Coordination Polymers Constructed from Two Vanillin Derivatives

DOI: 10.1021/cg9000945

Five Metal(II) Coordination Polymers Constructed from Two Vanillin Derivatives: From Discrete Structure to 3D Diamondoid Network

2010, Vol. 10 495–503

Shou-Hu Li, Shao-Kang Gao, Shi-Xiong Liu,* and Yun-Nan Guo Department of Chemistry, Fuzhou University, Fuzhou 350002, P.R. China Received January 24, 2009; Revised Manuscript Received November 3, 2009

ABSTRACT: Two vanillin derivatives, 4-hydroxy-3-methoxybenzaldehyde nicotinoylhydrazone (L1) and 4-hydroxy-3-methoxybenzaldehyde salicyloylhydrazone (L2), were synthesized. The two flexible ligands have been employed to assemble with Pb(II), Cu(II), or Co(II) ion, leading to the formation of five coordination polymers varying from zero- to three-dimensional structures. Complex [Pb2(L1)2(NO3)2] 3 3H2O (1) features a novel 3D diamond-like coordination network based on binuclear units as binodes and hydrazone ligands, L1, as linkers. However, complex Pb2(L1)2(OAc)2(H2O)2 (2) presents a 1D doublestrand chain structure. Two factors, the second ligand (acid ligand) and different coordination ability of water molecules, are investigated to further explore its relationship with the resultant crystalline architectures in complexes 1 and 2. The donor atoms in the two lead(II) complexes 1 and 2 can cluster to one side leaving an “open” coordination site to accommodate the stereochemically active 6s2 lone pair. Complex Cu(L2)2 (3) shows a 1D double-strand chain structure. There is an extended onedimensional structure in complex [Co3þ(L2)2(C5H5N)2] 3 ClO4 (4), while [Co2þ(L2)2(C5H5N)2] 3 2CH3OH 3 H2O (5) displays a discrete structure.

The design and construction of coordination polymers are of great interest not only because of their intriguing structural topologies1 but also because of their potential applications in gas adsorption, separation, ion exchange, heterogeneous catalysis, and so on.2,3 Using carefully selected multidentate ligands and metal ions has allowed the construction of polymers with defined geometry and special properties.4 From the structural point of view, selection of organic ligands formed by reaction between the vanillin group and the nicotinoyl hydrazine or salicyloyl hydrazine is a good choice to construct coordination polymers because of the following four reasons: (1) This kind of multidentate ligand has both two or more oxygen donors and two or more nitrogen donors. Several donors with suitable relative positions in the ligand can coordinate to two or three metal centers. (2) The vanillin group displays a variety of bonding geometries, such as monodentate, chelating, bidentate bridging, monodentate bridging, and chelating bridging, although the coordination ability of the vanillin group is not strong in some cases. (3) Nicotinoyl hydrazine or salicyloyl hydrazine contains nitrogen or oxygen donors with quite strong coordination ability.4c,5 (4) In many cases, a relatively large π-conjugated system may exist and might contribute much to a desirable fluorescence property resulting from the interaction between the ligand and the metal atom. Therefore, this kind of multidentate ligand should be a good candidate for the bridging ligands. Based on a thorough review of crystal data available in the Cambridge Structural Database (CSD), we were surprised at the following three research results: (1) only a few complexes with derivatives of vanillin have been reported;6 (2) there are discrete structures and 1D structures only, not any 3D structures in the known complexes with o-vanillin derivatives;7 (3) up to now, no complexes containing 4-hydroxy-3-methoxybenzaldehyde nicotinoylhydrazone (L1) have been synthesized. Therefore, we selected two vanillin derivatives, L1 and 4-hydroxy-3-methoxybenzaldehyde salicyloylhydrazone (L2),

as spacers to synthesize complexes with supramolecular architectures in this research. Due its the 5d106s2 electron configuration and large radius, Pb(II) exhibits the inert pair effect and variable coordination numbers and geometries. There has been a resurgence of interest in the coordination chemistry of lead(II) in recent years, not only owing to its biological activities but also because lead(II) possesses a large radius, a variable stereochemical activity, and a flexible coordination environment, which provides unique opportunities for the construction of novel network of topologies.8-10 There are two kinds of classifications in lead(II) complexes, holodirected and hemidirected configurations, depending on mainly the coordination number. The absence of crystal field stabilization energy effects allows the Pb ion to adopt varied coordination geometries to give rise to novel coordination networks. Several lead complexes have interesting photochemical and photophysical properties. Therefore, we have directed our attention to the syntheses of lead complexes with different structure dimensions.10g Herein, we report the syntheses and characterization of five Pb(II)/Cu(II)/Co(III)/Co(II) complexes with two vanillin derivatives (L1 or L2). The formation pathways of the five title complexes, 1-5, are shown in Scheme 1. Complexes [Pb2(L1)2(NO3)2] 3 3H2O (1) and Pb2(L1)2(OAc)2(H2O)2 (2) are based on lead(II) and ligand L1. The complexes 1 and 2 are the first two complexes of 4-hydroxy-3-methoxybenzaldehyde nicotinoylhydrazone. Complex 1 self-assembles into a novel 3D noninterpenetrated diamond network. Lead atoms in 1 and 2 are in a hemidirected five-coordinated and a hemidirected six-coordinated polyhedron, respectively. The reactions between L2 and Cu(II)/Co(II) under different conditions lead to the formation of the title complexes Cu(L2)2 (3), [Co3þ(L2)2(C5H5N)2] 3 ClO4 (4) and [Co2þ(L2)2(C5H5N)2] 3 2CH3OH 3 H2O (5). The bridging ligands L1 and L2 in the five complexes and a related ligand7g have different coordination modes (see Scheme 2).

