Synthesis and characterization of trinuclear NiII3 and CuII3 triplesalophen complexes: Evaluation of ligand folding and heteroradialene formation and their impact on the magnetic properties

FULL PAPER

DOI: 10.1002/ejic.201200990

Synthesis and Characterization of Trinuclear Ni^IIand Cu^IITriplesalophen

3

Complexes: Evaluation of Ligand Folding and Heteroradialene Formation and

their Impact on the Magnetic Properties

Carl-Georg Freiherr von Richthofen,^[a]Anja Stammler,^[a]Hartmut Bögge,^[a]and

Thorsten Glaser*^[a]

Keywords: Nickel / Copper / Schiff bases / Magnetic properties / Stacking interactions

The coordination chemistry of the triplesalophen ligands

H₆baron^R(R = Me, Cl, Br) with Cu^IIand Ni^IIhas been

studied. The triplesalophen ligand system is an extension of

the triplesalen ligand system and is composed of a bridging

phloroglucinol ring with three meta-phenylene salophen co-

ordination compartments. The completely sp²hybridized

backbone of the triplesalophen ligands should favor a more

planar molecular structure of the trinuclear complexes in

comparison to the triplesalen complexes. Reaction of the li-

gands with the metal acetates in n-butanol/CHCl₃provided

the complexes [(baron^Me)Ni₃]a, [(baron^Cl)Ni₃]a, [(baron^Br)-

Ni₃]a, [(baron^Me)Cu₃], [(baron^Cl)Cu₃], and [(baron^Br)Cu₃]. For

the Ni^IIcomplexes, recrystallization from pyridine or per-

forming the reaction in pyridine provided the compounds

[(baron^Me)Ni₃]b and [(baron^Cl)Ni₃]b, whereas for the bromo

derivative the complex [(baron^Br){Ni(py)₂}₂Ni] with one four-

coordinate and two six-coordinate Ni^IIions have been ob-

tained. In contrast, for the Cu^IIcomplexes, two

[(baron^R){Cu(py)}₂Cu] (R = Me, Cl, Br) units dimerize via

bridging of a coordinated phenolate. The structural analysis

reveals a strong tendency for π stacking of the trinuclear

complexes resulting in a planarization of the complexes. The

trinuclear triplesalophen complexes exhibit the four signa-

tures of heteroradialene formation, which were extracted

from single-crystal X-ray diffraction, NMR, FTIR, and UV/

Vis spectroscopy. Analysis of these experimental data with

regard to the respective data of the free ligands H₆baron^R(R

= Me, Cl, Br) and the mononuclear analogue H₂carl^Cland its

complexes [(carl^Cl)Ni] and [(carl^Cl)Cu] clearly demonstrates

that the heteroradialene resonance structure, which has been

established as the dominant resonance structure for the free

ligands, still has a strong but smaller contribution in the tri-

nuclear triplesalophen complexes. The magnetic properties

demonstrate weak intramolecular ferromagnetic interactions

mediated by the triplesalophen ligands in the trinuclear Cu^II

3

complexes, which are experimentally difficult to determine

due to intermolecular antiferromagnetic interactions of the

same order of magnitude.

molecular structures of the trinuclear Ni^II₃complexes^[2]and

Introduction

the trinuclear Cu^IIcomplexes^[11]of the tert-butyl ligand

3

We have designed the ligand system triplesalen

(Scheme 1, a) to rationally develop a new class of single-

molecule magnets (SMM).^[1–3]This is composed of (i) a

central phloroglucinol (1,3,5-trihydroxybenzene) backbone

to enforce ferromagnetic interactions by the spin-polariza-

tion mechanism^[4–9]and (ii) salen-like coordination environ-

ments to introduce a source of local magnetic anisotropy by

the strong tetragonal distortion of its ligand field.^[10]Due to

synthetic constraints in realizing unsymmetrically substi-

tuted diimine units in the first-generation triplesalen ligands

H₆talen^R,^[2]their salen compartments consist of a methyl

ketimine unit in the central position and a dimethyl methyl-

ene group in the ethylene diimine part (Scheme 1, b). The

H₆talen^tBuexhibit a strong ligand folding along the central

2

O–N vectors, resulting in overall bowl-shaped molecular

structures. This ligand folding preorganizes the axial coor-

dination sites of the metal salen subunits for the comple-

mentary binding of a hexacyanometallate. In combination

with a strong tendency of two [(talen^tBu)M ₃] complexes

to dimerize due to van der Waals interaction of the tert-

butyl phenyl groups,^[12]a high driving force results for

the formation of heptanuclear complexes [M^t₆M^c]ⁿ⁺

t

m+

2

(= [{(talen^tBu)M ₃}₂{M (CN)₆}]ⁿ⁺) by the supramolecular

t

c

2

assembly of two [(talen^tBu)M ₃]

molecular building blocks.^[3]In this respect, we could real-

ize the rationally developed SMM [Mn^III₆Cr^{III 3+ [13,14]}

and one [M^c(CN)₆]^p–

t

m+

2

]

.

The driving force for the formation of the hepta-

[a] Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie,

Universität Bielefeld,

nuclear complexes has been demonstrated by the

synthesis of [Mn^III₆Fe^{III 3+ [15]}

]

,

[Mn^III₆Co^{III 3+ [16]}

]

,

and

Universitätsstr. 25, 33615 Bielefeld, Germany

E-mail: thorsten.glaser@uni-bielefeld.de

[Mn^III₆Mn^{III 3+ [17,18]}

] ,

with the latter showing a hysteretic

Homepage: www.uni-bielefeld.de/chemie/ac1chair/

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejic.201200990.

opening up to 10 T at 0.3 K. However, despite this rational

approach, the blocking temperatures – at which hysteresis

5934

Eur. J. Inorg. Chem. 2012, 5934–5952

Trinuclear Ni^IIand Cu^IITriplesalophen Complexes

3

in the magnetization can be seen in these SMMs – does not earity, but with another planar trinuclear building block

exceed that of the archetype of SMMs Mn₁₂(= using CN^–, TCNE^–, or other linearly bridging ligands. This

[Mn₁₂O₁₂(O₂CR)₁₆(OH₂)₄]).^[19]

would result in nonanuclear complexes. A precondition for

this objective is the realization of planar molecular building

blocks related to the trinuclear triplesalen complexes. To

planarize the trinuclear triplesalen building blocks, we have

developed and synthesized the new ligand system triplesal-

ophen, realized by the first generation ligands H₆baron^R

(Scheme 1, b).^[25]The basic idea was that the completely sp²

hybridized salophen subunits should favor a more planar

molecular structure in trinuclear complexes. By a detailed

analysis of the spectroscopic and structural properties of

these ligands and other extended phloroglucinol li-

gands^[26–30]we have established that the central phloroglu-

cinol backbone (Scheme 1, c) is not in the O-protonated

tautomer I, but in the N-protonated tautomer, with the

main contribution of the radialene-like resonance structure

III termed heteroradialene. Because a radialene is a cross-

conjugated alicycle without an aromatic π system, this het-

eroradialene formation counteracts the spin-polarization

mechanism.

