Controlling the In situ Decomposition of Chain-Type Polyamines To

The in situ decomposition of tetraethylene-pentamine, triethylenetetramine, or diethylenetriamine has been controlled to direct the synthesis of three...
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Controlling the In situ Decomposition of Chain-Type Polyamines To Direct the Crystal Growth of Cobalt-zinc Phosphates Ailing Lu,† Niu Li,*,† Yanfeng Ma,‡ Haibin Song,§ Daiping Li,† Naijia Guan,† Honggen Wang,§ and Shouhe Xiang†

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 7 2377–2383

Institute of New Catalytic Material Science, Polymer, College of Chemistry, and State Key Laboratory of Elemento-Organo Chemistry, Nankai UniVersity, Tianjin 300071, P. R. China ReceiVed December 16, 2007; ReVised Manuscript ReceiVed February 17, 2008

ABSTRACT: The in situ decomposition of tetraethylene-pentamine, triethylenetetramine, or diethylenetriamine has been controlled to direct the synthesis of three open-framework cobalt-zinc phosphates, CoZnPO4-I, CoZnPO4-II, and CoZnPO4-III. These phosphates can be synthesized as the intergrowth from a single gel at 200 °C in the presence of diethylenetriamine with propylamine as the assistant organic additive. Structure analysis reveals that species encapsulated in the structures of CoZnPO4-I, CoZnPO4-II, and CoZnPO4-III are ammonium, ethylenediaminum, and diethylenetriaminum, respectively, which can be attributed to the in situ decomposition of diethylenetriamine molecules during the crystallization procedure. It has been found that the presence of second organic amine redound to controlling the decomposition of these linear polyamines, such as diethylenetriamine, to form these three CoZnPO4 materials from a single gel. Pure phase of CoZnPO4-I, CoZnPO4-II, and CoZnPO4-III have also been obtained by varying assistant amines, crystallizing at a lower temperature, or using other linear polyamines, such as triethylenetetramine or tetraethylenepentamine instead of diethylenetriamine as the main organic additives. Single-crystal X-ray diffraction analysis has shown that CoZnPO4-I is a novel metal phosphate. It crystallizes in hexagonal space group p63 (No.173), with a ) 10.7207(5) Å, c ) 8.7241(8) Å, V ) 868.36(10) Å3, and Z ) 4. Its three-dimensional framework can be considered as the stacking of six-ring sheet with the combination of UDUDUD (U, upward; D, downward) and UUUDDD linkages in the proportion 1:3. Its negative framework is charge-compensated by NH4+ cations, which are encapsulated in 6946 cage of the structure. CoZnPO4-II crystallizes in the tetragonal system, space group P42bc (No. 106), with a ) b ) 14.694(2) Å, c ) 8.936(2) Å, V ) 1929.4(6) Å3, and Z ) 8, possesses DFT topology, and is built of ZnO4 (or CoO4), and PO4 tetrahedra with ethylenediaminum cation resided in the 8-member ring channels to compensate the negative framework charge. The three-dimensional architecture of CoZnPO4-III crystallizes in the trigonal system, j (No. 148), with a ) 13.5393(8) Å, c ) 15.0443(10) Å, γ ) 120°, V ) 2388.3(3) Å3, and Z ) 3, is built up of space group R ZnO4(or CoO4), PO4 tetrahedra, and CoO6 octahedra with diethylenetriaminums encapsulated in the channels. Introduction Open-framework structures of metal phosphates have exhibited many fascinating structural features and potential applications in catalysis, separation processes, and photoluminant phosphor.1–6 The feasibility of zinc and cobalt to tetrahedrally coordinate their phosphates makes them comprise an important group among the family of transition metal phosphates.7–17 Usually, these materials have been synthesized by employing hydrothermal or solvothermal conditions in the presence of organic amines as the structure-directing agents (SDA). The important role of host–guest charge matching between the inorganic frameworks and the organic amines makes linear polyamines the preferred candidates as the structure-directing agents to form the higher negative charge framework of zinc and cobalt phosphates.18–21 For example, triethylenetetramine (TETA) and diethylenetriamine (DETA) are two typical amines and have directed the formation of a variety of open-framework structures of zinc (or cobalt) phosphates by varying their concentrations and the inorganic compositions.22–25 However, application of these SDAs for the synthesis of single-phase products is frequently hampered by hydrolysis of the amines during the network-forming reaction. Recently, a new synthesis route involving alkylformamide as template precursors has been reported.26–30 It seems that organic amines generated in situ by the decomposition of * Corresponding author. Tel.: 086-22-23509932. E-mail: [email protected]. † Institute of New Catalytic Material Science, Nankai University. ‡ Polymer, College of Chemistry, Nankai University. § State Key Laboratory of Elemento-Organo Chemistry, Nankai University.