r 2009 American Chemical Society

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Scheme 1. The Formation Pathways of the Five Title Complexes, 1-5

Experimental Section All chemicals were of reagent grade and were used without further purification. Caution! Although no problems were encountered in this work, perchlorate salts containing organic ligands are potentially explosive. Only a small amount of the material should be prepared, and they should be handled with care. Physical Measurements. Elemental analyses of carbon, hydrogen, and nitrogen were carried out with an Elementar Vario EL III microanalyser. Infrared spectra were recorded on a Perkin-Elmer Spectrum 2000 spectrophotometer over the frequency range 4000400 cm-1 using the KBr pellet technique. Solid-state fluorescent studies were conducted at room temperature on an Edinburgh FLFS920 TCSPC system. Thermal gravimetric analysis (TGA) was tested under nitrogen with a heating rate of 10 °C 3 min-1 using a Perkin-Elmer TGA-7 Thermal Analysis system. Syntheses of the Ligands. The synthesis and structure of ligand H2L1 (3-methoxysalicylaldehyde picoloylhydrazone) were reported.11 To salicyloyl hydrazine (10 mmol, 1.52 g) in 30 mL of ethanol was added a solution of 4-hydroxy-3-methoxybenzaldehyde (10 mmol, 1.52 g) in 10 mL of ethanol. The reaction mixture was stirred and refluxed for 3 h to give a suspension with a white precipitate. The suspension was cooled and filtered. The white precipitate was collected, washed with absolute ethanol and absolute ether, and dried to get a white powder of 4-hydroxy-3-methoxybenzaldehyde salicyloylhydrazone (L2, yield 66%). Synthesis of Pb2(C14H12N3O3)2(NO3)2 3 3H2O (1). To HL1 (0.0270 g, 0.10 mmol) in methanol (10 mL) was added solid Pb(NO3)2 (0.0331 g, 0.10 mmol). The resulting suspension was stirred about 30 min and filtered off. The yellow block crystals of the title complex 1 were formed upon slow evaporation of the filtrate at room temperature for seven days. Yield: 78%. Anal. Calcd for Pb2(C14H12N3O3)2(NO3)2 3 3H2O: C, 31.39; H, 2.30; N, 7.76. Found: C, 31.95; H, 2 0.34; N, 7.67. Synthesis of Pb2(C14H12N3O3)2(CH3COO)2(H2O)2 (2). Complex 2 was synthesized in a manner analogous to 1 with the substitution of Pb(OAc)2 3 3H2O for Pb(NO3)2. Yellow block crystals of 2 suitable for X-ray diffraction were obtained. Yield: 80%. Anal. Calcd for Pb2(C14H12N3O3)2(CH3COO)2(H2O): C, 34.62; H, 3.07; N, 7.57. Found: C, 33.95; H, 3.00; N, 7.64. Synthesis of [Cu(C15H13N2O4)2] (3). Ligand HL2 (0.0249 g, 0.1 mmol) was dissolved in a mixed solvent of methanol (7 mL) and