In this contribution, we present the synthesis, structural,

spectroscopic, and magnetic properties of trinuclear Ni^II

3

and Cu^IItriplesalophen complexes. The main questions

3

are:

i. Do the triplesalophen ligands H₆baron^Rplanarize the tri-

nuclear complexes or is ligand folding still active?

ii. Is there some source of driving force for close contacts

between the trinuclear complexes, which appears to be nec-

essary for the realization of nonanuclear complexes?

iii. How does variation of the ligand folding influence the

magnetic properties compared to the triplesalen complexes?

Scheme 1. Ligand design, ligands, and heteroradialene formation.

One major disadvantage of the [Mn^III₆M^c]ⁿ⁺SMMs is

the low magnetic anisotropy of the exchange coupled spin

ground state S_tdespite the presence of significant local sin-

gle-site magnetic anisotropy in the Mn^IIIsalen subunits.

The ground state magnetic anisotropy of a polynuclear

Results and Discussion

Synthesis

Reaction of the ligands H₆baron^R(R = Me, Cl, Br) with

transition metal complex usually has its main contribution nickel or copper acetate in common solvents such as meth-

from the projection of the single-site anisotropies onto the anol, ethanol, acetonitrile, or dimethylformamide results in

spin ground state, whereas dipolar and anisotropic interac- the formation of red or brown suspensions, respectively.

tions usually only lead to minor contributions.^[20–24]This Isolation and analysis of the solids indicated the formation

implies that in a polynuclear complex with large single-site of impure samples of trinuclear triplesalophen complexes.

anisotropies, the ground state anisotropy strongly depends This was mainly due to the insolubility of the complexes in

on the relative orientation of the local anisotropy tensors. these solvents, which prevented slow crystallization. A se-

The strongest ground state anisotropy is obtained by a col- arch for appropriate solvents and solvent mixtures iden-

linear alignment of the single-site anisotropy tensors. The tified reactions of solutions of the ligand in chloroform and

stronger the deviation from collinearity, the smaller is the of the metal acetates in n-butanol as being best suited. All

projection of the local anisotropies onto the spin ground reactions leading to pure compounds and all compounds

state. We have analyzed this orientation dependence for synthesized including their abbreviations are summarized in

[Mn^III₆Cr^{III 3+}

a collinear arrangement of the local anisotropies in

[Mn^III₆Cr^{III 3+}, the anisotropy barrier can be more than chloroform/n-butanol mixture resulted in the formation of

doubled keeping all other parameters fixed.

]

in detail.^[14]The interesting result is that by Scheme 2.

The reaction of H₆baron^Meand Ni(OAc)₂·4H₂O in a

]

a deep-red solution. Slow evaporation of the solvent re-

To obtain complexes related to [M^t₆M^c]ⁿ⁺but with all sulted in the deposition of very fine needles of [(baron^Me)-

anisotropy tensors oriented collinearly, we envisaged bridg- Ni₃]a. These needles were, at that time, not suitable for the

ing two planar trinuclear building blocks not by a hexacya- available single-crystal X-ray diffractometer (Mo-K_α).

nometallate, which enforces a strong deviation from collin- Therefore, these needles were dissolved in pyridine. Dif-

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T. Glaser et al.

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nable to single-crystal X-ray diffraction analysis. A some-

what different behavior occurred for the reaction of H₆ba-

ron^Brwith Ni(OAc)₂·4H₂O in chloroform/n-butanol, which

directly resulted in the formation of a red suspension of

[(baron^Br)Ni₃]a, which was barely soluble in common or-

ganic solvents but could be redissolved in the coordinating

solvent pyridine. Diffusion of n-pentane into the solution

obtained from the reaction in pyridine resulted in the for-

mation of the trinuclear nickel complex [(baron^Br){Ni-

(py)₂}₂Ni] with four coordinated pyridine donors, which

has been communicated recently.^[56]The fine needles of

[(baron^Me)Ni₃]a could now be analyzed using a new single-

crystal X-ray diffractometer with Cu-K_αradiation.

The reaction of the three triplesalophen ligands H₆ba-

ron^R(R = Me, Cl, Br) with Cu(OAc)₂·H₂O in a chloroform/

n-butanol mixture resulted in the formation of greenish-

brown solutions from which, in the case of R = Me and Cl,

golden brown needles of [(baron^R)Cu₃] (R = Me and Cl,

respectively) separated upon slow evaporation of the sol-

vent. In the case of H₆baron^Br, [(baron^Br)Cu₃] separated as

a brown solid directly during the reaction. These three com-

pounds have been fully characterized but no single crystals

could be obtained because these solids were barely soluble

in common organic solvents but well-soluble in the coordi-

nating solvent pyridine. Therefore, we redissolved [(ba-

ron^Me)Cu₃] in pyridine and, upon diffusion of n-pentane,

brown single crystals of [(baron^Me){Cu(py)}₂Cu] could be

obtained. The same kind of single crystals could also be

obtained by performing the reaction between H₆baron^Me

and Cu(OAc)₂·H₂O directly in pyridine. Reaction of H₆ba-

ron^Cland H₆baron^Brwith Cu(OAc)₂·H₂O in pyridine also

resulted in the analogous complexes [(baron^Cl)-

{Cu(py)}₂Cu] and [(baron^Br){Cu(py)}₂Cu], respectively.

We also prepared the red complex [(carl^Cl)Ni] and the

greenish-brown complex [(carl^Cl)Cu] as mononuclear model

complexes by reaction of H₂carl^Clwith Ni(OAc)₂·4H₂O and

Cu(OAc)₂·H₂O, respectively, in a chloroform/n-butanol

mixture. Both complexes were reported previously,^[31]in-

cluding a single-crystal X-ray diffraction study on [(carl^Cl)-

Cu] of lower resolution on a different solvate. However, the

characterization was not detailed enough for comparison

with the trinuclear triplesalophen complexes.

All compounds were characterized by mass spectrometry

and elemental analysis. Other methods of characterization

will be presented in more detail in the following sections.

