Role of incorporated SCN− or SO42− in organically templated chlorocadmates: synthesis, structural characterization and photoluminescence property

Polyhedron 127 (2017) 176–185

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Role of incorporated SCN
or SO2
4 in organically templated chlorocadmates: synthesis, structural characterization and photoluminescence property Bing Guo, Rong-Yan Wang, Jie-Hui Yu ⇑, Jia-Ning Xu ⇑, Ji-Qing Xu College of Chemistry, Jilin University, Changchun, Jilin 130012, China

a r t i c l e

i n f o

Article history: Received 27 March 2016 Accepted 25 January 2017 Available online 6 February 2017 Keywords: Hybrid materials Templating agent Organic amine Chlorocadmate Photoluminescence

a b s t r a c t Based on an aim of introducing the SCN
or SO2
4 group into the organically templated chlorocadmates, a series of room-temperature reactions at pH 2 were performed, creating four new Cd(II) hybrids as [L1]4[Cd4Cl6(SCN)10(H2O)2] (L1 = 1,10 -dibenzyl-4,40 -bipyridium) 1, [H4L2][CdCl4(SCN)2] (L2 = 1,4-bis(4pyridylmethyl)piperazine) 2, [HL3]3[CdCl3]SO4 (L3 = 2-amino-6-chloropyridine) 3, and [HL4]3[CdCl3] SO4 (L4 = 2-amino-6-bromopyridine) 4. X-ray single-crystal diffraction analysis reveals that (i) templated by L12+, 1 shows a 1-D single-chain structure, which is based on the dinuclear [Cd2Cl3(SCN)4(H2O)]3
clusters by the l-1,3-mode SCN
groups; (ii) templated by H4L24+, 2 only exhibits a mononuclear structure. However, via the intermolecular weak NpyridineAH  Cl, NpiperazineAH  Cl and SSCN  SSCN interactions, 2 self-assembles into a 3-D supramolecular network with a (4,6)-connected topology; (iii) 3 and 4 possess the similar structures. Via the Npyridine/aminoAH  O and p  p interactions, the introduced SO2
4 groups and the organic base molecules aggregate together into a 3-D supramolecular network with the 1-D channels. Within the channel, the Cl
ions triplely bridge the Cd2+ centers into a 1-D linear [CdCl3]
chain. Based on the structural information and the previous related reports, the role of the intro
duced SCN
or SO2
4 group in the hybrid is revealed. SCN acts as two roles: (i) a linker; (ii) a cutter. 2
Sometimes SO2
4 serves as a linker, while sometimes SO4 connects with organic base into a supramolecular aggregation, acting as a new templating agent. The photoluminescence analysis reveals that 2, 3 and 4 emit light with the maxima at 535 nm for 2 (kex = 465 nm), 462 nm for 3 (kex = 428 nm), and 465 nm for 4 (kex = 430 nm), respectively. In particular, the emissions for all are strong, and can be seen under the ultraviolet (UV) lamp. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction As an important branch of hybrid organic–inorganic materials, a certain attention has been paid to the design and synthesis of novel organically templated halo- or pseudohalomatalletes during the last four decades [1]. They not only exhibit the structural diversity [2], but also possess the potential applications in optics [3], magnetism [4], electrical conductivity [5] and electrochemistry [6]. For example, (i) the halogen or pseudohalogen ions can link the Cu(II) centers to form various magnetic exchange paths, so the organically templated halo- or pseudohalocuprate(II) exhibit the nice magnetic properties [7]; (ii) the organically templated iodocuprates(I) possess the luminescence properties. Some emit the high-energy blue light, while some emit the low-energy yellow

⇑ Corresponding authors. Fax: +86 431 85168624. E-mail addresses: [email protected] (J.-H. Yu), [email protected] (J.-N. Xu). http://dx.doi.org/10.1016/j.poly.2017.01.039 0277-5387/Ó 2017 Elsevier Ltd. All rights reserved.