CH2Cl2 (7 mL) with constant stirring for 5 min. Cu(SO4)2 3 5H2O (0.0249 g, 0.1 mmol) was added into this solution. After the sample was stirred for 30 min, a yellow-green solution was formed. Green rectangular crystals of 3 suitable for X-ray diffraction were obtained by slow evaporation at room temperature over 2 days. Yield: 74.5%. Anal. Calcd for Cu(C15H13N2O4)2: C, 56.77; H, 4.10; N, 8.83. Found: C, 56.05; H, 3.91; N, 8.67. Synthesis of [Co(C15H13N2O4)2(C5H5N)2] 3 ClO4 (4). Ligand HL2 (0.0249 g, 0.1 mmol) was dissolved in a mixed solvent of methanol (7 mL) and CH2Cl2 (7 mL) with constant stirring for 5 min. Co(ClO4)2 (0.0366 g, 0.1 mmol) and one drop of pyridine were added to the solution. The solution was stirred for 30 min; the color of solution changed to pink-red. The resultant solution was filtered and allowed to stand at room temperature for 5 days. Pink-red needle crystals of 4 suitable for X-ray diffraction were obtained. Yield: 73%. Anal. Calcd for [Co(C15H13N2O4)2(C5H5N)2] 3 ClO4: C, 54.11; H, 4.06; N, 9.47. Found: C, 55.05; H, 3.91; N, 9.67. Synthesis of [Co(C15H13N2O4)(C5H5N)2] 3 2CH3OH 3 H2O (5). A similar synthetic procedure as that for 4 was used except that Co(ClO4)2 and one drop of pyridine were replaced by Co(NO3)2 3 6H2O and five drops of pyridine, giving red-brown needle crystals of 5 in 78% yield. Anal. Calcd for [Co(C15H13N2O4)(C5H5N)2] 3 2CH3OH 3 H2O: C, 57.95; H, 5.29; N, 9.66. Found: C, 57.75; H, 5.34; N, 9.37. X-ray Structure Determination. Crystals of the five title complexes with suitable size were mounted on glass fibers. Intensity data of complexes 1, 2, 3, and 5 were collected on a Rigaku RAPID Weissengberg IP diffractometer with graphite-monochromated Mo KR radiation (λ = 0.710 73 A˚) and the ω scan mode at room temperature, while intensity data of complex 4 were collected on an Oxford Gemini R Ultra System with graphitemonochromated Cu KR radiation (λ = 1.5418 A˚) and the ψ and ω scan at 100 K. The structures of the five title compounds were solved by direct methods with SHELXS-9712 and refined by fullmatrix least-squares calculations with SHELXL-97.13 The all other non-hydrogen atoms in the five complexes were refined anisotropically, except that the solvent molecules in complexes 1 and 5 and the NO3- anions in 1 are disordered and were refined isotropically. Most of hydrogen atoms were placed in their calculated positions or from difference Fourier map. The crystallographic data for the complexes 1-5 are summarized in Table 1. Selected bond distances (A˚) and angles (deg) in complexes 1-5 are listed in Table 2.

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Scheme 2. The Two Title Ligands (HL1 and HL2), the Related Ligand, HL3, and Their Coordinating Modes in the Complexes

Results and Discussion Crystal Structure of Complex [Pb2(C14H12N3O3)2(NO3)2] 3 3H2O (1). As depicted in Figure 1, the Pb(1) atom in complex 1 is coordinated by four O/N donors (O(3), O(3A), O(1C), and N(1B)) from four surrounding 4-hydroxy-3-methoxybenzaldehyde nicotinoylhydrazone ligands, L1 (symmetry codes: A, -x, y, 0.5 - z; B, 0.5 - x, 0.5 þ y, 1.5 - z; C, x, 1 - y, -0.5 þ z) and one oxygen atom O(4) from coordinated nitrate anion. The coordination geometry of the lead atom is a square pyramid because the τ value of the pentacoordinated polyhedron is 0.05.14 The 5d106s2 metal ion of lead(II) is known to exhibit variable coordination number and geometry caused by the stereochemically active lone pair.8,9f Two lead atoms (Pb(1) and Pb(1A)) are bridged by two μ2hydroxy oxygen atoms (O(3) and O(3A)) to get a binuclear

lead structural unit Pb2(L1)6(NO3)2 (see Figure 2). The binuclear structural unit has a crystallographic C2 symmetry with Pb1 3 3 3 Pb1A separation of 3.771(2) A˚. The Pb2(μ2-O)2 core in the binuclear unit Pb2(L1)6(NO3)2 is essentially planar, bond distances of Pb1-O3 and Pb1-O3A in the core being 2.370(5) and 2.463(5) A˚, respectively, and angles of O3-Pb1-O3A and Pb1-O3-Pb1A being 72.8(2)° and 102.6(2)°, respectively. As illustrated in Figure 3, every lead binuclear structural unit, Pb2(L1)6(NO3)2, connects four adjacent binuclear units by its six hydrazone ligands L1. Every hydrazone ligand L1 acts as a triconnector to coordinate to three lead atoms of three binuclear lead structural units through its hydroxy oxygen atoms, O3, of the vanillin group, carboxy oxygen atom, O1, and pyridyl nitrogen atom, N1, shown in Figure 4.

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Table 1. Crystallographic Data of Complexes 1-5 compound formula formula weight cryst. syst. space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z Dcalcd (g cm-3) T (K) color shape dimension (mm3) μ (mm-1) F(000) θmin, θmax (deg) hmin, hmax kmin, kmax lmin, lmax Rint no. of unique data no. of obsd no. of variables R wR GOF (Δp)max,min (e/A˚3) (Δ/σ)max,(Δ/σ)min

1 C28H30N8O15Pb2 1132.98 monoclinic C2/c 17.497(10) 18.093(7) 13.224(6) 90 117.798(17) 90 3703(3) 4 2.032 293(2) yellow prism 0.24 0.16 0.11 9.158 2152 3.24, 27.48 -22, 22 -23, 20 -17, 17 0.0512 4250 3301 240 0.0447 0.1038 1.082 0.869, -1.192 0.001, 0.000

2 C32H34N6O12Pb2 1109.03 triclinic P1 9.177(5) 9.337(5) 11.582(7) 67.587(18) 89.67(2) 69.783(2) 851.9(8) 1 2.162 293(2) yellow prism 0.34 0.16 0.18 9.942 528 3.28, 27.48 -11, 11 -11, 12 -14, 14 0.0454 3851 3267 240 0.0348 0.0644 1.061 1.683, -0.896 0.000, 0.000