Scheme 2. Synthesis of compounds.

Molecular and Crystal Structures

fusion of acetone/acetonitrile resulted in the formation of

The main intention for the development of the triplesal-

red crystals of [(baron^Me)Ni₃]b, which were suitable for a ophen ligands was to planarize the molecular structures of

single-crystal X-ray diffraction study using Mo-K_αradia- the complexes in comparison to the triplesalen complexes

tion. In the same way, the reaction of H₆baron^Clwith and to study their intermolecular interactions. Therefore,

Ni(OAc)₂·4H₂O in chloroform/n-butanol resulted in the we will first describe and analyze the crystal structures and

formation of red needles of [(baron^Cl)Ni₃]a, which were not the various kinds of ligand foldings in these molecules. We

suitable for single-crystal X-ray diffraction, but diffusion of start with the mononuclear salophen complexes as refer-

acetonitrile into the solution from the reaction in pyridine ences. Selected interatomic distances and angles are summa-

provided dark-red needles of [(baron^Cl)Ni₃]b that were ame- rized in the Supporting Information as Tables S1–S8 and

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Trinuclear Ni^IIand Cu^IITriplesalophen Complexes

3

thermal ellipsoid plots are found in Figures S1–S8 for all interactions are sufficient to induce bending. Interestingly,

structures.

in the ketimine nickel complex that possesses two of the

phenyl ketimine units of [(carl^Cl)Ni], a strong bending of

the phenolates occurs with the phenylene diimine ring

pushed to the other side.^[31]

Mononuclear Salophen Complexes as Reference

Mononuclear, square-planar coordinated Ni^IIand Cu^II

complexes of salen and salophen ligands frequently un-

dergo dimerization through interaction of a coordinated

phenolate ligand with an axial position of a metal ion of a

second complex molecule. In the parent [(salophen)Cu], two

independent molecules occur in the asymmetric unit;^[32]one

molecule is relatively flat whereas the second molecule exhi-

bits a significant bending of the two phenol rings in the

same direction so that the phenylene diimine ring is forced

out of the plane in the opposite direction. On the other

hand, the bromo-derivative [(salophen^Br)Cu] is almost com-

pletely flat^[33]as is the parent nickel complex [(salophen)-

Ni].^[34,35]These observations indicate that there is a flat po-

tential energy surface with regard to the bending in sal-

ophen complexes so that weak noncovalent intermolecular

The two mononuclear complexes [(carl^Cl)Ni] and

[(carl^Cl)Cu] crystallize in the monoclinic space group P2₁/c

with one independent molecule and no solvent of crystalli-

zation without being isostructural. Despite van der Waals

and electrostatic interactions, no intermolecular interac-

tions were observed involving coordination or π stacking in

the crystal structures of [(carl^Cl)Ni] and [(carl^Cl)Cu]. The

orientations of [(carl^Cl)Ni] and [(carl^Cl)Cu] provided in Fig-

ure 1 (a and c), respectively, might indicate relatively planar

molecular structures for these two compounds, but the ori-

entations provided in Figure 1 (b and d) clearly demon-

Table 1. Selected structural properties of nickel and copper sal-

ophen and triplesalophen complexes determined in this study.

[a] α is the angle between the best planes of (1) N₂O₂and (2) benz-

ene of the central phloroglucinol backbone [aldimine for (carl^Cl)^2–

complexes]. [b] β is the angle between the best planes of (1) N₂O₂

and (2) benzene of the terminal phenolate [ketimine for (carl^Cl)^2–

complexes]. [c] γ is the angle between the best planes of (1) benzene

of the central phloroglucinol backbone and (2) benzene of the ter-

minal phenolate [aldimine and ketimine benzene planes for

(carl^Cl)^2–complexes, respectively]. [d] Bent angle φ = 180° – Є (M–

X_NO–X_R) (X_NO: midpoint of adjacent N and O donor atoms; X_R:

midpoint of the six-membered chelate ring containing the N and

O donor atoms). [e] Angle between the O–N vector and the best

plane of the associated benzene. [f] Angle between the two N–Cu–

O planes of CuN₂O₂compartment.

Figure 1. Molecular structures of [(carl^Cl)Ni] (a+b) and [(carl^Cl)Cu]

(c+d). The orientation in a+c is drawn perpendicular to the central

coordination site and in b+d the orientation is drawn parallel to

the aldimine benzene ring. Hydrogen atoms are omitted for clarity.

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T. Glaser et al.

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strate severe ligand folding. Whereas there is no significant

bending at the aldimine site in [(carl^Cl)Ni], the ketimine site

exhibits some bending. This bending is even more pro-

nounced in [(carl^Cl)Cu]. However, a major distortion in

[(carl^Cl)Cu] appears to be the deviation of the N₂O₂coordi-

nation environment from almost regular square-planar in

[(carl^Cl)Ni] to a strong tetrahedral distortion in [(carl^Cl)Cu].

In order to quantify these ligand foldings, we defined some

structural parameters in our studies on the triplesalen com-

plexes.^[2,11,16]These parameters are provided in Table 1 for

all structures determined in this study. The tetrahedral dis-

tortion parameter δ clearly quantifies the visual impression

of a stronger tetrahedral distortion in [(carl^Cl)Cu]. Al-

though the angles α, β, and γ provide a good first indication

of ligand folding, they are not suited to differentiate be-

tween a bending along the O–N vector of a phenol imine

unit or perpendicular to this vector resulting in a helical

distortion. The angle φ, as defined by Cavallo and Jacob-

son,^[36]is best suited to describe the folding along the O–N

vector, whereas the angle Θ is best suited to quantify the

helical distortion.^[16]The folding φ^terminalis strong at the

ketimine unit in both complexes, whereas the helical distor-

tion Θ^terminalis stronger in [(carl^Cl)Ni].

Crystal Structures of the Triplesalophen Complexes

Interestingly, the crystal and molecular structures of the

trinuclear triplesalophen complexes exhibit significant dif-

ferences compared with the mononuclear salophen com-

plexes. The complex [(baron^Me)Ni₃] crystallizes from the re-

action solution as [(baron^Me)Ni₃]·H₂O·1.5CHCl₃in the tri-

clinic space group P1 ([(baron^Me)Ni₃]a) with two indepen-

¯

dent trinuclear complexes (Ni1,2,3 and Ni4,5,6) lacking any

crystallographically imposed symmetry. Recrystallization

from pyridine results in the formation of [(baron^Me)Ni₃]·

1.5py·0.25C₃H₆O ([(baron^Me)Ni₃]b) in the triclinic space

¯

group P1 with one molecule in the asymmetric unit with no

imposed crystallographic symmetry. Figure 2 (a) provides,

as an example, the molecular structure of [(baron^Me)Ni₃]b.