alkylformamide show a special effect for the formation of metal phosphates with novel structure. For the matter of that, large amines can also be used as a source for smaller amines because of the hydrolysis of amines in the reaction mixture. For example, the gismondine framework with the Fddd space group symmetry can be formed from large amines including N,N,N′,N′′,N′′pentamethyldiethylenetriamine [((CH3)2NCH2CH2)2-NCH3].19 In our studies to synthesize transition metal phosphates, more than one cobalt-zinc phosphate with different framework structures has been obtained from a single gel using diethylenetriamine as the organic bases. It is noticed that the guest species encapsulated in their structures are not only diethylenetriamine but also some smaller amines decomposed from it. Controlling the in situ decomposition of these multiamines is the key role for directing the synthesis of pure-phase cobalt-zinc phosphates. The present work reports the synthesis of three CoZnPO4 microporous materials by controlling the in situ decomposition of linear polyamines (such as DETA, TETA, or TEPA (tetraethylenepentamine)) in the presence of a second organic amine (or ammonia). Experimental Section Synthesis and Characterization. The main reactants are Zn (CH3COO)2 (denoted as ZnAc2), Co(CH3COO)2 (denoted as CoAc2), H3PO4, DETA, and ethylene glycol. In a typical synthesis procedure, solution A was prepared by mixing ZnAc2 · 2H2O (2.217 g) with 85% H3PO4 (0.98 mL) and ethylene glycol (EG) (2.7 mL), and then stirring at room temperature until ZnAc2 · 2H2O was dissolved. Solution B was prepared by mixing CoAc2 · 4H2O (1.252 g), distilled water (8.6 mL), and 85% H3PO4 (2.6 mL). Solution A and DETA (0.97 mL) were added to solution B. The pH value of the mixture was adjusted to pH 8.0 by

10.1021/cg701231d CCC: $40.75  2008 American Chemical Society Published on Web 06/06/2008

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Table 1. Crystal Data and Structure Refinement Data for CoZnPO4-I, -II, and -III empirical formula fw T (K) wavelength (Å) cryst syst space group a ) b (Å) c (Å) R (deg) ) β (deg) γ (deg) V (Å3) Z density (Mg/m3) abs coeff (mm-1) F(000) cryst size(mm) 2θ range (deg) limiting indices no. of reflns collected/unique completeness to θ ) 27.49 (%) refinement method data/restraints/params GOF on F2 final R indices [I > 2σ(I)] R indices (all data) largest diff. peak and hole (e Å-3)

CoZnPO4-I

CoZnPO4-II

CoZnPO4-III

(NH4)2[Co2(PO4)2] 343.88 291(2) 0.71073 hexagonal P63 10.7207(5) 8.7241(8) 90 120 868.36(10) 4 2.630 4.212 680 0.50 × 0.44 × 0.33 3.20-27.49 -13e h e 13, -13e k e 13, -8e l e 11 5195/1204 [R(int) ) 0.0204] 99.7 full-matrix least-squares on F2 1204/14/107 1.132 R1 ) 0.0224, wR2 ) 0.0608 R1 ) 0.0225, wR2 ) 0.0611 0.307 and -1.151

(C2N2H10)[ Zn2(PO4)2] 382.80 293(2) 0.71073 tetragonal P42bc 14.694(2) 8.936(2) 90 90 1929.4(6) 8 2.636 5.336 1520 0.18 × 0.18 × 0.12 1.96-25.01 -17e h e 12, -17e k e 17, -10e l e 10 9027/1660 [R(int) ) 0.0685] 98.5 full-matrix least-squares on F2 1660/127/174 1.048 R1 ) 0.0616, wR2 ) 0.1222 R1 ) 0.0710, wR2 ) 0.1271 1.095 and -1.297

