions includ-

ing hydrogen bonding, CH–π, anion–π and π–π interactions

that are influenced by the presence or absence of methyl

groups on the pyrazolyl rings.

operative way and, in general, they can influence the final

molecular and supramolecular structure. The inorganic/

organic hybrid architectures can be tailored for different

applications including, among others, gas storage and sepa-

ration, catalysis and nanometric devices.^[7]The most com-

mon organic linkers are aromatic polycarboxylic acids and

nitrogenated ligands.^[7c,8]

Introduction

The coordination-driven self-assembly of organic and

metallic components to give discrete species or infinite

one-, two- or three-dimensional inorganic/organic hybrid

networks is an area of current interest.^[1]The key features

that influence the architecture of the self-assembled species

are the building blocks: (1) the metal centre, which usually

has a preferred coordination environment and may have a

different number of available coordination sites and (2) the

ligands that supply the donor atoms at specific positions

and may exhibit different degrees of flexibility and also pro-

vide potential interaction sites to generate noncovalent in-

teractions such as hydrogen-bonding,^[2]π–π stacking,^[3]cat-

ion–π,^[4]anion–π^[5]and XH–π interactions.^[6]Although

these interactions are usually weak, they may act in a co-

Ligands that contain the bis(pyrazol-1-yl) unit have been

widely reported in the literature, and the most commonly

used are bis(pyrazol-1-yl)methane (bpzm) or borate deriva-

tives.^[9]A third group with coordinating ability can be intro-

duced on the central atom. If the ligand can facially coordi-

nate, it is called a heteroscorpionate,^[9,10]but if this is not

the case, it will behave as a bridge, and polynuclear species

are expected. Ligands of this type were reported by Carrano

et al.^[11]and Marchio^[12]among others.^[13]The correspond-

ing complexes have been applied in different fields includ-

ing, for example, catalysis,^[14,15]gas storage^[12b]and magnet-

ism.^[16]Two or more bpzm fragments may be linked by or-

ganic spacers with different flexibilities and geometries to

produce di- or polytopic ligands.^[17]Reger et al. described

the ligands p- and m-bis[bis(1-pyrazolyl)methyl]benzene,

and different transition metal complexes were obtained

from them. Discrete mononuclear,^[18]homo- and heterodi-

metallic complexes^[18,19]or coordination polymers^[20]are

usually obtained with a chelate coordination of the bpzm

units and an anti disposition of the metallic fragments with

[a] Departamento de Química Inorgánica, Orgánica y Bioquímica,

Universidad de Castilla-La Mancha, Facultad de Ciencias y

Tecnologías Químicas – IRICA,

Avda. C. J. Cela, 10, 13071 Ciudad Real, Spain

http://ww w .irica.uclm.es/QuimicaCoordinacionAplicada/

index.asp

[b] Fundación PCYTA, Paseo de la Innovación,

1, Edificio Emprendedores, 02006 Albacete, Spain

[c] Departamento de Química Inorgánica, Orgánica y Bioquímica,

Universidad de Castilla – La Mancha, Escuela Técnica

Superior de Ingenieros Industriales,

Avda. C. J. Cela, 3, 13071 Ciudad Real, Spain

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejic.201300948.

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Scheme 1. Synthesis of the ligands L1–L4.

respect the benzene ring. A two-dimensional silver frame- of methyl groups on the pyrazole (pz) rings. We have pre-

work in which the ligand acts as μ₃-bridging system has viously found that such groups usually enhance the solubil-

also been reported.^[21]

ity of the complexes, and this might be advantageous for

Our group has worked with bpzm–palladium or –ruth- the growth of crystals suitable for X-ray diffraction.^[5h,22c,25]

enium complexes for several years, and these compounds More importantly, however, such groups may have a strong

generally contain a non-coordinating third substituent at influence on the crystalline structure and may also influence

the methine carbon atom.^[22]Recently, we reported a study the shape of the molecules. According to our previous re-

of the ditopic ligand bis(pyrazol-1-yl)(pyridin-4-yl)meth- sults, one would expect a higher tendency of the pyrazolyl

ane,^[23]and boxlike cyclic dimers and coordination poly- rings to be involved in π–π stacking than their 3,5-dimeth-

mers of different natures, including a chiral helix, were ob- ylated counterparts,^[23]which will mainly exhibit other in-

tained.

teractions such as CH–π or hydrogen-bond interactions. In

In the work described here, we explored the coordination this sense, the “pyrazolyl embrace” has been observed by

and supramolecular chemistry of different metallic frag- Reger in different complexes, and this phenomenon arises

ments with two types of ligands, both of which have a rigid because of a concerted set of intermolecular CH–π and π–

spacer and bpzm groups on both sides (see Scheme 1). In π stacking interactions involving four pyrazolyl rings from

the first instance, we used the ligands p-bis[bis(pyrazol-1-yl)- two bis(pyrazolyl)methane fragments.^{[19,20a,26,27]}This em-

methyl]benzene (L1) and its analogue with 3,5-dimethylpyr- brace could be observed in derivatives of ligands L1 and

azolyl (pz*) rings (L2). The synthesis of L2 has been re- L3, but its formation is less probable in complexes contain-

ported previously,^[24]but its coordination chemistry has not ing L2 or L4. Furthermore, in the derivatives with bpz*m

yet been explored. We also synthesized two new ligands that units, the methyl groups confer a more hydrophobic charac-

contain a biphenyl spacer group (L3 and L4). The specific ter to the pyrazole rings, and we recently observed a ten-

goals of the work were as follows: (1) To evaluate the influ- dency of these methyl groups to occupy nearby regions of

ence of the introduction of a second phenyl ring in the li- space and create hydrophobic regions within the crystal.^[23]

gands. Clearly, this change will have an effect on the supra-

molecular structures formed, but we were also interested in

Results and Discussion

other aspects such as the relative positions of the metallic

fragments, which would be expected to be much further

apart than with L1 and L2, and the coplanarity or not of

the two phenyl rings. (2) To study the influence that the type

Synthesis and Characterization of the Ligands

The ligands L1–L4 used in this work were synthesized in

of metallic fragment has on the final structure. Assuming a good yields according to a greener methodology developed

probable chelate coordination mode for the bpzm units, it in our research group for the synthesis of substituted bis-

is envisaged that metallic fragments with only two cis coor- (pyrazol-1-yl)methane ligands. This approach involves the

dination sites will produce dinuclear species that could be use of solid triphosgene instead of the previously reported

in relative syn or anti dispositions. On the grounds of steric and more volatile phosgene to obtain the intermediates

hindrance, an anti orientation is expected for L1 and L2 (pz)₂CO or (pz*)₂CO.^[15a,28]These ketone intermediates

(with one benzene ring), but for ligands L3 and L4 a syn were treated with terephthaldehyde and 4,4Ј-biphenyldi-

disposition could, in principle, also be obtained. With met- carbaldehyde in toluene under reflux. Ligands L1^[19,24]and

allic fragments with more than two free positions or with L2^[24]were reported previously, but our methodology is

trans positions, the formation of coordination polymers simpler and leads to better yields. Ligands L3 and L4 are

seems reasonable. (3) To analyse the effect of the presence described here for the first time. A biphenyl ligand, but with

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mono(pyrazolyl-1-ylmethyl) groups in the para position, of the C=N bonds typical of pyrazole rings. For the com-

has recently been described.^[29]

plexes with acetate groups, the IR data can differentiate the

1

The H NMR spectra of the ligands show that the four type of coordination if one considers the difference between

pyrazolyl groups and the two α-H atoms are equivalent. the symmetric and asymmetric stretching bands. This differ-

NOE effects are observed between α-H and both 2-H of ence is 164 cm^–1in the ionic acetate and the value is similar,

the benzene rings and 5-H/5-Me of the pyrazole rings. The reduced or increased when the acetate groups are bridging,

structures of the methylated ligands L2 and L4 were deter- chelate or monodentate, respectively.^[30]In complexes 5–8,

mined by X-ray diffraction (see Solid-State Characteriza- the difference is always larger than 200 cm^–1(201–

tion).

220 cm^–1), which is consistent with a monodentate coordi-

nation, as verified for 6 by X-ray diffraction (see below).

For 13 and 14, the difference is somewhat similar to the

value for the ionic acetate (185 and 186 cm^–1) and, thus, a

bidentate bridging coordination is expected (again con-

firmed by X-ray diffraction, see below). In the IR spectra

of the Zn complexes, bands corresponding to both mono-

dentate and bidentate nitrate groups are observed (see Ex-

Synthesis and General Characterization of New Metallic

Derivatives

The behaviour of the ligands in the presence of metal

centres with different geometries and available coordination

sites was assessed by reacting L1–L4 with different Pd^II,

Zn^II, Cu^Iand Cu^IIprecursors, as outlined in Scheme 2.

Dinuclear compounds with a bis(chelate) coordination of

the ligands were obtained in all cases after the reaction of

the ligands with PdCl₂(PhCN)₂(1–4), Pd(OAc)₂(5–8) or

Zn(NO₃)₂(9–12). The structure of a least one complex from

each series was determined by X-ray diffraction (see below)

and, as a consequence, the same structure is proposed for

the rest of the complexes in each series.

The reactions of L1 and L3 with Cu(OAc)₂gave one-

dimensional zigzag coordination polymers of stoichiometry

[Cu₂(OAc)₄(μ-L)]_n[L = L1 (13), L3 (14)], which contained

Cu₂(OAc)₄units bonded to bidentate ligands. In contrast,

the reaction of L3 with the [Cu(MeCN)₄]BF₄precursor,

from which the four acetonitrile molecules can be easily re-

moved, led to a helical polymer with alternating tetracoor-

dinate ligands and Cu^Icentres (15).

–

perimental Section).^[31]For 15, which contains the BF₄

anion, the ν(B–F) band is split, which indicates a possible

decrease in the symmetry of the anions.