or red light. This has been confirmed to be related to the Cu(I)   Cu(I) interactions in the hybrids [8]; (iii) the viologen-templated chlorobismuthates(III) maybe possess the photo/thermochromic properties. Its photo(thermo)chromic property has been verified to be related to the size of the chlorobismuthate(III) backbone [9]. Obviously, with the different organic base molecules as the templating agents, the different halo- or pseudohalomatallate anionic framework will be obtained. The structural difference will directly influence their functional properties. Our initial purpose is to prepare some new thiocyanatocadmates with the multi-dentate N-heterocyclic or amine molecules as the templating agents [10]. The Cd(SCN)2 precursor is obtained through the reaction of CdX2 with SCN
in a 1:2 molar ratio. However, we find that in the presence of the protonated organic base molecule, sometimes the X
ions in CdX2 cannot be thoroughly displaced by SCN
. As a result, a halocadmate with the additional SCN
group is produced [11]. We also find that H2SO4 as the H+

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B. Guo et al. / Polyhedron 127 (2017) 176–185

resource is used to acidify the organic base molecule, but sometimes SO2
4 can also appear in the final organically templated haloor pseudohalocadmate framework [12]. These give us an inspiration that the organ-templated halo- or pseudohalocadmate can be further modified by another kind of potential bridging-type inorganic group as SCN
or SO2
4 . Based on this conception, some new organically templated halo- or pseudohalocadmates with the interesting structures have now been obtained, including the 1-D [H2(pip)]4[Cd3Br8(SCN)2(SO4)2(H2O)]4H2O (pip = piperazine) [13], [H2(dabco)]2[Cd3Cl8(SCN)2]H2O (dabco = 1,4-diazabicyclo [2,2,2]octane) [14], [H2(bpp)][Cd3Br(SCN)7] (bpp = 1,3-bis(4-piperidyl)propane) [15], 2-D [H2(pdma)][Cd2(SCN)4(SO4)] (pdma = 1,4phenylenedimethanamine) [16], [H2L5][Cd2Cl5(SCN)] (L5 = bis (imidazole)methane) [17], and the 3-D [H2(tmen)][Cd3Cl6(SCN)2] (N,N,N0 ,N0 -tetramethylethylenediamine) [18]. It is noteworthy that (i) the hybrid [H2(pip)]4[Cd3Br8(SCN)2(SO4)2(H2O)]4H2O possesses a 1-D tube-like structure, whereas the hybrid [H2(tmen)] [Cd3Cl6(SCN)2] possesses a 3-D open-framework structure; (ii) due to the retainment of the Br
ion, the hybrid [H2(bpp)][Cd3Br (SCN)7] crystallizes in a non-center space group, which maybe makes it possess some special optical properties as the secondorder non linearity. In order to reveal the genuine role of the introduced SCN
or SO2
4 group on the organically templated halo- or pseudohalocadmate framework, in this article four new organic base molecules (1,10 -dibenzyl-4,40 -bipyridium dichloride hydrate, L12HCl; 1,4-bis(4-pyridylmethyl)piperazine, L2; 2-amino-6chloropyridine, L3; 2-amino-6-bromopyridine, L4) are selected to serve as the templating agents, yielding four new Cd(II) hybrids as [L1]4[Cd4Cl6(SCN)10(H2O)2] 1, [H4L2][CdCl4(SCN)2] 2, [HL3]3 [CdCl3]SO4 3, and [HL4]3[CdCl3]SO4 4. In 1 and 2, SCN
is introduced, whereas in 3 and 4, SO2
4 appears (see Scheme 1).

2. Experimental 2.1. Materials and physical measurement All chemicals are of reagent grade quality, obtained from commercial sources without further purification. Elemental analysis (C, H and N) was performed on a Perkin-Elmer 2400LS II elemental analyzer. Infrared (IR) spectrum was recorded on a Perkin Elmer