[C4N3H16]1.33 [CoZn6(PO4)6] 1162.57 113(2) 0.71070 trigonal R3j 13.5393(8) 15.0443(10) 90 120 2388.3(3) 3 2.425 5.346 1711 0.20 × 0.18 × 0.18 3.01-27.87 -17e h e 17, -16e k e 17,-19e l e 19 7408/1267 [R(int) ) 0.0687] 99.7 full-matrix least-squares on F2 1267/47/85 1.121 R1 ) 0.0519, wR2 ) 0.1632 R1 ) 0.0588, wR2 ) 0.1668 1.571 and -1.929

the addition of n-propylamine (4.5 mL). The final molar ratio of the mixture was 2:1:9.6:10.5:95.4:1.8 ZnAc2 · 2H2O:CoAc2 · 4H2O: HOCH2CH2OH:H3PO4:H2O:DETA. The mixture was then transferred to a stainless steel autoclave and heated at 200 °C for 6 days. Three types of large blue crystal were filtered and washed with deionized water and dried in air. X-ray powder diffraction (XRD) patterns were recorded on a Rigaku D/MAX-2500 diffractormeter with Ni-filtered Cu KR radiation (λ)1.5418Å). Raman spectrometer used was Renishaw in Via spectroscopy system. The laser used was Argon ion laser with 514.5 nm exitation source with power output of 20 mW. Thermal analysis was performed on Netzsch STA 409 PC thermal analyzer at a heating rate of 10 °C/min in air. Element analysis was performed on an Elementar Varioel element analyzer. The framework composition of three compounds was determined by Inductively Coupled Plasma (ICP) spectroscopy. The crystal morphology of these compounds was performed on a SHIMADZU SS-550 scanning microscope. UV–visible and solid-state photoluminescence (PL) studies were performed on powder samples at room temperature. The UV–vis spectra were measured on a JASCO V-570 spectrophotometer equipped with an integrating sphere attachment. PL spectra were measured on a Jobin Yvon FluoroMax-P spectro-fluorometer equipped with a Xe lamp (150 W) as the excitation light source. Structure Determination. A suitable single crystal of each compound was carefully selected and glued to a thin glass fiber with superglue adhesive. Crystal structure determination by X-ray diffraction was performed on a Bruker SMART 1000 CCD diffractometer equipped with a normal focus, 2.4-KW sealed-tube X-ray source using monochromatic MoKR (λ ) 0.71073Å) radiation. The final unit cell constants were determined by a least-squares fit of 2403 reflections for CoZnPO4I, 3095 reflections for CoZnPO4-II, and 2347 reflections for CoZnPO4III in the range 3.0° < 2θ < 25.0°. The crystallographic data of CoZnPO4-I, -II, and -III are summarized in Table 1. The SMART program package was used to determine the unit-cell parameters and for data collection. All structures were solved by direct methods and refined on F2 by full-matrix least-squares using the SHELXT-97 program system.31 The positional parameters for mental, P and O atoms were located by direct methods for all compounds. The remaining non-hydrogen atoms were routinely located from Fourier difference maps during the course of the refinement. All the hydrogen positions were placed geometrically and refinement by riding on their appropriate N and C atoms. The final positions of all non-hydrogen

atoms were refined anisotropically. The final atomic coordinates and displacement parameters are given in Table S1 and S2 for CoZnPO4-I.

Result and Discussion Three open-framework cobalt-zinc phosphates have been synthesized hydrothermally from a single gel at 200°c by using NH2CH2CH2NHCH2CH2NH2 as the SDA with n-propylamine as the assistant organic amine. They are all large vivid blue crystals with sizes more than 400 µm. Scanning electron micrograph (SEM) images show their morphologies being distinct from each other with elongated hexagonal-dipyramid, square bifrustum, and cubical, respectively (Figure 1). XRD patterns of CoZnPO4-I, -II, and -III (Figure 2) have shown that they are three distinguishing phases with different diffraction peaks. They are in agreement with those simulated from single-crystal data (Figure 2), indicating the purity of the three compounds. At the same time, the Raman spectra have been employed to detect the vibration of encapsulated species in CoZnPO4-I, -II, -III, and the starting gel (without npropylamine) (Figure 3). It is noticeable that the spectra of the three compounds show different vibration features in the region of 1300–1600 and 2750–3200 cm-1, which can be attributed to the deforming and stretching vibration of C-H and N-H. The spectra of CoZnPO4-III show four bands at 2800–3000 cm-1 region (Figure 3, inset c), similar to that of the starting gel (Figure 3, inset d). It indicates that diethylenetriamine may be still in the pores of CoZnPO4-III as the SDA. Differences in the relative strength of these bands may be attributed to restrict of the pore or the host–guest interaction between the inorganic framework and the organic amine in CoZnPO4-III. On the contrary, the Raman spectrum of CoZnPO4-I shows broad and weak bands at 2800–3000 cm-1 region, which can be assigned to H-bonded N-H vibrations in NH4+ without the vibrations of C-H species (Figure 3a). For CoZnPO4-II (Figure 3, inset b), its Raman spectrum exhibits three bands at 2800–3000 cm-1 range, which are due to C-H stretching vibrations, but differ from that of diethylenetriamine in the starting gel.

