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<ul><li><p>Syntheses, Crystal Structures and Magnetic Properties of Mixed-valenceLinear Trinuclear Cobalt and 2D Nickel Complexes</p><p>Tian-Fu Liu, Zai-Xin Wang</p><p>PII: S1387-7003(13)00004-XDOI: doi: 10.1016/j.inoche.2012.12.020Reference: INOCHE 4922</p><p>To appear in: Inorganic Chemistry Communications</p><p>Received date: 31 July 2012Accepted date: 21 December 2012</p><p>Please cite this article as: Tian-Fu Liu, Zai-Xin Wang, Syntheses, Crystal Structuresand Magnetic Properties of Mixed-valence Linear Trinuclear Cobalt and 2D Nickel Com-plexes, Inorganic Chemistry Communications (2013), doi: 10.1016/j.inoche.2012.12.020</p><p>This is a PDF le of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its nal form. Please note that during the production processerrors may be discovered which could aect the content, and all legal disclaimers thatapply to the journal pertain.</p></li><li><p>ACCE</p><p>PTED</p><p> MAN</p><p>USCR</p><p>IPT</p><p>ACCEPTED MANUSCRIPT</p><p>1 </p><p>Syntheses, Crystal Structures and Magnetic Properties of </p><p>Mixed-valence Linear Trinuclear Cobalt and 2D Nickel Complexes </p><p>Tian-Fu Liu* and Zai-Xin Wang </p><p>School of Chemistry, Beijing Institute of Technology, Beijing, 100081, P. R. China </p><p>Corresponding author: tel.: +86 10 68912667; fax: +86 10 68914780. </p><p>E-mail: liutf@bit.edu.cn </p><p>ABSTRACT: Two new complexes, [CoL2]2[Co(CH3OH)4] (1), and [Ni2L2(CH3OH)2]n </p><p>(2) (H2L = 2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid), have been </p><p>synthesized and structurally characterized. Single-crystal X-ray analysis reveals that </p><p>complex 1 is linear trinuclear mixed valence cobalt complex, while complex 2 is a 2D </p><p>complex by double naphtholate bridged and syn-anti carboxylate bridged. Magnetic </p><p>susceptibility measurements indicate that 1 shows mononuclear CoII behavior whereas </p><p>2 exhibits an antiferromagnetism behavior. </p><p>Keywords: cobalt complex; nickel complex; crystal structure; magnetic property </p><p>Over the past two decades, the rational design and synthesis of molecule-based </p><p>magnetic materials have attracted considerable interest [1-5]. In order to design </p><p>coordination complexes with interesting structure and performance, the match of </p><p>metal centers with suitable ligands is one of the most important factors [6]. The </p><p>tetradentate Schiff base ligands, derived from the condensation of an amino acid and </p><p>salicylaldehyde derivative, have been used extensively to construct various </p><p>polynuclear and coordination polymers of CoII and Ni</p><p>II that show interesting structural </p><p>and magnetic properties [7-11]. The carboxylate anion has shown versatile </p><p>coordinating ability to variety of transition metal ions through different coordination </p></li><li><p>ACCE</p><p>PTED</p><p> MAN</p><p>USCR</p><p>IPT</p><p>ACCEPTED MANUSCRIPT</p><p>2 </p><p>(syn-anti, syn-syn and anti-anti) modes and efficiently mediates ferromagnetic (FM) </p><p>and antiferromagnetic (AFM) coupling between metal centers [12-15]; and the </p><p>phenolate anion has also shown efficiently magnetic transmission capacity [16, 17]. </p><p>We report in this article the synthesis, crystal structures and the magnetic properties of </p><p>two complexes [CoL2]2[Co(CH3OH)4] (1) and [Ni2L2(CH3OH)2]n (2) using </p><p>2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid [18] (H2L , Scheme 1) as </p><p>building block ligands. </p><p>Scheme 1 </p><p>The reaction of Co(ClO4)26H2O, H2L and NaOH in a 1:1:2 molar ratios in MeOH </p><p>gave a red-brown solution from which (1) was subsequently isolated in 40% yields. In </p><p>a similar reaction, but employing Ni(ClO4)26H2O with H2L and NaOH in 1:1:2 ratio </p><p>in MeOH gave a green solution from which 2 was isolated in 45% yield [19]. The IR </p><p>spectra of complexes 1 and 2 are quite similar: the discussion is confined to the most </p><p>important vibrations of the 4000-400 cm-1</p><p> region in terms of the structure. A broad </p><p>peak centered at 3424 cm-1</p><p> is most likely due to the OH group. The C=N and C-O </p><p>vibration is assigned to the strong-intensity band at 1630, 1600 and 1544 