N+

Spectrum 1 spectrophotometer in 4000–400 cm
1 region using a powdered sample on a KBr plate. Powder X-ray diffraction (XRD) data were collected on a Rigaku/max-2550 diffractometer with Cu Ka radiation (k = 1.5418 Å). Thermogravimetric (TG) behavior was investigated on a Perkin-Elmer TGA-7 instrument with a heating rate of 10 °C min
1 in air. Fluorescence spectrum was obtained on a LS 55 florescence/phosphorescence spectrophotometer at room temperature. Ultraviolet–visible (UV–Vis) spectrum was obtained on a Rigaku-UV-3100 spectrophotometer. 2.2. Synthesis of title compounds [L1]4[Cd4Cl6(SCN)10(H2O)2] 1. A solution of L12HCl (409 mg, 1 mmol) in CH3OH (5 mL) was added slowly to an aqueous solution (7 mL) of a mixture of 3CdSO48H2O (257 mg, 1 mmol) and NH4SCN (152 mg, 2 mmol). A few drops of dilute H2SO4 were added to acidify the solution to pH 2. The mixture was stirred for ca. 2 days, and then filtered. The light-yellow needle crystals of 1 were obtained after ca. 8 days of slow evaporation from the filtrate. Yield: ca. 10% based on Cd(II). Anal. Calc. for C106H92N18O2S10Cd4Cl6 1: C, 49.02; H, 3.42. N, 9.71. Found: C, 48.76; H, 3.43; N, 9.55%. IR (cm
1): 3117 w, 3043 w, 2100 s, 2065 s, 1635 s, 1556 w, 1495 w, 1437 m, 1157 w, 905 w, 804 m, 755 m. [H4L][CdCl4(SCN)2] 2. A solution of L2 (268 mg, 1 mmol) in CH3CH2OH (3 ml) was added slowly to an aqueous solution (5 mL) of a mixture of CdCl22.5H2O (228 mg, 1 mmol) and NH4SCN (152 mg, 2 mmol). A few drops of dilute H2SO4 were added to acidify the solution to pH 2. The deep-yellow needle crystals of 2 were obtained after ca. 7 days of slow evaporation. Yield: ca. 25% based on Cd(II). Anal. Calc. for C18H24N6S2CdCl4 2: C, 33.63; H, 3.76; N, 13.08. Found: C, 33.21; H, 3.76; N, 12.69%. IR (cm
1): 3037 w, 2939 w, 2056 w, 1639 w, 1599 w, 1502 m, 1448 w, 1375 w, 1203 w, 1074 w, 955 w, 793 m. [HL]3[CdCl3]SO4 3. A solution of L3 (128 mg, 1 mmol) in CH3OH (3 mL) was added slowly to an aqueous solution (5 mL) of CdCl22.5H2O (114 mg, 0.5 mmol). A few drops of dilute H2SO4 were added to acidify the solution to pH 2. The mixture was stirred for ca. 2 days, and then filtered. The yellow needle crystals of 3 were obtained after about one week of slow evaporation from the filtrate. Yield: ca. 20% based on Cd(II). Anal. Calc. for C15H18N6O4SCdCl6 3: C, 25.60; H, 2.58; N, 11.95. Found: C, 25.14;

N

N

+N

N

N

L1

Cl

L2

N

L3

NH2

Br

N

L4

Scheme 1. Molecular structures of organic bases in 1–4.

NH2

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B. Guo et al. / Polyhedron 127 (2017) 176–185

