Journal of Molecular Structure 987 (2011) 138–143

Contents lists available at ScienceDirect

Journal of Molecular Structure

journal homepage: www.elsevier .com/locate /molstruc

p–p Stacking and magnetic coupling mechanism on a mono-nuclear Mn(II) complex

Li Yu a, Jing-Min Shi a,⇑, Yi-Quan Zhang b,⇑, Yu-Qing Wang a, Ya-Nan Fan a,Gui-Qiu Zhang a, Wei Shi c, Peng Cheng c

a College of Chemistry, Chemical Engineering and Materials Science, Key Laboratory of Molecular and Nano Probes,Engineering Research Center of Pesticide and Medicine Intermediate Clean Production, Ministry of Education,Shandong Provincial Key Laboratory of Clean Production of Fine Chemicals, Shandong Normal University, Jinan 250014, PR Chinab School of Physical Science and Technology, Nanjing Normal University, Nanjing 210046, PR Chinac Department of Chemistry, Nankai University, Tianjin 300071, PR China

a r t i c l e i n f o a b s t r a c t

Article history:Received 31 October 2010Received in revised form 30 November 2010Accepted 30 November 2010Available online 21 December 2010

Keywords:Crystal structureMagnetic couplingp–p StackingManganese complex

0022-2860/$ - see front matter � 2010 Elsevier B.V. Adoi:10.1016/j.molstruc.2010.11.074

⇑ Corresponding authors. Tel.: +86 531 86188367;E-mail addresses: shijingmin1955@yahoo.com.cn

njnu.edu.cn (Y.-Q. Zhang).

A novel magnetic coupling is observed in a unpublished crystal that consists of a mono-nuclear manga-nese(II) complex, namely, [Mn(DPP)(NCS)2] (DPP = 2-(3,5-dimethyl-1H-pyrazol-1-yl)-1,10-phenanthro-line), in which neutral DPP molecule functions as tridentate chelated ligand. In the complex Mn(II) ionassumes a distorted trigonal bipyramidal geometry and in the crystal there is a p–p stacking interactionbetween the adjacent complexes, which involves pyridyl ring and the symmetry-related pyrazolyl ringand pyridyl ring. The fitting for the data of the variable-temperature magnetic susceptibilities with infi-nite uniform Mn(II) chain formula gave the magnetic coupling constant J = �0.11 cm�1, and theoreticalcalculations reveal that there exists a very weak anti-ferromagnetic coupling between the adjacent Mn(II)ions with J = �0.02 cm�1. The magnetic coupling sign is explained based on McConnell I spin-polarizationmechanism with the analysis of the spin density population and the factors that dominate the magneticcoupling magnitude.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction fluorescent emission intensity for some compounds [35]. In the

For a long time, the field of molecular magnetism has attractedconsiderable attention, and major advances have been made inboth their description and their application as new molecular-based materials [1–3]. In the magnetostructure research, it is veryimportant to obtain the basic information about magnetic couplingmagnitudes and associated mechanism. In order to obtain thisinformation many fitting models or fitting formulas have beendeveloped and practiced, for example, on binuclear system [4], tri-nuclear system [5–8], tetranuclear system [9–15] and one-dimen-sional system [16–21]. At the same time, theoretical calculationsalso have been successfully developed and practiced to reveal thefactors that may dominate the magnetic coupling in binuclear sys-tem [22–31] and trinuclear system [32,33]. Mostly, fittings and cal-culations deal with the systems where the coupling metallic ionsare connected by bridging ligands, namely, the magnetic interac-tions are through bond exchange. In the materials science area,the p–p stacking interaction as one of the intermolecular forceshas been playing a pivotal role. For example, the p–p stackinginteraction resulted in a silver complex displaying a highly electri-cal conducting behaviour [34], and it also led to a change in the

ll rights reserved.

fax: +86 531 86180017.(J.-M. Shi), zhangyiquan@

magnetic coupling area, p–p stacking interaction also plays animportant role. For example, some authors attributed the strongferromagnetic order to p–p stacking interaction [36], and otherauthors found the p–p stacking interaction led to a strong anti-ferromagnetic interaction between spin-carriers [37–39]. In aword, the p–p stacking interaction should be one of the key factorsthat dominant magnetic coupling, and it may be used to designideal molecule-based magnets. But the papers on fitting treatmentand theoretical calculations of the magnetic coupling of p–pstacking systems are very scarce and mostly, these papers onlydeal with radicals or complexes with radicals as ligands to ourknowledge [37–42]. And in the area only the magnetic couplingsigns of a few compounds have been explained with McConnell Ispin-polarization mechanism and McConnell II charge transfermechanism [43,44], and the factors that dominate the magneticcoupling mechanism have not been mentioned by them. Therefore,it is interesting and meaningful work to design and synthesizecomplexes with p–p stacking and to study the factors thatdominate magnetic coupling signs and coupling magnitude.