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Figure 1. SEM images of the large crystals of three cobalt-zinc phosphates (a) crystal of CoZnPO4-I with elongated hexagonal-dipyramid morphology; (b) CoZnPO4-II crystal with square bifrustum morphology; (c) CoZnPO4-III crystal with cubical-like morphology.

Figure 2. XRD patterns of CoZnPO4-I, -II, and -III: (a) as-synthesized sample; (b) simulated from single-crystal data.

Figure 3. Raman spectra of (a) CoZnPO4-I; (b) CoZnPO4-II; (c) CoZnPO4-III; (d) gel without the assistant amine. Table 2. Elemental Analysis Results of CoZnPO4-I, -II, and -III calculating from crystal analysis data (wt %)

experimental (wt%) CoZnPO4

C

H

N

C

H

N

I II III

0.28 5.71 7.75

2.29 2.36 3.28

7.51 7.10 5.68

0.00 6.27 6.19

2.33 2.61 1.89

8.14 7.31 4.82

Elemental analysis of these compounds (Table 2) displays an outline of the encapsulated species, with ammonium for CoZnPO4-I, ethylenediamine (EDA) for CoZnPO4-II, and diethylenetriaminum for CoZnPO4-III. Single-crystal analysis has further verified this result (Figure 4). The elemental analysis

result of CoZnPO4-II especially is in good accordance with the calculated values (6.27, 2.61, and 7.31 wt %) from the singlecrystal analysis data. It is clear that there are only diethylenetriamine and npropylamine as the SDAs present in the starting materials. However, organic species encapsulated in the structure of CoZnPO4-I, -II, and -III are ammonium, ethylenediaminum, and diethylenetriaminum cations, respectively. The appearance of ammonium and ethylenediaminum may be attributed to the in situ decomposition of diethylenetriamine during the crystallization. Several reports have shown the usage of diethylenetriamine as the SDA for the synthesis of metal phosphates in the temperature below 180°c.32–35 It has been found that only one crystallizing product of porous metal phosphate has been obtained and with diethylenetriamine encapsulated in the structure with the concentration of diethylenetriamine (DETA/ P2O5) varied from 1.0 to 2.5.32 Obviously, temperature is an important factor for controlling the hydrolysis of linear polyamines. High temperature (200°c) favors the hydrolysis of linear polyamines. In the present investigation when crystallizing the mixture of 2:1:9.6:10.5:95.4:1.8 ZnAc2:CoAc2:EG:H3PO4: H2O:DETA at 200 °C for 6 days, only the pure phase of CoZnPO4-I has been obtained with only ammonium in the structure. It means the complete decomposition of DETA. Meanwhile, the case using triethylenetetramine or tetraethylenepentamine as the SDA also gives the same results, namely, crystallizing at 200 °C has also resulted in the formation of CoZnPO4-I as the only product (Table 3). However, when an assistant amine, such as n-propylamine, was added to the mixture to increase the pH value to 7–9, even if the mixture is

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Figure 4. (a) Crystal structure of CoZnPO4-I with ammonium cations encapsulated in the structure; (b) CoZnPO4-II with diprotonated ethylenediamine cations accommodated in the eight-membered rings channel; (c) CoZnPO4-III seen along the [100] direction shown with diethylenetriaminum cations accommodated in the eight-ring channel. Table 3. Products Obtained by Adding Various Assistant Amines to Adjust the pH Value of the Mixture to 7-9a CoZnPO4-I CoZnPO4-II