H, 2.56; N, 11.78%. IR (cm
1): 3097 m, 1876 w, 1668 s, 1618 s, 1473 w, 1385 w, 1319 w, 1171 m, 1070 m, 951 m, 799 m. [HL]3[CdCl3]SO4 4. A solution of L4 (173 mg, 1 mmol) in CH3OH (3 mL) was added slowly to an aqueous solution (5 mL) of CdCl22.5H2O (228 mg, 1 mmol). A few drops of dilute H2SO4 were added to acidify the solution to pH 2. The mixture was stirred for ca. 2 days, and then filtered. The yellow needle crystals of 4 were obtained after ca. 38 days of slow evaporation from the filtrate. Yield: ca. 20% based on Cd(II). Anal. Calc. for C15H18N6O4SCdCl3Br3 4: C, 21.52; H, 2.17; N, 10.04. Found: C, 21.53; H, 2.19; N, 9.90%. IR (cm
1): 3096 m, 1876 w, 1668 s, 1473 m, 1385 w, 1177 m, 1070 m, 951 m, 793 m. 2.3. X-ray crystallography The data were collected with Mo Ka radiation (k = 0.71073 Å) on a Rigaku R-AXIS RAPID IP diffractometer. With SHELXTL program, the structures for all were solved using direct methods [19]. The non-hydrogen atoms were assigned anisotropic displacement parameters in the refinement, and the other hydrogen atoms were treated using a riding model. The hydrogen atoms on the water molecule in 1 were not located. The hydrogen atoms on L3 in 3 were obtained from the difference Fourier map, in order to reveal the protonated situations of the N atoms on L3. For 2, the largest diffraction peak (B-level alert) derives from the existence of the Q1 atom around S1. But the S1–Q1 distance of 1.673 Å indicates that Q1 is insignificant. The structures were then refined on F2 using SHELXL-97 [19]. CCDC numbers are 1442334–1442337 for 1– 4, respectively. The crystallographic data for the title compounds are summarized in Table 1. 3. Results and discussion 3.1. Synthetic analysis All of the reactions were carried out at the room-temperature conditions, and all of the title compounds were obtained at a strongly acidic environment (pH 2). A strongly acidic environment can ensure the organic base molecule to be thoroughly protonated. Meanwhile, a strongly acidic environment can increase the solubility of the reactive precursors in the mixed solvents. H2SO4 can be selected to act as the H+ resourse. It can provide a pH 2 environ-

ment, but also possesses a possibility to be introduced into the final framework of the hybrid. As expected, SCN
is introduced in 1 and 2, while SO2
appears in 3 and 4. One interesting phe4 nomenon is observed when preparing 3 and 4. Although the reactions are performed at a strongly acidic environment, the L3 and L4 molecules just have a +1 charge. This means that the L3 and L4 molecules are not diprotonated at pH 2, but only monoprotonated. In the structural description section, we will reveal that for L3 and L4, only the pyridine N atom is protonated, while the amino N atom is non-protonated at pH 2. In the other aminopyridine-templated hybrids as [H(apy)][Cd(SCN)3] (apy = 4-aminopyridine) [18], [H(amp)][Cd(SCN)2(CH3COO)] (amp = 2-amino-6-methylpyridine), and [HL4]4[Cd(SCN)4]SO4H2O [12b], the same situations are observed. In these compounds, the aminopyridine molecules are monoprotonated, even though they have the potential to be diprotonated. Note that only on pyridine ring, the substituted amino group is not protonated even though at pH 2. At an acidic environment the amino group generally exists in a protonated form [11–18]. Moreover, we have stated in the previous reports that SO2
4 in CdSO4 navel appears in the hybrid [11,12,16]. When preparing 1, the exception does not occur. 3.2. Structural describtion [L1]4[Cd4Cl6(SCN)10(H2O)2] 1. 1 is a L12+-templated 1-D chained chlorocadmate(II) with the modified SCN
groups. The asymmetric unit of 1 is found to be composed of two types of Cd2+ ions (Cd1, Cd2), three types of Cl
ions (Cl1, Cl2, Cl3), five types of SCN
groups (SCN
I labeled as S(1)C(49)N(5), SCN
II labeled as S(2)C(50)N(6), SCN
III labeled as S(3)C(51)N(7), SCN
IV labeled as S(4)C(52)N(8), SCN
V labeled as S(5)C(53)N(9)), four types of L1 molecules (L1 I, L1 II, L1 III, L1 IV) and one coordinated water molecule (Ow1). For all of the L1 molecules, only a half appears in the asymmetric unit of 1. Templated by L12+, 1 exhibits a 1-D single-chain structure, as shown in Fig. 1. Cd1 and Cd2 are both involved in an octahedral site: Cd1 is coordinated by two Cl
ions (Cl1, Cl2), two SCN
N atoms (N7, N8) and two SCN
S atoms (S2, S5), while Cd2 is surrounded by three Cl
ions (Cl1, Cl2, Cl3), two SCN
N atoms (N5, N9a) and one water molecule (Ow1). In 1, the Cl
ions exhibit two types of coordination modes: the terminal mode for Cl1; the double-bridged mode for Cl2 and Cl3. The SCN
groups show three types of coordination modes: the l-1 mode for SCN


Table 1 Crystal data of 1–4.