At the same time, there are two hydrazone ligands, L1, between two lead binuclear structural units (see Figure 3). Therefore, complex 1 is a 3D coordination polymer with a novel 3D noninterpenetrated diamond-like network,1,15-18 the lead binuclear structural unit being a four-connected binode and the hydrazone ligand L1 being a three-connected spacer (see Figure 5a,b). Several complexes, such as [Ag2{OOC(CH2)2COO}], [Cu(L)2](ClO4), Cd(CN)2, Zn(CN)2,15 [M3(HCOO)6] porous frameworks,16 (CN4-C6H5)2Zn,17 and two complexes with other acid ligands,18 exhibit a diamond-like network structure. In a series of [M3(HCOO)6] compounds,16 the diamondlike structure consists of the apex-sharing M-centered MM4 tetrahedron nodes and bridging triconnectors COO-; every M node comes from a [M(HCOO)6] structure unit. However, the diamond-like structure in title complex 1 consists of apex-sharing M2-centered (M2)(M2)4 tetrahedron binodes and bridging triconnectors (hydrazone ligand L1). The M2 comes from the binuclear structural unit Pb2(L1)6(NO3)2. As a binode, every lead binuclear structural unit (M2) connects four neighboring binuclear structural units. Most diamondoid architectures use a tetrahedral metal (such cs Zn or Cd) as the node and cyanide ligands or acid ligands as the spacer. In most known diamondoid coordination frameworks, metal atoms possess a tetrahedral coordination.1,15,17,18a However, metal atoms in the [M3(HCOO)6] compounds and in the title lead compound 1 have octahedral coordination and square-pyramidal coordination, respectively. To the best of our knowledge, complex 1 is the first metal complex with a diamond-like network structure containing M2 binodes reported so far. Up to now, only a few complexes with 3D lead-organic supramolecular architecture have been reported, although many dimeric

3 C30H26N4O8Cu 634.09 hexagonal R3 33.916(11) 33.916(11) 6.263(2) 90 90 120 6239(4) 9 1.519 293(2) blue chunk 0.48 0.16 0.15 0.848 2943 3.18, 27.45 -43, 44 -43, 43 -8, 7 0.1125 3173 1817 199 0.0591 0.1190 1.041 0.989, -0.372 0.000, 0.000

4 C40H36ClN6O12Co 887.13 orthorhombic Ibca 16.1962(3) 21.7882(8) 21.8481(5) 90 90 90 7709.9(4) 8 1.529 173(2) red needle 0.44 0.36 0.21 4.767 3664 4.05, 67.05 -18, 18 -26, 26 -25, 16 0.0577 3057 2022 275 0.0739 0.1589 1.062 0.464, -0.362 0.000, 0.000

5 C42H46N6O11Co 869.78 monoclinic P21/c 12.517(5) 8.606(4) 19.864(7) 90 107.015(14) 90 2046.0(14) 2 1.412 293(2) red chunk 0.4 0.26 0.25 0.488 910 3.10, 27.47 -16, 16 -11, 11 -25, 25 0.0645 4673 3489 277 0.0651 0.1843 1.026 0.932, -0.538 0.000, 0.000

d10 Pb complexes with a Pb2(μ2-O)2 core have been synthesized.8a,9b,c,f,g,10a,10b,d There are some intermolecular hydrogen bonds, NH 3 3 3 O, between the NH (hydrazine group) and nitrato oxygen atom and hydrogen bonds, N-H 3 3 3 N, between the NH (hydrazine group) and nitrato nitrogen atom in complex 1 (see Table S1, Supporting Information). Crystal Structure of Complex Pb2(C14H12N3O3)2(OAc)2(H2O)2 (2). Figures 6 and 7 show the one-dimensional chain structure of complex 2. The 1D chain is made up of centrosymmetric binuclear structural units combined via two ligands, L1, derived from condensation of vanillin and nicotinoyl hydrazine. The complexes 1 and 2 are the first two examples of complexes with 4-hydroxy-3-methoxybenzaldehyde nicotinoylhydrazone. There is a centrosymmetric binuclear structural unit, Pb2(L 1)4(OAc)2(H2O)2, linked by two μ2-hydroxy oxygen atoms (O3 and O3A, with symmetry code A, 1 - x, -y, 1-z) of two hydrazone ligands, L 1, in complex 2. Pb 3 3 3 Pb interatomic distances in the core of the binuclear unit Pb2(L 1)6(NO3)2 of 1 and in the binuclear unit Pb2(L1)4(OAc)2(H2O)2 of 2 are 3.771(2) and 3.889(2) A˚, respectively. Each Pb2þ ion in the binuclear structure unit in 2 is coordinated by four O atoms (O2, O3, O3A, O1B) of three ligands, L1, one oxygen atom, O4, of an acetate anion, and one coordinated water oxygen, atom, O6, forming a hemidirected six-coordinated PbO6 polyhedron. The Pb-O bond lengths vary from 2.352(4) to 2.798(4) A˚. Every two neighboring lead binuclear units are connected together through a 22-membered ring constructed from two bridging ligands, L1, and two lead atoms, forming a 1D double chain along the b axis, shown in Figure 7.