CoZnPO4-III

Diethylenetriamine (Crystallizing at 200 °C) without assistant amine n-propylamine n-propylamine (180 °C) n-butylamine dipropylamine tripropylamine

y y n y y n

n y y y y y

n y n n y n

Triethylenetetramine (Crystallizing at 200 °C) without assistant amine y n-propylamine n n-propylamine (160°c) n

n n n

n y (and a new phase IV) (phase IV)

Tetraethylenepentamine (Crystallizing at 200 °C) without assistant amine y n-propylamine y n-propylamine (160 °C) n

n n n

n n y

Diversity of the Framework Composition CoPO4 CoZnPO4 ZnPO4

n y y

y y y

y y n

a The reacting mixture with the molar ratio of 2:1:9.6:10.5:95.4:1.8 ZnAc2 · 2H2O:CoAc2 · 4H2O:HOCH2CH2OH:H3PO4:H2O:DETA was crystallized for 6 days; y ) yes, compound has been obtained; n ) no, compound has not been obtained.

crystallized at 200 °C, three metal phosphates (CoZnPO4-I, -II, -III) have been obtained with diethylenetriamine still encapsulated in the pores of CoZnPO4-III. It indicates that the presence of n-propylamine can restrain the hydrolysis of diethylenetriamine during the crystallization. From Table 3, it can be found that, apart from n-propylamine, other assistant amines, such as n-butylamine, dipropylamine, and tripropylamine, can also restrain the decomposition of diethylenetriamine to some extent. The influence of second organic amine may be attributed to the effect of the pH on hydrolysis of the linear polyamines. In the case of triethylenetetramine or tetraethylenepentamine, the controlling effects of assistant amine are less prominent than them to diethylenetriamine. CoZnPO4-II and -III have only been obtained as the pure phases by varying assistant amine or crystallizing temperature (Table 3). The framework compositions of these compounds have been determined by using inductively coupled plasma atomic emission spectroscopy (ICP) analysis. The analysis result indicates that CoZnPO4-I contains 6.14 wt % Co, 34.75 wt % Zn, and 17.59 wt % P, with a 0.83: 0.17 Zn:Co molar ratio, and a (Zn

+ Co):P molar ratio of 0.64:0.57; CoZnPO4-II contains 2.74 wt % Co, 33.22 wt % Zn, and 16.31 wt % P, with a 0.92:0.08 Zn:Co molar ratio, and a (Zn + Co):P molar ratio of 0.56:0.53; CoZnPO4-III contains 14.68 wt% Co, 24.22 wt% Zn, and 16.33 wt% P, suggesting that the Zn:Co molar ratio is 0.60:0.40 and the (Zn + Co):P molar ratio is 0.62:0.53. Varying the molar ratio of zinc and cobalt has little impact on the formation of these structures. CoZnPO4-II can be obtained in the form of cobalt phosphate, zinc phosphate, and zinc-cobalt phosphate; CoZnPO4-III has been synthesized as cobalt phosphate, and zinc-cobalt phosphate; whereas CoZnPO4-I has been formed in the composition of zinc phosphate, and zinc-cobalt phosphate (Table 3). Our studies have shown that these structures (CoZnPO4-I, -II, -III) can be synthesized in a wide range of Zn-Co molar ratios. Single-crystal analysis reveals that CoZnPO4-I is a novel cobalt-zinc phosphate. It is composed of (NH4)2Co0.34Zn1.66(PO4)2, which was modeled as (NH4)2Co2(PO4)2 in the single-crystal data and crystallizes in the hexagonal system, space group P63 (No. 173), with a ) b ) 10.7207(5)Å, c ) 8.7241(8) Å, V ) 868.36(10) Å3, z ) 4 (Table 1). Its framework is built up of strict alternating corner-sharing phosphorus oxide PO4 tetrahedra and cobalt (or zinc) oxide MO4 tetrahedra. There are two crystallographically independent PO4 tetrahedra and two Co/ZnO4 tetrahedra in the asymmetric unit structure (see the Supporting Information, Figure S1). Each MO4 tetrahedron (M ) Co or Zn) is connected to the four neighboring P atoms via M-O-P linkage [(M-O-P)av ) 154.717(5)°]. M-O Distances are in the range of 1.863(7)-1.960(2) Å with d(M-O)av ) 1.911(9)Å. The P-O distance is in the range of 1.529(7)-1.542(2) Å and O-P-O angles are in the range of 108.40(12)-110.53(12)°. Assuming the normal valence of M, P, and O to be +2, +5, and -2, respectively, a negative framework with -2 charges has been formed in M2(PO4)2, which was compensated by protonated ammonium cations (see the Supporting Information, Figure S1). Viewing along the plane vertical to c-axis, a net consisting of six-ring channels has been found. The six-ring channels with regularly alternating Zn(Co)- and P-centered tetrahedral can be considered as the building units of CoZnPO4-I (Figure 5a). J. V. Smith determined a simple hexagonal net, which has only one type of 3-connected node and is described as the Schläfli symbol 63 because each node lies between three circuits of 6 nodes.36 For any node in a simple hexagonal net in horizational position, an additional perpendicular linkage pointing either upward (U)