cm-1</p><p>. </p><p>Fig. 1 </p><p>The structure of the linear trinuclear cobalt compound 1 [CoL2]2[Co(CH3OH)4] is </p><p>provided in Fig. S1 [20]. The deprotonated ligand L acts as a dianionic tetradentate </p><p>ligand: one naphtholate oxygen, one carboxyl and one Schiff base nitrogen in one </p><p>ligand are bound to the terminal cobalt ions and the other carboxyl is chelated to the </p><p>central cobalt ion. All cobalt are octahedral, they are connected by two bridging </p></li><li><p>ACCE</p><p>PTED</p><p> MAN</p><p>USCR</p><p>IPT</p><p>ACCEPTED MANUSCRIPT</p><p>3 </p><p>carboxyl, forming a linear trinuclear cobalt structure unit (Fig. 1) with a </p><p>CoO-COCoO-COCo core and the neighboring Co---Co distance is 5.225(1) . </p><p>The trinuclear cobalt complex molecule is strictly linear by symmetry, and the central </p><p>cobalt atom (Co2) is on a crystallographic symmetry center. The equatorial plane of </p><p>the octahedron is perfectly planar and the cobalt ion (Co2) lies in this plane. The plane </p><p>coordination sites are occupied by methanol molecules. The terminal cobalt ions have </p><p>an octahedral surrounding with another ligand. Co1 is in the +3 oxidation state, and </p><p>Co2 is in the +2 oxidation state, as confirmed by combination of bond-length </p><p>considerations, BVS calculations, and charge-balance [21]. The terminal CoO and </p><p>CoN bond lengths for CoO(naphtholate), CoO(carbonyl) and NiN(-C=N) are </p><p>1.887(2), 1.934(1) and 1.881(2) , respectively. They are slightly shorter than the </p><p>central Co-O bond lengths for CoO(carbonyl) which are 2.062(2) and 2.072(1) </p><p>respectively. Adjacent molecules are linked by intermolecular H bonds to form a 2D </p><p>infinite layer structure (Fig. S2), and there is no obvious - stacking interaction </p><p>between naphtholates. </p><p>Fig. 2 </p><p>Crystal structure of 2 [Ni2L2(CH3OH)2]n exhibits a 2D character. The </p><p>crystallographically independent Ni(II) atoms, Ni1, is hexa-coordinated in the form of </p><p>deformed octahedral cis NiO3O2N; three atoms are from the Schiff base H2L, one </p><p>oxygen atom from methanol, with Ni-N distance of 1.979(3) , and Ni-O distances in </p><p>the range of 2.013(2) to 2.146(3) (Fig. S3). The Ni(II) ions are related by inversion </p><p>centers and bridged by naphtholate oxygen atoms forming a binuclear unit with the </p></li><li><p>ACCE</p><p>PTED</p><p> MAN</p><p>USCR</p><p>IPT</p><p>ACCEPTED MANUSCRIPT</p><p>4 </p><p>Ni-Ni distances being 3.108(1) (Fig. 2). Furthermore, each unit is connected by </p><p>carboxylate bridging using syn-anti mode, resulting in a 2D layer with Ni---Ni </p><p>distance between the dimer units of 5.460(2) (Fig. S4). There are intramolecular </p><p>hydrogen bonding in the layers and no obvious - stacking interaction between </p><p>naphtholates. </p><p>Fig. 3 </p><p>The temperature dependence of the MT vs. T in a field of 1 kOe for 1 is shown in Fig. </p><p>3, where M is the magnetic susceptibility per Co3 unit. The MT value at 300 K is ca. </p><p>3.31 cm3 </p><p>mol-1</p><p> K, which is greater than the spin-only value expected for a high-spin </p><p>CoII and corresponds to the presence of the Co</p><p>III(l.s., S = 0)Co</p><p>II(h.s., S = 3/2)Co</p><p>III(l.s., S = 0) </p><p>trinuclear systems. The decrease of the magnetic moment at low-temperature is most </p><p>likely due to zero-filed splitting of CoII. Therefore, in order to estimate the magnitude </p><p>of zero-filed splitting, the magnetic susceptibility data were fitted to Co(II) ions (S = </p><p>3/2) with the Hamiltonian in the form ZFSH S D S , taking into account the TIP of </p><p>octahedral Co(III) ions possessing a 1A1g ground state [22]. The best least squares </p><p>fitting was obtained with g = 2.43, D = -4.79 cm-1</p><p> and TIP = 0.00168 cm3 mol</p><p>-1 with R </p><p>= 7.7110-5 </p><p>(R value is defined as 22</p><p>])[(/)()( obsMcalcMobsM ). </p><p>Fig. 4 </p><p>In the case of 2, the MT value is 2.61 cm3 </p><p>mol-1</p><p> K at room temperature, greater than </p><p>those expected for two spin only NiII with S = 1. Upon cooling, the MT values </p><p>decrease more and more rapidly, indicating an antiferromagnetic behavior (Fig. 4). </p><p>The maxima of M is observed at 20 K, suggesting antiferromagnetic