Formula M T (K) Crystal system Space group Unit cell dimensions a (Å) b (Å) c (Å) a (o) b (o) c (o) V (Å3) Z Dcalc (g cm
3) l (mm
1) Reflections collected Unique reflections Rint Goodness-of-fit R1, I > 2r(I) wR2, all data

1

2

3

4

C106H92N18O2S10Cd4Cl6 2632.88 293(2) monoclinic P21/c

C18H24N6S2CdCl4 642.78 293(2) triclinic P-1

C15H18N6O4SCdCl6 703.51 293(2) hexagonal P63/m

C15H18N6O4SCdCl3Br3 836.88 293(2) hexagonal P63/m

17.703(4) 18.586(4) 18.396(4) 90 111.72(3) 90 5622.7(19) 2 1.555 1.131 53703 12767 0.0234 1.067 0.0321 0.0942

7.5708(15) 9.2154(18) 9.761(2) 89.30(3) 72.35(3) 71.59(3) 613.1(2) 1 1.741 1.516 5726 2713 0.0684 1.088 0.0919 0.2895

14.652(2) 14.652(2) 6.7183(14) 90 90 120 1249.1(3) 2 1.871 1.635 12232 1027 0.0236 1.129 0.0202 0.0473

14.758(2) 14.758(2) 6.8267(14) 90 90 120 1287.6(4) 2 2.158 5.930 12196 1061 0.0364 1.083 0.0209 0.0494

B. Guo et al. / Polyhedron 127 (2017) 176–185

179

Fig. 1. 1-D single-chain structure of 1 (a: x,
y + 3/2, z + 1/2; b: x,
y + 3/2, z
1/2; c:
x + 1,
y + 1,
z + 2; d:
x,
y + 1,
z; e:
x + 1,
y + 1,
z + 1; f:
x,
y,
z).

II; the l-3 mode for SCN
I, SCN
III and SCN
IV; the l-1,3 mode for SCN
V. As far as the formation of the chain is concerned, Cl2 and Cl3 first doubly bridge the Cd1 and Cd2 centers into a dinuclear cluster with the composition of [Cd2Cl3(SCN)4(H2O)]3
. The Cd2Cl2 loop is slightly folded along the Cd1Cd2 line (dihedral angle: 13.9°). The Cd1  Cd2 contact distance is 3.913 Å. Then the l-1,3-mode SCN
V groups singly bridge these dinuclear units into a 1-D infinite chain, running down the c-axial direction. Between the inorganic chains and the L12+ molecules, no hydrogen-bonded interactions are observed. The Cd-N/S/Cl distances in 1 obey such a rule: Cd–N/S/Clterminal < Cd–N/S/Clbridged. The Cd-Ow1 distance is 2.450(2) Å. [H4L2][CdCl4(SCN)2] 2. 2 is a H4L24+-templated mononuclear chlorocadmate(II) modified by SCN
. The asymmetric unit of 2 is found to be composed of a half Cd2+ ion (Cd1), two types of Cl
ions (Cl1, Cl2), one SCN
group, and a half L2 molecule. All of the N atoms for L2 should be protonated in order to balance the systematic charges. So L2 has a +4 charge in 2. Templated by H4L24+, the inorganic anion only exhibits a mononuclear structure, as displayed in Fig. 2a. The octahedral Cd1 center lies on an inversion center. The equatorial plane is occupied by four Cl
ions (Cl1, Cl2, Cl1a, Cl2a; Cd1–Cl = 2.614(2)–2.627(2) Å), while the axial positions are occupied by two SCN
N atoms (N1, N1a, Cd1–N = 3.412 (12) Å). Between the inorganic anions and the organic cations, two types of hydrogen-bonded interactions are observed: the NpyridineAH  Cl interaction (N2  Cl1c = 3.109 Å) and the NpiperazineAH  Cl interaction (N3  Cl2d = 3.069 Å). Via these two types of NAH  Cl interactions, 2 self-assembles into a 2-D supramolecule layer network (also see Fig. 2a). As shown in Fig. 2b, the l-3-mode-SCN
groups protrude from the supramolecular sheet. There exists the S  S interaction between two neighboring SCN
S atoms (S1, S1e), which is revealed by the short contact distance of 3.506 Å. Via the S1  S1e interactions, 2 finally self-assembles into a 3-D supramolecular network. Based on the topological viewpoint, the inorganic anion can be viewed as a 6-connected