The trinuclear complexes [(baron^Me)Ni₃] form chains in

crystals of [(baron^Me)Ni₃]a and [(baron^Me)Ni₃]b via π–π in-

teractions enforced by the completely sp²-hybridized ligand

backbone of the triplesalophen ligand. The packing in [(ba-

ron^Me)Ni₃]a is shown in Figure 3 (a). The two independent

molecules Ni1,2,3 and Ni4,5,6 in the asymmetric unit sand-

wich a symmetry generated molecule. This leads to the repe-

tition unit Ni1,2,3/Ni1,2,3/Ni4,5,6/Ni4,5,6. The molecules

Figure 2. Molecular structures of (a) [(baron^Me)Ni₃] in crystals of

[(baron^Me)Ni₃]·1.5py·0.25C₃H₆O ([(baron^Me)Ni₃]b) and (b) [(ba-

ron^Cl)Ni₃] in crystals of [(baron^Cl)Ni₃]·py·0.3CH₃CN·H₂O ([(ba-

ron^Cl)Ni₃]b) drawn perpendicular to the central benzene ring of the

phloroglucinol backbone. Hydrogen atoms are omitted for clarity.

are not oriented on top of each other but exhibit some dis- tween Ni1,2,3/Ni1,2,3 and Ni1,2,3/Ni4,5,6, whereas 3.4 Å

placement (the orientations in Figure 3 were chosen to visu- was obtained for Ni4,5,6/Ni4,5,6.

alize the maximum displacement). Pairs of Ni1,2,3/Ni1,2,3

The packing in [(baron^Me)Ni₃]b is shown in Figure 3 (b).

and Ni4,5,6/Ni4,5,6 exhibit only small displacements, This chain, constructed from one molecule in the asymmet-

whereas pairs of Ni1,2,3/Ni4,5,6 exhibit a somewhat larger ric unit, has two different π stacking interfaces. The two

displacement. To obtain an estimate for the distance be- molecules in the bottom of Figure 3 (b) exhibit a small dis-

tween the planes, the atoms of a molecule involved in the π placement, whereas the second and third molecule from the

stacking were used to calculate either a best plane or a bottom exhibits only a small π overlapping area. The dis-

mean position. The distance between the best plane of one tances between both of these π stacking interfaces are esti-

molecule and the mean position of the second molecule was mated to be 3.4 Å.

used to estimate the distances between the π stacking areas.

The chloro-derivative crystallizes from pyridine as [(ba-

This procedure leads to a π stacking distance of 3.3 Å be- ron^Cl)Ni₃]·py·0.3CH₃CN·H₂O ([(baron^Cl)Ni₃]b) in the tri-

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Eur. J. Inorg. Chem. 2012, 5934–5952

Trinuclear Ni^IIand Cu^IITriplesalophen Complexes

3

related by a crystallographic center of inversion. The molec-

ular structures of the trinuclear complexes are shown in

part a of Figure 4 (and in the Supporting Information, Fig-

ures S9a and S10a), whereas the dimerized hexanuclear

units are shown in part b of Figure 4 (and Figures S9b,

and S10b). The overall molecular structures for these three

copper complexes are almost identical (despite the differ-

ence in the ligand folding), so the molecular structure of

[(baron^Me){Cu(py)}₂Cu] is described as a typical example.

Whereas in the trinuclear Ni^IIand Cu^IIcomplexes of the

3

triplesalen ligands the Ni^IIand Cu^IIions are exclusively

four-coordinate in a square-planar coordination environ-

ment, the Cu^II₃triplesalophen complexes exhibit exclusively

five-coordinate Cu^IIions in a square-pyramidal environ-

ment. As can be seen from Figure 4 (a), Cu2 and Cu3 are

Figure 3. Chain formation by π stacking in crystals of (a) [(ba-

ron^Me)Ni₃]a, (b) [(baron^Me)Ni₃]b, and (c) [(baron^Cl)Ni₃]b.

¯

clinic space group P1 with no crystallographically imposed

symmetry. Again, molecules of [(baron^Cl)Ni₃] form π-

stacked chains. The two molecules in the bottom of Fig-

ure 3 (c) possess a large π stacking interface with a distance

of 3.3 Å, whereas the second and third molecule from the

bottom has a slightly smaller overlapping π stacking area

with a distance of 3.4 Å.

Figure 4. Molecular structure of [(baron^Me){Cu(py)}₂Cu] in crys-

tals of [(baron^Me){Cu(py)}₂Cu]·2.5py (a) drawn perpendicularly to

the central benzene ring of the phloroglucinol backbone, and (b)

drawn as dimer parallel to the central benzene ring of the phloro-

The three trinuclear copper complexes crystallize from

pyridine in the triclinic space group P1 as [(baron^Me)-

¯

{Cu(py)}₂Cu]·2.5py,

[(baron^Cl){Cu(py)}₂Cu]·5py,

and

[(baron^Br){Cu(py)}₂Cu]·5py with a dimerization (see below) glucinol backbone. Hydrogen atoms are omitted for clarity.

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coordinated by a pyridine in the fifth coordination site, ligand folding in the Ni^II₃triplesalophen complexes is much

whereas Cu1 coordinates to a coordinated phenolate (O12Ј) lower than in the Ni^IItriplesalen complexes.^[2]

3

of a second molecule generated by a crystallographic center

The situation is less clear in the trinuclear Cu^II₃triplesal-

of inversion (Figure 4, b). This leads to a central Cu₂O₂ophen complexes. Dimerization through the Cu1/O12Ј in-

rhomb in the hexanuclear complex. Again, in contrast to teraction also enforces a distance between the molecular

the trinuclear Cu^IItriplesalen complexes with a bowl- planes of 3.3 Å, but this close contact only concerns a small

3

shaped molecular structure, the dimerization in the Cu^II

part of the molecule. The other two copper salophen sub-

triplesalophen complexes requires a certain degree of plana- units not involved in the coordinative dimerization are bent

3

rization.

towards the other trinuclear subunits in order to maximize

the van der Waals interactions. This results in very large

φ^terminalvalues of approximately 38° compared to 7–24° in

the nickel complexes.