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Table 2. Selected Bond Distances (A˚) and Angles (deg) in Complexes 1-5a

Pb(1)-O(3) Pb(1)-N(1)#2 Pb(1)-O(4) O(3)-Pb(1)-O(3)#1 O(3)-Pb(1)-O(1)#3 O(3)#1-Pb(1)-N(1)#2 O(3)#1-Pb(1)-O(4) N(1)#2-Pb(1)-O(4)

Compound 1 2.370(5) Pb(1)-O(3)#1 2.485(6) Pb(1)-O(1)#3 2.7678(13) 72.83(17) O(3)-Pb(1)-N(1)#2 78.96(18) O(3)-Pb(1)-O(4) 82.41(18) O(3)#1-Pb(1)-O(1)#3 121.83(31) N(1)#2-Pb(1)-O(1)#3 78.56(31) O(1)#3-Pb(1)-O(4)

Pb(1)-O(3) Pb(1)-O(4) Pb(1)-O(1)#2 Pb(1) 3 3 3 Pb(1)#1 O(3)-Pb(1)-O(3)#1 O(3)-Pb(1)-O(6) O(3)-Pb(1)-O(2) O(3)#1-Pb(1)-O(6) O(3A)#1-Pb(1)-O(2) O(4)-Pb(1)-O(1)#2 O(6)-Pb(1)-O(1)#2 O(1)#2-Pb(1)-O(2)

Compound 2 2.389(4) Pb(1)-O(3)#1 2.530(5) Pb(1)-O(6) 2.740(5) Pb(1)-O(2) 3.889(2) 69.80(14) O(3)-Pb(1)-O(4) 70.83(15) O(3)-Pb(1)-O(1)#2 60.24(11) O(3)#1-Pb(1)-O(4) 88.40(14) O(3)#1-Pb(1)-O(1)#2 125.23(13) O(4)-Pb(1)-O(6) 120.60(16) O(4)-Pb(1)-O(2) 76.07(15) O(6)-Pb(1)-O(2) 155.42(13)

Cu(1)-O(2) Cu1-O(1)#2 O(2)-Cu(1)-N(2) N(2)-Cu(1)-O(1)#2

Compound 3 1.914(3) Cu(1)-N(2) 2.622(3) 81.7(1) O(2)-Cu(1)-O(1)#2 90.5(1)

Co(1)-O(2) Co(1)-N(3) O(2)-Co(1)-O(2)#1 O(2)-Co(1)-N(3) O(2)-Co(1)-N(3)#1 N(2)-Co(1)-N(2)#1 N(3)-Co(1)-N(3)#1

Compound 4 1.875(3) Co(1)-N(2) 1.961(5) 177.6(2) O(2)-Co(1)-N(2) 90.4(2) O(2)-Co(1)-N(2)#1 91.3(2) N(3)-Co(1)-N(2)#1 91.7(3) N(2)-Co(1)-N(3) 92.0(3)

Co(1)-O(2) Co(1)-N(3) O(2)-Co(1)-N(2) N(2)-Co(1)-N(3)

Compound 5 1.872(2) Co(1)-N(2) 1.956(3) 83.5(1) O(2)-Co(1)-N(3) 89.39(11)

2.463(5) 2.504(5) 74.60(18) 147.25(31) 150.11(18) 80.76(17) 78.53(32)

Figure 2. Binuclear lead structure unit in 1. 2.352(3) 2.677(5) 2.7977(41) 84.26(15) 133.73(12) 77.66(14) 77.99(13) 154.50(15) 76.54(15) 95.01(15)

1.971(3) 92.3(1)

1.903(5)

Figure 3. Connection mode among the neighboring binuclear structure units in 1.

82.3(2) 96.0(2) 173.6(2) 88.5(2)

1.906(2) 90.11(10)

Symmetry codes: for 1, #1, -x, y, -z þ 1/2; #2, -x þ 1/2, y þ 1/2, -z þ 3/2; #3, x, -y þ 1, z - 1/2; for 2, #1, -x þ 1, -y, -z þ 1; #2, -x þ 1, -y þ 1, -z þ 1; for 3, #1, -x þ 1, -y, -z; #2, x, y, -1 þ z; #3, -x þ 1, -y, 1 - z; #4, x, y, 1 þ z; for 4, #1, -x þ 1, -y þ 0.5, z. a

Figure 1. The coordination environment of the lead atom in 1.