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Figure 5. (a) Crystal structure of CoZnPO4-I consisted of six-ring viewed down [001]; (b) the complex ways of adding a vertical linkage to each node of a hexagonal net in (001) layer of tetrahedral emphasizing the mutual orientation of the clusters of four U- and U-pointing tetrahedral shown in Figure 3c; (c) clusters of four U- and D tetrahedral.

Figure 6. (a) Sheet extends along the (010) plane consisted of 4-, 6-, and 10-rings; (b) The sheets stacked along the direction vertical to the (010) plane (each node is a T-atom, oxygen atoms are omitted for clarity).

or downward (D) may result in the linkage joined to a node of another simple hexagonal net lying either above or below the first hexagonal net. Eight ways of the sequence of U and D linkages around each 6-ring has been used to enumerate 4-connected, 3-dimensional nets and classification of framework of silicates and aluminophosphates.37,38 The linking sequences of UDUDUD around each 6-ring produces a dense tridymite framework, whereas the UUUDDD results in an open framework ABW containing 8-ring channels.1 However, Infinity of frameworks can be produced if more than one sequence occurs in the hexagons of a 63 net. This has just happened in the structure of CoZnPO4-I. In its framework, the 6-rings of tetrahedral are present in two different conformations based on the more than one type circuit as the following sequence of up and down tetrahedral: UDUDUD and UUUDDD in the proportion 1:3. A second building unit, which is called a 6946 cage, has been formed (Figure 4a). This result has appeared in the framework topology of megakalsilicate, KAlGeO4, and KFeGeO4.39–41 On the other hand, it can be found along the (010) plane that double 4-ring and one 6-ring linked in turn by sharing edges to form an infinite chain (Figure 6a). These chains are cross-linked

along the c-axis direction to the similar chains from the linkage Zn-O-P or P-O-Zn to form the sheet structure with edgesharing infinite 10-ring chains (Figure 6a). Adjacent sheets are cross-linked with each other along the vertical direction of (010) plane via the Zn-O-P bonds displaced by +1/2 in the [001] direction to form the three-dimensional framework of CoZnPO4-I (Figure 6b). Each 10-member ring is blocked by double 4- and 6-rings around it. So the tendency to construct 10-member ring channels is interdicted with only clathrate 6946 cages to be formed (Figure 2a). Ammonium cations are encapsulated into the cages to balance the negative charge of the inorganic framework. Meanwhile, they interact with the inorganic framework through strong hydrogen bonds with all the N-H of the ammonium molecule participating in extensive hydrogen bonding to the acceptor oxygen species. The representative hydrogen bonds are N(1) · · · O(1), N(1) · · · O(3), N(1) · · · O(4), N(1) · · · O(6), N(2) · · · O(2), and N(2) · · · O(3), whose lengths are 2.787(4), 2.889(3), 2.785(4), 2.829(4), 2.897(4), and 3.044(2) Å, respectively. CoZnPO4-II and -III are isostructural with DTF topology and C6N4H22Co7(PO4)6,35,42–44 respectively. The three-dimensional framework of CoZnPO4-II can be described as the stacking of

