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A unique manganese (II)2D polymer containing 2,

5-di(2′,4′-dicarboxylphenyl)pyridine and oxalate mixed ligands:Structure and magnetic property

Xun Feng a ,?,Jing Liu b ,a ,Jun Ling Chen c ,Su Zhen Huo a ,Li Ya Wang a ,c ,??,Seik Weng Ng d

College of Chemistry and Chemical Engineering,Luoyang Normal University,Luoyang 471022,China b

College of Chemistry and Molecular Engineering,Zhengzhou University,Zhengzhou 450002,China c

College of Chemistry and Pharmacy Engineering,Nanyang Normal University,Nanyang 473601,China d

Department of Chemistry,University of Malaya,Kuala Lumpur 50603,Malaysia

a b s t r a c t

a r t i c l e i n f o Article history:

Received 2September 2014

Received in revised form 17October 2014Accepted 17October 2014Available online xxxx

Keywords:

Oxalate bridging

Manganese (II)complex Tetranuclear cluster

Anti-ferromagnetic interactions

Solvothermal reaction of conjugated pyridine/benzene dicarboxylic acid ligand with manganese acetate in the presence of ammonium oxalate afforded a novel 2D polymer,{[Mn 4(ddpp)2(μ4-C 2O 4)·6H 2O]·2H 2O}n (ddpp =2,5-di(2′,4′-dicarboxylphenyl)pyridine)(1).It has been characterized by element analysis,thermogravimetry,infrared spectroscopy and single-crystal X-ray diffraction studies.Polymer 1is constructed from tetranuclear Mn II clusters through oxalate bridging,in which four adjacent Mn II ions are linked into a parallelogram-core aggregate,and the polymer 1exhibits 1D double-zigzag chains bearing a ladder-like topology feature.The ddpp ligands further interconnect these 1D double chains into 2D corrugated-shape network.Vari-able temperature magnetic susceptibility measurements indicate that polymer 1exhibits weak antiferromagnet-ic interactions.

?2014Published by Elsevier B.V.

Contents

Acknowledgments ..............................................................46Appendix A.Supplementary material.....................................................46References (46)

Recently,the synthesis and characterization of extended frame-works containing transition metals bridged by carboxylic groups have attracted considerable interest,because of their extraordinary archi-tectures,intriguing topologies and potential applications [1–3].It is well known that a variety of multicarboxylate imidazoline/triazine/pyridine-based ligands have been extensively employed for exhibiting various coordination fashions to transmit magnetic interactions and accompany diversity of interesting structures with rectangular grid,honeycomb,1D ladder,bilayer lattice and diamond frameworks [4–6].Meanwhile,biphenyl tetracarboxylic acid possesses multiple bridging modes and its phenyl rings can be rotated around the C –C single bond.Thus,a variety of connection modes with metal centers provide

abundant structural motifs,as well as it is a good choice for construction of MOFs.Some MOFs based on biphenyl tetracarboxylic acid show antiferromagnetic interactions [7].However,it has been seldom reported for the combined biphenyl tetracarboxylic acid with pyridine as the new kind of organic ligand with introduction an extended π-conjugated system,2,5-di(2′,4′-dicarboxylphenyl)pyridine (ddpp),which acts as a multi-donor linker for construction of coordination poly-mers.Moreover,the carboxylic-bridged Mn II complexes are well recog-nized from magnetic point of view as the high-spin Mn II ion contains ?ve unpaired electrons,and thus assembly of Mn II with multicarboxylic is inclined to formation of single-molecule magnets (SMMs)[8,9].On the other hand,oxalate,as the shortest dicarboxylic rigid ligand,has been proved to be a good candidate for pillar ligand due to strong coordination tendency to generate 1D to 3D moderately robust net-works,exhibiting tunable ferro-or antiferro-magnetic exchanges [10,11].Oxalate-bridged polynuclear complex plays a key role due to the remarkable ability to transmit electronic effects between magnetic

Inorganic Chemistry Communications 50(2014)42–47

?Corresponding author.

??Correspondence to:L.Y.Wang,College of Chemistry and Chemical Engineering,Luoyang Normal University,Luoyang 471022,China.

E-mail addresses:fengx@https://www.wendangku.net/doc/1b8937941.html, (X.Feng),wlya@https://www.wendangku.net/doc/1b8937941.html, (L.Y.