The dihedral angles between the pyridyl ring and the benzene ring in the same ligand in complexes 1 and 2 are 8.70(9)° and 44.9(3)°, respectively. This indicates that the hydrazone ligand, L1, in 1 is approximately planar, while the

Figure 4. Connection models of hydrazone ligand in 1.

same ligand in 2 is twisted. The corresponding dihedral angle in the free ligand is 30.9(6)°.11 There are some intermolecular hydrogen bonds, O-H 3 3 3 O and O-H 3 3 3 N, between the coordinated water molecule and nitrato oxygen atom or hydrazone nitrogen atom and a hydrogen bond, N-H 3 3 3 O, between the NH (hydrazine group) and acetate oxygen atom in complex 2 (see Table S1, Supporting Information). For the complexes 1 and 2, the coordination number of the lead(II) ion is five and six, respectively. The donor atoms in the two lead(II) complexes 1 and 2 can cluster to one side leaving an “open” coordination site to accommodate the stereochemically active 6s2 lone pair. The 6s2 lone electron pair on the lead(II) ion seems to be stereochemically active in the two lead(II) complexes. The complexes 1 and 2 possess a similar binuclear lead basic structural unit. However, there is a 3D metal-organic diamond-like framework in 1, while there is a 1D chain in 2. Influence of the Second Ligand (Acid Ligand) and Coordination Ability of Water Molecule on Structural Dimensionality in Complexes 1 and 2. Complexes [Pb2(C14H12N3O3)2(NO3)2] 3 3H2O (1) and Pb2(C14H12N3O3)2(OAc)2(H2O)2 (2)

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Figure 5. 3D diamond-like coordination network of 1: (a) packing diagram along the c axis; (b) view of the topology with 3D diamond-like structure.

Figure 6. View of binuclear lead structural unit in 2.

Figure 7. View of 1D double-strand chain in 2.

contain the same bridging hydrazone ligand, L1, and similar centrosymmetric binuclear lead(II) structural units with a Pb2(μ2-O)2 core. However, there are two different structural features between 1 and 2. First, the second ligand (acid ligand) in 1 and 2 is NO3and OAc-, respectively. The bond distance of Pb-O(NO3-) (2.77(1) A˚) in 1 is much longer than that of Pb-O(OAc-) (2.530(5) A˚) in 2. This means that the coordination of Pb-O(NO3-) is much weaker than that of Pb-O(OAc-). At the same time, the coordination ability of the oxygen atom to lead center is much stronger than that of the nitrogen atom. In comparison with many lead complexes containing Pb-O bonds, only a few lead complexes with Pb-N bond

have been synthesized, in which the nitrogen atom comes from a phen ligand or a pyridyl/pyrazolyl fragment.10d,h,i The nitrogen atom (pyridyl ring) of ligand L1 in complex 1 is coordinated to the lead atom, but the same nitrogen atom (pyridyl ring) of ligand L1 in 2 is not coordinated to lead atom. The weak Pb-O(NO3-) bond in 1 promotes the coordination of the nitrogen atom to the lead atom; the stronger Pb-O(OAc-) bond in 2 degrades the coordination of the nitrogen atom to the lead atom. Coordination of the pyridyl nitrogen in the ligand of complex 1 to the lead atom plays an important role in constructing the supramolecular structure. The Pb-N (pyridyl ring of L1) bonding in 1 results in the existence of four-connected binuclear lead(II) structural units in 1 and then results in the formation of the novel 3D noninterpenetrated diamond-like network in 1. Without Pb-N (pyridyl ring of L1) bonding in 2, two-connected binuclear lead(II) structural units may result in 2, which then may result in the formation of the 1D chain structure in 2. Second, the two water molecules coordinate to lead atoms in the binuclear structural unit Pb2(L1)4(OAc)2(H2O)2 in 2. However, no water molecules are involved in the binuclear unit Pb2(L1)6(NO3)2 in 1; all water molecules in 1 are crystallographic water molecules only. The disturbance caused by the larger number of water molecules involved in the binuclear unit of 2 may benefit that lesser donors coordinating to a binuclear lead structural unit and then can influence the node of the binuclear lead structural unit in 2 being a two-connected, not four-connected, node. Therefore, the lower dimensionality in 2 can also be explained. Corresponding to the 3D supramolecular structure in 1, there is 1D structure in 2 only. Crystal Structure of Complex Cu(C15H13N2O4)2 (3). As shown in Figure 8, complex 3 belongs to space group R3 and contains a CuII ion on a cryastallographic inversion center. The CuII ion has a highly Jahn-Teller distorted transCuN2O4 octahedron with equatorial plane defined by the two carboxy oxygen atoms (O2 and O2A, symmetry code A, 1 - x, -y, -z) and two hydrazine nitrogen atoms (N2 and N2A) of two 4-hydroxy-3-methoxybenzaldehyde salicyloylhydrazone ligands, L2, bond lengths of Cu1-O2 and Cu1-N2 being 1.914(3) and 1.971(3) A˚, respectively. The

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Figure 8. Perspective view of the coordination geometry of the copper atom in 3.

Figure 10. Molecular structure of Co (III) complex 4 and hydrogen bonds.