Solid-State Characterization

Crystals suitable for X-ray diffraction studies were ob-

tained for the ligands L2 and L4 and the complexes 1, 2, 6,

12, 13, 14 and 15. Tables with crystallographic data, a selec-

tion of bond lengths and angles, detailed data for the non-

covalent interactions and ORTEP representations are pro-

vided in the Supporting Information. The structures of the

free ligands L2 and L4 will be described first. As far as the

structures of the metal complexes are concerned, the three

dinuclear complexes containing L1 or L2 (1, 2 and 6) will

be discussed together and this is followed by a discussion

of the other dimetallic derivative (12), which contains L4.

Finally, the structures of the coordination polymers will be

covered (13 and 14 together, and finally 15).

The complexes were soluble in dimethyl sulfoxide

(DMSO) and partially soluble in methanol. Higher solubil-

ity was observed for the methylated derivatives. In the case

of the palladium dichloride complexes, those with one

phenyl ring were more soluble than the complexes contain-

ing two rings.

L2 and L4

The ligands L2 and L4 crystallize in the space groups

¯

The IR spectra of all complexes prepared in this study P1 (triclinic) and P2₁/c (monoclinic), respectively, with two

showed bands corresponding to the stretching frequencies independent molecules in the asymmetric unit (A and B).

Scheme 2. Synthesis of the new complexes 1–15.

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The two halves of each molecule are related by an inversion

The interactions between molecules of the same type (ex-

centre. A representation of the B molecules of each ligand cept for the A molecules in L4) occur through a double

is included in Figure 1. In both derivatives, the two pyrazole hydrogen bond of the type N···CH/CH···N involving the

rings of each end are arranged in an anti disposition to free nitrogen atom of one pyrazole ring of one molecule

avoid repulsion between the free electron pairs of the nitro- and α-H of the other (see Supporting Information for more

gen atoms. The two α-H atoms of each molecule (and, thus, detailed data). This bonding produces chains that extend

the two bpz*m units) are also arranged in an anti orienta- along the a axis (L2) or the c axis (L4). Despite this com-

tion. In L4, the two phenyl rings are perfectly coplanar, a mon characteristic, the three-dimensional structures of the

situation that favours electron delocalization between the two ligands are different. The chains formed with the A

two rings. In both cases, there are some differences between molecules in L2 interact with one another along the b axis

the two A and B molecules. The most important difference through a weak double CH–π interaction to form a sheet

concerns the orientation of the benzene or biphenyl frag- that extends along the ab plane. Molecules of A and B in-

ment with respect to the bpz*m units, and this is measured teract through hydrogen bonds and CH–π contacts (see

by the dihedral angle formed between the benzene (L2) or Supporting Information). In L4, the A molecules are ori-

biphenyl (L4) plane and the plane formed by the α-H, C-α ented in a zigzag fashion and are intercalated with the

and C_ipso(bonded to C-α) atoms (this angle is denoted θ; chains of B molecules. Both types of molecule interact

see Table 1). The value of θ is larger for the A molecules through hydrogen bonds.

than for the B molecules. The angle between the two pyr-

azole rings of each end is smaller for the A molecules. This

angle is clearly larger for L4 than for L2. The different rela-

tive orientations of the pyrazole and phenyl rings in the A

and B molecules in both ligands mean that two intramolec-

ular CH–π interactions between a Me group and the phenyl

ring are observed in the B molecules but not in the A mo-

lecules. Furthermore, in both molecules of the two ligands,

intramolecular CH–π interactions are observed that involve

hydrogen atoms of the phenyl rings as donors and pyrazolyl

rings as acceptors.

Structures of [(PdCl₂)₂(μ-L1)]·(Me₂CO) [1·(Me₂CO)],

[(PdCl₂)₂(μ-L2)]·(H₂O)₂[2·(H₂O)₂] and [{Pd(OAc)₂}₂-

(μ-L2)] (6)

The complexes 1, 2 and 6 crystallize in the space groups

¯

P1 (triclinic), Pna2₁(orthorhombic) and P4/n (tetragonal),

respectively. The three derivatives are dinuclear with an anti

disposition of the bpzm or bpz*m units (Figure 2). Except

for 2, there is an inversion centre in the molecules. One mo-

lecule of acetone or two of water crystallized in the struc-

tures of 1 and 2, respectively. The Pd atoms exhibit square-

planar geometries (τ₄= 0.03 for 1; 0.07 for Pd1, 0.06 for

Pd2 of 2; 0.11 for 6; a value of 0 represents a perfect square-

planar geometry)^[32]with coordination of two nitrogen

atoms of the pyrazole rings and two chlorido ligands (1

and 2) or two oxygen atoms from two monodentate acetate

groups (6). The Pd–donor-atom distances are in the ex-

pected range with values of 2.024(5)–2.055(9) Å for the Pd–

N, 2.272(3)–2.290(1) Å for the Pd–Cl (1 and 2) and

1.982(6)–1.998(5) Å for the Pd–O (6) distances. The ranges

found in the Cambridge Structural Database (CSD) for

similar systems containing pyrazolyl rings were 1.975–

2.068 Å for the Pd–N, 2.269–2.318 Å for the Pd–Cl and

1.999–2.049 Å for the Pd–O distances.

Figure 1. X-ray structure of the B molecules of (a) L2 and (b) L4.

CH–π interactions are represented as blue dashed lines.

Table 1. Selected angles [°] of the nitrogenated ligands for L2, L4, 1, 2, 6, 12, 13, 14 and 15.^[a]

Product

θ (Ph/C-α/α-H/C_ipso

)

pz–pz

NMN/N4(pz)

NCN/N4(pz)

Bite angle

L2 A*

L2 B*

L4 A*

L4 B*

1

76.8

65.0

84.4

65.9

88.5

102.1

90.7

119.2

109.6

–

155.2

138.4, 137.9

142.0

163.9

–

130.3

129.4, 129.7

130.9

128.0

–

89.9

85.1, 85.6

87.0

93.6

–

127.7

2*

85.6; 85.9

84.8

113.9, 110.7

6*

12*

13

14

15

119.0

132.6

89.4

82.2

108.2

122.9 (C-8 ring), 97.3 (C-15 ring)

120.5

80.9 (C-8 ring), 26.8 (C-15 ring)

73.0

–

93.9

160.5

128.1

[a] The products marked with * contain methylated pyrazole rings.

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Figure 2. Dimers of (a) 1, (b) 2 and (c) 6 showing the intramolec-

ular noncovalent interactions. Hydrogen bonds are in red and CH–

π and anion–π interactions are in blue and green, respectively. In

(b) and (c), the interactions at the back of the molecules are not

indicated for clarity.

The values of the angle θ in the three complexes are not

far from 90° (84–88°, Table 1), and they are relatively sim-

ilar to the angle in molecule A of the free ligand L2. The

coordination of both pyrazole rings to the metal fragments

involves a rotation of the C-α–N(pz) bonds, and the dihe-

dral pz–pz angles in this case are much larger than those in

the free ligand (from 110.69° in 2 to 127.73° in 1; see

Table 1). In the three complexes, the four hydrogen atoms

of the benzene ring form CH–π interactions with the pyr-

azole rings (see Supporting Information and Figure 2). In

6, one of the two acetate ligands of each palladium centre

has the free oxygen atom oriented towards the inside of

the molecule, and this atom forms hydrogen bonds with the

hydrogen atoms of the benzene ring. This atom is also in-

volved in an anion–π interaction with a pyrazole ring.

At both ends, the ligand forms a six-membered metalla-

cycle by coordination to the Pd atoms, and this ring adopts

the typical boat conformation. The values of the NPdN/

N4(pz) and NCN/N4(pz) dihedral angles and the bite angle

are listed in Table 1. In previous studies with bis(pyrazolyl)-

methane ligands, we found a correlation between these pa-

rameters and also the dihedral pz–pz angle with the pres-

ence or absence of methyl groups in the 3,5-positions of the

pyrazole rings.^[15a,22e]Higher values for all these parameters

are usually found for nonmethylated ligands and this may

caused by steric repulsion between the methyl groups and

the metallic fragments. This is also the case for 1, 2 and 6.

In 1, each molecule interacts on both sides with other

molecules in a head-to-tail fashion through weak hydrogen

bonds between the two chlorido ligands and hydrogen

atoms of the pyrazole rings. These interactions lead to one-

dimensional ribbons that extend along the a axis. These

Figure 3. Supramolecular ladders formed through hydrogen bond-

ing (red dashed lines). (a) Complex 1: the ladder extends along the

a axis. (b) Complex 2: the ladder extends along the b axis.

Figure 4. Sheet formed for 1 through a double hydrogen bond (in

red).

Figure 5. (a) Three-dimensional X-ray structure of 1 with different

colours for each sheet. (b) CH–π and π–π interactions between two

sheets to form the pyrazolyl embrace (region of the circle in a).

ribbons can be considered as supramolecular ladders in CH–π and π–π interactions in blue and black dashed lines, respec-

tively.

which the rungs are the benzene rings (see Figure 3).

The one-dimensional ribbons are linked by double

hydrogen bonds (Cl···HC/CH···Cl), which result in sheets

that extend along the ac plane (Figure 4). The sheets stack Figure 3b). The two water molecules also participate in the

through a combination of a double CH–π interaction and formation of hydrogen bonds in the ladders. These one-di-

π–π stacking involving pyrazole rings. This set of interac- mensional ladders are linked through hydrogen bonds to

tions is the aforementioned pyrazolyl embrace (see Fig- form sheets. These sheets are stacked along the c axis and

ure 5).

interact through hydrogen bonds as well as a double CH–π

In 2, which crystallizes as a solvate with two water mo- interaction between the methyl groups of one sheet and the

lecules, supramolecular ladders are also formed along the b pyrazole rings of the other (Figure 6). The methyl group is

axis through head-to-tail bifurcated hydrogen bonds involv- enclosed between the two pyrazole rings. The hydrogen

ing, in this case, only one chloride ion on each side (see bonds always involve the participation of chlorido ligands.

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nitrate anion and one from a monodentate nitrate anion.

