Structural diversity of 1,3-propylenediaminetetraacetato metal complexes: From coordination monomers to coordination polymers and MOF materials

Accepted Manuscript Review article Structural diversity of 1,3-propylenediaminetetraacetato metal complexes: from coordination monomers to coordination polymers and MOF materials Mao-Long Chen, Zhao-Hui Zhou PII: DOI: Reference:

S0020-1693(17)30066-X http://dx.doi.org/10.1016/j.ica.2017.01.012 ICA 17405

To appear in:

Inorganica Chimica Acta

Received Date: Revised Date: Accepted Date:

12 September 2016 12 January 2017 13 January 2017

Please cite this article as: M-L. Chen, Z-H. Zhou, Structural diversity of 1,3-propylenediaminetetraacetato metal complexes: from coordination monomers to coordination polymers and MOF materials, Inorganica Chimica Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.01.012

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Structural diversity of 1,3-propylenediaminetetraacetato metal complexes: from coordination monomers to coordination polymers and MOF materials Mao-Long Chen1,*, Zhao-Hui Zhou 2,* 1

College of Chemistry and Biological Engineering, Changsha University of Science & Technology,

Changsha 410114, China; 2 State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China Abstract 1,3-propylenediaminetetraacetic acid (1,3-H4 pdta, C11 H 18 N2 O 8 ) is an aminopolycarboxylic acid and has been researched widely. It is a hexadentate ("six-toothed") ligand as a typical chelating agent. In neutral solution, it mainly formed water-soluble monomeric coordination complexes [TM(1,3-pdta)(H 2 O)x] y- (TM = transition metal; x = 0,1; y = 1,2) when coordinated with first transition metals. When involving lanthanide complexes, monomeric and dimeric complexes, different kinds of one-dimensional (1D) and two-dimensional (2D) coordination polymers were isolated. In acidic solution, the coordination modes of 1,3-pdta ligand were widely increased with the variation of acidity and temperature of the solution. Keywords: 1,3-propylenediaminetetraacetic

acid; coordination complex; coordination polymer;

coordination mode; transition metal; lanthanide _________________________ * Corresponding author. E-mail address: [email protected] (M.-L. Chen). * Corresponding author. Tel.: +86 592 2184531; fax: +86 592 2183047 E-mail address: [email protected] (Z.-H. Zhou). _________________________

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Contents 1. Introduction ..........................................................................................................................................3 2. Monomeric complexes ..........................................................................................................................6 2.1 Monomeric transition metal complexes ........................................................................................6 2.2 Other monomeric complexes .......................................................................................................9 3. Dimeric and multi-meric complexes .....................................................................................................9 3.1 Lanthanide complexes ............................................................................................................... 10 3.2 Transition metal complexes ....................................................................................................... 11 4. CPs isolated in neutral solution ........................................................................................................... 12 4.1 Lanthanide CPs isolated in neutral solution ................................................................................ 12 4.2 Other CPs isolated in neutral solution ........................................................................................ 14 5. CPs isolated in acidic solution............................................................................................................. 16 5.1 Lanthanide CPs isolated in acidic solution ................................................................................. 16 5.2 Other CPs isolated in acidic solution .......................................................................................... 18 Acknowledgements ................................................................................................................................ 26 Appendix A ............................................................................................................................................ 27

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1. Introduction In recent years, the chemistry of metal-coordination complexes has been advanced due to their diverse topologies and potential applications in smart optoelectronic, magnetic, microporous and biomimetic materials with specific structures, properties, and reactivity [1-10]. Metal carboxylate chemistry has enhanced extensively because of the increasing importance of hybrid inorganic-organic complexes with potential applications in separation, catalysis, and gas storage [10-16]. So far, research on coordination complexes has considerably been concentrated on incorporation of s-, d-, and f-block metal ions or two or more type of metal ions as coordination centers and kinds of carboxylates as ligands. Aminopolycarboxylic ligands especially edta-type (H 4edta = ethylenediaminetetraacetic acid) ligands are an important type of polycarboxylic ligands. There are many ligands similar to edta ligand

(e.g.

1,3-H 4pdta

=

1,3-propylenediaminetetraacetic

acid;

1,4-H 4bdta

=1,4-

butylenediaminetetraacetic acid; 1,2-H4cdta = 1,2-cyclohexylenediaminetetraacetic acid). The skeletal formulae of H 4edta and 1,3-H 4pdta were shown in Scheme 1. In general, 1,3-H 4pdta ligand is a tetrabasic acid with eight potential O-donor and two N-donor atoms for the formations of coordination complexes [17]. In coordination chemistry, 1,3-pdta coordinates with transition metal ions through its four carboxyl oxygen atoms and two amino-nitrogen atoms to form monomeric complexes which is similar to those of edta complexes. As shown in Scheme 2, monomeric complexes consist of discrete complex units, which may differ in coordination number and geometry. Based on the 1,3-pdta ligand coordination mode two different structural types of dimeric complexes can be distinguished. In one structural type two monomeric complex units are connected through carboxylate bridges of 1,3-pdta chelates, while in the other one 1,3propylenediamine chain serves as a bridge between metallic centers (bis-tridentate coordination mode of ligand). In addition, multimeric complexes consist of discrete unit which contain multimetal centers (A Cu4-center in Scheme 2), and a polymeric complexes consist of continuous units which are connected through 1,3-propylenediamine or carboxylate bridges. Many of the resulting coordination complexes adopt octahedral geometry with chirality. Comparing with transition 3

metals, lanthanide ions have high coordination number (CN) and coordination flexibility. For meeting the high CN of lanthanide ions, 1,3-pdta mainly form dimeric complexes with light rare earth ions and one-dimensional coordination polymers (1D-CPs) with heavy rare earth ions through bridged carboxyl oxygen atoms in similar synthetic conditions, which were different to those of edta complexes. In addition, the dentate number (DN, in this manuscript, it means the number of all coordination bonds including bridged bonds that one ligand formed) of 1,3-pdta reached eight. Douglas and Radanovic [18] had reviewed the coordination chemistry of hexadentate edta-type and structurally related ligands with M(III) ions in 1993. They had given descriptions for the configuration and conformation of the early reported coordination complexes of edta and structurally related ligands. Here we will focus on the coordination diversity of 1,3pdta ligand in different coordination complexes that synthesized from different conditions.

Scheme 1. Skeletal formulae of ethylenediaminetetraacetic and 1,3propylenediaminetetraacetic acids.

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Scheme 2. Skeletal structures of monomeric, dimeric, tetrameric and polymeric coordination complexes with 1,3-propylenediaminetetraacetes. In industry, these chelate ligands mainly been used to sequester metal ions in aqueous solution. In the textile industry, they prevent metal ion impurities from modifying colors of dyed products by competitive chelation of metal ions [19]. In the pulp and paper industry, they inhibit the catalytic ability of metal ions from catalyzing the disproportionation of hydrogen peroxide by chelating metal ions, which was used in "chlorine-free bleaching" [20]. In decades of years, these ligands have assumed an important place among quantitative chemical techniques, ie., edta titration method in analytical chemistry [21]. Most of the interest in this work comes from the fact that 1,3-pdta ligand shows higher ability to act as a hexadentate ligand than that of edta. This is because the increased length and flexibility of the diamine ring. For ethylenediaminetetraacetato lanthanide complexes, they often form monomeric complexes like transition metal complexes [22], while 1,3-propylenediaminetetraacetato lanthanides exists as dimeric complexes [Ln2(1,3pdta)2(H2O)4]2- or polymeric complexes [Ln(1,3-pdta)(H 2O)]n-. These differences come from the high CN of lanthanide ions and the coordination flexibility of 1,3-pdta ligand. Due to these reasons, sorts of 1,3-pdta lanthanide complexes were isolated and showed different coordination modes to those of 1,3-pdta transition metal complexes. In this review, we focus on 1,3-pdta complexes by emphasizing the coordination diversity of 1,3-pdta ligand from all X-ray determined structures, which related directly to the synthetic conditions and the type of central metal ions, rather than describing potential applications of these complexes. In this perspective, we aim to highlight the important roles or advantage of changing synthetic conditions especially the pH value in the isolation of different coordination complexes from the same metal ion and ligand, thereby increasing our understanding of synthesis–structure relationships and aiding the further design of coordination complexes with potential applications. We can conclude that the 1,3-pdta is not only a strong chelate ligand to form monomeric complexes, but also a complicated ligand to form kinds of CPs from different synthetic conditions.