Figure 9. The 1D double-strand chain structure in 3.

two axial positions are occupied by two phenolic oxygen atoms (O1B and O1C) of two hydrazone ligands, L2 (symmetry codes B, x, y, -1 þ z; C, 1 - x, -y, 1 - z), with a weak coordination bond of 2.622(3) A˚. The tridentate hydrazone ligand L2 is a bridging ligand to coordinate to two neighboring copper atoms through its carboxy oxygen O2, hydrazine nitrogen N2, and phenolic oxygen O1 donors. Therefore, a 1D double-strand chain consists of CuN2O4 octahedra connected linearly by two hydrazone L2 ligands along the c axis, shown in Figure 9. Complex 3 is a neutral one-dimensional coordination polymer. The hydroxy O4 atom and methoxy O3 atom of the vanillin group in ligand L2 are not coordinated to the metal atom. The 1D structure, not 2D or 3D structure, may be caused by the structural phenomenon mentioned above. Crystal Structure of Complex [Co(C15H13N2O4)2(C5H5N)2] 3 ClO4 (4). As depicted in Figure 10, the CoIII center is located on a 2-fold rotation axis [001] and adopts a distorted cisCoN4O2 octahedral geometry with two hydrazine nitrogen atoms (N2 and N2A, with symmetry code A, 1 - x, 0.5 - y, z) and two carboxy oxygen atoms (O2 and O2A) from two hydrazone ligands L2 and two nitrogen atoms (N3 and N3A) from two coordinated pyridine molecules. Therefore, the whole [Co(C15H13N2O4)2(C5H5N)2]þ cation exhibits C2 crystallographic symmetry. There are intermolecular hydrogen bonds, O-H (phenolic) 3 3 3 O(ClO4-), and intramolecular hydgogen bonds of O-H(phenolic) 3 3 3 N(hydrazine) and O-H(phenolic) 3 3 3 O(methoxy) in complex 4. Every ClO4- anion links two neighboring cobalt complex cations through two O-H 3 3 3 O(ClO4-) hydrogen bonds, and every cobalt complex molecule connects to two ClO4- anions by two OH 3 3 3 O(ClO4-) hydrogen bonds. Thus, a 1D supramolecular motif in 4 is afforded, running along the a axis (see Figure 11).

Figure 11. Extended 1D chain in 4 along the b axis.

Figure 12. Coordination configuration of Co(II) atom and the hydrogen bonds in 5.

Crystal Structure of Complex [Co(C15H13N2O4)2(C5H5N)2] 3 2CH3OH 3 H2O (5). The coordinate environment of the Co2þ center with the atom numbering scheme in 5 is shown in Figure 12. The Co2þ cation is situated on a cryastallographic inversion center. Each Co2þ center displays a trans-CoN4O2 octahedron surrounded by four donors (O2, O2A, N2, and N2A, symmetry code A, 1 - x, 1 - y, -z) from two 4-hydroxy-3-methoxybenzaldehyde from two salicyloylhydrazone ligands L2 and two nitrogen atoms from two pyridine molecules. The complex 5 has a discrete structure. The ligand L2 derived from vanillin and salicyloyl hydrazine in 4 and 5 is coordinated to one metal atom through its two donors (carboxy oxygen O2 and hydrazine nitrogen N2) in a chelating form. But the ligand L2 in 3 is coordinated to two metal atoms through its three donors in a bridging form. These phenomena lead to complexes 4 and 5 having an extended 1D structure caused by hydrogen bonds and

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Figure 14. Solid-state emission spectra of complexes 1 and 2 at room temperature. Figure 13. Solid-state emission spectrum of ligand L1 at room temperature.

discrete structure, respectively, and complex 3 displaying a 1D chain structure. The dihedral angle between the two benzene rings in the same hydrazone ligand L2 is 17.9(3)° and 13.5(4)° for complexes 3 and 4, respectively. However, the corresponding angle is 37.8(2)° for 5. It indicates that the twist degree of the hydrazone ligand in 5 is more than that in 3 and 4. There are two types of hydrogen bonds (O1-H(phenoxy) 3 3 3 N1(hydrazine) and O4-H 3 3 3 O5(uncoordinated methanol, symmetry code B, x þ 1, y, z)) in 5. IR Spectroscopic Studies and Fluorescent Properties. A medium aromatic C-OH absorption (1178 cm-1) in the free ligand L1 disappears in the IR spectra of complexes 1 and 2, providing strong evidence for coordination of the hydroxy oxygen atom in the vanillin group of L1 to a lead(II) atom in complexes 1 and 2. However, the bands at 1145, 1151, 1162, and 1161 cm-1 in the spectra of free ligand L2 and complexes 3, 4 and 5 are assigned to ArC-OH absorption, indicating that the hydroxy oxygen atom in the vanillin group of L2 is not coordinated to the metal atom for 3, 4, and 5. The bands at 3242, 3258, 3411, and 3429 cm-1 are related to the hydrazinic N-H streching in the free ligands L1 and L2 and complexes 1 and 2. The absence of the hydrazinic N-H streching in complexes 3, 4, and 5 is observed. This implies that the hydrazinic nitrogen atom in nicotinoyl fragment in L1 is not coordinated to the lead atom for complexes 1 and 2 and that the nitrogen atom in L2 is coordinated to the metal atom for 3, 4, and 5. The coordination of the azomethine nitrogen atom to the metal ions in complexes 3, 4, and 5 is also indicated by the displacement of ν(CdN) from 1606 cm-1 in the ligand L2 to 1587-1588 cm-1 in the complexes 3, 4, and 5, which overlapped with the band ν(CdN-NdC). This result shows that the contribution of CdN stretching has been reduced because the nitrogen atom is involved in bond formation with the metal ion. The bands of the coordinated CdO group appeared at 1626(m), 1638(s), 1587(s), 1588(s), and 1587(s) cm-1 for the five title complexes, respectively, which are lowered from the frequencies of 1659(s) and 1635(s) cm-1 seen in the free ligands L1 and L2, respectively. The bands found at 698, 709, and 710 cm-1 in ligand L1 and complexes 1 and 2 are due to the presence of the pyridine ring. The Pb-O stretching frequencies in the two lead(II) complexes are found in the far-infrared region at 503 cm-1 for complex 1 and at 491 cm-1 for complex 2.9g The fluorescent properties of the pure ligand L1 and the complexes 1 and 2 were investigated in the solid state at room