The bidentate nitrate anion is not coordinated in a symmet-

ric way, and one of the Zn–O distances is longer than the

other [2.344(5) vs. 2.112(5) Å]. As in the free ligand, the two

phenyl rings are perfectly coplanar, an indication of elec-

tron delocalization through both rings (see Figure 8). The

θ angle is 89.4°, which shows that both planes are nearly

perpendicular (see Table 1). As in the previous examples,

CH–π interactions also exist with atoms of the phenyl rings

as H donors and the pyrazole rings as acceptors. In this

case, intramolecular anion–π interactions are also present,

and they involve both phenyl rings and both oxygen atoms

of the bidentate nitrate anion. Hydrogen bonds are also

formed that involve oxygen atoms (these are not indicated

in Figure 8 for the sake of clarity).

Figure 6. (a) Three-dimensional X-ray structure of 2 with two

sheets in different colours. In one region of the left-hand sheet, the

hydrogen bonds are indicated by red lines. (b) Detail of the interac-

tion between the sheets that corresponds to the circle in (a). The

CH–π interaction is shown in blue.

In the acetate complex 6, the molecules interact on both

sides through several weak hydrogen bonds involving both

free and coordinated oxygen atoms of the acetate groups

and different hydrogen atoms of the contiguous molecules.

This arrangement leads to a one-dimensional chain that ex-

tends along the c axis (Figure 7a). These infinite chains are

surrounded by four other chains with different orientations

to generate the 3D supramolecular structure (Figure 7b).

The interaction between the chains occurs through hydro-

gen bonds involving one oxygen atom of one acetate group

and a CH–π contact involving pyrazole rings.

Figure 8. X-ray molecular structure of 12 with the noncovalent in-

tramolecular interactions shown. CH–π and anion–π interactions

are in blue and green, respectively. The CH–π interactions at the

back are not indicated.

As in the previously discussed complexes, the ligand

forms a six-membered metallacycle by coordination to the

Zn atoms, and this ring adopts a boat conformation. How-

ever, in this case the region of the metal centre is flatter,

and the NMN/N4(pz) angle (163.92°) is larger than that in

the square-planar complexes; this indicates possible steric

hindrance between the bidentate nitrate anion and the bi-

phenyl fragment. Coincidentally, larger values for this angle

have been found, for example, in octahedral derivatives.^[23a]

In 12, with this disposition, the aforementioned anion–π

interaction is established with an appropriate distance (Fig-

ure 8). The other structural parameters of the ligand (see

Table 1) are also different from those found for 1, 2 and 6.

Molecules of the dinuclear complex interact on both

sides, and this leads to the formation of a chain that extends

along the [101] direction (see Figure 9a). In this structure,

three kinds of interactions are present: (1) hydrogen bonds

on the upper and lower sides of the chain involving nitrate

Figure 7. X-ray structure of 6. (a) One-dimensional chain along the

c axis. Hydrogen bonds are indicated as red dashed lines. H atoms

are omitted for clarity. (b) View of the three-dimensional supra-

molecular structure along the c axis.

Structure of [{Zn(NO₃)₂}₂(μ-L4)]·DMF (12)

Complex 12 crystallizes in the monoclinic space group and methyl groups; (2) bifurcated anion–π interactions be-

P2₁/c and is also a dinuclear complex with the metallic frag- tween an oxygen atom of the monodentate nitrate anion

ments in an anti disposition with an inversion centre. The and two pyrazole rings; (3) an interaction between two oxy-

coordination number of the Zn ion is five, and the τ₅value gen atoms of adjacent molecules (O6–O6 2.874 Å).^[34]The

of 0.014 reflects a square-pyramidal structure [τ₅= 1: trigo- chains interact through hydrogen bonds to form sheets. The

nal-bipyramidal (tbp); τ₅= 0: square-pyramidal].^[33]The sheets, which stack in two different orientations, are as-

metallic centre is bonded to two nitrogen atoms of the pyr- sembled through hydrogen bonds to complete the 3D sup-

azole rings and three oxygen atoms, two from a bidentate ramolecular structure (see Figure 9b).

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Figure 10. Polymer chains of (a) 13 and (b) 14. Hydrogen atoms

have been omitted for clarity.

Figure 9. X-ray structure of 12. (a) Chain formed by the interaction

of the dimers through noncovalent interactions. Hydrogen bonds

in red, anion–π interactions in green and O···O contacts in purple.

Although not indicated for the sake of clarity, all the interactions

are present in each contact between two molecules. H atoms are

omitted. (b) Three-dimensional structure viewed along the c axis

showing the stacking of the sheets.

The θ angle for 13 is 82.2°, and this is similar to those in

the previously discussed complexes (Table 1). The situation

is different in 14. Firstly, the two phenyl rings are not copla-

nar and have a dihedral angle of 40.96°. This reflects a de-

crease in the degree of electron delocalization between the

two rings in comparison to that found in L4. This is the

case both in the free ligand and in 12, in which the two

rings are perfectly coplanar. Furthermore, the two θ angles

are very different and have values of 80.9 (ring with C-8)

and 26.8° (ring with C-15).

Structure of [Cu₂(CH₃COO)₄(μ-L1)]_n(13) and

[Cu₂(CH₃COO)₄(μ-L3)]_n(14)

Complexes 13 and 14 are zigzag coordination polymers

There are several weak intramolecular interactions in the

that run along the c axis for 13 and the a axis for 14 (Fig- coordination polymers, and these include hydrogen bonds

¯

ure 10). The space groups are P1 (triclinic) and P2₁/c (mo- either involving oxygen atoms of the acetate groups or ni-

noclinic) for 13 and 14, respectively. The complexes com- trogen atoms of the non-coordinated pyrazole. CH–π inter-

prise dicopper(II) tetraacetate paddle-wheel units that be- actions similar to those found in the previous derivatives,

have as linear-directional units that alternate with the corre- that is, involving both pyrazole rings as acceptors and the

sponding ligands. The asymmetric unit contains half of a hydrogen atoms of the phenyl rings as donors, are also pres-

dimer. A dinuclear copper motif is formed, because inver- ent.

sion centres are present in the middle of the metallic frag-

The supramolecular structures of 13 and 14 are different,

ment and in the centre of the arene ring. In the paddle- and this will be explained separately. In 13, the presence of

wheel units, each copper atom is bonded to the oxygen a non-coordinated pyrazole ring makes it possible to form

atoms of the four bridging acetate groups and one pyrazole double hydrogen bonds of the type N···HC/CH···N (involv-

ring of the ligand. The separation between the copper ing 3Ј-H of the non-coordinated pyrazole ring), which are

atoms is 2.618(2) Å in 13 and 2.613(2) Å in 14, within the fairly similar to those found in the free ligands L2 and L4.

normal range found in other reported paddle-wheel This interaction results in the formation of sheets that ex-

units.^[35]In each bpzm unit, only one pyrazole ring is coor- tend along the (220) plane (Figure 11a). The 3D structure

dinated, and the two rings are arranged in an anti disposi- is formed by the stacking of the sheets through different

tion. The distinct nature of the two pyrazole rings means hydrogen bonds with the participation of oxygen atoms

that the C-α atoms are chiral in both complexes, and both (Figure 11b).

types of stereogenic centre alternate in the polymers. As in

In the supramolecular structure of 14, the chains interact

the previous complexes, the metallic fragments are also lo- to form a sheet in the ac plane. When viewed along the c

cated on opposite sides of the plane formed by the phenyl axis, the zigzag polymers are seen in these sheets as alternat-

(13) or biphenyl rings (14). The torsion angle N1–Cu1– ing waves that are out of phase (see Figure 12a). In contrast

Cu1–N1 is 180.0° in 13 and 177.5° in 14. The Cu–O bond to 13 and ligands L1 and L2, complex 14 does not show

lengths are in the range 1.957(7)–1.981(7) Å. The Cu–N any double hydrogen bonds. However, this nitrogen atom

bond length in 13 is 2.193(5) Å, and in 14 the values are participates in the interaction between chains that are “out

2.172(8) and 2.181(8) Å, in the expected range for these of phase”, along with other hydrogen bonds involving an

types of bonds. For species with paddle-wheel units bonded oxygen atom of an acetate group. The contact between

to nitrogen atoms, the ranges found in the CSD for the these chains is completed with CH–π interactions involving

Cu–O and Cu–N distances were 1.924–2.021 Å and 1.991– the two phenyl rings, which act both as donors and ac-

2.326 Å, respectively.

ceptors (see Figure 12b). The formation of these interac-

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helical pitch of 15 is 17.10 Å and it comprises two Cu

centres and two ligands.

Figure 11. X-ray structure of 13. (a) Formation of sheets by inter-

actions through double hydrogen bonds (red dashed lines) between

the chains. (b) Stacking of the sheets to complete the three-dimen-

sional structure. In one area, the double hydrogen bonding between

chains is highlighted.

tions may cause the lack of coplanarity of the two phenyl

rings. Contiguous chains that are “in phase” interact

through hydrogen bonds and also a CH–π interaction with

the coordinated pyrazole ring as acceptor. Parallel sheets

are assembled along the b axis through hydrogen bonds,

and the sheets are offset by a/2.

Figure 13. X-ray structure of 15. (a) Structure of the helix.

(b) Schematic representation of the racemic helix. (c) Hydrogen

bonds (red lines) and CH–π interactions (blue lines) that may con-

tribute to the folding of the helix.

The parameters related to the metallacycle formed after

coordination of the ligand (see Table 1) differ from those in

systems containing square-planar metal ions, and they are

more similar (except the pz/pz angle) to those found for 12,

which has a pentacoordinate Zn centre. As in 12, the NMN/

N4 angle is larger (160.5°) than those in 1, 2 and 6, and

this indicates greater planarity in this part of the metallacy-

cle. This situation is possibly caused by steric restrictions

between a pyrazole and a phenyl ring that are quite close

to one another.