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2. Monomeric complexes As mentioned before, 1,3-pdta often coordinates with central metal ions through two amino-nitrogen atoms and four carboxyl oxygen atoms to form monomeric complexes. The central metal ions are mainly first transition metals and very few other metals. 2.1 Monomeric transition metal complexes Interest for 1,3-pdta complexes started in the 1960s and was motivated by the research of the edta complexes in analytical uses [23-26]. Nagao et al. [27] reported the first explicit crystal structure of 1,3-pdta cobalt complex K[CoIII(1,3-pdta)]·2H 2O (1) in 1972 as shown in Figure 1. Two amino-nitrogen atoms and four carboxyl oxygen atoms coordinated with the central cobalt ion. The six-membered 1,3-propylenediamine-cobalt ring takes a twist-boat conformation and the absolute structure of 1 was determined by the measurement of its optical properties and could be designated as Λ configuration [27]. Due to the limited calculation ability at that time, they did not attach hydrogen atoms to the structure. Herak et al. [28] reported two structures Na[M(1,3pdta)]·3H 2O [M = CrIII, 2; RhIII, 3] in later. They further reported the detail structures of this two complexes with attached hydrogen atoms (Figure 2) in a full research article [29]. Complexes 2 and 3 were isormorphous and belonged to the orthorhombic system, which showed one more crystal water molecule than that of complex 1. These two complexes both took a twist-boat conformation and a Λ configuration. Detailed bond lengths and angles, hydrogen bonds and conformation of chelate rings were shown in the full research article [29]. Thus, these reports were good guide to the later research work of 1,3-pdta complexes. [Figures 1 and 2] Bommeli et al. [30] reported a 1,3-pdta iron complex NH 4[FeIII (1,3-pdta)]·H 2O (4). This complex showed a similar structure to the former complexes 1-3. It is also worth to note that they thought that the anion [FeIII(1,3-pdta)]- of this complex may exist an equilibrium with [FeIII(1,3pdta)(H2O)]- in aqueous solution. By contrast, the corresponding edta complex adopts a sevencoordinated structure with the seventh coordination site occupied by a water molecule [31]. This 6

observation implies that the iron ion was slightly big to be encircled in an octahedral environment by edta but can just be encircled by [1,3-pdta]4-. Quickly, Yamamoto et al. [32] and Okamoto et al. [33] reported another two iron complexes Li[FeIII(1,3-pdta)]·3H2O (5) and Na[FeIII(1,3pdta)]·3H 2O (6) respectively. These two complexes also had a similar anion structure with the same configuration to those of complexes 1-4. Meier et al. [34] discovered that there was an equilibrium between the twist-boat (tb) and half-chair (hc) conformers of the central diamine chelate ring of [FeIII (1,3-pdta)]- in solid and aqueous solution which was supported by experimental and calculated Raman spectra using Density Functional Theory. They first demonstrated how the combined applications of Raman spectroscopy and quantum chemical methods could be used to quantify the equilibrium species involved in the inter-conversion of labile coordination isomers. Robles et al. [35] reported a crystal structure of vanadium complex Na[VIII(1,3-pdta)]·3H2O (7) in 1993. This was the first example of a hexacoordinated vanadium complex containing a diamine-polycarboxylate ligand. Its anion structure was also in a distorted octahedral geometry with Λ configuration as shown in Figure 3. The authors also researched the temperature dependence of the electronic spectra for an aqueous solution of Na[VIII(1,3-pdta)]·3H 2O (7) between 10 and 50 oC. Interestingly, they found that the spectral change exhibited an new point at 628 nm and gave a possible explanation that this system existed an equilibrium between the sixand seven-coordinated species ([VIII (1,3-pdta)]− and [VIII(1,3-pdta)(H 2O)]−). This phenomenon was similar to those of iron complexes. The central metal ions of complexes 1-7 were all trivalent. [Figure 3] After the report of 1,3-pdta vanadium complex, the next crystal structure of monomeric 1,3pdta complex was reported until 2000, and its central metal ion was a divalent copper ion [36]. Then, a series of divalent central metal complexes including [Mg(H 2O)6][M(1,3-pdta)]·2H2O [M = CuII, 8 [36]; NiII, 9 [37]; CoII, 10 [38]; Zn, 11 [39] and Mg0.5Mn0.5, 12 [40]], [MnII(H 2O)6][CuII (1,3-pdta)]·2H 2O (13) [41], [CoII(H 2O)6][Co II(1,3-pdta)]·2H2O (14) [38], [Zn(H2O)6][Zn(1,37

pdta)]·2H 2O (15) [39], [Mg(H2O)6][M(1,3-pdta)(H2O)]·2H 2O [M = CdII, 16 [39, 40]; and MnII, 17 [40]] were reported. Complexes 8-15 were all crystallized in space group of Pnna and contained two octahedral coordination sites. Their central ions were surrounded by two amino-nitrogen atoms and four carboxyl oxygen atoms of the 1,3-pdta ligand, making a tetragonaly distorted MN2O 4 octahedron as shown in Figure 4a. The cation [M’(H2O)6]2+ could be described as a very regular M’O 6 octahedron (Figure 4b). Figure 5 shows the packing polyhedral diagram of these complexes. The central metal ions of complexes 16 and 17 display a seven fold coordination with the hexadentate 1,3-pdta ligand and one coordination water molecule (Figure 6) which was different to those of complexes 8-15. It was worth to note that thermal analysis of complex 13 showing it loses its eight water molecules to yield an anhydrous complex [MnCu(1,3-pdta)] (18) at 110 °C. Further variable-temperature magnetic susceptibility measurements indicated that no magnetic interactions were present in 13 while weak antiferromagnetic interactions were found in 18 [41]. This result could lead the researches to synthesize some new materials from thermal treatments to precursors of coordination complexes. All complexes 8-17 contained a divalent cation. The first divalent central metal 1,3-pdta complex Li2[CoII(1,3-pdta)]·5H 2O (19) with two monovalent cations was reported by Rychlewska et al. [42]. This complex constituted the first example of a metal (II) complex of 1,3-pdta with two monovalent ions as the chargecompensating cations. The structure was built of two tetrahedrally coordinated Li+ cations, one octahedral [CoII (1,3-pdta)]2- anion and five water molecules, two of which were uncoordinated. In order to obtain 19, authors applied the ion exchange column technique. Though attempts to use the same technique for the preparation of the analogous salts with other monovalent ions always yield the corresponding [CoIII(1,3-pdta)]- complex, this technique was a quite meaningful method to isolate kinds of complexes with different compensating ions. [Figures 4-6] A

mixed

cobalt-ion-based

octamolybdate

(H 3O)4[CoII(H 2O)6)]·[CoIII(1,3-

pdta)]2·[MoVI8O 26]·6H 2O (20) without spectroscopic characterization was reported by Sun et al.

8

[43]. In the hydrothermal reaction process (stirred at 353 K for about two hours), some diavlent CoII ions were oxidized to CoIII ions. This complex featured two anionic cobalt complexes and one octamolybdate anion, three cationic hydronium and one hexaaquacobalt (II) ions, and six crystal water molecules, formed an inorganic-organic hybrid. These cationic and anionic components and crystal water molecules were linked together to form a three-dimensional framework connected by various hydrogen bonds as shown in Figure 7. [Figure 7] 2.2 Other monomeric complexes Besides the monomeric transition metal complexes, there are also few complexes with alkaline earth, lanthanide or other metals. A magnesium complex [Mg(H2O)6][Mg(1,3pdta)]·2H 2O (21) was isolated by adding Ba[Ba(1,3-pdta)]·2H2O to the solution of MgSO 4·6H 2O, and stirring for nine hour at 90 °C (the reaction mixture was kept at a certain volume by adding distilled water), then removing precipitated BaSO 4 by filtration [44]. The crystal structure of this complex appeared to be isomorphic with the other 1,3-pdta metal (II) complexes 8-15. Wang et al. [45] reported a gallium complex K[GaIII (1,3-pdta)]·3H 2O (22) with similar structure to those of some trivalent transition metal complexes. As mentioned in the first section, 1,3-pdta lanthanide complexes often form polymeric complexes, and only one monomeric lanthanide complex NH 4[Yb(1,3-pdta)(H 2O)2]·5H 2O (23) was reported [46]. The central ytterbium ion was eight-coordinated with one hexdentate 1,3-pdta ligand and two coordinated water molecules (Figure 8) and the YbN 2O 6 of the anion formed a pseudo-square anti-prismatic polyhedron. [Figure 8] 3. Dimeric and multi-meric complexes This type of 1,3-pdta complexes are mainly affected by central metal. To our knowledge, there are only two metal type (Ln3+ and Mo VI) formed dimeric 1,3-pdta complexes [30, 47-50]. Interestingly, two