2-(3,5-Dimethyl-1H-pyrazol-1-yl)-1,10-phenanthroline is oneof ideal ligands that possess both strong chelated coordinationgroup and larger conjugation plane which may be used to formcomplexes with strong p–p stacking and relevant magnetic cou-pling pathway, but up to now no such complexes have been re-ported except for three mono-nuclear Cd(II) complexes to our

L. Yu et al. / Journal of Molecular Structure 987 (2011) 138–143 139

knowledge [45–47]. The interest in magnetic coupling mechanismof p–p stacking system resulted in us synthesizing the title mono-nuclear complex, and here we report its synthesis, crystal structureand magnetic coupling mechanism involving both experimentalfitting and theoretical calculations.

Table 1Crystal data and structure refinements for the complex.

Formula C19H14MnN6S2

Mr 445.42Crystal system MonoclinicSpace group P21

a(Å) 7.6271(18)b(Å) 14.846(4)c(Å) 8.668(2)b(�) 102.927(4)V(Å3) 956.6(4)Z 2Dc (g cm�1) 1.546l (mm�1) 0.926Reflections collected 5315Unique reflections/Rin 3795/0.053R1 [I > 2r(I)] 0.0744wR2 (all data) 0.1192GOF 0.937

Dqmax (e ÅA0�3) 0.539

Dqmin (e ÅA0�3) �0.277

2. Experimental

2.1. Materials

2-(3,5-Dimethyl-1H-pyrazol-1-yl)-1,10-phenanthroline wassynthesized through the reaction of 2-chlorine-1,10-phenanthro-line and 3,5-dimethyl-1H-pyrazole and all other chemicals areanalytical grade and used without further purification.

2.2. Preparation of [Mn(DPP)(NCS)2]

Methanol solution (5 ml) of NaSCN (0.0131 g, 1.62 � 10�4 mol)was added into 20 ml methanol solution containing Mn(ClO4)2�6H2O (0.0583 g, 1.61 � 10�4 mol) and 2-(3,5-dimethyl-1H-pyra-zol-1-yl)-1,10-phenanthroline (0.0434 g, 1.58 � 10�4 mol), andthe mixed solution was stirred for a few minutes. The yellow singlecrystals were obtained after the filtrate was allowed to stand slowevaporation at room temperature for about 2 weeks. IR (cm�1):2053(s), 1608(m), 1583(m), 1563(m), 1512(s), 1364(s), 846(s). Ele-mental anal. Calcd. for C19H14MnN6S2: (fw 445.42) C, 51.23; H,3.17; N, 18.87; Mn, 12.33. Found: C, 51.45; H, 3.44; N, 18.41; Mn,12.89%.

2.3. Physical measurements

Infrared spectra were recorded with a Bruker Tensor 27 infraredspectrometer in the 4000–500 cm�1 region using KBr disks. C, Hand N elemental analyses were carried out on a Perkin–Elmer240 instrument and the Mn element content analysis was per-formed on an atomic absorption spectrophotometer, ModelZ-8000. Variable-temperature magnetic susceptibilities of micro-crystalline powder sample were measured in a magnetic field1 K Oe in the temperature range 2–300 K on a SQUID magnetome-ter. The data were corrected for the magnetization of the sampleholder and for the diamagnetic contributions of the complex whichwere estimated from Pascal’s constants.

