0012-5008/05/0007- © 2005 Pleiades Publishing, Inc.0136

Doklady Chemistry, Vol. 403, Part 1, 2005, pp. 136–139. Translated from Doklady Akademii Nauk, Vol. 403, No. 3, 2005, pp. 345–348.Original Russian Text Copyright © 2005 by Sushev, Kornev, Shvedenkov, Kurskii, Fukin, Baranov, Abakumov.

Nickel complexes are known to be prone to the for-mation of associates and cluster-type compounds [1].Clusters exhibit radically different physicochemicalproperties than their constituting monomeric units. It isof great interest to study both the chemical properties ofclusters and the exchange coupling between their con-stituting paramagnetic centers. However, as distinctfrom the clusters formed by zerovalent and divalentnickel, clusters of monovalent nickel have not hithertobeen studied. In this paper, we report on the first synthe-sis and the structure and magnetic properties of thecomplex {[(Ph

3

P)Ni(

µ

2

-Cl)]

4

[

µ

2

,

η

2

-PhC

≡

CPh]

2

} (

1

),which contains four equivalent nickel atoms in the oxi-dation state +1 involved in coordination with phosphineand diphenylacetylene (tolane) molecules and chlorineatoms.

The reaction of bis(triphenylphosphine)nickel(I)chloride

(Ph

3

P)

2

NiCl(THF)

[2] with an equimolaramount of diphenylacetylene

PhC

≡

CPh

in toluene isaccompanied by a change in color to red-brown. Thereaction mixture was kept at

20°ë

for 5 h. Toluene wasremoved in vacuum and was exchanged for diethylether. It took 12 h for complex

1

to crystallize. Crystalsof deep red-brown color were separated from the solu-tion, washed with ether, and dried in vacuum. The yieldwas 70%.

Complex

1

is readily soluble in methylene chloride andvirtually insoluble in ether and toluene. Compound

1

israther air-stable, evidently, due to the fact that the Ni(I)centers are tightly protected by the phenyl rings of sub-stituents. Among the chemical properties of

1

, its dis-

2PhC≡CPh 4 Ph3P( )2NiCl[ ]+ THF ⋅

Ph3P( )Ni µ2-Cl( )[ ]4 µ2 η2-PhC≡CPh,[ ]2{ } 4Ph3P.+

proportionation to Ni(0) and Ni(II) under the action ofcarbon monoxide is noteworthy. As one of the products,the zerovalent nickel complex

(Ph

3

P)

2

Ni(CO)

2

was iso-lated, which gave rise to a

31

P NMR signal at 34 ppm.

Unit cell parameters were refined and reflectionintensities were collected on a Bruker AXS Smart Apexdiffractometer. At

T

= 100(2) K,

a

= 15.0826(6) Å,

b

=15.5811(6) Å,

c

= 24.1082(10) Å,

α

= 78.178(1)

°

,

β

=73.733(1)

°

,

γ

= 63.548(1)

°

,

V

= 4848.1(3) Å

3

, spacegroup

P-

1,

Z

= 2,

d

calcd

= 1.410 mg/cm

3

,

µ

= 0.994 mm

–1

,1.470

≤

θ

≤

23°

. A total of 32442 reflections were mea-sured, of which 13483 reflections (

R

int

= 0.0701) wereunique. The structure was solved by direct methods andrefined by the full-matrix least-squares method in theanisotropic approximation for non-hydrogen atoms to

R

= 0.0649 (

I

> 2

σ

(

I

)),

R

w

= 0.1089 (all reflections), andGOF(

F

2

) = 1.056. The hydrogen atoms were placedgeometrically and refined as riding on their bondedatoms. All calculations were performed with theSHELXTL program package [Sheldrick, G.M.,

SHELXTL, v. 6.12, Structure Determination SoftwareSuite

, Bruker AXS, Madison (WI), USA, 2000].Absorption corrections were applied using the SADABSprogram [Sheldrick, G.M.,

SADABS, v. 2.01,Bruker/Siemens Area Detector Absorption CorrectionProgram

, Bruker AXS, Madison (WI), USA, 1998].Selected bond lengths and bond angles are listed in thetable.

Complex

1

contains a

Ni

4

Cl

4

cluster in which thenickel atoms are coordinated by diphenylacetylene andtriphenylphosphine molecules (Fig. 1a).