9

tetrameric 1,3-pdta copper complexes and one hexameric tungsten complexes were also reported recently [51, 52]. 3.1 Lanthanide complexes The first reported dimeric 1,3-pdta coordination complex was a lanthanum complex (NH 4)2[La2(1,3-pdta)2(H2O)4]·4H 2O (24) [30]. Recently, structures of four dimeric 1,3-pdta lanthanide complexes (NH4)2[Ln 2(1,3-pdta)2(H 2O)4]·8H2O [Ln = La, 25; Ce, 26] and K 2[Ln2(1,3pdta)2(H2O)4]·11H 2O [Ln = La, 27; Ce, 28] that isolated in neutral solution with different numbers of crystal water molecules were reported [50]. A similar dimeric 1,3-pdta samarium complex K2[Sm2(1,3-pdta)2(H2O)4]·4.5H2O (29) was also reported [47]. Figure 9 shows the typical dimeric anion structure of these complexes. Each Ln(III) ion exists in a decadentate coordination environment, which is different from those of usual nonadentate coordination complexes in lanthanide ethylenediaminetetraacetates [22]. Here the flexible 1,3-pdta ligand plays an important role in the formation of the decadentate coordination environment. Usually, a nonadentate coordination number often exist in lanthanum or cerium ethylenediaminetetraacetates with rigid ethylene chains. Moreover, in these complexes, 1,3-pdta acted as an octadentate ligand (including bridged bonds). It used two nitrogen atoms and four carboxyl oxygen atoms to chelate one lanthanide ion, while one of the carboxyl group forms a four-membered ring with the other lanthanide ion, forming a dimeric structure. Lanthanum complex 24 was a good precursor for the lanthanum oxide, which showed good catalytic activities for oxidative coupling of methane. Moreover, authors also studied the solution state of dimeric lanthanum complex 24. The results of solution NMR showed it might convert to a monomeric state when dissolving in water as shown in Scheme 3. This process may result in the increase of entropy of the system, which makes the dissociation process be favorable. When referred to heavier lanthanide elements like europium, it formed a dimeric complex K 2[Eu2(1,3-pdta)2(H 2O)2]·6H 2O (30) with fewer coordination water molecules for the lanthanide contraction [49]. [Figure 9]

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Scheme 3 Conversion of dimeric lanthanum 1,3-propylenediaminetetraacetate to its monomer when dissolving in water. 3.2 Transition metal complexes Two dimeric 1,3-pdta molybdenum(VI) complexes (NH4)5[MoVI2O 6(1,3-pdta)]Cl·2H 2O (31) and

K 4[MoVI2O 6(1,3-pdta)]·3H 2O

(32)

were

reported

in

the

investigations

on

aminopolycarboxylato molybdates [48]. Complexes 31 and 32 consisted of a molybdenumpropylenediaminetetraacetate adduct in 2:1 stoichiometric ratio. Figure 10 shows the perspective view of the dimeric anion structure. Each molybdenum atom was octahedrally surrounded by three terminal oxygen atoms, and a tridentate iminodiacetate ligand, which binds through two carboxyl oxygen atoms and one nitrogen atom. Authors also studied the solution 1

13

C-NMR and

H-NMR spectra of complexes 31 and 32 for the solution state of these complexes. The NMR

spectra showed that these two complexes partially decomposed in the solution. The amount of free ligands (～5% for 31 and ～27% for 32) were estimated from the 1H NMR spectra. At first, it was quite confusing that the amounts were different between 31 and 32. After a meticulous check, the authors attribute this to different pH values of the solution of 31 and 32. [Figure 10] A tetrameric 1,3-pdta copper complex [CuII4Cl4(1,3-H2pdta)2] (33) was isolated from an acidic solution [51]. It could be converted to its hydrated derivative [CuII4(1,3-pdta)2(H2O)4]·H2 O (34) under heating at 70 oC with the addition of Zn(OAc)2. The four copper ions of both complexes were in tetrahedral configuration (Cu 4-cluster) as shown in Figures 11 and 12. Complex 33 consisted of a tetrameric neutral unit [CuII4Cl4(1,3-H 2pdta)2] with four coordinated Cl−, which extended into a 3D supramolecular structure by inter-molecular hydrogen bonds 11

[O3···Cl(1) 3.155(6) Å] as shown in Figure 11b. The structural unit of complex 34 consisted of a tetrameric neutral unit and a crystallized water molecule but without Cl−. From the Infrared Spectroscopy (IR), obvious absorption band at 1725 cm-1 was attributed to the protonated carboxyl groups in 33. Moreover, these two tetrameric copper complexes could be used for the catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone with hydrogen peroxide in acetonitrile. Because the coordinated water molecule was more labile than the coordinated chlorine, complex 34 showed better catalytic activities than that of 33. [Figures 11 and 12] Besides the dimer and tetramer, Yu et al. [52] reported a tungsten complex (PPh4)4[(WVI3SO 3)2(1,3-pdta)3]·39H 2O

(35)

characterized

by

UV-vis,

NMR

and

Mass

Spectroscopy. The structures of 35 showing that two W3SO 3 clusters were both coordinated and linked by three 1,3-pdta ligands to form 2:3 cluster-ligand or 2:1 metal-ligand complexes as shown in Figure 13. It also contained a C2 symmetry in the center of the molecule which related the two coordinated W3SO 3 units and a pseudo C3 axis existing through the two u 3-S atoms. The properties of tungsten (such as easy to form polyoxometalates) should play a key factor in the formations of this complex. [Figure 13] 4. CPs isolated in neutral solution In recent years, many 1,3-pdta CPs were isolated from both neutral and acidic solutions. For the clear classification of the 1,3-pdta CPs, we will only discuss the CPs isolated from neutral solution in this section. We will discuss the CPs isolated from acidic solution was different to those of the CPs isolated from neutral solution in next section. 4.1 Lanthanide CPs isolated in neutral solution Lanthanide ions with high charge states always tend to coordinate with oxygen atoms easier than nitrogen atoms. This is due to that there is a high affinity between lanthanide ions and hard oxygen donor atoms. When in neutral solution, the amino-nitrogen and carboxyl oxygen atoms will both chelate the central lanthanide ions but bond distances of Ln-N were longer than that of 12

Ln-O bonds. Wang et al. [53-57] had reported a series of 1D 1,3-pdta lanthanide CPs [H 2en]0.5n[Ln(1,3-pdta)(H 2O)]n·4nH2O {Ln = Gd, 36 [53]; Tb, 37 [54]; Y, 38 [58]} and [NH 4]n[Ln(1,3-pdta)(H2O)]n·nH 2O {Ln = Sm, 39 [55]; Eu,40 [56]; Er, 41 [57]} in recent years. Yttrium (Y) is a silvery-metallic transition metal chemically that is similar to the lanthanides and has often been classified as a "rare earth element". Therefore, we will discuss yttrium complexes in the part of lanthanide complexes too. These complexes had the same anion coordination mode with [Ln(1,3-pdta)(H 2O)]-. The central lanthanide ions of these complexes were all eightcoordinated with two amino-nitrogen atoms and four carboxyl oxygen atoms from one hexadentate 1,3-pdta ligand, one water molecule and one bridging carboxyl oxygen atom from a neighboring 1,3-pdta ligand as shown in Figure 14. The bridging carboxyl oxygen atom connects each [Ln(1,3-pdta)(H2O)]- anion to generate an extended 1D zigzag chain. The authors reported that complex 39 was [Ln(1,3-Hpdta)(H2O)]n·2nH 2O [55], but we think it is same as those of complexes 40 and 41 for they all had same crystal cell parameters. [Figure 14] When involving the synthesis of lanthanum complexes in neutral solution, a new type of thermal stable metal-organic framework (MOF) [La(H2O)4[La(1,3-pdta)(H 2O)]3]n·12nH 2O (42) was isolated and characterized [59]. This complex contained open-channels that showed significant and unusual solvent transport properties and demonstrates use for low-pressure desalination. Moreover, it could be converted reversibly to its trihydrates [La(H 2O)4[La(1,3pdta)(H2O)]3]n·3nH 2O (42a), dehydrated product [La(H 2O)4[La(1,3-pdta)(H2O)]3]n (42b) and ethanol adduct [La(H2O)4[La(1,3-pdta)(H 2O)]3} n·3nH 2O·3nEtOH (42c). Due to the 10.0 Å hydrophobic open-channel (Figure 15a), crystal 42 with regular hexagonal appearance could be used directly for saline water desalination in small-scale at an ambient temperature, demonstrating a low energy consumption and environmentally friendly method for desalination as shown in Figure 15b. The hydrophobic open-channel also contained water nanotubes (WNTs, Φ = 4.2 Å;