Wang).https://www.wendangku.net/doc/1b8937941.html,/10.1016/j.inoche.2014.10.0151387-7003/?2014Published by Elsevier

B.V.

Contents lists available at ScienceDirect

Inorganic Chemistry Communications

j o u r n a l h o me pa g e :ww w.e l s e v i e r.c o m /l o c a t e /i no c h e

centers[12].The homonuclear or heteronuclear of oxalate-bridged binuclear complexes has been extensively achieved[13,14].However, to the best of our knowledge,oxalate-bridged tetranuclear complexes containing aromatic tetracarboxylic acid have not been reported. Inspired by the aforementioned considerations,and as a continuation of our previous investigation[15,16],a novel polymer based on ddpp and oxalate mixed ligands employing tetranuclear Mn II as SUB has been synthesized through solvothermal reaction and has been charac-terized systematically[17].

Single crystal X-ray diffraction[18]reveals that basic unit of polymer 1crystallizes in the triclinic system,space group P?1.The asymmetric unit contains two Mn II cations,one ddpp ligand,half of an oxalate ligand and three coordinated water molecules,as well as one lattice water molecule.There are two crystallographically independent Mn II ions in this unit and both of the Mn II ions are hexa-coordinated,with a slightly distorted octahedral geometry.The coordination environments around them are slightly different from each other,as depicted in Fig.1.The Mn1is ligated with two oxygen atoms(O9and O10)from an oxalate, three carboxylic oxygen atoms(O2,O5and O7)of two ddpp ligands, as well as the remaining one site is occupied by oxygen atom(O1W) of water molecule completed the distorted octahedral con?guration. Whereas,Mn2is coordinated with six oxygen atoms,which are provid-ed by one oxalate moiety(O9),three ddpp ligands(O1,O6and O8)and two terminal coordinated water molecules(O2W and O3W).The Mn II–O distances fall in the normal range of2.044(7)–2.368(6)?,which are closely similar to those found in other reported Mn II complexes[20].

Three carboxylic groups of ddpp are deprotonated completely, leaving one protonated carboxylic group corresponding to stretching vibration of ca1710cm?1in IR spectrum.The spectra of compound1 also display two strong absorptions at1643and1387cm?1,which are due to the characteristicνas(COO?)andνs(COO?)stretching modes of carboxylic groups.The absorption band at1608cm?1is assigned to the characteristic stretching vibration of oxalate moiety. The dihedral angle between two phenyl rings of ddpp ligand is8.03°, and the ddpp ligand acts as aμ5-bridge linking?ve Mn II ions,in which three carboxylic groups adoptμ2-η1:η1bridging modes to connect two adjacent Mn II ions,while accompanying chelating mode to coordi-nate one central ion,with three different Mn1\Mn2separations of 4.095?,5.278?and5.506?,respectively.Among which,the adjacent Mn1\Mn2is further linked by oxalate resulting in the shortest Mn1\Mn2distance of4.095?,and oxalate exhibits chelating and bridgingμ4mode.The bond angles of O(2)–Mn(1)–O(10)#2,O(10)#2–Mn(1)–O(9)(symmetry code:#2:?x+1,?y+2,?z)are found to be164.3(3)°and72.5(2)°,which are derived from the normal values of octahedron geometry coordination mode.Interestingly,the N atom in the pyridine ring of ddpp ligand does not participate in the coordination to Mn II ion(see Scheme1(a)).Mn II ion connects three car-boxylic groups addicted to different compartmental tetracarboxylic moieties,which is seldom observed[21].Meanwhile,oxalate ligand acts as both bidentate and chelating ligand linking two asymmetric units(Mn1and Mn2)into tetranuclear cluster,as secondary building unit(SBU),as illustrated in Fig.2.In this cluster,four adjacent Mn II ions form an parallelogram-core with two different Mn1\Mn2dis-tances of4.095?and5.563?,as well as two complementary interior alternate angles Mn(1)–Mn(2)–Mn(1)[72.06°]and Mn(2)–Mn(1)–Mn(2)[107.94°],respectively(see Scheme1(b)).The distance between two adjacent sheets in which Mn4subunits are located is4.494?. Furthermore,these clusters are combined into1D double-zigzag chains by terminal carboxylic oxygen atoms(O8)of ddpp ligands along the b axis,possessing a ladder-like topology feature,with the double chain distance of5.203?,as shown in Fig.3.Simultaneously,the2,5-carboxylic oxygen atoms from isophthalic acid moiety(O6and O7)of ddpp ligands are coordinated with Mn1and Mn2atoms in neighboring chains,and further interconnected these1D chains into2D corrugated-shape network along a c plane,as depicted in Fig.4.In addition,there is a large number of hydrogen bonding entities from carboxylates,lattice and coordinated water molecules present in the compound,and hydro-gen bonding parameters are listed in Table S2(Supporting information) for details.Meanwhile,the2D structures are further connected via hy-drogen bonding and C–H\O interactions,resulting in a3D structure as illustrated in Fig.S2(Supporting information).The interactions are stronger,playing a dominant role for the formation of the3D supramo-lecular edi?ce and the crystal packing.