Molecular Structures of the Triplesalophen Complexes:

Ligand Folding

The trinuclear complexes sometimes exhibit nonregular

folding, with the folding at the different metal salen sub-

units occurring in different directions. This is reflected by

the signs of the angles provided in Table 1. By starting with

the angle α, a positive sign reflects folding in the same direc-

tion relative to the central phloroglucinol unit. A negative

sign therefore means that one of the α angles points in the

opposite direction. Based on this direction definition, the

signs of the other angles are determined.

The parts of the trinuclear nickel complexes in [(ba-

ron^Me)Ni₃]a, [(baron^Me)Ni₃]b, and [(baron^Cl)Ni₃]b that are

involved in the π stacking interactions are almost flat, ne-

glecting the phenyl ring of the phenyl ketimine unit, which

exhibits dihedral angles (CX92-CX91–CX9–CX02 with X

Overall, the trinuclear triplesalophen complexes seem to

be very flexible with regard to ligand folding, depending on

the intermolecular interactions. The attractive π–π interac-

tions observed in the trinuclear Ni^IItriplesalen complexes

3

indicate that highly planar structures for the triplesalophen

complexes are possible. Moreover, the π stacking interac-

tions in the trinuclear Ni^IIcomplexes and the covalent di-

3

merization in the Cu^IIcomplexes clearly establish that our

3

anticipated assembly of three triplesalophen complexes

seems to be feasible.

Molecular Structures of the Triplesalophen Complexes:

Bond Lengths

A careful inspection of the bond lengths in the triplesal-

= 1–6 for the respective Ni^IIion) in the range of 80–114°. ophen complexes provides information on the heteroradia-

In contrast, the parts that are not involved in the π stacking lene content in these complexes. For this purpose, Table 2

interactions show some ligand folding. This is nicely illus- summarizes mean values for selected bond lengths in the

trated for [(baron^Me)Ni₃]b, with one metal salophen unit trinuclear triplesalophen complexes but also in valuable

(Ni2) exhibiting a significant bending out of the molecular compounds for comparison. We compare mean bond

plane (Figure 3, b). This is quantified by a value for φ^centrallengths to only two decimal places to avoid an overinter-

of 24.1°, which is the largest value for the central ligand pretation of experimental accuracy and to avoid the impres-

folding in the nickel triplesalophen complexes. The larger π sion of differences that are chemically not significant.

stacking interface in [(baron^Cl)Ni₃]b correlates with the low-

The complexation of the ligand H₂carl^Clby Ni^IIor Cu^II

est degree of ligand folding (Table 1). Overall, the degree of results in a severe shortening of the C–O bond, ac-

Table 2. Comparison of mean bond lengths in the nickel and copper triplesalophen complexes.

C–O

cent

C=N

term cent

C^ar–C^imine

term cent

C^ar–C^ar

term cent

M–O

term cent

M–N

term cent

HOMA^[a]

term cent term

H₂carl^{Cl [b][c]}

1.36

1.30

1.31

1.30

1.29

1.25

1.26

1.25

1.29

1.35

1.29

1.30

n.a.

1.35

1.30

1.31

1.30

1.29

1.31

1.30

1.29

1.32

1.31

1.32

1.31

1.29

1.32

1.31

n.a.

1.29

1.32

1.33

1.32

1.31

1.30

1.45

1.42

1.43

1.38

1.40

1.42

1.41

1.48

1.45

1.46

n.a.

1.47

1.45

1.44

1.46

1.45

1.46

1.47

1.39

1.40

1.39

1.46

1.43

1.44

1.40

n.a.

1.39

1.40

n.a.

1.83

1.91

1.84

1.88

n.a.

1.86

1.85

1.86

1.94

1.93

1.92

n.a.

1.83

1.88

n.a.

1.83

1.89

1.90

n.a.

1.85

1.91

1.84

1.94

n.a.

1.84

1.92

1.93

n.a.

1.87

1.98

n.a.

1.89

1.87

1.89

1.98

0.96

0.87

0.83

0.82

0.84

–0.28 0.96

–0.24 0.94

–0.26 0.94

0.42

0.53

0.46

0.26

0.31

0.39

0.93

0.82

0.80

n.a.

[c]

[(carl^Cl)Ni]

[c]

[(carl^Cl)Cu]

[d]

[e]

[(salophen)Ni]

[(salophen)Cu]

H₆baron^{Me [b]}

H₆baron^{Cl [b]}

H₆baron^{Br [b]}

[(baron^Me)Ni₃]a

[(baron^Me)Ni₃]b

[(baron^Cl)Ni₃]b

0.81

0.80

0.75

0.76

[(baron^Me){Cu(py)}₂Cu] 1.29

[(baron^Cl){Cu(py)}₂Cu] 1.28

[(baron^Br){Cu(py)}₂Cu] 1.29

[a] The HOMA value (harmonic oscillator model for aromaticity) is defined as the normalized sum of individual bond lengths R_iand an

α

optimal bond length R_opt, which corresponds to full π-electron delocalization. HOMA = 1 – ∑(R_opt– R_i)². Here n is the number of

n

bonds taken into account and α is an empirical constant (α = 257.7) chosen to give a HOMA value of 1 for a system with all bond

lengths equal R_opt= 1.388 Å (e.g., benzene) and a value of 0 for a nonaromatic localized 1,3,5-cyclohexatriene.^[38,39][b] Ref.^[25][c] Cent:

aldimine compartment; term: ketimine compartment. [d] Ref.^[34,35][e] Ref.^[33]

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Trinuclear Ni^IIand Cu^IITriplesalophen Complexes

3

companied by a less pronounced shortening of the

It is interesting to analyze how much heteroradialene

C^ar–C^iminebond and an almost insignificant increase of the character VII is in the trinuclear triplesalophen complexes

C=N double bond. The observation that the C^ar–C^ardis- (Scheme 4). There are no significant differences between

tance does not change significantly from 1.39 Å in the li- [(baron^Me)Ni₃]a, [(baron^Me)Ni₃]b, and [(baron^Cl)Ni₃]b

gand to 1.40 Å in the complexes could imply that the aro- (Table 2), so we compare [(baron^Cl)Ni₃]b with [(carl^Cl)Ni]

matic character is not affected by complexation. However, as an example. There are only minor variations in the cen-

the HOMA index (harmonic oscillator model for aromatic- tral C–O and C=N bond lengths, whereas the central C^ar–

ity)^[37–40]is a more precise geometrical parameter that can C^iminebond length exhibits a slight shortening from 1.42 Å

be used to evaluate the aromatic character and takes the in [(carl^Cl)Ni] to 1.40 Å in [(baron^Cl)Ni₃]b. The central ring

variance of bond lengths as well as the deviation from the has a mean C^ar–C^ardistance of 1.43 Å, which is increased

mean bond length from R_optinto account. The HOMA compared with [(carl^Cl)Ni] (1.40 Å) but which is much less

value is defined as the normalized sum of individual bond compared with the value of 1.46 Å in the free ligands. This

length R_iand an optimal bond length R_opt, which corre- is also corroborated by the HOMA value, which is reduced

sponds to full π electron delocalization (Table 2). A HOMA from 0.87 in [(carl^Cl)Ni] to 0.46 in [(baron^Cl)Ni₃]b, but these

value of 1 results for an aromatic system with all bond values are still much higher than the negative values for the

lengths equaling R_opt= 1.388 Å (e.g., benzene) and a value free ligands. These comparisons strongly indicate that the

of 0 for a nonaromatic localized 1,3,5-cyclohexatriene. heteroradialene character VII (Scheme 4) in the triplesal-