13

the detail water nanotubes were shown in Figure 16), which was favorable for the mobility of water molecules in the open-channel. [Figures 15 and 16] Interestingly, when adding excess strontium nitrate in neutral solution of 1,3-pdta and lanthanum ions, a 2D-CP [La2(1,3-pdta)2(H 2O)4]n[Sr2(H 2O)6]n[La2(1,3-pdta)2(H2O)2]n·18nH2O (43) was isolated at 70

o

C [50]. It used two kinds of dimeric lanthanum units [La2(1,3-

pdta)2(H2O)4] and La2(1,3-pdta)2(H 2O)2] to form a chain and extended to a 2D-CP through strontium ions and bridged oxygen atoms as shown in Figure 17. This made it form a kind of fourteen membered metals ring linked by oxygen atoms from carboxyl oxygen atoms of 1,3-pdta. Its poly-shaped thermal decomposition product showed good catalytic activities for the reaction of oxidative coupling of methane. [Figure 17] 4.2 Other CPs isolated in neutral solution Only two neutral 1,3-pdta transition metal CPs were reported because 1,3-pdta often coordinate with transition metal through its two nitrogen atoms and four carboxyl oxygen atoms to form monomeric complexes. The reaction of molybdates with 1,3-pdta ligand resulted in a 1DCP [NH 4]8n[MoVI10O 32(1,3-pdta)]n·30nH 2O (44) [60]. Its decamolybdate clusters were covalently linked by1,3-pdta ligands to form unusual meso-helical chains as shown in Figure 18. This was the first time to synthesize organopolyoxometalate polymer in aqueous media, which opened a green chemical approach to the fabrication of polyoxometalate-based polymers. We also found that polymer 44 could be transformed from the dimeric complex (NH 4)5[MoVI 2O 6(1,3pdta)]Cl·2H 2O (31) and γ-MoVI 8O26 [48], and it seems that each γ-MoVI8O 26 unit was linked by [MoVI 2O 6(1,3-pdta)] to form the 1D meso-helical chain. This polymer was isolated from weak acidic solution (3.5-4.5), but the ligand was fully deprotonated to coordinate with central molybdenum ion. Thus, we discussed this polymer in this section. The second transition CP was [Cd 2(1,3-pdta)(H2O)2]n (45) [61], which was reported recently. The center Cd2+ ion was sevensurrounded by one nitrogen atom, five oxygen atoms from four different carboxyl groups 14

belonging to three 1,3-pdta ligands, and one coordinated water molecule. This polymer was also microporous (7.0%), containing small 1D open channel along the c direction. [Figure 18] Because of the long radius and less affinity to donor atoms, alkaline earth metals often coordinate with carboxylate ligand weakly. Thus, when alkaline earth metals (except for Mg) react with 1,3-pdta ligand, they often form CPs without discrete units. The first structural report was a calcium complex [Ca2(H 2O)6]n[Ca(1,3-pdta)(H2O)]2n·4nH2O (46) [44] which was synthesized in a similar method to that of monomeric magnesium complex 21. It consisted of infinite one-dimensional chains of ligand-bridged coordination complexes connected by hydrogen bonds (Figure 19). And no discrete complex was isolated. After this, another calcium coordination polymer K 4n[Ca2(1,3-pdta)2]n ∙ 2H 2O ∙ 2CH3OH (47) was solvent-thermal (80 oC, 18 hours) isolated at pH = 9.0 [62]. The calcium ions in this complex exist in hepta-coordination environment. Except the IR characterization, authors also did NMR techniques to characterize this complex and found an obvious downfield shift (∆δ = 2.09 ppm, differs from methanol in D2 O solvent) for methanol in 47. The synthesis conditions showed that different pH values, compensation cations and solvent might result in different products. [Figure 19] In recent years, three other IR characterized 1,3-pdta alkaline earth complexes [M2(1,3pdta)(H2O)6]n·nH2O [M = Sr, 48 [63]; Ba, 49 [64]] and [Sr2(1,3-pdta)(H 2O)3.5]n (50) [64] were reported. In these complexes, the hexadentate 1,3-pdta ligand joined to two central ions via the diamine chain and acted as a bis-tridentate ligand as shown in Figures 20 and 21. All Sr and Ba ions displayed coordination number nine and formed CPs through bridged oxygen atoms. In complexes 48 and 49, each alkaline earth ion triply bridged to other two alkaline earth ions. The triple bridging achieved via one water molecule and two carboxyl oxygen atoms. In complex 50, there were two coordination modes of Sr2+ ion, which was different to those of 48 and 49. [Figures 20 and 21]

15

A lead CP [PbII4(1,3-pdta)(aip)2(H 2O)4]n (51) [61] which was the only one 1,3-pdta complex with a second organic ligand (aip = 5-aminoisophthalate anion) was reported recently. In complex 51, there were two types of Pb 2+ ions with different coordination environments. Pb1 connected with five carboxyl oxygen atoms from three aip, one nitrogen atom from one aip and two carboxyl oxygen atoms from two 1,3-pdta ligands, while Pb2 was seven-coordinated by four oxygen atoms from two 1,3-pdta ligands, one nitrogen atom from one of the two 1,3-pdta ligands, and two oxygen atoms from two coordinated water molecules. These made it form a 3D network with a free volume of about 8.6%. Except for this multi-ligand lead complex, Dai et al. [65] report three lead 1,3-pdta CPs K 4n[PbII2(1,3-pdta)2]n·6nH2O (52), [PbII 2(1,3-pdta)(H2O)4]·4nH2O (53) and [PbII 2(1,3-pdta)(H2O)2]n (54) which were obtained from the direct reactions of lead nitrate with 1,3-propylenediaminetetraacetic acid in different conditions. These complexes had been fully characterized by EA, IR, solution and solid-state

13

C NMR spectra, thermogravimetric and

structural analyses. Interestingly, the MOF structure of 53 contains a unique (H 2O)26 cluster and a 5.2 Å pore, which exhibits selective and reversible adsorption for methanol. 5. CPs isolated in acidic solution Recently, many 1,3-pdta CPs were isolated from acidic solution. Many new coordination modes of 1,3-pdta ligand were found in these complexes. In acidic solution, at least one nitrogen atom of 1,3-pdta ligand would protonated and often not coordinated with central ions except with copper ions. For copper complexes, the nitrogen atoms were coordinated with copper ions while two carboxyl oxygen atoms were protonated, which showed that copper ions were affinitive to the donor of nitrogen atoms. Although many acidic CPs had been isolated and characterized but little CPs with good properties had been reported. There is still much room for us to do more research work. 5.1 Lanthanide CPs isolated in acidic solution Gao et al. [66] reported the first acidic 2D lanthanide CP [Y(1,3-Hpdta)(H 2O)]n·3nH 2O (55) which was isolated from the direct hydrothermal reaction of Y2O 3 and 1,3-H 4pdta at the ratio of 1:2. Recently, twenty acidic 1,3-propylenediaminetetraaceto lanthanide CPs were isolated from acidic solution [67]. In the former section, we showed that reactions of lanthanide salts with 1,316