The nickel and chlorine atoms in the

Ni

4

Cl

4

clusterform a distorted gyrobifastigium (digonal gyrobicu-pola) (Fig. 1b). The chlorine atoms are located in theequatorial plane (the average deviation from the planeis

0.018

Å), whereas the apical positions are occupiedby the nickel atoms. The

Cl

···

Cl

distances and ClClClangles at the base of the bicupola are within 3.384(4)–3.461(4) Å and 88.3(2)

°

–90.5(2)

°

, respectively. Themidpoints of the Ni(1)–Ni(2) and Ni(3)–Ni(4) edgesare roughly above and below the centroid of the Cl

4

fragment at a distance of 1.518 Å from it.

Synthesis, Structure, and Magnetic Properties of the Tetranuclear Cluster of Monovalent Nickel

{[(Ph

3

P)Ni(

m

2

-Cl)]

4

[

m

2

,

h

2

-PhC

∫

CPh]

2

}

V. V. Sushev*, A. N. Kornev*, Yu. G. Shvedenkov**, Yu. A. Kurskii*, G. K. Fukin*, E. V. Baranov*, and

Academician

G. A. Abakumov*

Received April 11, 2005

* Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, ul. Tropinina 49, Nizhni Novgorod, 603950 Russia

** International Tomographic Center, Siberian Division, Russian Academy of Sciences, Institutskaya ul. 3a, Novosibirsk, 630090 Russia

CHEMISTRY

DOKLADY CHEMISTRY

Vol. 403

Part 1

2005

SYNTHESIS, STRUCTURE, AND MAGNETIC PROPERTIES 137

The Ni(1)–Ni(2) and Ni(3)–Ni(4) distances aresomewhat different and equal to 2.5145(8) and2.4784(9) Å, respectively. In complexes where theNi atoms are formally monovalent, the Ni–Ni dis-tances change in a wide range. In particular, in thecyclopentadienyl derivatives

[(Bu

t

C

5

H

4

)Ni]

4

[3] and{(

CpNi)

2

(

µ2,η2-C2Ph2)} [4], the Ni–Ni distances are2.462–2.479 and 2.339 Å, respectively. It is worth not-ing that the distances between the atoms Ni(1,2) andNi(3,4) in 1 are within 3.474(1)–3.540(1) Å, which issmaller than the sum of the van der Waals radii of Niatoms (4.0 Å [5]). The Ni–(µ2-Cl) distances, 2.325(1)–

2.352(1) Å, are close to the analogous bridging dis-

tances in the dimer [( PCH2CH2PBut)NiCl]2

(2.351–2.386 Å [6]). The diphenylacetylene moleculesare µ2,η2-coordinated to the Ni atoms. The nickel andsp-carbon atoms {Ni(1)Ni(2), C(69)C(76)} and{Ni(3)Ni(4), C(19)C(26)} are located in roughly mutu-ally perpendicular planes (91.3°) that pass through themidpoints of the C≡C and Ni–Ni distances. The dis-tances between the midpoints of the Ni(1)–Ni(2) andC(19)–C(26) bonds and between the midpoints of theNi(3)–Ni(4) and C(69)–C(76) bonds are 1.315(4) and1.333(4) Å, respectively. The Ni(1,2)–(C(19,26) and

Bu2t

(a)

P(1)

C(27)C(20)

C(19)C(26) P(2)

Ni(2)Ni(1)

Cl(2)Cl(1)

Cl(4)Cl(3)

Ni(3)Ni(4)

P(3)

P(4)

C(69)

C(70)

C(76)

C(77)

Cl(2)Cl(4)

Cl(3)

Ni(1) Ni(2)

Cl(1)

Ni(3)

Ni(4)

(b)

Fig. 1. (a) Molecular structure of complex 1 (the Ph groups at the P atoms and the C(20), C(27), C(70), and C(77) atoms are notshown); (b) the polyhedron that characterizes the arrangement of the atoms in the Ni4Cl4 cluster.

0.9

0 50

µeff (β)

1.2

0.6

100 150 200 250 T, K

Fig. 2. Effective magnetic moment µeff of complex 1 vs.temperature in the paramagnetic region.

30

02

σ, G cm3 mol–1

40

10

3 4 5

20

6T, K

Fig. 3. Remanent magnetization vs. temperature for 1.

138

DOKLADY CHEMISTRY Vol. 403 Part 1 2005

SUSHEV et al.