ordering. The </p></li><li><p>ACCE</p><p>PTED</p><p> MAN</p><p>USCR</p><p>IPT</p><p>ACCEPTED MANUSCRIPT</p><p>5 </p><p>Neel temperature, TN, determined by the peaks of d(MT)/dT, is 9.0 K. The </p><p>field-dependent magnetizations (insert Fig. 8), even at 1.8 K and 70 kOe, being 0.27 </p><p>B, far from the saturated values, confirm the significant antiferromagnetic </p><p>interactions in material. </p><p>Regarding the structure feature, 2 consists of two types of bridges connecting the </p><p>Ni(II) sites. While layer consists of double symmetric 2 naphtholate-O bridges that </p><p>lead to the formation of the dimer locally. These dimers which are subsequently </p><p>interconnected through syn-anti carboxylate bridges give rise to the infinite 2D layer. </p><p>It should be noted that complex 2 exhibits four types of magnetic exchange </p><p>interactions between two Ni(II) ions: (1) a doubly naphtholate-bridged Ni(II) dimer, </p><p>(2) A carboxylate bridged Ni(II) dimer, (3) Ni(II) dimer intralayer, and (4) interlayer </p><p>(Fig. 7). Actually, because of the long distance of COO-, the overlap of magnetic </p><p>orbitals through the O atoms of COO- is weak. Hence, the double naphtholate-bridged </p><p>Ni(II) dimer cage plays an important role in the magnetic properties. </p><p>Therefore, the magnetic susceptibility data of 2 were fitted to the modified </p><p>Bleaney-Bowers equation for two interacting Ni(II) ions (S = 1) with the Hamiltonian </p><p>in the form 1 2H JS S taking into account the interaction between the dimers [23]. </p><p>The susceptibility equation for such a dimeric system, with an interdimer parameter </p><p>zJ, can be written as follows: </p><p>2 2' 2 exp( / ) 5exp(3 / )</p><p>1 3exp( / ) 5exp(3 / )M</p><p>N g J kT J kT</p><p>kT J kT J kT</p><p>'</p><p>2 21 (2 ' )</p><p>MM</p><p>MZJ Ng</p></li><li><p>ACCE</p><p>PTED</p><p> MAN</p><p>USCR</p><p>IPT</p><p>ACCEPTED MANUSCRIPT</p><p>6 </p><p>where N, g, and k parameters in the equation bear their usual meanings. The best </p><p>least squares fitting was obtained with g = 2.23, J = -8.12 cm-1</p><p> and J = 0.71 cm-1 with </p><p>R = 5.8710-6 </p><p>(R value is defined as 22</p><p>])[(/)()( obsMcalcMobsM ). </p><p>In summary, the tetradentate Schiff base ligand </p><p>2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid produces two new </p><p>complexes, linear trinuclear mixed valence cobalt complex [CoL2]2[Co(CH3OH)4] </p><p>and 2D nickel complex [Ni2L2(CH3OH)2]n, respectively. Compound 1 shows a </p><p>mononuclear CoII whereas 2 exhibits an antiferromagnetism behavior. Magnetic </p><p>investigation reveals 2 naphtholate bridge transmitting antiferromagnetic interaction </p><p>and syn-anti carboxylate bridge transmitting ferromagnetic coupling in complex 2. </p></li><li><p>ACCE</p><p>PTED</p><p> MAN</p><p>USCR</p><p>IPT</p><p>ACCEPTED MANUSCRIPT</p><p>7 </p><p>Supplementary materials </p><p>Crystallographic data for the structural analysis have been deposited with the </p><p>Cambridge Crystallographic Data Center, CCDC 887618 &amp; 887619, for complexes 1 </p><p>&amp; 2. These data can be obtained free of charge at </p><p>www.ccdc.cam.ac.uk/conts/retrieving.html. </p><p>Acknowledgement </p><p>We are very grateful to the Natural Science Foundation Council of China (NSFC) </p><p>(grant No. 21171021), Beijing National Laboratory for Molecular Sciences (BNLMS) </p><p>and Scientific Research Foundation for the Returned Overseas Chinese Scholars, </p><p>State Education Ministry for financial support. </p><p>References </p><p>[1] P.G. Lacroix, I. 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Yu, P.-T. </p><p>Chou, Site-Selective DNA Photocleavage Involving Unusual Photoinitiated Tautomerization of Chiral </p><p>Tridentate Vanadyl(V) Complexes Derived from N-Salicylidene -Amino Acids, Org. Lett., 6 (2004) </p><p>4471-4474. </p><p>[19] Caution! Perchlorate compounds are potentially explosive, especially in the presence of organic </p><p>ligands. Only a small amount of these materials should be prepared and handled with </p><p>care.Preparation of complex (1): A solution of Co(ClO4)26H2O (365 mg, 1 mmol) was added to a </p><p>solution of 2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid (229 mg, 1 mmol) and N...</p></li></ul>