2.4. Computational details

The magnetic interaction between Mn(II) ions were studied onthe basis of density functional theory (DFT) coupling with the bro-ken-symmetry approach (BS) [48–50]. The exchange coupling con-stants J have been evaluated by calculating the energy differencebetween the high-spin state (EHS) and the broken symmetry state(EBS). Assume the spin Hamiltonian is defined as:

bH ¼ �2JbS1 � bS2 ð1Þ

If the spin projected approach is used, the equation proposed byNoodleman [48–50] to extract the J value for a binuclear transi-tion-metal complex is thus:

J ¼ EBS � EHS

4S1S2ð2Þ

For all the models, where S1 = 5/2, S2 = 5/2 for Mn(II) ion, from Eq.(2), we get the expression:

J ¼ ðEBS � EHSÞ25

ð3Þ

While with the non-projected approach proposed by Ruiz et al.[51]:

2J ¼ EBS � EHS

2S1S2 þ S2ð4Þ

where S1 and S2 are the total spins of the two interacting paramag-netic centers and S1 > S2 is assumed for heterodinuclear complexes.For all the models, where S1 = 5/2, S2 = 5/2 for Mn(II) ion, from Eq.(4), we get the expression:

J ¼ ðEBS � EHSÞ=30 ð5Þ

To obtain exchange coupling constants J, Orca 2.8.0 calculations[52] were performed with the popular spin-unrestricted hybridfunctional B3LYP proposed by Becke [53,54] and Lee et al. [55],which can provide J values in agreement with the experimental datafor transition metal complexes [56]. Tri-f with one polarizationfunction def2-TZVP [57,58] basis set proposed by Ahlrichs and co-workers for all atoms was used in our calculations. Strong conver-gence criteria was used in order to ensure that the results are wellconverged with respect to technical parameters (the system energywas set to be small than 10�7 hartree).

2.5. X-ray crystallographic analysis of the complex

A yellow single crystal of dimensions 0.16 � 0.12 � 0.05 mmwas selected and subsequently glued to the tip of a glass fiber.The determination of the crystal structure at 25 �C was carriedout on an X-ray diffractometer (Bruker Smart-1000 CCD) usinggraphite monochromated Mo Ka radiation (k = 0.71073 ÅA

0

). Correc-tions for Lp factors were applied and all non-hydrogen atoms wererefined with anisotropic thermal parameters. Hydrogen atomswere placed in calculated positions and refined as riding. The pro-grams for structure solution and refinement were SHELXS-97 andSHELXL-97, respectively. The pertinent crystallographic data andstructural refinement parameters are summed in Table 1.

3. Results and discussion

3.1. Crystal structure of [Mn(DPP)(NCS)2]

Fig. 1 shows the coordination diagram with the atom number-ing scheme and Table 2 gives the coordination bond lengths andthe associated angles. From Table 2 it can be known that thecoordination bonds lengths range from 2.055(6) Å to 2.273(6) Å

Fig. 1. Coordination diagram of the present complex with the atom numbering scheme.

Table 2Selected bond lengths (Å) and angles (�) for the complex.

Mn1–N5 2.055(6) Mn1–N6 2.063(7) Mn1–N3 2.172(6)Mn1–N1 2.222(6) Mn1–N4 2.273(6)

N5–Mn1–N6 105.4(3) N5–Mn1–N3 130.1(2) N6–Mn1–N3 124.4(2)N5–Mn1–N1 101.4(2) N6–Mn1–N1 98.6(3) N3–Mn1–N1 70.5(2)N5–Mn1–N4 102.5(2) N6–Mn1–N4 101.5(3) N3–Mn1–N4 72.8(2)N1–Mn1–N4 143.2(2)

Fig. 2. The p–p stacking betwe

140 L. Yu et al. / Journal of Molecular Structure 987 (2011) 138–143

and the associated angles change from 70.5(2)� to 143.2(2)�, andobviously the Mn(II) atom is located in a distorted triangle bipyra-midal coordination environment. The non-hydrogen atoms of 2-(3,5-dimethyl-1H-pyrazol-1-yl)-1,10-phenanthroline ligand definea plane within 0.0737 Å with a maximum deviation of0.2117(74) Å for C7 atom. In the crystal there is a p–p stacking be-tween adjacent complex as shown in Fig. 2, which involves pyridylring C8–11C13/N8 and symmetric-related pyrazolyl ring and

en the adjacent complexes.

Fig. 3. Plots of vM (the open triangle for the experimental data and the curve for the fitting values) and leff (the open circle for the experimental data and the curve for thefitting value) versus T for the present complex.

Table 3Calculated atomic spin population of the ground state for the model.