node, while the organic cation acts as a 4-connected node. So this 3-D supramolecular network for 2 exhibits a (4,6)-connected topology. [HL3]3[CdCl3]SO4 3. 3 is a HL3+-templated chained chlorocadmate(II). SO2
4 is introduced in the final framework of 3, and exists in a free way. The asymmetric unit of 3 is found to be composed of a third Cd2+ ion (Cd1), one Cl
ion (Cl1), one L3 molecule and a third SO2
group. Based on the difference Fourier map of 3, a Q 4 atom is observed around N1, suggesting that the pyridine N atom for L3 is protonated. But around N2, only two Q atoms are found, and N2 is in a planar trigonal site. This implies that N2 is not protonated. Otherwise, N2 should be in a tetrahedral site. So L3 in 3 has a +1 charge. In 3, the introduced SO2
group first links the 4 organic HL3+ cations into a discrete supramolecular aggregation. As shown in Fig. 3a, each two symmetry-related O1 atoms for SO2
4 head-to-head form the inter(intra)molecular hydrogen bonds to two L3 N atoms (R22(6); N1pyridine  O1 = 2.641 Å; N2amino  O1h = 2.851 Å). Via this kind of hydrogen-bonded syn+ thon, each SO2
4 group links three HL3 cations together to form this discrete supramolecular aggregation. Along the a-axial direction, the adjacent L3 molecules trans-mode array in a parallel form, producing finally a 3-D supramolecular network with a 1-D channels, as shown in Fig. 3b. Within the channel, the Cl
ions triplely bridge the Cd2+ centers into a 1-D endless chain (see Fig. 3c). Cd1 with an octahedral geometry is coordinated by six Cl
ions (Cd1ACl1 = 2.6553(5) Å). The shortest Cd  Cd separation in the chain is Cd1  Cd1a = 3.359 Å. Moreover, between the CdCl
3 chain and the 3-D supramolecular network, the weak Cl  Cl interaction (Cl1  Cl2i = 3.774 Å; i =
x + y,
x + 1,
z + 1/2) is found, via which 3 is further stabilized (see Fig. 3d). [HL4]3[CdCl3]SO4 4. 4 is a HL4+-templated chlorocadmate(II). SO2
4 also appears in 4. Although the 6-position substituent group on pyridine ring for L4 is different from that of L3, 4 shows the same supramolecular network as that of 3. Here we do not describe the structure of 4 any more. The weak Cl  Br interactions are

180

B. Guo et al. / Polyhedron 127 (2017) 176–185

Fig. 2. 2-D supramolecular layer (a), and 3-D supramolecular network (b) in 2 (a:
x + 2, y,
z; c:
x + 1,
y + 1,
z + 1; d:
x + 1,
y + 1,
z; e:
x + 2,
y + 1,
z + 1).

observed in the supramolecular network of 4. The Cl  Br contact distance is 3.706 Å. The shortest Cd  Cd separation in 4 is 3.413 Å. 3.3. Structural discussion As mentioned above, SCN
is introduced in 1 and 2, while SO2
4 appears in 3 and 4. Based on the dimensional reduction concept [20], the anionic formation of 1 should undergo three indispensable steps: (i) with the interactions of the organic base molecule and the SCN
group, the 2-D CdCl2 layer is cut into a dimer with a composition of [Cd2Cl10]6
; (ii) the SCN
group and the water molecule displace the partial terminal Cl
ions, foming a new cluster with a composition of [Cd2Cl3(SCN)6(H2O)]5
; (iii) Via the CdAS and CdAN interactions, the SCN
groups singlely bridge the dinuclear [Cd2Cl3(SCN)4(H2O)]3
units into a 1-D winding chain. For some hybrids as [H2(pip)][CdCl3(SCN)]2H2O, [H2(dabco)]2 [Cd3Cl8(SCN)2]H2O [14], and [H(dpa)][Cd2Cl3(SCN)2(CH3OH)] (dpa = dipropylamine) [17], the formation of the inorganic anions in these hybrids should underge a similar precess as that of 1. Since the different base molecules are used, the 2-D CdCl2 layer is cut into the different oligomers, and the SCN
groups adopt the different linking ways. For example, templated by H2(pip)2+, CdCl2 is cut into a dimer. The SCN
groups doubly bridge the dimers into a lin-