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peaked at 385 nm as excited by 312 nm wavelength, but no emission when excited by 632 nm wavelength. Thus these visible emissions of CoZnPO4-I, -II, and -III are related with the defeat sites in framework. The UV–vis spectra (see the Supporting Information, Figure S2) show that, although there is crystallographically independent CoO6 in CoZnPO4-III, there are quite a few distorted CoO4 in CoZnPO4-III. And PL results show that CoZnPO4-III emits more intense red luminescence than CoZnPO4-I and -II. It has been reported that the red-light emission in MCM-41 was interpreted as nonbridging oxygen hole center in the strcture,46,47 and the defect sites induced by disorderliness in the lattice of zinc gallophosphate48 caused the yellow emission. Combining the UV–vis results, we are informed that the distorted or broken Co-O bond of the framework may induce defeat sites and causing the red luminescence. The UV–vis results are also in agreement with element analysis of the framework composition, which show the concentration of Co in CoZnPO4-I larger than that in CoZnPO4-II. Conclusion

Figure 7. Emission spectra of DETA (black), EDA (red), CoZnPO4-I (navy), CoZnPO4-II (magenta), and CoZnPO4-III (purple): (A) λex ) 312 nm and (B) λex ) 632 nm.

4.82 nets along the [001] direction connecting through the UUDDUUDD linkages of each tetrahedral atom around the 8-ring channel with protonated ethylenediame cations accommodated in the 8-ring channel,20,45 (Figure 4b). CoZnPO4-III possesses a three-dimensional architecture similar to C6N4H22Co7(PO4)6,35 but with the composition of [C4N3H16]1.33[Co2.41Zn3.59(PO4)6], which was modeled as [C4N3H16]1.33[CoZn6(PO4)6] in the single-crystal data (Table 1). Its structure is made of CoO6, ZnO4 (or CoO4), and PO4 polyhedra. The cobalt octahedron is surrounded by six zinc tetrahedra to form the CoZn(or Co)6O6 cluster which are linked via six PO4 tetrahedra to other clusters to form its framework. The clusters are arranged in such a manner that each cluster is displaced by half the length of the a-axis from its neighbors, forming a honeycomb layer. The next layer of clusters is identical to the first but is displaced along the a-axis by half the unit cell so that the honeycomb channels are capped. The framework of AB type stacking results in the formation of 8-membered channels at an angle to a-axis (Figure 4c). The photoluminescence properties of CoZnPO4-I, -II, and -III were studied in the solid state (ground into powder) at room temperature. The measurements were carried out under the same experimental conditions. In Figure 7 A, several distinct features can be observed: ultraviolet (UV) emission peaked at 352 and 395 nm, broad violet-blue emission centered at 449 and 466 nm, green emission at 535 nm, and yellow-orange emission centered at 592 nm. These compounds also emit intensive red luminescence centered at 665 nm as excited by 632 nm wavelength (Figure 7 B). DETA show strong and broad emission

The synthesis of zinc-cobalt phosphate materials have been investigated by using linear polyamines, such as tetraethylene-pentamine, triethylenetetramine or diethylenetriamine as SDA. Generally, temperature is an important factor, favoring the hydrolysis of linear polyamines at higher temperature. Our investigations have found that the in situ decomposition of tetraethylene-pentamine, triethylenetetramine, or diethylenetriamine can be controlled by using second organic amine, such as propylamine as the assistant organic additive. Three open-framework cobalt-zinc phosphates, CoZnPO4-I, CoZnPO4-II, and CoZnPO4-III, have been synthesized from a single gel at 200 °C in the presence of diethylenetriamine as the structure directing agent. Structural analysis reveals that species encapsulated in the structures of CoZnPO4-I, CoZnPO4-II, and CoZnPO4-III are ammonium, ethylenediaminum, and diethylenetriaminum, respectively, which can be attributed to the partly in situ decomposition of diethylenetriamine molecules during the crystallization procedure. The presence of second organic amine plays an important role on controlling the in situ decomposition of linear polyamines. A novel metal phosphate CoZnPO4-I has been structure refined. Its three-dimensional framework can be considered as the stacking of six-ring sheet with the combination of UDUDUD (U, upward; D, downward) and UUUDDD linkages in the proportion 1:3. The influence of second organic amine may be attributed to the effect of the pH on hydrolysis of the long chain polyamines. Acknowledgment. This work was funded by the Natural Science Foundation of China (20473040) and the State Basic Research Project (2003CB615801). Supporting Information Available: Figures S1 and S2; Tables S1 and S2 (PDF). Crystallographic information in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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Decomposition of Polyamines for Growth of Co-Zn Phosphates

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