C1 0.122567 C1A �0.127734C2 0.135419 C2A �0.119361C3 0.054572 C3A �0.052033C4 �0.002594 C4A 0.003603C5 �0.022027 C5A 0.024228C6 0.111301 C6A �0.109876C7 �0.006026 C7A 0.003259C8 0.0646 C8A �0.053925C9 �0.009743 C9A �0.005003C10 0.033649 C10A �0.036324C11 0.012496 C11A �0.013437C12 �0.011913 C12A 0.01218C13 0.080507 C13A �0.082564C14 �0.025961 C14A 0.018461C15 �0.036704 C15A 0.039778C16 0.008513 C16A �0.008475C17 0.12928 C17A �0.132853C18 �0.050135 C18A 0.052435C19 0.078355 C19A �0.072307N1 0.026462 N1A �0.030201N2 �0.098487 N2A 0.112006N3 0.030669 N3A �0.037494N4 �0.06305 N4A 0.046406N5 �0.127472 N5A 0.121125N6 �0.110602 N6A 0.110681S1 0.085327 S1A �0.086823S2 0.079465 S2A �0.078354Mn1 4.483691 Mn1A �4.469874

L. Yu et al. / Journal of Molecular Structure 987 (2011) 138–143 141

pyridyl ring with the relevant atoms’ distances within 3.7 Å andthe detailed distances are 3.394(10) Å (C9� � �N1A), 3.545(9) Å(N4� � �C5A), 3.674(10) Å (C13� � �C6A), 3.452(10) Å (C8� � �C3A),3.494 Å (C10� � �N2A) and 3.447(10) Å (C10� � �C19A). The p–p stack-ing led to the formation of a supramolecular one-dimensionalMn(II) chain along a axis, in which the distance between theadjacent Mn(II) ions is 7.6271(18) Å.

3.2. Magnetic studies

3.2.1. Experimental data fitting resultsThe experimental data of variable-temperature (2–300 K) mag-

netic susceptibilities are shown in Fig. 3, where vM is the molarmagnetic susceptibility per Mn(II) unit, leff is the magnetic mo-ment per Mn(II) ion. Fig. 3 displays that the vM value increaseswith decreasing temperature, reaches a maximum at 2.00 K. Theleff value at 300 K is 6.01 BM, which is a little large to isolatedmono-nuclear Mn(II) ion (5.92 BM for gav = 2) at room tempera-ture, and the leff value decreases slowly with temperature dropand reaches 5.80 BM at 40 K, and then follows a sharp decreaseand reaches 3.89 BM at 2 K. Although the fitting formula of infiniteuniform Mn(II) chain (7) was obtained on bridge coordinationmodel and an isotropic Hamiltonian as presented as in Eq. (6),we tried to fit the data of the present experimental susceptibilitieswith this formula in order to obtain the magnetic couplingmagnitude.

bH ¼ �2JXbSMni

bSMniþ1 ð6Þ

vM ¼Nb2g2SðSþ 1Þ

3jT1þ u1� u

ð7Þ

u ¼ coth2JSðSþ 1Þ

jT

� �� jT

JSðSþ 1Þ ð8Þ

The formula (2) gave a good fitting for the experimental dataas shown in Fig. 3, and the relevant fitting parameters are g =2.02, J = �0.11 cm�1 and agreement factor R = 1.13 � 10�3

[R =P

(vobsd � vcalcd)2/(vobsd)2]. The value of J = �0.11 cm�1 indi-cates that there is a weaker anti-ferromagnetic coupling betweenthe adjacent mono-nuclear Mn(II) complexes. Obviously the weakeranti-ferromagnetic coupling should be from the p–p stacking path-way. Although previous paper reported the magnetic fitting for p–pstacking pathway of radical [Ni(mnt)2]� complex [41], the presentcomplex is the first fitting example of non-radical complexes withp–p stacking pathway. In order to further understand the p–p mag-netic coupling pathway and the associated magnetic coupling mech-anism the theoretical calculations were performed.

Fig. 4. The calculated spin density population, in which the atoms with positive spin density being drawn in red and the atoms with negative spin density being drawn inblue. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

142 L. Yu et al. / Journal of Molecular Structure 987 (2011) 138–143

3.2.2. Theoretical study on magnetic interactionDensity function calculations were based on the model as

shown in Fig. 2, which stand for the adjacent p–p stacking com-plexes as mentioned above. The calculations were constrained bythe data of the bond lengths, the associated angles and the relevantlocations of the adjacent p–p stacking complexes which are fromthe X-ray structure of the present crystal. According to Eq. (2),the calculated J is �0.024 cm�1, which is the similar with the valuethat obtained J (�0.02 cm�1) according to Eq. (4) that was sug-gested by Ruiz et al. [59]. It means that the magnetic coupling signfrom the calculations is identical with that of experimental result.And for the magnetic coupling magnitude there is some differencebetween calculations value and the experimental value, but theabsolute error is relatively small from the view of the presentpractice.