Therefore, the reduction of the HOMA value from 0.96 in ophen complexes is severe but not as strong as in the free

H₂carl to 0.87 and 0.83 in [(carl^Cl)Ni] and [(carl^Cl)Cu], triplesalophen ligands. The reduced phenolate character of

respectively, indicates a variance of the bond lengths, which the central oxygen atoms is also reflected in an elongated

does not affect the mean bond lengths. In this respect, the Ni–O bond length of 1.86 Å in [(baron^Cl)Ni₃]b compared

HOMA and the C^ar–C^armean value corroborated by the with 1.83 Å in [(carl^Cl)Ni].

other variations in the bond lengths is in agreement with a

hetero-ortho-quinodimethane character

V

(Scheme 3),

which we found in Cu^IISchiff-base complexes^[27]and in a

study on resonance-assisted hydrogen-bonding (RAHB) in

salicylaldehydes and ortho-Schiff bases.^[41]

Scheme 4. Heteroradialene character in trinuclear triplesalophen

and triplesalen complexes.

The same trends are observed when the trinuclear Cu^II

Scheme 3. Hetero-ortho-quinodimethane character in Schiff base

complexes.

3

triplesalophen complexes are compared with [(carl^Cl)Cu].

The most important difference is that the heteroradialene

character VII in the trinuclear Cu^II₃complexes appeared to

be slightly stronger, as indicated by the slightly increased

C^ar–C^arbond length of 1.44 Å and the reduced HOMA

value of 0.26–0.39 compared with 1.43 and 0.42–0.53 Å,

A comparison of [(carl^Cl)Ni] with [(salophen)Ni]^[34,35]

and [(carl^Cl)Cu] with [(salophen)Cu]^[33]demonstrates that

the introduction of the terminal phenyl ketimine units and

substitution of the phenol groups has no significant impact

on the bond lengths.

respectively, in the trinuclear Ni^IIcomplexes.

A comparison of the triplesalophen ligands H₆baron^R(R

= Me, Cl, Br) with H₂carl^Clclearly demonstrates the strong

contribution of the N-protonated heteroradialene resonance

structure III (Scheme 1, c).^[25]Whereas no significant varia-

tions occur on the terminal phenol imine units, the central

3

NMR Spectroscopy

NMR spectroscopy proved to be a valuable tool with

phloroglucinol backbone is strongly perturbed. The C–O which to evaluate the heteroradialene formation in solution

bond length is reduced from 1.36 Å in H₂carl^Clto 1.26 Å of extended phloroglucinol ligands in general^[26–30]and the

in H₆baron^Cl, demonstrating the strong C=O double bond triplesalophen ligands H₆baron^Rin particular.^[25]The

character. The exocyclic C^ar–C^iminedouble bond character chemical shift and the coupling of the acidic proton of the

is evidenced by the shortening from 1.45 Å in H₂carl to central unit provides clear evidence for N-protonation of

1.38 Å in H₆baron^Cl, whereas the C=N distance is slightly these ligands, although this feature is not available in the

increased from 1.29 to 1.32 Å, indicating less C=N double complexed forms. However, other NMR spectroscopic sig-

bond character. The nonaromatic character of the heterora- natures have been identified for the ligands: (i) The ¹³C

dialene is demonstrated by the C^ar–C^arbond length of NMR chemical shift of the C–O carbon atoms C1, C3, C5.

2

1.46 Å, which almost coincides with a C^sp–C^spsingle The chemical shift of the C–O carbon atom is 161.1 ppm

bond^[42]and a negative HOMA value of –0.24 in H₆baron^Clin H₂salen, 161.3 ppm in H₂salophen,^[43]and ca. 161 ppm

compared to 0.96 in H₂carl^Cl.

in H₂carl.^[25]The terminal C–O carbon atoms in H₆baron^R

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5941

T. Glaser et al.

FULL PAPER

and H₆talen^R[2]have values of ca. 161 and ca. 162 ppm, character.^[41]The H₆baron^Rligands exhibit additional vi-

respectively. The C–O carbon atoms of the central phloro- brations at ca. 1580 and ca. 1480 cm^–1for the C=N and

glucinol backbone in H₆baron^Rand H₆talen^Rexhibit a low- C=C stretching modes for the terminal units, respec-

field signal that is shifted to ca. 185 ppm, which is consis- tively.^[25]The FTIR spectra of the triplesalophen ligands

tent with the strong C=O double bond character in the het- and complexes, as well as of the mononuclear model com-

eroradialene description. (ii) The C^ar–C^iminecarbon atom pounds of the ligand H₂carl^Cl, are provided in Figure 5.

bearing the “imine” group resonates at δ = 117 ppm in

The first assignments of vibrational modes in complexes

H₂salen, 119 ppm in H₂salophen,^[43]and at ca. 120 ppm for of extended phloroglucinol have been made in a compara-

both units in H₂carl^Cl. Almost the same values are found tive study of the first generation triplesalen ligand H₆ta-

for the terminal ketimine units in H₆baron^Rat ca. 120 ppm len^tBuand the inverted triplesalen ligand H₆feld^Me, which

2

and the terminal aldimine units in H₆talen^Rat ca. 118 ppm, has central aldimine units and terminal ketimine units, and

whereas values of ca. 107 ppm for the central unit in both their trinuclear (Fe^IIICl)₃complexes.^[29]In the complex

H₆baron^Rand H₆talen^Ridentifies the heteroradialene char- [(feld^Me)(FeCl)₃] the terminal ketimine units give rise to a

acter. (iii) The chemical shifts of the imine carbon atoms C=N stretch as a shoulder at 1600 cm^–1. Two intense bands

also differ significantly but not in a straightforward manner. have been attributed to the central heteroradialene part,

For the aldimine parts in H₂salen, H₂salophen,^[43]H₂carl^Cl, with the C=C stretch at 1578 cm^–1and the C=O stretch at

and H₆talen^R[2]it is in the range 162–167 ppm, whereas the 1503 cm^–1.

ketimine signals are shifted to 174–176 ppm in H₂carl^Cland

In [(carl^Cl)Ni] and [(carl^Cl)Cu]

a strong band at

in H₆baron^R.^[25]The radialene formation in H₆talen^Rre- 1609 cm^–1seems to arise from the C=N stretch of the aldi-

sults in a chemical shift of the central imine group to 170– mine part, whereas the ketimine part gives rise to a weaker

171 ppm, whereas it is shifted to ca. 148 ppm in H₆baron^Me

.

band at 1591 cm^–1in [(carl^Cl)Ni] and a shoulder at ca.