There are several noncovalent intramolecular interac-

tions that may have an influence on the folding of the helix,

mainly the hydrogen bonds between the phenyl rings and

the BF₄^–anions. There is a double hydrogen bond involving

a single anion and two phenyl rings from two different li-

gands bonded to the same metallic centre (H12–F1–B1–F1–

H12, d_H12–F1= 2.52 Å; see Figure 13c). There is also a CH–

π interaction with a pyrazole ring as donor and a phenyl

ring as acceptor, and this involves the same pair of ligands

(see Figure 13c). In addition, there are other weaker CH–π

interactions with H atoms of the phenyl rings as donors

and pyrazole rings as acceptors, but these are from the same

ligand, and it is not expected that they would have a marked

influence on the structure of the helix.

Figure 12. (a) Three-dimensional X-ray structure of 14. Two dif-

ferent sheets with polymers in pink and blue or in green and purple

are shown. (b) Complex system of CH–π interactions between the

phenyl rings. It corresponds, for example, to the region indicated

with a circle in (a) but viewed from another perspective.

Structure of [Cu(μ-L3)]_n(BF₄)_n(15)

Complex 15 crystallizes in the monoclinic space group

C2/c. The complex has a helical structure with alternating

ligands and Cu^Icentres. There are two possible helical coor-

dination assemblies from achiral building blocks: racemic

[(P) and (M), centrosymmetric space group] and chiral [(P)

or (M), non-centrosymmetric space group] helical crys-

tals.^[36]In this case, the group is centrosymmetric, and the

helix is arrayed in an alternating right handed (P), left-han-

ded (M) fashion in the solid state and, thus, it is racemic

(Figure 13a and b). The helix runs along the [101] direction.

The biphenyl unit is linear, and, therefore, the helix forms

because of the skewed orientation of the [Cu(bpz)₂] frag-

ments, which act as angular-directional units. The local ge-

ometry around the copper ion approximates a tetrahedral

arrangement with a τ₄value of 0.84.^[32]The bite angle is

93.94°, and the Cu–N distances are 2.046(7) and

2.011(6) Å. In a way similar to L4 and 12 (with L4), the two

phenyl rings are perfectly coplanar, which indicates electron

delocalization between the two rings. This situation is dif-

ferent to that found in 14 and signifies that the lack of plan-

arity in 14 is not typical of L3 but is probably caused by a

special characteristic of the complex. The value of the θ

Figure 14. Three-dimensional structure of 15 showing how each

chain (one colour) is surrounded by another four. The circle repre-

angle is 73.0°, and this is not far from orthogonality. The sents one position in which the pyrazolyl embrace is present.

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As far as the three-dimensional structure is concerned, served (8% at room temperature and 17% at 80 °C) in ad-

there are interactions between contiguous chains through dition to a broadening of all of the signals owing to the

–

hydrogen bonds involving the BF₄anions, which act as existence of interchange processes between both compo-

bridges in such a way that each chain is surrounded by an- nents. The process was reversible. As expected, the coordi-

1

other four (see Figure 14). The pyrazolyl embrace also ex- nation of the pyrazole rings causes a shift in the H NMR

ists between the bpzm groups of different helices.

resonances to higher frequency with respect the signals of

the free ligand. The most marked changes correspond to

the signals for 5Ј-H and α-H. For the phenyl resonances, a

small shift towards higher frequencies is usually detected.

However, in the case of the Pd dichloride non-methylated

derivatives 1 and 3, the signals of the protons of this ring

are shifted to lower frequencies by 0.4 ppm. These protons

can participate in the formation of CH–π interactions (as

observed in the structures determined by X-ray diffraction,

see above), and the resonance positions may be an indica-

tion that the interaction is maintained in solution. This

phenomenon is not observed for 2 and 4 maybe because of

the existence of weaker interactions in these complexes. A

comparison of these CH–π interactions in the solid-state

structures of 1 and 2 shows that they are weaker for the

methylated derivative 2 (see Table S7 of the Supporting In-

formation).

Thermogravimetric Analysis of 13

As there is interest in paddle-wheel polymers owing to

their potential magnetic or electronic properties,^[37]their

stability was assessed by thermogravimetric analysis of crys-

tals of 13. The thermogravimetric analysis/differential ther-

mal analysis (TGA/DTA) curves (see Supporting Infor-

mation) show multistep decomposition. Complex 13 grad-

ually loses weight in three steps accompanied by endother-

mic peaks, and these should correspond to decomposition

events. The process starts at ca. 200 °C and finishes at ca.

380 °C.

Behaviour in Solution

The Zn complexes 9–12 showed different behaviour de-

The behaviour of the complexes in solution was studied pending on the presence or absence of methyl groups in the

1

by H and ¹³C{¹H} NMR spectroscopy and by mass spec- pyrazole rings. For these complexes, it was possible to re-

trometry (FAB+ or MALDI-TOF; see Tables S8–S10).

cord the spectra with samples in [D₄]methanol. For 9 and

In the mass spectra, peaks for the same types of frag- 11, resonances corresponding to the free ligand were ob-

ments were generally observed for the products in the same tained, and this provides evidence of ligand decoordination.

series (1–4, 5–8 and 9–12). Complexes 3 and 4 are very in- For the methylated derivatives 10 and 12, a large number

soluble, and only small peaks were observed that corre- of broad signals were observed. This is consistent with the

sponded to dinuclear fragments. For 1 and 2, the most in- existence of several products, probably because of an ex-

tense peaks also correspond to the dinuclear species change process. This should correspond to the formation

[M₂LX₂]⁺and [M₂LX]⁺. For the palladium acetate deriva- of different species in solution and not to the presence of

tives, although the most intense peak usually corresponds impurities in the samples, because crystals with good ele-

1

to [MLX]⁺, there are also intense peaks corresponding to mental analysis data were used. The H NMR spectra of

species with the group [M₂L] and different numbers of acet- 10 was also recorded at 60 °C. The eight broad signals ob-

ate groups. All of the Zn derivatives exhibit a peak of vari- served at room temperature were transformed into three

able intensity for the [M₂LX₃]⁺fragment and an intense very broad resonances (see Supporting Information) that

peak for [MLX]⁺. Bearing these results in mind, we propose should correspond to α-H, 4Ј-H and the protons of the

that the dinuclear character is maintained in solution, at phenyl ring of the interchanging species. The ¹H NMR

least in part, for 1–12. For the polymeric derivatives 13–15, spectra of 10 and 12 were also obtained with samples in

peaks corresponding to different fragmentations are ob- [D₆]DMSO, but only signals corresponding to free ligand

served. [ML₂]⁺is a common peak for the three derivatives, were obtained. All these data are indicative of an easier

and peaks corresponding to dinuclear fragments are also dissociation of the ligands in the Zn complexes, a process

observed for 13 and 15.

that is even more pronounced in the non-methylated deriva-

1

The H and ¹³C NMR spectra of the palladium com- tives.

plexes 1–8 were recorded with samples in [D₆]DMSO, be-

Complex 15 was also rather insoluble, and it was neces-

cause the products were not soluble in other less-coordinat- sary to record the ¹H and ¹³C{¹H} NMR spectra with sam-

ing solvents. Signals of a new product, that is, different from ples in [D₆]DMSO. In both spectra, resonances correspond-

those of the free ligand and with equivalent α-H atoms and ing to a single product, which was not the free ligand, were

bis(pyrazolyl)methane units, were observed for the major obtained. With the exception of one resonance of the

component, but other minor resonances (2–18% depending phenyl rings, the signals were broad, and this could indicate

on the product) were also present. Some of the minor sig- possible exchange processes between different species.

nals were similar to those of the free ligand, and we propose

that species with partial decoordination of the ligand were

Conclusions

present owing to the coordination of the DMSO molecules.

1

A H NMR spectrum of 1 was recorded at 80 °C, and an

Two new all-nitrogen donor ditopic ligands, p-bis[bis-

increase of the amount of the minor component was ob- (pyrazol-1-yl)methyl]biphenyl (L3) and p-bis[bis(3,5-di-

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methylpyrazol-1-yl)methyl]biphenyl (L4), have been synthe- ally observed by NMR spectroscopy. The M–N bonds in

sized. Their coordination chemistry, along with that of the the Zn derivatives with non-methylated ligands are the most

ligands containing a phenyl spacer between the bis(pyrazo- labile.

lyl)methane units (L1 and L2), has been explored with dif-

ferent metallic fragments.

The new complexes could be useful as secondary build-

ing units for the construction of more complex materials

When the metal centre has other ligands coordinated and through the “two-step self-assembly” methodology. The li-

two vacant coordination sites with a cis disposition are gands coordinated to the metal ions in the dinuclear com-

available, the formation of dinuclear species with an anti plexes could be removed, and the non-coordinated pyrazole

orientation of the metallic units is always observed. This is rings of the paddle-wheel derivatives could be used to incor-

even the case for the longer biphenyl spacer for which steric porate other metallic fragments.

hindrance between the metallic fragments is not expected.

The dinuclear derivatives contain PdCl₂, Pd(OAc)₂and

Zn(NO₃)₂units, and the ligands behave in a bis(bidentate)

chelating manner with the formation of metallacycles on

both sides.

Experimental Section

General Comments: The syntheses of the ligands and palladium

and copper(I) complexes were performed under nitrogen by using

The reactions of L1 and L3 with Cu(OAc)₂produced

standard Schlenk techniques. The rest of the reactions were per-

zigzag polymers with dicopper tetraacetate paddle-wheel

formed in air. Elemental analyses were performed with a Thermo

fragments that behave as linear-directional units and alter-

Quest Flash EA1112 microanalyzer. The IR spectra of solid sam-

nate with the corresponding ligands. Only one pyrazole ring

ples were recorded with a Shimadzu IRPRESTIGE-21 (4000–

of each end of the ligand is coordinated in these complexes.