On magnetic coupling sign of p–p stacking McConnell I spin-polarization mechanism [43] has been used to explain theferromagnetic interaction of [Mn(Cp�)2]+[Ni(dmit)2]� complexsuccessfully [60], and McConnell I spin-polarization mechanismconsiders that a global ferromagnetic coupling arises from theinteraction between spin densities of opposite sign being predom-inant, whereas an anti-ferromagnetic coupling results from dom-inant interaction between spin densities of the same sign. Table 3and Fig. 4 displays the spin density population of the ground stateof the model, and from Table 3 it can be known that the absolutespin density population on the two Mn(II) ions are both smallerthan 5, which suggests the a part of unpaired electrons on theMn(II) 3d orbitals have localized on the some coordinated atoms.Table 3 and Fig. 4 also indicate that the most atoms’ spin densitypopulations arise from spin-polarization, which may benefit themagnetic coupling through the p–p stacking pathway. In thep–p stacking area there are four pairs of atoms (N4� � �C5A,C13� � �C6A, C8� � �C3A, C10� � �C19A) that exhibit positive–negativespin density interactions and there are two pairs of atoms(C9� � �N1A, C10� � �N2A) that display the same spin density interac-tion, and the number of the different spin density interaction islarger than that of the same spin density interaction. Accordingto McConnell I spin-polarization mechanism It seems that themagnetic coupling sign through the p–p stacking pathway shouldbe a ferromagnetic interaction. Generally, in p–p stackingpathway the one of factors that dominate magnetic couplingmagnitude should be spin densities of the atoms that dealingwith p–p stacking, and another factor should be distances

between p–p stacking atoms. In the six pairs of atoms the abso-lute value of spin density for atom N2A is the largest one andthe distance between C9� � �N1A is the shortest one. Thereforethe magnetic coupling magnitude from the two pairs of the samespin density interaction may be larger than that from the fourpairs of the different spin density interaction. But the key factorshould be the shortest distance of C9� � �N1A because the sum ofspin density absolute value from atoms C13 and N6A is largerthan the sum from atoms C10 and N2A. Maybe it is the shortestdistance between C9� � �N1A that led to the anti-ferromagneticinteraction between the adjacent Mn(II) ions, of course moreexamples should be investigated to confirm this point.

4. Conclusions

A new mono-nuclear Mn(II) complex with 2-(3,5-dimethyl-1H-pyrazol-1-yl)-1,10-phenanthroline as ligand has been synthesizedand its crystal structure determined, which displays that there isa p–p stacking between adjacent complexes and it led to the for-mation of the supramolecular one-dimensional chain. The experi-mental fitting for the data of the variable-temperature magneticsusceptibilities indicates that there exits a weaker anti-ferromag-netic coupling between adjacent Mn(II) ions. The theoretical calcu-lations also confirm the weaker anti-ferromagnetic coupling, andthe anti-ferromagnetic coupling interaction is explained based onthe data of the spin density population and McConnell I spin-polar-ization mechanism. It is suggested that the distance between theatoms of p–p stacking may be the key factor that dominates mag-netic coupling magnitude.

Supporting information

The X-ray crystallographic file of the complex in CIF format isavailable. CCDC 782566 contains the supplementary crystallo-graphic data for this paper. These data can be obtained free ofcharge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (orfrom the Cambridge Crystallographic Data Centre, 12, Union Road,Cambridge CB2 1EZ, UK; fax: +44 1223 336033).

Acknowledgements

This work was supported by the National Natural Science Foun-dation of China (Grant No. 20971080), the National Natural Science

L. Yu et al. / Journal of Molecular Structure 987 (2011) 138–143 143

Foundation for the Youth of China (Grant No. 10704041) and theNatural Science Foundation of Shandong Province (Grant No.ZR2009BM026).

References

[1] J.R. Friedman, M.P. Sarachik, J. Tejada, R. Ziolo, Phys. Rev. Lett. 76 (1996) 3830.[2] G.L.J.A. Rickken, E. Raupack, Nature 405 (2000) 932.[3] S. Tanase, J. Reedijk, Coord. Chem. Rev. 250 (2006) 2501.[4] R. Boca, Theoretical Foundations of Molecular Magnetism, Current Methods in

Inorganic Chemistry, vol. 1, Elsevier, 1999.[5] E. Aznar, S. Ferrer, J. Borras, F. Lloret, M. Liu-Gonzalez, H. Rodrigue-Prieto, S.