pdta resulted in the coordination of amino-nitrogen atoms and carboxyl oxygen atoms in neutral solution. In this section, water-soluble CPs had been isolated from acidic solution which showed that amino-nitrogen atoms do not coordinate with lanthanide ions and could be transformed to the other acidic CPs in different synthetic conditions as shown in Scheme 4. The synthesis of water soluble CPs [Ln(1,3-H 3pdta)(H2O)5]n·Cl2n·3nH 2O [Ln = La, 56; Ce, 57; Pr, 58; Nd, 59; Sm, 60] (type a) were carried out in strong acidic aqueous solution with high yields. Moreover, they could convert to two new 1D-CPs [Ln(1,3-H 2pdta)(H 2O)3]n·Cln·2nH 2O [Ln = Sm, 61; Gd, 62] (type b), seven 2D-CPs [Ln(1,3-H 2pdta)(H 2O)2]n·Cln·2nH 2O [Ln = La, 63; Ce, 64; Pr, 65; Nd, 66; Sm, 67; Eu, 68; Gd, 69] (type c), four 3D-CPs [Ln(1,3-Hpdta)]n·nH 2O [Ln = La, 70; Ce, 71; Pr, 72; Nd, 73] (type d) and two 2D-CPs [Ln(1,3-Hpdta)(H2O)]n·4nH 2O (Sm, 74; Eu, 75) (type e). In moderate acidic solution, lanthanide complexes showed little lanthanide contraction effect at moderate temperature. But in strong acidic solution, there were obvious differences that make the isolation of similar complexes of europium and gadolinium difficult. In high temperature, the lanthanide contraction effect made complexes 74 and 75 show different structures to those of complexes 7073 in similar reaction conditions. The type of lanthanide elements and synthetic conditions played key roles in the synthetic process. Early lanthanides like La, Ce, Pr and Nd form decadentate coordination numbers easier than those of heavy lanthanides with short ion radius due to the lanthanide contraction. The polyhedral diagrams of these five types of coordination modes were shown in Figures 22−26. The structural descriptions were not shown here and can be found in reference [67].

17

Scheme 4. Synthesis and conversions of five types of acidic lanthanide 1,3-pdta CPs. [Figures 22−26] In these CPs, at least one nitrogen atom of the 1,3-pdta ligand was protonated and not coordinated with any central lanthanide ion. This phenomenon in turn reflected that the lanthanide ions were affinity to oxygen atom. Thus, when considering the synthesis of lanthanide complexes, we must choose the oxygen donor firstly and the nitrogen donor secondly to construct lanthanide materials especially for the constructions of stable porous metal-organic frameworks. 5.2 Other CPs isolated in acidic solution Besides the acidic lanthanide CPs, a few 1,3-propylenediaminetetraacetato zinc [68, 69], copper [51], lead [65], calcium [62], strontium and barium [64] CPs were also isolated from acidic solution. The zinc and copper coordination polymers were 1D-CPs. The alkaline earth coordination polymers were 3D-CPs with two uncoordinated nitrogen atoms. In a very acidic solution, water soluble potassium 1,3-propylenediaminetetraacetato zinc chloride K 2n[ZnCl2(1,3-H2pdta)ZnCl2]n (76) and its substituted products [Zn(NO3)2(H 2O)(1,3H 4pdta)]n

(77),

[ZnBr2(H2O)(1,3-H4pdta)]n

(78),

[ZnI2(H 2O)(1,3-H 4pdta)]n

(79)

and

[Zn(NCS)2(H 2O)(1,3-H 4pdta)]n (80) were isolated as 1D-CPs as shown in Scheme 5 [68, 69]. The former was obtained from the reaction of zinc chloride and 1,3-H 4pdta at pH ~ 1.5. As shown in Figure 27, complex 76 consisted of a dimeric anionic unit [ZnCl2(1,3-H 2pdta)ZnCl2]2- with strong 18

intra-molecular hydrogen bonds. In the neutral complexes 77-80, 1,3-H 4pdta ligand linked each monomeric unit [Zn(H 2O)X2] (X = NO3, Br, I and NCS) to form the infinite 1D chain, which extended into 3D supramolecular structures by very strong inter-molecular hydrogen bonds as shown in Figure 28. 1D-CPs of 76 and 77 were both highly water-soluble. The amino-nitrogen atoms of these polymers were all protonated and showed no coordination, which implied the oxygen donor affinity of zinc ions. The solubility of 77 and insolubility of 78-80 showed that counter anion was one of the key factors in the finding of water-soluble CPs.

Scheme 5. Transformation of water soluble chloride K2n[ZnCl 2(1,3-H 2pdta)ZnCl 2]n (72) to [ZnBr2(H 2O)(1,3-H 4pdta)]n (74), [ZnI2(H 2O)(1,3-H 4pdta)]n (75) and [Zn(NCS)2(H 2O)(1,3H 4pdta)]n (76). [Figures 27 and 28] In hydrothermal condition, a [1,3-H 2pdta]2- ligand linked neutral copper polymeric chain [Cu II(1,3-H 2pdta)]n (81) was isolated, which contained strong intra-molecular hydrogen bonds [O4···O2 2.620(7) Å] [51]. The protonated carboxyl groups in 81 showed weak coordination; while nitrogen atoms were in coordination mode, which implied copper ions were affinity to nitrogen atoms. Structural analysis of 81 revealed that [1,3-H 2pdta]2- ligand links each copper ion to generate a neutral polymeric chain [CuII(1,3-H 2pdta)]n as shown in Figure 29. The coordination

19

mode was different from the usual octahedral or heptahedral coordination in mononuclear edta and 1,3-pdta copper complexes. Synthesis of copper 1,3-propylenediaminetetraacetate complexes show pH and temperature dependent modes, the pH value may affect the protonation of 1,3-pdta. Tetramer 33 and CP 81 were obtained from an acidic medium of pH 2.5 but at different temperature as shown in Scheme 6. Transformation of tetramer 33 under heating condition resulted in the formation of CP 81.

Scheme 6. Transformations of water soluble tetramer [CuII4Cl4(1,3-H 2pdta)2](33) to [CuII(1,3H 2pdta)]n (81) and [CuII4(1,3-pdta)2(H2O)4]·H2O (34). [Figure 29] Besides many lanthanide and transition CPs, there were also four alkaline earth CPs [Ca(1,3H 4pdta)(NO 3)2(H 2O)2]n (82) [62], [Ca(1,3-H 2pdta)]n·nH 2O (83) [62], [Sr(1,3-H 2pdta)]n·nH 2O (84) [64], [Ba(1,3-H 2pdta)(H 2O)3]n (85) [64] and one lead CPs [PbII(1,3-H2pdta)(H 2O)]n∙2nH 2O (86) [65] were isolated from acidic solution. CPs 82 and 83 were both isolated at acidic solution. At pH = 2.5, two of the four carboxyl groups deprotonated and coordinated strongly with calcium ions, the charge was balanced by nitrates for 82 which are similar to those of 1,3-pdta zinc CPs 74–76. When the pH value is in the range of 3.0–5.0, the nitrogen atoms still protonated and did 20

not coordinate with calcium ions, but the four-carboxyl groups all deprotonated and chelated to calcium ions to construct 83. As shown in Figures 30 and 31, in complexes 84 and 85, the nitrogen atoms of 1,3-pdta ligand were also protonated and showed no coordination with central metal ions. It was worth to note that there was no water molecule coordinate with strontium ions in complex 84 whose coordination number (CN) was eight. This was a quite abnormal coordination mode for strontium ion. The CN of complex 85 was nine and there were three coordination water molecules for each barium ion. Interestingly, there was one uncoordinated carboxyl group of the 1,3-pdta ligand in complex 85. The 2D bilayer lead CP 86 was induced by higher concentration of reactants and lower pH value [65]. In an asymmetric unit, the coordination environment of Pb (II) ion was fulfilled by seven carboxyl oxygen atoms from four different 1,3-pdta ligands and one coordination water molecules and formed a PbO 8 polyhedron. [Figures 30 and 31] 6. Summary and outlook Selected bond lengths (Å), coordination number (CN) of central metal ions and dentate number (dentate number = DN, in this manuscript, it means the number of all coordination bonds including bridged bonds that one ligand formed) of 1,3-pdta ligands for all complexes were shown in Table 1. In neutral solutions, the DN of 1,3-pdta ligands was not smaller than six. The DN was six for all monomeric 1,3-pdta complexes. This testified that 1,3-pdta used its four carboxyl oxygen atoms and two nitrogen atoms to coordinate with one central ion in neutral solution which demonstrated the huge chelate ability. The chelate ability can be utilized to improve the metal availability and mobility for environment concern or the other concerns [7073]. The dimeric complexes mainly come from the lanthanide complexes. The DN of 1,3-pdta was eight for these seven dimeric lanthanide complexes and was six for other five dimeric and multimeric transition metal complexes. In these complexes, only one complex was isolated from acidic solution, and it was a tetrameric copper complex. Fifteen 1,3-pdta CPs (eight for lanthanide, four for alkaline earth, two for transition metal and one for carbon family element Pb) were also isolated from neutral or weak acidic solution. These CPs showed many new coordination modes 21