The reaction with a precursor of a “bare” Cu^Icentre,

[Cu(CH₃CN)₄](BF₄), also leads to the formation of a chain,

600 cm^–1) spectrophotometer equipped with an attenuated total re-

flectance (ATR) system. Mass spectrometry measurements were

performed with an Applied Biosystems Voyager DE STR matrix-

but in this case it is a helical racemic polymer composed of assisted laser desorption/ionization time-of-flight (MALDI-TOF)

Cu^Icentres and bis(bidentate) chelating ligands. The helix

system. The FAB+ mass spectrometry measurements were obtained

with a Thermo MAT95XP mass spectrophotometer with a mag-

netic sector. Thermogravimetric analysis (TGA) and differential

is racemic, because it is arrayed in an alternating right-han-

ded (P), left-handed (M) fashion.

thermal analysis (DTA) were performed with an ATDTG SETA-

Some parameters of the ligands, including the bite angle

RAM apparatus with a 92-16.18 graphite oven and CS32 control-

and the NMN/N4 dihedral angle, are influenced by the

ler. The analyses were performed without the application of an ini-

presence of methyl groups on the pyrazole rings and mainly

tial vacuum and with a heating rate of 5 °C/min under an air flow

by the geometry of the metallic centre. For the derivatives

with ligands containing a biphenyl unit, the two rings are

coplanar except in the case of the paddle-wheel copper

complex.

Several noncovalent interactions have been observed in

the supramolecular structure, including hydrogen-bonding,

CH–π, anion–π and π–π interactions. The non-coordinating

pyrazole rings in the free ligands or in the paddle-wheel

complex with L1 participate in double N···HC/CH···N

hydrogen bonds. In the dinuclear complexes, the noncova-

lent interactions lead to the formation of ribbons that ar-

range in different ways to yield the 3D structure. It is pro-

posed that a complex system of CH–π interactions involv-

in a platinum crucible. ¹H, ¹³C{¹H} and ¹⁹F{¹H} NMR spectra

were recorded with Varian Gemini 400 and Inova 500 spectrome-

ters. Chemical shifts (ppm) are relative to tetramethylsilane (¹H,

¹³C NMR) and CFCl₃(¹⁹F NMR). Coupling constants (J) are in

Hertz. The NOE difference spectra were recorded with a 5000 Hz

spectral width, an acquisition time of 3.27 s, a pulse width of 90°,

a relaxation delay of 4 s, an irradiation power of 5–10 dB and 240

scans. The standard VARIAN pulse sequences were used (VNMR

6.1 C software) to obtain ¹H–¹³C gradient heteronuclear multiple

quantum coherence (g-HMQC) and g-HMBC spectra. The spectra

were acquired with 7996 (¹H) and 25133.5 Hz (¹³C) spectral widths;

16 transients of 2048 data points were collected for each of the 256

increments. For variable-temperature spectra, the probe tempera-

ture (Ϯ1 K) was controlled by a standard unit calibrated with a

ing the phenyl rings both as donors and acceptors is the methanol reference. In the NMR spectroscopic data, s, d, m and

br. refer to singlet, doublet, multiplet and broad signals, respec-

tively. The carbon resonances are singlets. The ligands L1 and L2

were described previously in the literature, but in this work they

were prepared by a different methodology, which is described in

this section.^[15a]The NMR spectroscopic data of samples in [D₆]-

DMSO and [D₄]methanol are included for comparison with the

possible reason for the non-coplanarity of the two rings in

the paddle-wheel copper complex. CH–π interactions and

hydrogen bonds involving the counteranions are the prob-

able reason for the folding of the helical polymer. The pyr-

azolyl embrace is observed in all of the derivatives that con-

tain non-methylated pyrazolyl groups and chelating ligands.

This set of interactions is not observed when methyl substit-

uents are present in these rings, and this possibly reflects

the lower tendency of these heterocycles to exhibit π–π in-

teractions. However, there is a tendency for the methyl

groups to be located in the same region of space, possibly

because of hydrophobic contacts.

[39]

data of the complexes. [PdCl₂(PhCN)₂]^[38]and [Cu(MeCN)₄]BF₄

were prepared according to literature procedures. The salts

Pd(OAc)₂, Zn(NO₃)₂·6H₂O and [Cu₂(OAc)₄]·2H₂O were purchased

from Aldrich and were used without further purification.

X-ray Crystallography: A summary of the crystal data collection

and refinement parameters for all compounds is given in the Sup-

porting Information. Single crystals of L2, L4, 1·C₂H₆O, 2·2H₂O,

6, 12·DMF, 13, 14 and 15·DMF were mounted on a glass fibre and

transferred to a Bruker X8 APEX II CCD-based diffractometer

The solution behaviour of the compounds has been ana-

lyzed. Evidence for dinuclear species was found in the mass

spectra, and partial decoordination of the ligands was usu- equipped with a graphite-monochromated Mo-K_αradiation source

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(λ = 0.71073 Å). The highly redundant datasets were integrated by

using SAINT^[40]and corrected for Lorentz and polarization effects.

The absorption corrections were based on fitting a function to the

empirical transmission surface as sampled by multiple equivalent

measurements with the program SADABS.^[41]The software pack-

age SHELXTL (version 6.10)^[42]was used for space-group determi-

nation, structure solutions and refinement by full-matrix least-

squares methods based on F². A successful solution by direct meth-

ods provided most non-hydrogen atoms from the E-map. The re-

maining non-hydrogen atoms were located in an alternating series

of least-squares cycles and difference Fourier maps. All non-hydro-

gen atoms were refined with anisotropic displacement coefficients

unless specified otherwise. Hydrogen atoms were placed by using a

“riding model” and included in the refinement at calculated posi-

tions. Complexes 1 and 6 crystallized with some disordered acetone

solvent molecules. For 1, only one acetone molecule was found in

the difference Fourier map. In all other cases, a correct model could

not be defined and, therefore, the squeeze command^[43]was used

to eliminate the contribution of the electron density in the solvent

region from the intensity data. The solvent-free model was em-

ployed for the final refinement. Complex 12 crystallized with one

molecule of highly disordered N,N-dimethylformamide (DMF) sol-

vent. During the structure refinement, the positions of these atoms

were located initially, and it was then necessary to fix them and

refine them isotropically. The crystals of 6, 14 and 15 were very

weakly diffracting. As a result, for 15, it was only possible to locate

half a BF₄^–counterion per copper atom. The other half BF₄^–anion

was delocalized in one principal void with some disordered DMF

molecules. As it was difficult to obtain a satisfactory model of the

solvent molecules and anion within this void, the contributions of

L3: bpzCO (1.5 g, 9.0 mmol) and 4,4Ј-biphenyldicarbaldehyde

(0.6 g, 3.0 mmol) were mixed in toluene (50 mL) and heated at re-

flux for 7 d. The colourless solution was concentrated, and addition

of pentane precipitated L3 as a white solid, which was collected by

filtration and dried under vacuum. Yield: 0.80 g, 60%. C₂₆H₂₂N₈

(446.51): calcd. C 69.94, H 4.97, N 25.09; found C 70.22, H 4.71,

1

N 24.87. H NMR (500 MHz, [D₆]DMSO, 25 °C): δ = 6.36 (m, 4

H, 4Ј-H), 7.10 (d, J = 8.0 Hz, 4 H, 2-H, 6-H), 7.60 (br. s, 4 H, 3Ј-

H), 7.67 (d, J = 8.0 Hz, 4 H, 3-H, 5-H), 7.89 (d, J = 2.2 Hz, 4 H,

5Ј-H), 8.11 (s, 2 H, α-H) ppm. ¹H NMR (400 MHz, [D₄]methanol,

25 °C): δ = 6.43 (m, 4 H, 4Ј-H), 7.14 (d, J = 8.2 Hz, 4 H, 2-H, 6-

H), 7.65 (d, J = 1.5 Hz, 4 H, 3Ј-H), 7.69 (d, J = 8.2 Hz, 4 H, 3-H,

5-H), 7.74 (d, J = 2.4 Hz, 4 H, 5Ј-H), 7.95 (s, 2 H, α-H) ppm.

¹³C{¹H} NMR (125 MHz, [D₆]DMSO, 25 °C): δ = 76.39 (C-α),

106.76 (C-4Ј), 127.40 (C-3, C-5), 127.96 (C-2, C-6), 130.88 (C-5Ј),

136.93 (C-1), 140.28 (C-4), 140.57 (C-3Ј) ppm. IR (ATR): ν = 1506

˜

ν(C=N/C=C) cm^–1.

L4: bpz*CO (1.5 g, 6.9 mmol) and 4,4Ј-biphenyldicarbaldehyde

(0.4 g, 1.7 mmol) were mixed in toluene (50 mL) and heated at re-

flux for 7 d. The colourless solution was concentrated, and addition

of pentane precipitated L4 as a white solid, which was collected by

filtration and dried under vacuum. Yield: 0.65 g, 68%. C₃₄H₃₈N₈

(558.73): calcd. C 73.09, H 6.86, N 20.05; found C 73.26, H 6.61,

1

N 20.35. H NMR (500 MHz, [D₆]DMSO, 25 °C): δ = 2.09 (s, 12

H, 5Ј-Me), 2.14 (s, 12 H, 3Ј-Me), 5.92 (s, 4 H, 4Ј-H), 7.08 (d, J =

8.4 Hz, 4 H, 2-H, 6-H), 7.68 (d, J = 8.4 Hz, 4 H, 3-H, 5-H), 7.75

(s, 2 H, α-H) ppm. ¹H NMR (400 MHz, [D₄]methanol, 25 °C): δ =

2.10 (s, 24 H, 5Ј-Me, 3Ј-Me), 5.96 (s, 4 H, 4Ј-H), 7.01 (d, J = 7.3 Hz,

4 H, 2-H, 6-H), 7.63 (s, 2 H, α-H), 7.66 (d, J = 7.3 Hz, 4 H, 3-H,

5-H) ppm. ¹³C{¹H} NMR (125 MHz, [D₆]DMSO, 25 °C): δ =

11.53 (5Ј-Me), 13.95 (3Ј-Me), 72.54 (C-α), 106.80 (C-4Ј), 126.98 (C-

3, C-5), 128.35 (C-2, C-6), 136.58 (C-1), 139.76 (C-4), 140.70 (C-

–

all of the electron density in the void, including that of the BF₄

ion, were subtracted from the observed structure factors.^[43]The

–

5Ј), 147.37 (C-3Ј) ppm. IR (ATR): ν = 1556 ν(C=N/C=C) cm^–1.

presence of an extra BF₄anion is needed to balance the charge,

˜

–

but it has been proved by NMR measurements that the BF₄/Cu

[(PdCl₂)₂(μ-L1)] (1): The product was obtained by careful diffusion

of an acetone solution (1 mL) of L1 (10.0 mg, 0.027 mmol) into an

acetone solution (2 mL) of [PdCl₂(PhCN)₂] (20.0 mg, 0.054 mmol);

acetone (1 mL) was used as the middle phase to slow the diffusion.