Ni(3,4)–C(69,76) distances—1.935(4)–1.947(4) and1.939(4)–1.953(4) Å, respectively—characterize aslight asymmetry in the coordination of the dipheny-lacetylene molecules. A similar situation is observed inthe binuclear complex [CpNi]2(µ2,η2-C2Ph2) [4]. TheC(19)–C(26) and C(69)–C(76) bond lengths in thecoordinated diphenylacetylene molecules are 1.341(7)and 1.366(5) Å, respectively, and considerably exceedthe corresponding bonds in free diphenylacetylene(1.210 Å [7]). It is worth noting that the somewhatlonger C(69)–C(76) bond (1.366(5) Å) corresponds tothe shorter Ni(3)–Ni(4) bond (2.4784(9) Å) as com-pared with the C(19)–C(26) and Ni(1)–Ni(2) bondlengths. This can be presumably interpreted as a higherelectron density transfer from the triple bond C(69)–C(76) to the Ni(3)–Ni(4) bond. In addition, it should benoted that the C≡C bond lengths in the molecules of η2-coordinated diphenylacetylene (1.276–1.336 Å [8, 9])are systematically smaller than the analogous distancesin the molecules of µ2,η2-coordinated diphenylacety-lene (1.352–1.388 Å [4, 10]). The Ni–P bond lengthsare 2.287(2)–2.338(1) Å, which almost coincides withthe analogous distances in the mononuclear polymor-phous complex (Ph3P)3NiCl (2.288–2.308 Å [2]).

Magnetic Measurements

Magnetic properties were measured on a QuantumDesign SQUID magnetometer in the temperaturerange 2–300 K with an external magnetic field of ashigh as 15 kOe. In calculations of the molar magneticsusceptibility (χ), the diamagnetism of atoms wastaken into account using the Pascal scheme. In theparamagnetic region, the effective magnetic moment

was determined as µeff = χT ≈ (8χT)1/2,

where k is the Boltzmann constant, NA is Avogadro’snumber, and β is the Bohr magneton. The temperatureof the magnetic phase transition was determined as theextreme point of the derivative of susceptibility with

respect to temperature .

With decreasing temperature, µeff(T) decreases(Fig. 2), which indicates that antiferromagneticexchange coupling is dominating. The efficiency of thiscoupling is high since µeff is 1.175 β even at room tem-perature; this value is considerably lower than the the-oretical limit 3.46 β for four noninteracting spinss = 1/2 with g = 2. Below 60 K, the µeff(T) curve startsincreasing. This indicates that, in addition to antiferro-magnetic exchange, weak ferromagnetic exchangeexists.

Below 5 K, compound 1 undergoes a phase transi-tion into a magnetically ordered state. Figure 3 showsthe remanent magnetization curve (σ(T)) measured in azero magnetic field. This σ(T) dependence demon-

3k

NAβ2-------------

1/2

∂χ∂T------

Selected bond lengths (d) and bond angles (ω) in complex 1

Distance d, Å Distance d, Å

Ni(1)–Ni(2) 2.5145(8) Ni(1)–C(19) 1.935(5)

Ni(3)–Ni(4) 2.4784(9) Ni(1)–C(26) 1.939(4)

Ni(1)…Ni(3) 3.474(1) Ni(2)–C(26) 1.947(4)

Ni(1)…Ni(4) 3.520(1) Ni(2)–C(19) 1.935(4)

Ni(2)…Ni(3) 3.540(1) Ni(3)–C(76) 1.939(4)

Ni(2)…Ni(4) 3.514(1) Ni(3)–C(69) 1.940(4)

Ni(1)–Cl(2) 2.333(1) Ni(4)–C(69) 1.943(4)

Ni(1)–Cl(1) 2.347(1) Ni(4)–C(76) 1.953(4)

Ni(2)–Cl(3) 2.325(1) Ni(1)–P(1) 2.291(1)

Ni(2)–Cl(4)) 2.347(1) Ni(2)–P(2) 2.338(1)

Ni(3)–Cl(2) 2.351(1) Ni(3)–P(3) 2.287(2)

Ni(3)–Cl(4) 2.352(1) Ni(4)–P(4) 2.303(2)

Ni(4)–Cl(3) 2.335(1) C(19)–C(26) 1.341(7)

Ni(4)–Cl(1) 2.341(1) C(69)–C(76) 1.366(5)

Angle ω, deg Angle ω, deg

Cl(3)Ni(2)P(2) 98.44(5) C(69)Ni(3)Cl(2) 111.7(1)