To further con?rm the presence of water molecules and to charac-terize the complex more fully in terms of thermal stability,polymer1 was measured on the thermo-gravimetric analysis(TG)and differential thermal analysis(DTA)in a dry nitrogen atmosphere from room tem-perature to900°C.As illustrated in Fig.5,the TG curve exhibits an initial mass loss of10.5%between120and190°C,corresponding to the initial departure of lattice water molecules followed by the escaping of coordi-nated water molecules(calcd.11.4%).The decomposition begins from 410to440°C with the weight loss of7.05%,which is attributed to release of oxalate moiety(calcd.6.98%).which indicates that the dehydrated framework of1is thermally stable over a wide range

of Fig.1.Coordination environments of Mn II ions in the asymmetric unit of1with some hydrogen atoms are omitted for clarity.

43 X.Feng et al./Inorganic Chemistry Communications50(2014)42–47

temperature.The further degradation process takes place beyond 450°C,corresponding to the destruction of ddpp organic ligands,which is in consistent with crystal structure analysis.The DTA curve ex-hibits two exothermic peaks at approximately 370°C and 470°C,which is attributed to decompose the oxalate and ddpp ligand,respectively.

Phase purity of the bulk materials of polymer 1was con ?rmed by powder X-ray diffraction (PXRD)patterns.As shown in Fig.S3(Supporting information),the main peak positions of the simulated and experimental patterns are in agreement with each other,dem-onstrating the phase purity of the synthesized products.

The magnetic susceptibilities were determined in the temperature range of 2–300K.The magnetic behavior of polymer 1is presented in Fig.6.The value of χM T at 300K amounts to 17.2cm 3mol ?1K,close to that expected for four uncoupled high-spin Mn II ions (17.5cm 3mol ?1K)[22].As the temperature is lowered,the χM T value is almost constant in the region of 150–300K and then rapidly decreases to 1.1cm 3mol ?1K at 1.9K,indicating the presence of possible antiferromagnetic interactions between the adjacent Mn II ions.According to the structure analysis men-tioned above,the intramolecular Mn II \Mn II distances are 4.095?,and the shortest intermolecular Mn II \Mn II distance is 7.858?.It could be pre-sumed that the main magnetic interactions between the Mn II centers should happen between the intracluster units through oxalate bridging.Meanwhile,considering the magnetic interaction between manganese pairs within these 1D double chains,two coupling parameters J and z J ′may be considered to interpret two possible magnetic interactions in polymer 1.Here,J is the exchange coupling parameter between adjacent Mn II –Mn II of tetranuclear cluster and z J ′accounts for the chains of interac-tions.The magnetic data were thus approximately analyzed by an isotro-pic Heisenberg model for the uniform chains with coef ?cient generated by Hiller et al.[23],for spin S =5/2.The 2D system can be magnetically regarded as an isolated 1D chain with μ2-oxalate bridges.Thus,the data of 1were ?tted to the well-known expression proposed by Fisher for

O O

Mn 2O

Mn 2

Mn 1

Mn 2

O O

Mn 1

Mn 2

(a)

(b)

Scheme 1.The coordination fashions of ligands observed in polymer 1.

Fig.2.Perspective view of the tetranuclear Mn II cluster as the SBU in polymer 1(hydrogen atoms are omitted for clarity).

44X.Feng et al./Inorganic Chemistry Communications 50(2014)42–47

1D uniform chains of classical spins [24,25]based on the spin Hamiltonian H =?=?J ?1?2.The magnetic data of polymer 1can be properly ?tted using the following equations (Eqs.(1)and (2)),where N ,g ,βand k have their usual meanings.^H ??J ^S 1^

S 2e1T

χbi ?