Some orange crystals were suitable for an X-ray diffraction study.

The rest of the sample was dried under vacuum. Yield: 8.8 mg

(45%). C₂₀H₁₈Cl₄N₈Pd₂·0.5Me₂CO (725.03 + 29.0): calcd. C 34.25,

H 2.81, N 14.86; found C 34.15, H 2.31, N 15.25. ¹H NMR

(500 MHz, [D₆]DMSO, 25 °C): δ = 6.67 (s, 4 H, Ph-H), 6.72 (m, 4

H, 4Ј-H), 8.08 (br. s, 4 H, 3Ј-H), 8.61 (br. s, 4 H, 5Ј-H), 8.77 (s, 2

H, α-H) ppm. ¹³C{¹H} NMR (125 MHz, [D₆]DMSO, 25 °C): δ =

74.20 (C-α), 108.06 (C-4Ј), 126.72 (C-Ph), 137.11 (C-5Ј), 144.94 (C-

ratio is 1:1 (see below). CCDC-951864 (for 1), -951865 (for 2),

-951866 (for 6), -951867 (for 12), -951868 (for 13), -951869 (for

14), -951870 (for 15), -951871 (for L2) and -951872 (for L4) contain

the supplementary crystallographic data for this paper. These data

can be obtained free of charge from The Cambridge Crystallo-

graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

L1: bpzCO (1.5 g, 9.0 mmol) and terephthaldehyde (0.6 g,

4.5 mmol) were mixed in toluene (50 mL) and heated at reflux for

72 h. The colourless solution was concentrated, and the residue was

washed with pentane to afford (bpzm)₂C₆H₄as a white solid. Yield:

1.45 g, 87%. The spectroscopy data agree with the results pre-

viously described. ¹H NMR (500 MHz, [D₆]DMSO, 25 °C): δ =

6.36 (m, 4 H, 4Ј-H), 7.08 (s, 4 H, Ph-H), 7.59 (br. s, 4 H, 3Ј-H),

7.88 (br. s, 4 H, 5Ј-H), 8.09 (s, 2 H, α-H) ppm. ¹H NMR (400 MHz,

[D₄]methanol, 25 °C): δ = 6.40 (m, 4 H, 4Ј-H), 7.09 (s, 4 H, Ph-H),

7.63 (d, J = 1.2 Hz, 4 H, 3Ј-H), 7.73 (d, J = 2.5 Hz, 4 H, 5Ј-H),

3Ј) ppm. MS (MALDI-TOF, BP): m/z (%)

= 654 (100)

[Pd (L1)(Cl )]⁺, 619 (87.5) [Pd (L1)(Cl)]⁺. IR (ATR): ν = 1517

˜

2

ν(C=N/C=C) cm^–1.

[(PdCl₂)₂(μ-L2)] (2): The product was obtained by careful diffusion

of an acetone solution (1 mL) of L2 (10.0 mg, 0.021 mmol) into an

acetone solution (2 mL) of [PdCl₂(PhCN)₂] (15.0 mg, 0.042 mmol);

acetone (1 mL) was used as the middle phase to slow the diffusion.

Some orange crystals were suitable for an X-ray diffraction study.

The rest of the sample was dried under vacuum. Yield: 7.0 mg

(40%). C₂₈H₃₄Cl₄N₈Pd₂(837.24): calcd. C 40.17, H 4.09, N 13.38;

7.93 (s, 2 H, α-H) ppm. IR (ATR): ν = 1514 ν(C=N/C=C) cm^–1.

˜

L2: bpz*CO (1.5 g, 6.9 mmol) and terephthaldehyde (0.5 g,

3.4 mmol) were mixed in toluene (50 mL) and heated at reflux for

72 h. The colourless solution was concentrated, and the residue was

washed with pentane to afford (bpz*m)₂C₆H₄as a white solid.

Yield: 1.5 g, 91%. The spectroscopy data agree with the results pre-

viously described. ¹H NMR (500 MHz, [D₆]DMSO, 25 °C): δ =

1

found C 40.08, H 4.01, N 13.65. H NMR (500 MHz, [D₆]DMSO,

25 °C): δ = 2.43 (s, 12 H, 3Ј-Me), 2.53 (s, 12 H, 5Ј-Me), 6.26 (s, 4

H, 4Ј-H), 7.17 (s, 4 H, Ph-H), 8.33 (s, 2 H, α-H) ppm. ¹³C{¹H}

NMR (125 MHz, [D₆]DMSO, 25 °C): δ = 11.41 (5Ј-Me), 15.09 (3Ј-

2.07 (s, 12 H, 5Ј-Me), 2.12 (s, 12 H, 3Ј-Me), 5.90 (m, 4 H, 4Ј-H),

1

6.98 (s, 4 H, Ph-H), 7.71 (s, 2 H, α-H) ppm. H NMR (400 MHz, Me), 69.38 (C-α), 108.57 (C-4Ј), 128.34 (C-Ph), 145.04 (C-5Ј),

[D₄]methanol, 25 °C): δ = 2.17 (s, 12 H, 5Ј-Me), 2.18 (s, 12 H, 3Ј-

154.18 (C-3Ј) ppm. MS (MALDI-TOF, BP): m/z (%) = 766 (100)

Me), 5.95 (m, 4 H, 4Ј-H), 6.94 (s, 4 H, Ph-H), 7.65 (s, 2 H, α-H) [Pd (L2)Cl ]⁺, 731 (75.2) [Pd (L2)Cl]⁺. IR (ATR): ν = 1556 ν(C=N/

˜

2

ppm. IR (ATR): ν = 1552 ν(C=N/C=C) cm^–1.

C=C) cm^–1.

˜

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[(PdCl₂)₂(μ-L3)] (3): Orange crystals of the product were obtained

by careful diffusion of an acetone solution (1 mL) of L3 (10.0 mg,

0.022 mmol) into a DMF solution (2 mL) of [PdCl₂(PhCN)₂]

(17.0 mg, 0.044 mmol); acetone (1 mL) was used as the middle

phase to slow the diffusion. Yield: 7.4 mg (42%). C₂₆H₂₂Cl₄N₈Pd₂

(801.13): calcd. C 38.98, H 2.77, N 13.99; found C 38.62, H 2.52,

[{Pd(OAc)₂}₂(μ-L3)] (7): The product was obtained by careful dif-

fusion of an acetone solution (1 mL) of L3 (10.0 mg, 0.022 mmol)

into a DMF solution (2 mL) of Pd(OAc)₂(10.0 mg, 0.044 mmol).

The yellow solid was collected by filtration and dried under vac-

uum. Yield: 3.7 mg (19%). C₃₄H₃₄N₈O₈Pd₂(895.49): calcd. C

1

45.60, H 3.83, N 12.51; found C 45.29, H 3.81, N 12.37. H NMR

(400 MHz, [D₆]DMSO, 25 °C): δ = 1.72 (s, 12 H, Me-OAc), 6.68

1

N 13.26. H NMR (400 MHz, [D₆]DMSO, 25 °C): δ = 6.70 (d, J

= 8.2 Hz, 4 H, 2-H, 6-H), 6.74 (m, 4 H, 4Ј-H), 7.93 (d, J = 8.2 Hz, (m, 4 H, 4Ј-H), 7.14 (d, J = 8.6 Hz, 4 H, 2-H, 6-H), 7.65 (d, J =

4 H, 3-H, 5-H), 8.1 (br. s, 4 H, 3Ј-H), 8.59 (d, J = 2.2 Hz, 4 H, 5Ј- 2.3 Hz, 4 H, 3Ј-H), 7.85 (d, J = 8.6 Hz, 4 H, 3-H, 5-H), 8.55 (d, J

H), 8.68 (s, 2 H, α-H) ppm. ¹³C{¹H} NMR (100 MHz, [D₆]DMSO,

= 3.0 Hz, 4 H, 5Ј-H), 8.63 (s, 2 H, α-H) ppm. ¹³C{¹H} NMR

25 °C): δ = 70.49 (C-α), 102.63 (C-4Ј), 119.60 (C-2, C-6), 125.25 (100 MHz, [D₆]DMSO, 25 °C): δ = 23.66 (Me-OAc), 74.25 (C-α),

(C-5Ј), 132.84 (C-3, C-6), 136.68 (C-3Ј) ppm. MS (FAB+, 3-NBA):

108.37 (C-4Ј), 127.05 (C-2, C-6), 127.93 (C-3, C-5), 136.51 (C-5Ј),

144.49 (C-3Ј), 174.01 (CO) ppm. MS (FAB+, 3-NBA): m/z (%) =

837 (9.8) [Pd₂(L3)(OAc)₃]⁺, 778 (30.2) [Pd₂(L3)(OAc)₂]⁺, 719 (60.3)

m/z (%) = 767 (100) [Pd (L3)Cl ]⁺. IR (ATR): ν = 1516 ν(C=N/

˜

2

3

C=C) cm^–1.

[Pd (L3)(OAc)]⁺, 611 (100) [Pd(L3)(OAc)]⁺. IR (ATR): ν = 1631

˜

2

[(PdCl₂)₂(μ-L4)] (4): Orange crystals of the product were obtained

by careful diffusion of an acetone solution (1 mL) of L4 (10.0 mg,

0.018 mmol) into a DMF solution (2 mL) of [PdCl₂(PhCN)₂]

(13.8 mg, 0.036 mmol); acetone (1 mL) was used as the middle

phase to slow the diffusion. Yield: 7.2 mg (44%).