Garicia-Granda, Eur. J. Inorg. Chem. (2006) 5115.[6] V. Psycharis, C.P. Raptopoulou, A.K. Boudalis, Y. Sanakis, M. Fardis, G.

Diamantopoulos, G. Papavassiliou, Eur. J. Inorg. Chem. (2006) 3710.[7] S. Wang, J.-L. Zuo, H.-C. Zhou, Y. Song, S. Gao, X.-Z. You, Eur. J. Inorg. Chem.

(2004) 3681.[8] K.S. Gavrilenko, A. Vertes, G. Vanko, L.F. Kiss, A.W. Addison, T. Weyhermüller,

V.V. Pavlishchuk, Eur. J. Inorg. Chem. (2002) 3347.[9] P. Mialane, C. Duboc, J. Marrot, E. Riviere, A. Dolbecq, F. Sechersse, Chem. Eur. J.

12 (2006) 1950.[10] V. Lozan, P.Y. Solntsev, G. Leibeling, K.V. Domasevitch, B. Kersting, Eur. J. Inorg.

Chem. (2007) 3217.[11] P. Mialane, A. Dolbecq, J. Marrot, E. Riviere, F. Secheresse, Chem. Eur. J. 11

(2005) 1771.[12] G.S. Papaefstathiou, A. Escuer, C.P. Paplopoulou, A. Terzis, S.P. Perlepes, R.

Vicente, Eur. J. Inorg. Chem. (2001) 1567.[13] M.-L. Tong, C.-G. Hong, L.-L. Zheng, M.-X. Peng, A. Gaita-Arino, J.M. Clemente

Juan, Eur. J. Inorg. Chem. (2007) 3710.[14] C. Desroches, G. Pilet, P.A. Szilagyi, G. Molnar, S.A. Borshch, A. Bousseksou, S.

Parola, D. Luneau, Eur. J. Inorg. Chem. (2006) 357.[15] G. Aromi, P. Gamez, C. Boldron, H. Kooijman, A.L. Spek, J. Reedijk, Eur. J. Inorg.

Chem. (2006) 1940.[16] M.E. Fisher, Am. J. Phys. 32 (1964) 343.[17] M.E. Fisher, J. Math. Phys. 4 (1963) 124.[18] J.C. Bonner, M.E. Fisher, Phys. Rev. A 135 (1964) A640.[19] W. Hiller, J. Strähle, A. Datz, M. Hanack, W.E. Hatfield, L.W. Haar, P. Gütlich, J.

Am. Chem. Soc. 106 (1984) 329.[20] W.E. Hatfield, R.R. Weller, J.W. Hall, Inorg. Chem. 19 (1980) 3825.[21] A. Meyer, A. Gleizes, J.-J. Girerd, M. Verdayuer, Inorg. Chem. 21 (1982) 1729.[22] F.F. de Bianni, E. Ruiz, J. Cano, J.J. Novoa, S. Alvarez, Inorg. Chem. 39 (2000)

3221.[23] E. Ruiz, P. Alemany, S. Alvarez, J. Cano, J. Am. Chem. Soc. 119 (1997) 1297.[24] J. Miralles, J.P. Daudey, R. Caballol, Chem. Phys. Lett. 198 (1992) 555.[25] O. Castell, J. Miralles, R. Caballoll, Chem. Phys. 179 (1994) 377.[26] P. de Loth, P. Cassoux, J.P. Daudey, J.P. Malrieu, J. Am. Chem. Soc. 103 (1981)

4007.[27] Z.-D. Chen, Z.-T. Xu, L. Zhang, F. Yan, Z.-Y. Liu, J. Phys. Chem. A 105 (2001) 9710.

[28] J.-M. Shi, Y.-M. Sun, X. Zhang, L. Yi, P. Cheng, L.-D. Liu, J. Phys. Chem. A 110(2006) 7677.