This differing behavior of the imine carbon chemical shift 1596 cm^–1in [(carl^Cl)Cu] (Figure 5, d). Thus, the weak band

in the triplesalophen and the triplesalen ligands may be as- at 1591 cm^–1in [(baron^Me)Ni₃] is assigned to the terminal

sociated with conjugation with the phenylenediamine benz- ketimine C–N stretch. The situation is less straightforward

ene unit in the triplesalophen ligands, which is absent in the in [(baron^Me)Cu₃] because no maximum appears in that re-

triplesalen ligands.

gion but only a shoulder around 1590 cm^–1. Following the

For the Ni^IIcomplexes, the chemical shift of the C–O assignment for the (Fe^IIICl)₃complexes of H₆talen^tBu²and

carbon atoms appeared to be quite informative. Whereas H₆feld^Me, the strong vibrations around 1550 and around

for H₂salen and H₂salophen, as well as the terminal units 1500 cm^–1in the Ni^IIas well as Cu^IIcomplexes of the H₆ba-

of H₆baron^Rand H₆talen^R, complexation with Ni^IIresults ron^Rligands should be assigned to the C=C and the C=O

in a shift from ca. 161 ppm in the free ligands to 164– stretching modes of the central heteroradialene, respectively.

165 ppm in the Ni^IIcomplexes,^[2,44]the central unit in However, the whole situation is complicated by the presence

H₆baron^Rand H₆talen^Rshifts from ca. 185 ppm to ca. 171– of three additional benzene units, namely the terminal phe-

172 ppm upon complexation. This implies a small increase nolates, the ketimine phenyl substituents, and the phenylene

of the double bond character for the simple salen and sal- diamine units, which must also give rise to ring stretching

ophen ligands upon complexation, but a reduction of the modes in the 1600–1400 cm^–1region. Therefore, these as-

double bond character for the heteroradialene ligands. This signments are only tentative and should be investigated fur-

comparison implies that the heteroradialene contribution ther by DFT calculations.

VII to the resonance structure of the central ring is lower

in the complexes than that of III in the free ligands.

UV/Vis Spectroscopy

As noted in the synthesis section, the trinuclear triplesal-

IR Spectroscopy

ophen complexes exhibit only low solubility. Single crystals

In the study of the triplesalophen ligands H₆baron^R(R have been obtained from chloroform/n-butanol mixtures,

= Me, Cl, Br), three intense vibrations were identified in however, these solid compounds are only soluble in pyr-

the IR spectra as a typical signature for heteroradialene for- idine, which is a coordinating solvent. Thus, recrystalli-

mation (III in Scheme 1, c): ca. 1611, ca. 1553, and ca. zation from pyridine or from reactions in pyridine directly

1443 cm^–1.^[25]Due to conflicting assignments in the litera- results in trinuclear triplesalophen complexes with either no

ture, we were not confident in making definite assignments coordinated pyridine ([(baron^Me)Ni₃]b and [(baron^Cl)Ni₃]b),

of these vibrations at that time. However, based on an in- partial pyridine coordination [(baron^Br){Ni(py)₂}₂Ni],^[56]or

depth combined experimental and theoretical study, we dimerized trinuclear complexes with further pyridine coor-

have been able to assign the band at ca. 1611 cm^–1to the dination ([(baron^R){Cu(py)}₂Cu], R = Me, Cl, Br). These

C=C stretching mode of the exocyclic double bonds cou- observations imply that in the coordinating solvent pyr-

pled with the C–N stretching vibration, the ca. 1553 cm^–1idine, the trinuclear complexes are not four-coordinate

band to the C=O stretching mode, and the ca. 1443 cm^–1square-planar but five- or six-coordinate. UV/Vis spec-

vibration to a nonspecific normal mode delocalized over troscopy seems to be the appropriate tool to investigate

the whole molecule with strong CH₂deformation mode these questions in more detail. Figure 6 shows the UV/Vis

5942

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Eur. J. Inorg. Chem. 2012, 5934–5952

Trinuclear Ni^IIand Cu^IITriplesalophen Complexes

3

spectra of [(baron^Me)Ni₃]a dissolved in chloroform and in

pyridine. The spectrum in chloroform exhibits no absorp-

tion intensity above 15000 cm^–1. A shoulder around

17600 cm^–1is a typical d-d transition of a square-planar

four-coordinate Ni^IIcomplex (¹A_1gǞ¹A_2g).^[45–48]On the

other hand, the spectrum measured in pyridine exhibits a

band around 12000 cm^–1with no counterpart in the spec-

trum measured in chloroform. This band can be simulated

with three Gaussians of restrained half-widths and can be

3

assigned to the typical A_2gǞ³T_2g(F) transition in O_hsym-

metry, which is split into its components due to low sym-

metry.^[49]The occurrence of this band indicates the presence

of a five- or six-coordinate Ni^IIsite in pyridine solution,

however, its intensity (ε ≈ 200 m^–1cm^–1) did not allow us to

distinguish whether all Ni^IIions are more than four-coordi-

nate, whether partial pyridine coordination is present (as

observed in [(baron^Br){Ni(py)₂}₂Ni]) or whether only minor

amounts of pyridine coordination is present in solution. It

has been observed that the extinction coefficient of d-d

transitions in trinuclear triplesalen complexes^[2,11]and also

other extended phloroglucinol complexes^[26–28]are much

higher than in the related mononuclear analogues. This has

been attributed to the reduced symmetry caused by the dif-

ferent central vs. terminal coordination sites in the tri-

plesalen complexes. Thus, we cannot deduce from the inten-

sity of the spectrum of [(baron^Me)Ni₃] in pyridine the con-

centration of more than four-coordinate Ni^IIsites. The

same behavior has been observed for [(baron^Br)Ni₃]. For

this complex, we have dissolved the pyridine-coordinated

[(baron^Br){Ni(py)₂}₂Ni] derivative in CDCl₃and measured

its NMR spectrum. This NMR spectrum corresponds to

the NMR spectrum of [(baron^Br)Ni₃]a in C₂D₂Cl₄, in ad-

dition to the three resonances for pyridine. This implies that

the coordinated pyridine in the solid state decoordinates in

chloroform solution.