C₃₄H₃₈Cl₄N₈Pd₂·DMF (913.3 + 73.1): calcd. C 45.05, H 4.60, N

ν_asym(OAc), 1606 ν(C=N/C=C), 1411 ν_sym(OAc) cm^–1.

[{Pd(OAc)₂}₂(μ-L4)] (8): L4 (10.0 mg, 0.018 mmol) was dissolved in

acetone (1 mL), and this solution was added to an acetone (2 mL)

solution of Pd(OAc)₂(8.2 mg, 0.036 mmol). The mixture was

stirred at room temperature for 30 min. The solvent was evaporated

to dryness, and the yellow product was dried under vacuum. Yield:

9.2 mg (51%). C₄₂H₅₀N₈O₈Pd₂(1007.71): calcd. C 50.06, H 5.00,

N 11.12; found C 50.29, H 4.93, N 11.27. ¹H NMR (400 MHz,

[D₆]DMSO, 25 °C): δ = 1.44 (s, 12 H, Me-OAc), 2.28 (s, 12 H, 3Ј-

Me), 2.53 (s, 12 H, 5Ј-Me), 6.24 (s, 4 H, 4Ј-H), 7.14 (d, J = 8.2 Hz,

4 H, 2-H, 6-H), 7.88 (d, J = 8.2 Hz, 4 H, 3-H, 5-H), 7.99 (s, 2 H,

α-H) ppm. ¹³C{¹H} NMR (100 MHz, [D₆]DMSO, 25 °C): δ =

11.06 (5Ј-Me), 12.93 (3Ј-Me), 23.45 (Me-OAc), 68.85 (C-α), 108.07

(C-4Ј), 135.10 (C-2, C-6), 140.38 (C-3, C-5), 144.83 (C-5Ј), 153.69

(C-3Ј), 175.06 (CO) ppm. MS (FAB+, 3-NBA): m/z (%) = 890

(14.8) [Pd₂(L4)(OAc)₂]⁺, 831 (25.7) [Pd₂(L4)(OAc)]⁺, 723 (100)

1

12.78; found C 45.05, H 4.88, N 12.77. H NMR (500 MHz, [D₆]-

DMSO, 25 °C): δ = 2.43 (s, 12 H, 3Ј-Me), 2.55 (s, 12 H, 5Ј-Me),

6.25 (s, 4 H, 4Ј-H), 7.07 (d, J = 8.2 Hz, 4 H, 2-H, 6-H), 7.97 (d, J

= 8.2 Hz, 4 H, 3-H, 5-H), 8.13 (s, 2 H, α-H) ppm. ¹³C{¹H} NMR

(125 MHz, [D₆]DMSO, 25 °C): δ = 11.44 (Me-5Ј), 15.08 (Me-3Ј),

69.62 (C-α), 108.47 (C-4Ј), 135.78 (C-3, C-5), 140.20 (C-2, C-6),

144.98 (C-5Ј), 153.98 (C-3Ј) ppm. MS (FAB+, 3-NBA): m/z (%) =

842 (100) [Pd (L4)Cl ]⁺. IR(ATR): ν = 1556 ν(C=N/C=C) cm^–1.

˜

2

[{Pd(OAc)₂}₂(μ-L1)] (5): Yellow crystals were obtained by careful

diffusion of an acetone solution (1 mL) of L1 (10.0 mg,

0.027 mmol) into an acetone solution (2 mL) of Pd(OAc)₂

(12.4 mg, 0.054 mmol); acetone (1 mL) was used as the middle

phase to slow the diffusion. Yield: 4.4 mg (20%). C₂₈H₃₀N₈O₈Pd₂

(819.39): calcd. C 41.04, H 3.69, N 13.68; found C 41.05, H 3.55,

[Pd(L4)(OAc)]⁺, 664 (41.4) [Pd(L4)]⁺. IR (ATR): ν

= 1668

˜

ν_asym(OAc), 1562 ν(C=N/C=C), 1467 ν_sym(OAc) cm^–1.

[{Zn(NO₃)₂}₂(μ-L1)] (9): Zn(NO₃)₂·6H₂O (16.1 mg, 0.054 mmol)

and L1 (10.0 mg, 0.027 mmol) were dissolved in DMF (1 mL) at

room temperature. The mixture was stirred for 5 min. By slow dif-

fusion of diethyl ether through the gas phase into the DMF solu-

tion, a crystalline colourless solid was obtained. The solid was

dried under vacuum. Yield: 7.3 mg (36%). C₂₀H₁₈N₁₂O₁₂Zn₂·DMF

(749.20 + 73.1): calcd. C 33.60, H 3.06, N 22.14; found C 33.95, H

3.19, N 22.61. MS (FAB+, 3-NBA): m/z (%) = 687 (49.7)

1

N 13.43. H NMR (400 MHz, [D₆]DMSO, 25 °C): δ = 1.73 (s, 12

H, Me-OAc), 6.67 (m, 4 H, 4Ј-H), 7.30 (s, 4 H, Ph-H), 7.64 (d, J

= 2.2 Hz, 4 H, 3Ј-H), 8.55 (d, J = 2.9 Hz, 4 H, 5Ј-H), 8.69 (s, 2 H,

α-H) ppm. ¹³C{¹H} NMR (100 MHz, [D₆]DMSO, 25 °C): δ =

23.61 (Me-OAc), 74.33 (C-α), 108.44 (C-4Ј), 127.37 (C-Ph), 136.52

(C-5Ј), 144.59 (C-3Ј), 176.00 (CO) ppm. MS (FAB+, 3-NBA): m/z

(%) = 761 (63.3) [Pd₂(L1)(OAc)₃]⁺, 702 (59.8) [Pd₂(L1)(OAc)₂]⁺,

643 (95.1) [Pd₂(L1)(OAc)]⁺, 535 (100) [Pd(L1)(OAc)]⁺. IR (ATR):

[Zn (L1)(NO ) + H]⁺, 496 (100) [Zn(L1)(NO )]⁺. IR (ATR): ν =

˜

2

3 3

3

ν = 1627 ν_asym(OAc), 1606 ν(C=N/C=C), 1409 ν_sym(OAc) cm^–1.

˜

1660 ν(C=N/C=C), 1467, 1290, 1060 (κ²-NO₃), 1406, 1338 (κ¹-

–

NO₃) cm^–1.

–

[{Pd(OAc)₂}₂(μ-L2)] (6): L2 (10.0 mg, 0.021 mmol) was dissolved in

acetone (1 mL), and this solution was added to an acetone (2 mL)

solution of Pd(OAc)₂(9.6 mg, 0.042 mmol). The mixture was

stirred at room temperature for 30 min. The solvent was evaporated

to dryness, and the yellow product was dried under vacuum. Yield:

12.4 mg (64%). C₃₆H₄₆N₈O₈Pd₂·Me₂CO (931.6 + 58.1): calcd. C

[{Zn(NO₃)₂}₂(μ-L2)] (10): Zn(NO₃)₂·6H₂O (12.5 mg, 0.042 mmol)

and L2 (10.0 mg, 0.021 mmol) were dissolved in DMF (1 mL) at

room temperature. The mixture was stirred for 5 min. By slow dif-

fusion of diethyl ether through the gas phase into the DMF solu-

tion, 10 was obtained as a crystalline colourless solid, which was

dried under vacuum. Yield: 5.4 mg (30%). C₂₈H₃₄N₁₂O₁₂Zn₂

(861.41): calcd. C 39.04, H 3.98, N 19.51; found C 39.69, H 3.93,

N 19.33. MS (FAB+, 3-NBA): m/z (%) = 800 (100) [Zn₂(L2)-

1

47.33, H 5.30, N 11.32; found C 47.47, H 5.29, N 11.58. H NMR

([D₆]DMSO, 400 MHz, 25 °C): δ = 1.56 (br. s, 12 H, Me-OAc),

2.26 (br. s, 12 H, 3Ј-Me), 2.55 (br. s, 12 H, 5Ј-Me), 6.21 (br. s, 4 H,

4Ј-H), 7.17 (s, 4 H, Ph-H), 7.95 (s, 2 H, α-H) ppm. ¹³C{¹H} NMR

(100 MHz, [D₆]DMSO, 25 °C): δ = 11.30 (5Ј-Me), 13.03 (3Ј-Me),

23.66 (Me-OAc), 69.43 (C-α), 108.33 (C-4Ј), 127.95 (C-Ph), 136.65

(C-5Ј), 145.05 (C-3Ј), 174.99 (CO) ppm. MS (FAB+, 3-NBA): m/z

(NO )]⁺, 608 (69.3) [Zn(L2)(NO )]⁺. IR (ATR): ν = 1660 ν(C=N/

˜

3

–

C=C), 1487, 1295, 1049 (κ²-NO₃), 1454, 1321 (κ¹-NO₃) cm^–1.

–

[{Zn(NO₃)₂}₂(μ-L3)] (11): Zn(NO₃)₂·6H₂O (13.1 mg, 0.044 mmol)

(%) = 891 (46.2) [Pd₂(L2)(OAc)₃·H₂O]⁺, 873 (77.2) [Pd₂(L2)- and L3 (10.0 mg, 0.022 mmol) were dissolved in DMF (1 mL) at

(OAc)₃]⁺, 814 (70.5) [Pd₂(L2)(OAc)₂]⁺, 773 (31.8) [Pd₂(L2)(OAc)·

room temperature. The mixture was stirred for 5 min. By slow dif-

fusion of diethyl ether through the gas phase into the DMF solu-

tion, crystalline colourless crystals of 11 were obtained. The crys-

tals were dried under vacuum. Yield: 6.0 mg (33%).