for 1,3-pdta ligand and had very big differences between different types of coordination modes. In acidic solution, only one tetrameric 1,3-pdta complex 33 was isolated to until now, other 29 complexes were all kinds of CPs. In these CPs, the CN of center metal ions and the DN of 1,3pdta both showed differences while the synthetic conditions changed. For lanthanide complexes, obvious lanthanide contraction effects are shown in this table. The bond distances decrease with the increases of lanthanide number. The number of coordinate water molecules decreases and the DN of 1,3-pdta increases with the increase of pH values cursorily. The coordination numbers are different with the acidic condition and temperature of the solution, the minimum DN of 1,3-pdta was two in some zinc coordination polymers which had been isolated from acidic conditions. For same synthetic temperature and central metal ions, 1,3-pdta show fewer DN from acidic solutions than that from neutral solution. In the same synthetic conditions, central metal ions with larger ion radius may show bigger DN than those of central metal ions with smaller ion radius (i.e. in neutral solution and room temperature, 1,3-pdta in lanthanides complexes had bigger DN than those of trivalent transition metal complexes). These complexes highly enlarged the coordination modes of 1,3-pdta ligand.

Table 1. Selected bond lengths (Å), coordination numbers (CN) of central metal ions and dentate numbers (DN) of 1,3-pdta ligands for reported 1,3-pdta complexes.

22

Entry

M–Ocarboxy(av) M–N(av) M–Ow(av) CN DN

Ref.

Monomeric 1,3-pdta complexes K[CoIII(1,3-pdta)]·2H2O (1)

1.881(1)

1.966(1)

－

6

6

Na[CrIII(1,3-pdta)]·3H2 O (2)

1.961(1)

2.065(1)

－

6

6 [28, 29]

Na[RhIII(1,3-pdta)]·3H2 O (3)

2.024(2)

2.032(1)

－

6

6 [28, 29]

NH4[FeIII(1,3-pdta)]·H2 O (4)

1.974(3)

2.190(4)

－

6

6

[30]

Li[FeIII(1,3-pdta)]·3H2O (5)

1.989(2)

2.194(2)

－

6

6

[32]

Na[FeIII(1,3-pdta)]·3H2 O (6)

1.973(2)

2.175(2)

－

6

6

[33]

Na[VIII(1,3-pdta)]·3H2O (7)

1.978(2)

2.142(2)

－

6

6

[35]

[Mg(H2 O)6][CuII(1,3-pdta)]·2H2O (8)

2.123(2)

2.047(2)

－

6

6

[36]

[Mg(H2 O)6][NiII(1,3-pdta)]·2H2 O (9)

2.052(5)

2.073(5)

－

6

6

[37]

[Mg(H2 O)6][CoII(1,3-pdta)]·2H2O (10)

2.083(2)

2.142(2)

－

6

6

[38]

[Mg(H2 O)6][Zn(1,3-pdta)]·2H2O (11)

2.092(3)

2.155(2)

－

6

6

[39]

[Mg(H2 O)6][Mg0.5 MnII0.5(1,3-pdta)]·2H2 O (12)

2.100(2)

2.253(2)

－

6

6

[40]

[Mn(H2 O)6][CuII(1,3-pdta)]·2H2O (13)

2.129(2)

2.049(2)

－

6

6

[41]

[CoII(H2O)6][CoII(1,3-pdta)]·2H2 O (14)

2.083(2)

2.143(2)

－

6

6

[38]

[Zn(H2O)6][Zn(1,3-pdta)]·2H2O (15)

2.093(2)

2.153(2)

－

6

6

[39]

[Mg(H2 O)6][Mg(1,3-pdta)]·2H2 O (21)

2.051(2)

2.199(2)

－

6

6

[44]

[Mg(H2 O)6][CdII(1,3-pdta)(H2 O)]·2H2O (16)

2.410(1)

2.442(1) 2.252(2)

7

6 [39, 40]

[Mg(H2 O)6][MnII(1,3-pdta)(H2O)]·2H2O (17)

2.314(3)

2.429(4) 2.154(5)

7

6

[40]

Li 2[CoII(1,3-pdta)]·5H2O (19)

2.093(2)

2.131(2)

－

6

6

[42]

1.900(4)

1.950(3)

－

6

6

[43]

K[GaIII(1,3-pdta)]·3H2O (22)

1.954(2)

2.100(2)

－

6

6

[45]

NH4[Yb(1,3-pdta)(H2O)2]·5H2O (23)

2.289(2)

2.562(2)

8

6

[46]

(H3O)4[CoII(H2O)6)][CoIII(1,3-pdta)]2· [MoVI8O26]·6H2 O (20)

Dimeric and multi-meric 1,3-pdta complexes

23

[27]

(NH4)2[La2(1,3-pdta)2(H2O)4]·4H2 O (24)

No atoms

10 8

[30]

(NH4)2[La2(1,3-pdta)2(H2O)4]· 8H2O (25)

2.531(2)

2.840(2) 2.574(2) 10 8

[50]

(NH4)2[Ce2(1,3-pdta)2(H2O)4]·8H2 O (26)

2.506(2)

2.827(2) 2.552(2) 10 8

[50]

K2[La2(1,3-pdta)2(H2 O)4]· 11H2O (27)

2.531(2)

2.832(2) 2.584(2) 10 8

[50]

K2[Ce2(1,3-pdta)2(H2O)4]· 11H2O (28)

2.509(2)

2.817(2) 2.570(2) 10 8

[50]

K2[Sm2(1,3-pdta)2(H2O)4]· 4.5H2O (29)

2.454(2)

2.884(3) 2.485(2) 10 8

[47]

K2[Eu2(1,3-pdta)2(H2O)2]· 6H2 O (30)

2.36(3)

2.61(4)

2.44(3)

8

[49]

(NH4)5[MoVI2O6(1,3-pdta)]Cl· 2H2 O (31)

2.203(3)

2.342(3)

－

－ 6

[48]

K4[MoVI2O6(1,3-pdta)]· 3H2 O (32)

2.202(4)

2.350(4)

－

－ 6

[48]

[CuII4Cl4(1,3-H2 pdta)2] (33)

1.953(5)

2.031(6)

－

4

6

[51]

[CuII4(1,3-pdta)2(H2O)4]· H2O (34)

1.985(6)

2.020(7) 2.158(7)

4

6

[51]

(PPh4)4[(WVI3SO3)2(1,3-pdta)3]·39H2O (35)

2.086(7)

2.250(8)

－ 6

[52]

－

9

Neutral 1,3-pdta CPs [H2en]0.5n[Gd(1,3-pdta)(H2O)]n· 4nH2O (36)

2.368(2)

2.636(2) 2.379(2)

8

7

[53]

[H2en]0.5n[Tb(1,3-pdta)(H2 O)]n· 4nH2O (37)

2.349(2)

2.623(2) 2.368(2)

8

7

[54]

[H2en]0.5n[Y(1,3-pdta)(H2O)]n· 4nH2O (38)

2.316(2)

2.580(2) 2.348(2)

8

7

[58]

[NH4]n[Sm(1,3-pdta)(H2O)]n· nH2O (39)

2.379(2)

2.641(2) 2.450(2)

8

7

[55]

[NH4]n[Eu(1,3-pdta)(H2O)]n· nH2O (40)

2.371(2)

2.632(2) 2.363(2)

8

7

[56]

[NH4]n[Er(1,3-pdta)(H2O)]n· nH2O (41)