C(19)Ni(1)P(1) 104.1(1) P(3)Ni(3)Cl(2) 94.11(5)

C(26)Ni(1)P(1) 101.5(1) C(76)Ni(3)Cl(4) 105.7(1)

C(19)Ni(1)Cl(2) 149.2(1) C(69)Ni(3)Cl(4) 144.1(1)

C(26)Ni(1)Cl(2) 112.9(2) P(3)Ni(3)Cl(4) 98.47(5)

P(1)Ni(1)Cl(2) 95.81(5) C(76)Ni(3)Ni(4) 50.7(1)

C(19)Ni(1)Cl(1) 106.7(1) C(69)Ni(3)Ni(4) 50.4(1)

C(26)Ni(1)Cl(1) 144.8(2) P(3)Ni(3)Ni(4) 152.65(4)

P(1)Ni(1)Cl(1) 99.58(4) Cl(2)Ni(3)Ni(4) 103.34(4)

C(19)Ni(1)Ni(2) 49.5(1) Cl(4)Ni(3)Ni(4) 101.00(4)

C(26)Ni(1)Ni(2) 49.8(1) C(69)Ni(4)C(76) 41.1(2)

P(1)Ni(1)Ni(2) 149.86(4) C(69)Ni(4)P(4) 108.8(1)

C(19)Ni(2)C(26) 40.4(2) C(76)Ni(4)P(4) 106.6(1)

C(19)Ni(2)Cl(3) 105.2(1) C(69)Ni(4)Cl(3) 146.6(1)

C(26)Ni(2)Cl(3) 143.1(1) C(76)Ni(4)Cl(3) 108.1(1)

C(19)Ni(2)P(2) 111.2(2) P(4)Ni(4)Cl(3) 90.43(5)

C(26)Ni(2)P(2) 106.5(1) C(69)Ni(4)Cl(1) 107.3(1)

C(19)Ni(2)Cl(4) 144.9(2) C(76)Ni(4)Cl(1) 144.0(1)

C(26)Ni(2)Cl(4) 109.7(2) C(26)C(19)C(20) 148.0(4)

P(2)Ni(2)Cl(4) 92.99(4) C(19)Ni(1)C(26) 40.5(2)

C(19)Ni(2)Ni(1) 49.5(2) Cl(2)Ni(1)Cl(1) 92.59(5)

C(26)Ni(2)Ni(1) 49.5(1) Cl(3)Ni(2)Cl(4) 95.45(4)

Cl(3)Ni(2)Ni(1) 101.24(4) Cl(2)Ni(3)Cl(4) 94.30(4)

P(2)Ni(2)Ni(1) 155.65(4) Cl(3)Ni(4)Cl(1) 95.51(4)

Cl(4)Ni(2)Ni(1) 99.25(4) Ni(4)Cl(1)Ni(1) 97.34(4)

C(76)Ni(3)C(69) 41.3(2) Ni(1)Cl(2)Ni(3) 95.73(5)

C(76)Ni(3)P(3) 105.4(1) Ni(2)Cl(3)Ni(4) 97.90(5)

C(69)Ni(3)P(3) 103.6(1) Ni(2)Cl(4)Ni(3) 97.77(4)

C(76)Ni(3)Cl(2) 149.4(1)

DOKLADY CHEMISTRY Vol. 403 Part 1 2005

SYNTHESIS, STRUCTURE, AND MAGNETIC PROPERTIES 139

strates that magnetic ordering of complex 1 takes placeat 4.3 K. The basic magnetization curve and the remag-netization curve for complex 1 measured at 2 K areshown in Fig. 4. Upon remagnetization of the sample,hysteresis with a loop width of 6000 Oe was observed(Fig. 3). The nascent spontaneous magnetic moment(σs) is equal to 47 G cm3 mol–1. Our findings allow usto conclude that complex 1 is an antiferromagnet withweak ferromagnetism.

ACKNOWLEDGMENTS

This work was supported by grants from the Presi-dent of the Russian Federation (project nos. NSh–1649.2003.2 and NSh–1652.2003.3) and the CRDF,grant no. Y1–C–08–12.

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0

–15

σ, G cm3 mol–1

100

–200

–5 0 10

–100

H, kOe5–10

200

15

Fig. 4. Basic magnetization curve and remagnetizationcurve for complex 1 at 2 K.