ear chain [14]. Templated by H2(dabco)2+, CdCl2 is cut into a planar tetramer. The SCN
groups doubly bridge the tetramers into a zigzag chain [14]. Templated by H(dpa)+, CdCl2 is cut into a non-planar tetranuclear cluster. The SCN
groups quadruplely bridge the tetranuclear clusters into a 1-D ribbon [17]. Sometimes the formed Cd2+ACl
oligomers can also undergo a recombination, in order to finally form a more stable network, as observed in [H2(tmen)][Cd3Cl6(SCN)2] [18]. Templated by H2(tmen)2+, CdCl2 is first cut into a tetranuclear Cd2+ACl
cluster. Then these tetranuclear clusters recombine into a 1-D Cd2+ACl
chain. The SCN
groups finally extend the 1-D Cd2+ACl
chains into a 3-D open-framework network. These indicate that the first role of the introduced SCN
group in the hybrid is to serve as the second linker. These also suggest that the organic base molecule possesses the templating effect on the whole inorganic anion. With or without SCN
, CdCl2 will be cut into the different oligomers. For example, without SCN
, H2(pip)2+ cuts CdCl2 into a 1-D single chain, whereas with SCN
, H2(pip)2+ cuts CdCl2 into a dimer [14]. Without SCN
, H2(dabco)2+ cuts CdCl2 into a 1-D double chain, while with SCN
, H2(dabco)2+ cuts CdCl2 into a tetramer [14]. These imply that another role for SCN
is to act as a cutter. The degree for SCN
to displace the Cl
ion are unpredictable. In [H2(tmen)][Cd3Cl6(SCN)2] [18] and [H2(dabco)]2[Cd3Cl8(SCN)2]H2O [14], only the limited Cl
ions

B. Guo et al. / Polyhedron 127 (2017) 176–185

181

Fig. 3. Discrete supramolecular aggregation (a), 3-D supramolecular network (b), 1-D [CdCl3]
chain (c), and Cl  Cl interactions in 3 (a:
x + y,
x, z; b:
y, x
y, z; c:
x,
y,
z + 1; d: x
y, x,
z + 1; e: y,
x + y,
z + 1; f:
x,
y, z + 1/2; g:
x,
y, z
1/2; h:
x + y,
x + 1, z; i:
y + 1, x
y + 1, z; j:
x + 1,
y + 1,
z + 1).