C₂₆H₂₂N₁₂O₁₂Zn₂·2DMF (825.3 + 146.2): calcd. C 39.56, H 3.74,

N 20.19; found C 39.64, H 3.74, N 20.03. MS (FAB+, 3-NBA):

H₂O]⁺, 755 (100) [Pd₂(L2)(OAc)]⁺, 647 (89.8) [Pd(L2)(OAc)]⁺, 588

(35.7) [Pd(L2)]⁺. IR (ATR): ν = 1668 ν_asym(OAc), 1552 ν(C=N/

˜

C=C), 1463 ν_sym(OAc) cm^–1. Crystals suitable for X-ray diffraction

were obtained by careful diffusion of an acetone solution of L2

into an acetone solution of [Pd(OAc)₂].

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FULL PAPER

m/z (%) = 764 (21.4) [Zn₂(L3)(NO₃)₃]⁺, 572 (100) [Zn(L3)(NO₃)]⁺.

determined from integration of the different fluorinated anions

–

IR (ATR): ν = 1650 ν(C=N/C=C), 1473, 1290, 1063 (κ²-NO ), conveniently corrected by the calibration coefficients. This verified

˜

3

1437, 1325 (κ¹-NO₃) cm^–1.

the presence of one BF₄anion per copper atom. MS (FAB+, 3-

–

NBA): m/z (%)

=

1107 (4.9) [Cu₂(L3)₂(BF₄)]⁺, 955 (32.1)

[{Zn(NO₃)₂}₂(μ-L4)] (12): Zn(NO₃)₂·6H₂O (10.7 mg, 0.036 mmol)

and L4 (10.0 mg, 0.018 mmol) were dissolved in DMF (1 mL) at

room temperature. The mixture was stirred for 5 min. By slow dif-

fusion of diethyl ether through the gas phase into the DMF solu-

tion, a crystalline colourless sample of the complex was obtained.

Some crystals were suitable for an X-ray diffraction study. The rest

of the sample was dried under vacuum. Yield: 5.9 mg (35%).

C₃₄H₃₈N₁₂O₁₂Zn₂·2DMF (937.51 + 146.2): calcd. C 44.33, H 4.84,

N 18.10; found C 44.63, H 4.93, N 17.85. MS (FAB+, 3-NBA):

m/z (%) = 876 (46.6) [Zn₂(L4)(NO₃)₃]⁺, 850 (7.9) [Zn₂(L4)(NO₃)₂

[Cu(L3) ]⁺, 509 (100) [(L3)Cu]⁺. IR (ATR): ν = 1668 ν(C=N/C=C),

˜

2

–

1095, 1048 ν(BF₄).

Supporting Information (see footnote on the first page of this arti-

cle): Tables with crystallographic data, selected bond lengths and

angles, and data for noncovalent interactions. ORTEP representa-

1

tions, tables with data from mass spectra and H NMR spectra.

Note Added in Proof (October 21, 2013): While this paper was being

reviewed, the synthesis of L3 by a different method was reported

by Gardinier et al.^[44]

+ 2H O]⁺, 684 (100) [Zn(L4)(NO )]⁺. IR (ATR): ν = 1655 ν(C=N/

˜

2

3

–

C=C), 1487, 1290, 1053 (κ²-NO₃), 1416, 1267 (κ¹-NO₃) cm^–1.

–

Acknowledgments

[Cu₂(CH₃COO)₄(μ-L1)]_n(13): [Cu₂(OAc)₄]·2H₂O (10.8 mg,

0.027 mmol) and L1 (10.0 mg, 0.027 mmol) were dissolved in DMF

(2 mL) at room temperature. The mixture was stirred for 5 min. By

slow diffusion of diethyl ether through the gas phase into the DMF

solution, a crystalline green sample of the complex was obtained.

Some crystals were suitable for an X-ray diffraction study. The rest

of the sample was dried under vacuum. Yield: 8.7 mg (44%).

C₂₈H₃₀Cu₂N₈O₈(733.69): calcd. C 45.84, H 4.12, N 15.27; found

C 45.87, H 3.92, N 15.52. MS (FAB+, 3-NBA): m/z (%) = 919

This work was supported by the Ministerio de Ciencia e Innovación

(MICINN) of Spain [CTQ2011-24434, Fondo Europeo de Desar-

rollo Regional (FEDER) Funds]. We thank the Instituto de Re-

cursos Humanos para la Ciencia y la Tecnología (INCRECYT)

program of Castilla–La Mancha (contract to M. C. C.) and the

Ministerio de Economía y Competitividad (MINECO) of Spain for

a Formación del Personal Universitario (FPU) grant (G. D.).

Thanks are due to the Consejo Superior de Investigaciones Científ-

icas (CSIC) of Spain for the award of a license for the use of the

Cambridge Crystallographic Database (CSD).

(10.8) [Cu₂(L1)(L1 – pz)(OAc)₂]⁺, 819 (8.3) [Cu(L1)₂(OAc)₂

2 H]⁺, 803 (19.2) [Cu(L1)₂]⁺, 614 (100) [Cu₂(L1)(OAc)₂]⁺. IR

(ATR): ν = 1668 ν(C=N/C=C), 1610 ν_asym(AcO), 1425 ν_sym(AcO).

–

˜

[Cu₂(CH₃COO)₄(μ-L3)]_n

(14):

[Cu₂(OAc)₄]·2H₂O

(8.8 mg,

[1] a) J. M. Lehn, Supramolecular Chemistry: Concepts and Per-

spectives, VCH, Weinheim, 1995; b) B. J. Holliday, C. A. Mir-

kin, Angew. Chem. 2001, 113, 2076; Angew. Chem. Int. Ed.

2001, 40, 2022–2043; c) B. Moulton, M. J. Zaworotko, Chem.

Rev. 2001, 101, 1629–1658; d) S. R. Seidel, P. J. Stang, Acc.

Chem. Res. 2002, 35, 972–983; e) W. L. Leong, J. J. Vittal,

Chem. Rev. 2011, 111, 688–764; f) C. P. Pradeep, L. Cronin,

Annu. Rep. Prog. Chem. Sect. A 2007, 103, 287–332.

0.022 mmol) and L3 (10.0 mg, 0.022 mmol) were dissolved in DMF

(2 mL) at room temperature. The mixture was stirred for 5 min. By

slow diffusion of diethyl ether through the gas phase into the DMF

solution, a crystalline green sample of the complex was obtained.

Some crystals were suitable for an X-ray diffraction study. The rest

of the sample was dried under vacuum. Yield: 8.4 mg (47%).

C₃₄H₃₄Cu₂N₈O₈(809.78): calcd. C 50.43, H 4.23, N 13.84; found

C 50.24, H 4.05, N 13.20. MS (FAB+, 3-NBA): m/z (%): 558 (23.3)

[Cu(L3)₂]⁺, 560 (100) [Cu(L3 – pz)(OAc)₂]⁺, 509 (42.1) [Cu(L3)]⁺.

[2] a) G. A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford

University Press, New York, 1997; b) A. M. Beatty, Coord.

Chem. Rev. 2003, 246, 131–143; c) M. O. Awaleh, A. Badia, F.

Brisse, Cryst. Growth Des. 2005, 5, 1897–1906; d) S. Subraman-

ian, M. J. Zaworotko, Coord. Chem. Rev. 1994, 137, 357–401.

[3] a) C. Janiak, J. Chem. Soc., Dalton Trans. 2000, 3885–3896,

and references cited therein; b) F. Ponzini, R. Zagha, K. Hardc-

astle, J. S. Siegel, Angew. Chem. 2000, 112, 2413; Angew. Chem.

Int. Ed. 2000, 39, 2323–2325; c) J. L. Kim, D. B. Nikolov, S. K.

Burley, Nature 1993, 365, 520–527; d) Y. Kim, J. H. Geiger, S.

Hahn, P. B. Sigler, Nature 1993, 365, 512–520; e) L. M. Sa-

lonen, M. Ellermann, F. Diederich, Angew. Chem. 2011, 123,

4908; Angew. Chem. Int. Ed. 2011, 50, 4808–4842.

IR (ATR): ν = 1613 ν_asym(AcO), 1586, ν(C=N/C=C), 1427

˜

ν_sym(AcO) cm^–1.

[Cu(μ-L3)]_n(BF₄)_n(15): An acetone solution (2 mL) of L3 (10.0 mg,

0.022 mmol) was added by careful diffusion to a DMF solution of

[Cu(MeCN)₄]BF₄(13.8 mg, 0.044 mmol). A crystalline colourless

sample was obtained. Some crystals were suitable for an X-ray dif-

fraction study. The rest of the sample was dried under vacuum.

Yield: 2.5 mg (19%). C₂₆H₂₂BCuF₄N₈·DMF (596.86 + 73.1): calcd.

C 51.99, H 4.36, N 18.82; found C 51.38, H 4.29, N 18.38. ¹H

NMR (500 MHz, [D₆]DMSO, 25 °C): δ = 6.41 (br. s, 4 H, 4Ј-H),

6.68 (br. s, 4 H, 2-H, 6-H), 7.29 (br. s, 4 H, 3Ј-H), 7.67 (d, J =

7.7 Hz, 4 H, 3-H, 5-H), 8.22 (br. s, 4 H, 5Ј-H), 8.36 (br. s, 2 H, α-

H) ppm. ¹³C{¹H} NMR (125 MHz, [D₆]DMSO, 25 °C): δ = 76.76

(C-α), 106.71 (C-4Ј), 127.07 (C-2, C-6), 127.59 (C-3, C-5), 136.82

(C-5Ј), 140.38 (C-3Ј) ppm. ¹⁹F NMR ([D₆]DMSO, 282 MHz,

25 °C): δ = –148.34 ppm. A quantification of the amount of the

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BF₄anion was made. Firstly, equimolar amounts of TBA(BF₄)

(5.4 mg, 1.49ϫ10^–5mol; TBA

= tetrabutylammonium) and

TBA(OTf) (5.8 mg, 1.49ϫ10^–5mol; OTf = trifluoromethanesulf-

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Received: July 24, 2013

Published Online: October 22, 2013

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5957

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Dinuclear species versus zigzag or helical polymers in palladium, zinc, and copper complexes with ditopic bis(pyrazolyl)methane ligands

DOI: 10.1002/ejic.201300948

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