2.315(2)

2.572(3) 2.371(3)

8

7

[57]

[La(H2O)4[La(1,3-pdta)(H2O)]3]n· 12nH2 O (42)

2.511(4)

2.866(5) 2.530(4) 10 11

[59]

[La2(1,3-pdta)2(H2O)4]n[Sr2(H2O)6]n

2.542(2)

2.864(2) 2.504(2)

[La2(1,3-pdta)2(H2O)2]n· 18nH2O (43)

2.555(2)

2.861(2) 2.557(2)

[NH4]8n[Mo VI10O32(1,3-pdta)]n·30nH2 O(44)

2.164(8)

2.352(8)

[Cd2(1,3-pdta)(H2O)2]n(45)

2.305(3)

[Ca2(H2O)6]n[Ca(1,3-pdta)(H2 O)]2n·4nH2O (46)

10 8/9

[50]

－ 6

[60]

2.448(3) 2.335(3)

6 10

[61]

2.415(4)

2.681(4) 2.553(4)

8 11

[44]

K4n[Ca2(1,3-pdta)2]n·2H2 O·2CH3OH (47)

2.379(3)

2.566(3)

－

7

7

[62]

[Sr2(1,3-pdta)(H2O)6]n· nH2 O (48)

2.78(1)

2.98(1)

2.85(2)

9 10

[63]

24

－

[Ba2(1,3-pdta)(H2O)6]n· nH2 O (49)

2.790(4)

2.955(4) 2.851(5)

9 10

[64]

[Sr2(1,3-pdta)(H2O)3.5]n (50)

2.586(5)

2.832(4) 2.776(8)

9 12

[64]

[PbII4(1,3-pdta)(aip)2(H2O)4 ]n (51)

2.538(2)

2.701(5) 2.696(5)

8 16

[61]

K4n[PbII2(1,3-pdta)2]n·6nH2 O (52)

2.698(4)

2.665(4)

8

8

[65]

[PbII2(1,3-pdta)(H2O)4]·4nH2O (53)

2.710(8)

2.628(8) 3.092(8) 8/9 13

[65]

[PbII2(1,3-pdta)(H2O)2]n (54)

2.644(5)

2.599(5) 2.901(5)

8 14

[65]

－

Acidic 1,3-pdta CPs [Y(1,3-Hpdta)(H2O)]n· 3nH2 O (55)

2.37(2)

2.60(2)

2.34(2)

8

7

[66]

[La(1,3-H3 pdta)(H2O)5]n· Cl2n· 3nH2O (56)

2.562(5)

－

2.566(5)

9

4

[67]

[Ce(1,3-H3pdta)(H2O)5]n· Cl2n· 3nH2O (57)

2.541(4)

－

2.537(4)

9

4

[67]

[Pr(1,3-H3pdta)(H2O)5]n· Cl2n· 3nH2O (58)

2.528(4)

－

2.526(5)

9

4

[67]

[Nd(1,3-H3 pdta)(H2O)5]n· Cl2n· 3nH2O (59)

2.522(7)

－

2.513(7)

9

4

[67]

[Sm(1,3-H3pdta)(H2O)5]n· Cl 2n· 3nH2O (60)

2.493(3)

－

2.488(3)

9

4

[67]

[Sm(1,3-H2pdta)(H2O)3]n· Cl n· 2nH2O (61)

2.488(4)

－

2.445(4)

9

6

[67]

[Gd(1,3-H2 pdta)(H2O)3]n· Cln· 2nH2 O (62)

2.461(3)

－

2.417(3)

9

6

[67]

[La(1,3-H2 pdta)(H2O)2]n· Cln· 2nH2O (63)

2.505(2)

－

2.553(2)

8

6

[67]

[Ce(1,3-H2pdta)(H2O)2]n· Cln· 2nH2O (64)

2.478(2)

－

2.523(2)

8

6

[67]

[Pr(1,3-H2pdta)(H2O)2]n· Cln· 2nH2O (65)

2.460(2)

－

2.505(2)

8

6

[67]

[Nd(1,3-H2 pdta)(H2O)2]n· Cln· 2nH2 O (66)

2.447(2)

－

2.491(2)

8

6

[67]

[Sm(1,3-H2pdta)(H2O)2]n· Cl n· 2nH2O (67)

2.416(2)

－

2.464(2)

8

6

[67]

[Eu(1,3-H2pdta)(H2O)2]n· Cln· 2nH2O (68)

2.407(2)

－

2.445(2)

8

6

[67]

[Gd(1,3-H2 pdta)(H2O)2]n· Cln· 2nH2 O (69)

2.392(2)

－

2.432(2)

8

6

[67]

[La(1,3-Hpdta)]n· nH2O (70)

2.571(4)

2.858(3)

－

9

9

[67]

[Ce(1,3-Hpdta)]n· nH2O (71)

2.552(5)

2.825(3)

－

9

9

[67]

[Pr(1,3-Hpdta)]n· nH2O (72)

2.553(6)

2.798(4)

－

9

9

[67]

[Nd(1,3-Hpdta)]n· nH2 O (73)

2.523(3)

2.780(2)

－

9

9

[67]

25

[Sm(1,3-Hpdta)(H2O)]n· 4nH2 O (74)

2.481(5)

2.711(5) 2.450(6)

8

7

[67]

[Eu(1,3-Hpdta)(H2O)]n· 4nH2 O (75)

2.471(5)

2.692(5) 2.441(5)

8

7

[67]

K2n[ZnCl2(1,3-H2pdta)ZnCl2]n (76)

1.975(3)

－

－

4

4

[68]

[Zn(NO3)2(H2O)(1,3-H4pdta)]n (77)

2.075(2)

－

2.020(4)

4

4

[69]

[ZnBr2(H2O)(1,3-H4 pdta)]n (78)

2.304(4)

－

1.992(6)

5

2

[69]

[ZnI2(H2O)(1,3-H4 pdta)]n (79)

2.236(6)

－

2.04(1)

5

2

[68]

[Zn(NCS)2(H2O)(1,3-H4pdta)]n (80)

2.175(3)

－

1.986(4)

5

2

[69]

[CuII(1,3-H2 pdta)]n(81)

1.896(4)

2.068(4)

－

4

4

[51]

[Ca(1,3-H4pdta)(NO3)2(H2O)2]n (82)

2.321(3)

－

2.418(4)

8

2

[62]

[Ca(1,3-H2pdta)]n·nH2 O (83)

2.466(2)

－

－

8

8

[62]

[Sr(1,3-H2pdta)]n· nH2 O (84)

2.598(2)

－

－

8

8

[64]

[Ba(1,3-H2pdta)(H2O)3]n (85)

2.812(2)

－

2.793(2)

9

6

[64]

[PbII(1,3-H2 pdta)(H2O)]n·2nH2 O (86)

2.406(4)

－

2.601(4)

8

7

[65]

In summary, the structural determination and analysis of all 1,3-pdta metal complexes have provided many data for the coordination chemistry of chelate ligands. Formerly, it is considered that 1,3-pdta was a strong chelate ligand and always form monomeric complexes with transition metals. Here we have shown that 1,3-pdta is not only a strong chelate ligand, but also with coordination diversities to form kinds of metal CPs in different synthetic conditions. Up to now, there was only one multi-ligand metal complex isolated and structural solved. Efforts could be placed on the research of 1,3-pdta metal complexes with other ligands, the complementarities of coordination diversities of 1,3-pdta ligand and the systematic studies of 1,3-pdta metal complexes. It can forecast that with the advancement of synthetic methods and characterization technique, more and more metal complexes with kinds of potential usage constructed by chelate ligand will be isolated and reported in future. Acknowledgements 26

This project was financially supported by the Chinese National Natural Science Foundation (No. 31601550), the Foundation of State Key Laboratory of Coal Clean Utilization and Ecological Chemical Engineering (No. 2016-16) and research Funds for the Central Universities (No. 20720150041). Appendix A † ABBREVIATIONS:

1,3-H4pdta,

1,3-propylenediaminetetraacetic

acid;

H4edta,

ethylenediaminetetraacetic acid; CP, coordination polymer; 1D-CP, one dimensional coordination polymer; 2D-CP, two dimensional coordination polymer; 3D-CP, three dimensional coordination polymer; eq., equivalent; 1D, one-dimensional; 2D, two-dimensional; 3D, three-dimensional; DN, dentate number; CN, coordination number; IR, Infrared spectroscopy.