Figure 6. Comparison of the electronic absorption spectra of [(ba-

ron^Me)Ni₃]a measured in CHCl₃and pyridine.

The UV/Vis/NIR spectra of the trinuclear Ni^IIand

3

Figure 5. Sections of the FTIR spectra of the triplesalophen ligands

H₆baron^Rand its trinuclear Ni^II₃and Cu^II₃complexes: (a) R = Me,

(b) R = Cl, (c) R = Br. (d) Corresponding mononuclear salophen

ligand H₂carl^Cland its Ni^IIand Cu^IIcomplex.

Cu^IItriplesalophen complexes in chloroform solutions are

3

provided in Figure 7 (a and b), together with the spectra of

the free ligands. The spectra exhibit very strong (ε ≈ 70–

Eur. J. Inorg. Chem. 2012, 5934–5952

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T. Glaser et al.

FULL PAPER

Figure 7. Electronic absorption spectra of the triplesalophen complexes. For comparison, the spectra of the triplesalophen ligands as well

as salen, salophen, triplesalen ligands and complexes have been included.

90ϫ10^{–3 –1}cm^–1) in the 20000–30000 cm^–1range. To ob- tributed to the larger π delocalization over the whole ligand

m

tain further insight from these spectra, comparisons with mediated by the phenylene diamine unit in salophen ligands

the spectra of salen, salophen, and triplesalen ligands and (Figure 7, c). This larger π conjugation in triplesalophen

complexes are provided in Figure 7 (c–e).

ligands such as H₆baron^Clmay also be the reason for the

A special feature of the triplesalen ligands such as further low-energy shift with increased intensity compared

H₆talen is the tenfold stronger intensity in the 25000 to with triplesalen ligands with two strong transitions in H₆ba-

37000 cm^–1region compared with the H₂salen with two ron^Clat ca. 23000 and ca. 30000 cm^–1.

strong maxima around 29000 and 34000 cm^–1(Figure 7, c).

The shift of the intense absorption features to lower en-

The observed low-energy shift with increased intensity of ergy with higher intensity on going from triplesalen ligands

the imine π–π* bands of salophen ligands such as H₂carl^Clto triplesalophen ligands is also observed upon going from

compared with salen ligands such as H₂salen has been at- the trinuclear Ni^IIand Cu^IItriplesalen complexes to the

3

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Trinuclear Ni^IIand Cu^IITriplesalophen Complexes

3

triplesalophen complexes (Figure 7, d and e). The main Magnetic Properties

contribution to this shift may again be by the enlarged delo-

The trinuclear Cu^IItriplesalophen complexes have been

3

calized π system in the triplesalophen complexes. However,

these shifts cannot be used for a quantitative estimate of

the extent of heteroradialene resonance structure contri-

bution in the trinuclear triplesalophen complexes relative

to the trinuclear triplesalen complexes. For such purposes,

detailed computational investigations would be necessary,

which are beyond the scope of this study. The main conclu-

sion for this study is that the strong absorption maxima,

which are shifted to lower energy by an increase in intensity

compared with the triplesalen complexes, are a signature

for the heteroradialene contribution and the increased con-

jugated system in the triplesalophen complexes.

investigated with regard to their magnetic behavior. Some

experimental and simulated data are shown in Figure 8. The

pyridine-free complexes [(baron^R)Cu^II₃] (R = Me, Cl, Br)

have been analyzed with the model of an equilateral trinu-

clear complex using the spin-Hamiltonian provided in

Equation (1).

3

ˆ

H = –2J(S₁S₂+ S₂S₃+ S₃S₁) + μ_B∑ (gS_iB)

(1)

i = 1

It must be emphasized that the structure of these com-

pounds could not be determined because they are only ob-

Figure 8. Temperature-dependence of the effective magnetic moment, μ_eff, of the Cu^IItriplesalophen complexes at 1 T. The solid lines

correspond to fits of the experimental data by using the values given in Table 3. χ_TIPis subtracted from experimental and simulated data.

Eur. J. Inorg. Chem. 2012, 5934–5952

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5945

T. Glaser et al.

FULL PAPER

tained in microcrystalline form and are insoluble in nonco- lated data provided in Figure 8 and in Table 3 must be han-

ordinating solvents so that recrystallization without chang- dled with the appropriate care.

ing the molecular structures could not be performed. Dis-

solution in the coordinating solvent pyridine results in the

complexes [(baron^R){Cu^II(py)}₂Cu^II] (R = Me, Cl, Br) with

Table 3. Parameters obtained from simulations of the experimental

pyridine coordinated at the Cu^IIions. Considering the

magnetic data of the copper triplesalophen complexes. Please note

the limitations of these data provided in the text.

structures obtained for the corresponding Ni^IIcomplexes

3

[(baron^R)Ni₃]b (R = Me, Cl) and the trinuclear Cu^IIcom-

J

χ_TIP

3

g

Θ [K]

[cm^–1]

[10^–6cm³mol^–1]

plexes [(baron^R){Cu(py)}₂Cu] (R = Me, Cl, Br) implies that

there might be intermolecular interactions in [(baron^R)

Cu^II₃] either by coordination and/or by π stacking interac-

tions. These π stacking interactions have been considered

using a Curie–Weiss correction Θ_W.

[(baron^Me)Cu₃]

[(baron^Cl)Cu₃]

[(baron^Br)Cu₃]

1.03

1.05

3.10

2.130

2.109

2.063

2.117

2.116

150

165

255

150

390

–1.14

–1.25

–2.85

–2.01

–2.53

[(baron^Me){Cu(py)}₂Cu] 1.09

[(baron^Br){Cu(py)}₂Cu] 3.04

It must be emphasized that severe problems were encoun-

tered in obtaining “good” magnetic measurements. This is

Article Doi

Synthesis and characterization of trinuclear NiII3 and CuII3 triplesalophen complexes: Evaluation of ligand folding and heteroradialene formation and their impact on the magnetic properties

DOI: 10.1002/ejic.201200990

Source and publish data:

Authors:

Article abstract of DOI:10.1002/ejic.201200990

Full text of DOI:10.1002/ejic.201200990

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