Ng 2β2k T

A t

B x 2h i 1t

C x t

D x 3h i ?1

e2T

χM ?

χbi 1?2z J 0N βg χbi

e3T

where A =2.9167,B =208.04,C =15.543,D =2707.2and x =|J |/k T.Molecular ?eld approximation [26](z J ′)was added in Eq.(3)to

explain the actual magnetic property of 1.The least-squares ?tting of magnetic susceptibilities leads to J =?1.27cm ?1,g =2.02,z J ′=?0.22cm ?1,and R =1.16×10?3(R is the agreement factor de ?ned as R =Σ[(χM )obs ?(χM )calc ]2/Σ[(χM )obs ]2).The small negative values of J and z J ′further corroborate the presence of weak antiferromagnetic in-teractions between Mn II ions through carboxylic bridging.It is interesting to compare the magnetic properties with analogous complexes con-taining Mn 4units previously reported,[Mn 4(tbip)4(bbp)2(H 2O)2](J =?0.49cm ?1,g =2.26,H 2tbip =5-tert-butyl isophthalic acid,bbp =1,3-bis(benzimidazol)propane);[C(NH 2)3]8[(Mn II )4(cit)4]·8H 2O (J =?0.82cm ?1,g =1.92,cit =citrate);[L14Mn 4](ClO 4)4(J =?0.87±0.01cm ?1,g =2.06,HL1=2-((2-(bis(pyridin-2-ylmethyl)amino)ethyl)(methyl)amino)acetic acid);[L24Mn 4](ClO 4)4(J =?0.91±0.01cm ?1,g =2.02,HL2=2-(benzyl(2-(bis(pyridin-2-ylmethyl)amino)ethyl)amino)acetic acid);[Mn 4(L)2(phen)8(H 2O)2][ClO 4]2·3H 2O (J =?0.7cm ?1,g =2.0,H 2L =5′-methyl-2,2′-bipy-6-phosphonic acid),which shows very weak antiferromagnetic interactions [22,27–29].In this case,J =?1.27cm ?1,the moderate weak antiferro-magnetic exchange coupling is possibly attributed to complete

coplanar

Fig.3.Illustration of the 1D double-zigzag chains along the b

axis.

Fig.4.Schematic illustration of 1D double chains are extended into a 2D corrugated-shape structure via isophthalic acid moieties along a b plane,and some fragments of oxalate and bipyridine are omitted for clarity.

X.Feng et al./Inorganic Chemistry Communications 50(2014)42–47

Mn 4subunits and in which the shorter Mn II \Mn II distances,as well as supramolecular interactions such as various H-bonding in contributing the electron transferring.

In summary,a novel Mn II polymer containing both the ddpp and oxalate auxiliary ligand has been successfully synthesized.Polymer 1displays a 2D corrugated-shape structure with 1D double-zigzag chains constructed from tetranuclear Mn II clusters.It shows high thermal sta-bility and moderate antiferromagnetic interactions within polymer.Subsequent works will be focused on the construction of novel coordi-nation polymers based on other polynuclear metal clusters by using similar organic ligands.Acknowledgments

This work is supported by the National Natural Science Foundation of China (Nos.21273101and 21271098),the Program for Backbone Teachers in Universities of Henan,(No.2012GGJS158),the Program for Science &Technology Innovation Talents in Universities of Henan (2014HASTIT014),the Tackle Key Problem of Science and Technology Project of Henan,China (No.142102310483),and the Program for University of Malaya (UM.C/625/1/HIR/247).Appendix A.Supplementary material

CCDC 1016767contains the supplementary crystallographic data for this paper.These data can be obtained free of charge from the

Cambridge Crystallographic Data Centre via https://www.wendangku.net/doc/1b8937941.html,/data_request/cif ,or e-mail:deposit@https://www.wendangku.net/doc/1b8937941.html, .Supplementary data associated with this article can be found in the online version,at https://www.wendangku.net/doc/1b8937941.html,/10.1016/j.inoche.2014.10.015.References

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The

Fig.5.Thermo-gravimetric (black)and differential thermal analysis (blue)curves for polymer 1.(For interpretation of the references to color in this ?gure legend,the reader is referred to the web version of this

article.)

Fig.6.Temperature dependence of χM T (□)and χM (○)versus T for polymer 1.The solid line represents the best ?t obtained from the Hamiltonian given in the text.

46X.Feng et al./Inorganic Chemistry Communications 50(2014)42–47

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