[29] E. Ruiz, P. Alemany, S. Alvarez, J. Cano, Inorg. Chem. 36 (1997) 3683.[30] Y.-M. Sun, C.-B. Liu, X.-J. Lin, S.-W. Bi, New J. Chem. 28 (2004) 270.[31] S. Triki, C.J. Gomez-Garcia, E. Ruiz, J. Sala-Pala, Inorg. Chem. 44 (2005) 5501.[32] Y.-M. Sun, C.-B. Liu, Z.-N. Qi, D.-J. Zhang, J. Mol. Struct. (Theochem) 718 (2005)

49.[33] L.-L. Wang, Y.-M. Sun, Z.-Y. Yu, Z.-N. Qi, C.-B. Liu, J. Phys. Chem. A 113 (2009)

10534.[34] S.-L. Zheng, J.-P. Zhang, W.-T. Wong, X.-M. Chen, J. Am.Chem. Soc. 125 (2003)

6882.[35] J.L. Scott, T. Yamada, K. Tanaka, Bull. Chem. Soc. Jpn. 77 (2004) 1697.[36] L.-L. Li, K.-J. Lin, C.-J. Ho, C.-P. Sun, H.-D. Yang, Chem. Commun. (2006)

1286.[37] N.P. Gritsan, A.V. Lonchakov, E. Lork, R. Mews, E.A. Pritchina, A.V. Zibarev, Eur.

J. Inorg. Chem. (2008) 1994.[38] K. Goto, T. Kubo, K. Yamanoto, K. Nakasuji, K. Sato, D. Shiomi, T. Takui, M.

Kubota, T. Kobayashi, K. Yakusi, J. Ouyang, J. Am. Chem. Soc. 121 (1999) 1619.[39] B.D. Koivisto, A.S. Ichimura, R. McDonald, M.T. Lemaire, L.K. Thompson, R.G.

Hicks, J. Am. Chem. Soc. 128 (2006) 690.[40] L. Norel, F. Pointillart, C. Train, L.-M. Chamoreau, K. Boubekeur, Y. Journaux, A.

Brieger, D.J.R. Brook, Inorg. Chem. 47 (2008) 2396.[41] X.M. Ren, S. Nishihara, T. Akutagawa, S. Noro, T. Nakamura, Inorg. Chem. 45

(2006) 2229.[42] R.K. Kremer, B. Kanellakopulos, P. Bele, H. Brunner, F.A. Neugebauer, Chem.

Phys. Lett. 230 (1994) 255.[43] K. Yoshizawa, R. Hoffmann, J. Am. Chem. Soc. 117 (1995) 6921.[44] J.S. Miller, A.J. Epstein, J. Am. Chem. Soc. 109 (1987) 3850.[45] Y.-Q. Wang, L. Meng, J.-M. Shi, Acta Cryst. Sect. E 65 (2009) m1317.[46] Y.-M. Sun, Y.-Q. Wang, H.-X. Ren, Acta Cryst. Sect. E 66 (2010) m663.[47] J.-M. Shi, L. Meng, Y.-Q. Wang, Acta Cryst. Sect. E 66 (2010) m878.[48] L. Noodleman, J. Chem. Phys. 74 (1981) 5737.[49] L. Noodleman, E.J. Baerends, J. Am. Chem. Soc. 106 (1984) 2316.[50] L. Noodleman, D.A. Case, Adv. Inorg. Chem. 38 (1992) 423.[51] E. Ruiz, J. Cano, S. Awarez, P. Alemany, J. Comput. Chem. 20 (1999) 1391.[52] Frank Neese, An Ab Initio, DFT and Semiempirical electronic structure package,

Program Version 2.7, Revision 0, Lehrstuhl fuer Theoretische Chemie Institutfuer Physikalische und Theoretische Chemie, Universitaet Bonn, Germany, 20,January 2010.

[53] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.[54] A.D. Beck, Phys. Rev. A 38 (1988) 3098.[55] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.[56] J. Cano, E. Ruiz, S. Alvarez, M. Verdaguer, Comments Inorg. Chem. 20 (1998) 27.[57] A. Schäfer, H. Horn, R. Ahlrichs, J. Chem. Phys. 97 (1992) 2571.[58] F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys. 7 (2005) 3297.[59] E. Ruiz, S. Alvarez, A. Rodriguez-Fortea, P. Alemany, Y. Pouillon, C. Massobrio,

in: J.S. Miller, M. Drillon, (Eds.), Magnetism: Molecules to Materials, Wiley-VCH, 2002.

[60] C. Faulmann, E. Rivie‘re, S. Dorbes, F. Senocq, E. Coronado, P. Cassoux, Eur. J.Inorg. Chem. (2003) 2880.