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31

Figure legends

Figure 1. The first reported crystal structure of 1,3-pdta complex K[Co III(1,3-pdta)]·2H2O (1) although without determined hydrogen [27]. Figure 2. Anion structure of Na[CrIII(1,3-pdta)]·3H2O (2) [29]. Figure 3. Anion structure of Na[V III(1,3-pdta)]·3H2O (7) in a distorted octahedral geometry [35]. Figure 4. Typical diagram of [M(H2O)6][MII(1,3-pdta)]·2H 2O. (a) anion structure of [M(1,3pdta)]2- with MN2O 4 octahedron; (b) crystal structure of [Mg(H 2O)6][M(1,3pdta)]·2H 2O with cation of [Mg(H2O)6]2+ which could be described as a very regular MgO6 octahedron [36]. Figure 5. The packing polyhedral diagram of the type of complexes [M(H 2O)6][MII(1,3pdta)]·2H 2O [36]. Figure 6. Crystal structure of [Mg(H2O)6][CdII(1,3-pdta)(H 2O)]·2H 2O (16) showed that the central Cd ions was seven-coordinated with the hexadentate 1,3-pdta ligand and one water molecule [39]. Figure 7. Polyhedral diagram of (H 3O)4[CoII(H2O)6)][CoIII(1,3-pdta)]2·[MoVI8O 26]·6H 2O (20) showed that the three-dimensional framework was connected by various hydrogen bonds [43]. Figure 8. Ortep anion structure of complex NH 4[Yb(1,3-pdta)(H2O)2]·5H 2O (23) which showed the central ytterbium ion was eight-coordinated with one 1,3-pdta ligand and two water molecules [46]. Figure 9. Ortep anion structure of dimeric 1,3-pdta lanthanide complexes which shows the central lanthanide ions were deca-coordinated [50]. Figure 10. Ortep anion structure of dimeric 1,3-pdta molybdenum complexes which showed each molybdenum ion was octahedrally surrounded by three terminal oxygen atoms, and a tridendtate iminodiacetate ligand [48]. © Royal Society Chemistry

32

Figure 11. Ortep diagram of [CuII4Cl4(1,3-H2pdta)2](33). (a) crystal structure of the tetrameric 1,3pdta copper complex 33 which shows the four copper ions exist in a quasi-symmetrical tetrahedral environment; (b) complex 33 was extends into a 3D supramolecular structure by inter-molecular hydrogen bonds [O3···Cl(1) 3.155(6) Å] [51]. Figure 12. Crystal structure of the tetrameric 1,3-pdta copper complex [CuII4(1,3-pdta)2(H2O)4]·H2O (34) which showed the four copper ions exist in a quasi-symmetrical tetrahedral environment [51]. Figure 13. Crystal structure of a tungsten complex (PPh4)4 [(WVI3SO 3)2(1,3-pdta)3]·39H2O (35) [52]. Figure 14. Polyhedral diagram of 1D lanthanide polymer of [Ln(1,3-pdta)(H2O)]- which shows the monomeric unit was extended by one bridging carboxyl oxygen atom from a neighboring 1,3-pdta ligand [56]. Figure 15. The related diagram of complex 42. (a) The diagram shows that the crystal 42 with regular hexagonal appearance could be used directly for saline water desalination in smallscale at an ambient temperature; (b) The polyhedral structure of 42 which showing the 10.0 Å hydrophobic open-channel [59]. Figure 16. The water nanotubes (WNTs, Φ = 4.2 Å) in the open-channel of crystal 42 (Hydrogen atoms were omitted for the clarity). (a) A side view of one WNT; (b) viewed down the c direction of the WNT and the contact with the open channel and shows a 4.2 Å nanotube; (c) hydrogen bonds in the open channel. The oxygen atoms in red color are from the water nano tubes, violet color represents the crystal water O4w outside the channel and the green color shows the oxygen atom of 1,3-pdta [59]. © Royal Society Chemistry Figure 17. Polyhedral diagram of the 2D-CP [La2(1,3-pdta)2(H 2O)4 ]n[Sr2 (H2O)6]n[La2 (1,3pdta)2(H2O)2]n·18nH2O (43) which was extended into 2D structure by strontium ions and bridged oxygen atoms [50].

33

Figure 18. Crystal structure of [NH4]8n[MoVI10O32(1,3-pdta)]n·30nH2O (44) which showed its decamolybdate clusters were covalently linked by 1,3-pdta ligands to form an unusual meso-helical chain [60]. Figure 19. Crystal structure of a calcium complex [Ca2 (H2O)6]n[Ca(1,3-pdta)(H2O)]2n·4nH2O (46) which shows it consists of infinite ligand-bridged one-dimensional chains [44]. Figure 20. Crystal structure of complex [Ba2(1,3-pdta)(H2O)6 ]n·nH2O (49) at 30% probability levels which shows the 1,3-pdta ligand joined to two central ions via the diamine chain and acted as a bis-tridentate ligand [64]. Figure 21. Crystal structure of complex [Sr2 (1,3-pdta)(H2O)3.5 ]n (50) at 30% probability levels which shows the 1,3-pdtaligand joined to two central ions via the diamine chain and acted as a bis-tridentate ligand [64]. Figure

22.

The

infinite

1D

acidic

zonal

coordination

structure

of

[La(1,3-

H 3pdta)(H 2O)5]n·Cl2n·3nH2O (56) [67]. Figure 23. The infinite 1D structure of [Sm(1,3-H2pdta)(H2O)3]n·Cln·2nH 2O (61) [67]. Figure 24. The infinite 2D structure of [La(1,3-H 2pdta)(H 2O)2]n·Cln·2nH2O (63) [67]. Figure 25. The infinite 3D structure of [La(1,3-Hpdta)]n·nH2O (70) [67]. Figure 26. The infinite 2D layered structure of [Sm(1,3-Hpdta)(H 2O)]n·4nH 2O (74) [67]. Figure 27. Crystal structure of water soluble potassium 1,3-propylenediaminetetraacetate zinc chloride K 2n[ZnCl2(1,3-H 2pdta)ZnCl2]n (76) [68]. Figure 28. Strong inter-molecular hydrogen bonds in the one-dimensional chains of 79 extended the infinite 1D chain into a 3D supramolecular structure [68]. Figure 29. Diagram of neutral copper polymeric chain of [CuII(1,3-H2pdta)]n (81) [51]. Figure 30. Perspective view of [Sr(1,3-H 2pdta)]n·nH 2O (84) at 30% probability levels [64]. Figure 31. Perspective view of [Ba(1,3-H2pdta)(H 2O)3]n (85) at 30% probability levels [64].

34

Figure 1

35

Figure 2

36

Figure 3

37

Figure 4

Figure 5

39

Figure 6

40

Figure 7

41

Figure 8

42

Figure 9

43

Figure 10

44

Figure 11

45

Figure 12

46

Figure 13

47

Figure 14

48

Figure 15

49

Figure 16

50

Figure 17

51

Figure 18

52

Figure 19

53

Figure 20

54

Figure 21

55

Figure 22

56

Figure 23

57

Figure 24

58

Figure 25

59

Figure 26

60

Figure 27

61

Figure 28

62

Figure 29

63

Figure 30

64

Figure 31

65

Dr. Mao-Long Chen 2008-2014: PhD. Physical Chemistry, College of Chemistry and Chemical Engineering，Xiamen University 2004-2008: BS. Pharmaceutical Engineering, College of Chemistry and Chemical Engineering, Hunan Normal University Research Interests: Coordination complexes and Food safety. Now working in College of Chemistry and Biological Engineering, Changsha University of Science & Technology

Professor Zhao-Hui Zhou PhD., MS, BS (1989, 1986, 1983), Xiamen University; Researcher (2009-2010), Lawrence Berkeley National Laboratory, Associate Professor (2009, Fiscal Year), University of California at Davis Visiting scholar (1997-1998), Eidgenössische Technische Hochschule Zürich Research Associate (1990-1992), The Chinese University of Hong Kong Research Interests: Coordination Catalysis and Enzyme Catalysis. Now working in College of Chemistry and Chemical Engineering, Xiamen University

66