temperature (Figures 13 and 14). The pure ligand shows an intense emission band at 454 nm (λex = 348 nm). The emission of pure ligand may be attributed to the π f π* transition. There are quite strong emissions at 518 nm for complex 1 and at 529 nm for 2, which are red-shifted about 64 and 75 nm compared with that of free hydrazone ligand. We assume that the emissions may arise from the Pb2þ lone pair to ligand charge transfer.10j The study of crystal structures in 1 and 2 gives evidence for the stereochemically active 6s2 lone pair on the lead(II) ion. The phase purity of complex 2 was confirmed by comparison of its powder diffraction (XRPD) pattern with that calculated from singlecrystal X-ray diffraction studies (Figure S1, Supporting Information). Thermogravimetric analysis. Thermogravimetric analysis on the complexes 1-4 was carried out, and results are given in Figures S2-S5 of the Supporting Information. The thermogravimetric analysis of 1 shows that the loss of three lattice water molecules in 1 is between 43 and 93 °C (found, 4.84%; calcd, 4.77%) and that the complete decomposition of 1 was finished at ca. 630 °C. The TGA curve of 2 indicates that the complete decomposition of 2 was finished at ca. 640 °C. For complex 3, the first weight loss between 53 and 312 °C is with the decomposition of the first ligand (calcd 45.0%; found 46.5%). The second one in 3 between 398 and 466 °C corresponds to the decomposition of the second ligand (calcd 45.0%; found 48.7%) and is characteristic of the complete decomposition of the compound. TGA analysis of 4 reveals two weight-loss stages: the first starts at 212 to 260 °C, giving a weight loss of about 29.08%, corresponding to the loss of one ClO4 anion and two coordinated pyridine moieties, following by a major stage until 498 °C. The major stage corresponds to the decomposition of two ligands (found, 64.4%; calcd, 64.4%). Conclusions Two ligands derived from vanillin, 4-hydroxy-3-methoxybenzaldehyde nicotinoylhydrazone (L1) and 4-hydroxy-3-methoxybenzaldehyde salicyloylhydrazone (L2), have been employed to assemble with Pb(II), Cu(II), and Co(II) ions, resulting in the formation of five complexes ranging from a discrete structure to a complicated 3D coordination network. (a) The complexes [Pb2(C14H12N3O3)2(NO3)2] 3 3H2O (1) and Pb2(C14H12N3O3)2(OAc)2(H2O)2 (2) are the first two complexes of 4-hydroxy-3-methoxybenzaldehyde nicotinoylhydrazone. The lead atoms in 1 and 2 are in a hemidirected five-coordinated polyhedron and a hemidirected six-coordinated polyhedron, respectively. These two Pb(II) polyhedra have a stereochemically active lone pair of electrons.

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(b) Complex 1 is the first example of any metal complexes with a diamond-like network structure containing M2 binodes reported so far. However, complex 2 shows a 1D double-strand chain structure. The different second ligand (acid ligand, NO3- in 1 and OAc- in 2) and different situation (noncoordination in 1 and coordination in 2) of water molecules influence the final geometry of the structures in the products 1 and 2. Therefore, complex Pb2(L1)2(NO3)2 3 3H2O (1) exhibits a 3D structure, while complex Pb2(L1)2(OAc)2(H2O)2 (2) has 1D structure only. (c) Complex Cu(L2)2 (3) presents a 1D double-strand chain structure. There is an extended 1D chain structure in complex [Co3þ(L2)2(C5H5N)2] 3 ClO4 (4), while [Co2þ(L2)2(C5H5N)2] 3 2CH3OH 3 H2O (5) features a zero-dimension structure.

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Acknowledgment. This project was financially supported by the Natural Science Foundation of China (Grant Nos. 20431010 and 20171012) and the Natural Science Foundation of Fujian Province, China (Grant No. E0110010). Supporting Information Available: Simulated and experimental powder XRD patterns of complex 2, TGA curves of complexes 1-4, and hydrogen bonds in complexes 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data for the structures have been deposited with the Cambridge Crystallographic data center, CCDC numbers for the five title complexes are CCDC 701647, 701648, 701649, 701650, and 701651, respectively. Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (e-mail [email protected] or on the Web http://www.ccdc.cam.ac.uk).

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Coordination Polymers Constructed from Two Vanillin Derivatives

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