are replaced by SCN
, whereas in [H2(bpp)][Cd3Br(SCN)7] [15] and [H2(mbcha)][Cd3Br2(SCN)6] [11b], most of the Cl
ions are replaced. If only the space is permitted, the SCN
group will replace the Cl
ions as far as possible, as observed in 1. The NbaseAH  NSCN and SSCN  SSCN interactions can induce the replacement reaction to occur, as observed in 2, while the NbaseAH  Cl interaction can deter the occurrence of the replacement reaction, as found in [H(ba)]2[CdCl2(SCN)2] (ba = tert-butylamine) [18]. Even though the inorganic anions in some hybrids possess the same compositions, they display the different structures, since the used organic base molecules are different. For instance, the inorganic anion in [H2(bpyp)][CdBr2(SCN)2] (bpyp = 1,2-bis(4-pyridyl)propane) shows a mononuclear structure [11b], the inorganic anion in [H2(bpe)][CdBr2(SCN)2] (bpe = 1,2-bis (4-pyridyl)ethene) displays a dinuclear structure [11a], while the inorganic anion in [H2(bpy)][CdBr2(SCN)2] (bpy = 4,40 -bipyridine) exhibits a 1-D zigzag-chain structure [15]. These further confirm that the organic base molecule affects the structure of the overall inorganic anion. In the hybrid, SO2
4 exists in two ways: (i) existing in a coordination form; (ii) existing in a free form. If the introduced SO2
4 group exists in a coordination mode, it mainly acts as the second linker. As found in [H2(pdma)][Cd2(SCN)4(SO4)], the SO2
4 groups propagate the 1-D Cd2+-SCN
ribbons into a 2-D layer [16]. In [H2(pip)]4[Cd3Br8(SCN)2(SO4)2(H2O)]4H2O, the SO2
4 groups extend the Cd2+ABr
clusters into a tube-like chain [14]. Once SO2
4 exists in a free form, it generally forms a supramolecular aggregation with the organic base molecule via the hydrogenbonded interactions. This supramolecular aggregation serves as a new templating agent, as observed in 3 and 4. In [H2(dtdpy)]2

[CdBr4]SO42.5H2O (dtdpy = 4,40 -dithioidipyridine) [12a] and [H (L4)]4[Cd(SCN)4]SO4H2O [12b], the same situations are observed. 2+ With or without the free SO2
and X
will form the 4 group, Cd different oligomers or a mononuclear species. For instance, 2+ without SO2
in [H2(dtdpy)][Cd2Br6] cuts CdBr2 into 4 , H2(dtdpy) 2
a 1-D ribbon [11b], while with SO2
4 , only a mononuclear CdBr4 unit forms in [H2(dtdpy)]2[CdBr4]SO42.5H2O [12a]. The supramolecular aggregation generally possesses a large volume, so a smaller Cd2+-X
oligomer is obtained. This indicates that the free SO2
4 group acts as an indirect cutter in the hybrid. 3.4. Characterization Fig. S1 gives the IR spectra of the title compounds. Based on these spectra, some structural information about 1–4 can be preliminarily known. (i) In 1 and 2, SCN
is introduced. This is revealed by the peak around 2100 cm
1. The characteristic stretching vibration band of C„N appears at this position. (ii) In 3 and 4,
1 SO2
(1070 cm
1 in 3; 1070 cm
1 in 4 is mixed. Around 1070 cm 4), a strong wide band is found, which is the peak associated with the SO2
4 group [21]. In 1 and 2, this peak is not observed. (iii) In 1, there exist two-types of SCN
groups: the terminal and bridging modes, whereas in 2, SCN
exists only in a terminal form. m (C„N) for the terminal SCN
group is generally smaller than 2090 cm
1, while m(C„N) for the bridging group is larger than 2090 cm
1 [22]. Therefore, just one peak at 2056 cm
1 is observed, suggesting that in 2, SCN
adopts a terminal mode, whereas the appearence of two peaks (2100 cm
1, 2065 cm
1) implies the existence of two-types of SCN
groups in 1. These results from the IR

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B. Guo et al. / Polyhedron 127 (2017) 176–185 100

2

1

535 465

Intensity (a.u.)

Weight loss (%)

80

60

40

20

0 150

300

450

Temperature

600

750

300

450

o

C

600

750

Wavelength (nm)

(a)

(a)

100

3

428

4

462

Intensity (a.u.)

Weight loss (%)

80

60

40

20

0 150

300

450

Temperature

600

750

250

300

350

400

o

C

450

500

550

600

650

700

750

800

Wavelength (nm)

(b)

(b)

Fig. 4. TG curves of 1 (a) and 4 (b).

4

465

spectra are basically in agreement with those revealed by X-ray single-crystal diffraction. Fig. 4 gives the TG curves of 1 and 4. As shown in Fig. 4, the minor weight loss of ca. 2% for the first step should be ascribed to the removal of the coordinated water molecule in 1 (Calc.: 1.4%). Upon further heating from 170 °C to 330 °C, 1 lost ca. 46.5% weight, corresponding to the sublimation of [L1]3(SCN)6 (Calc.: 45.2%). The intermediate is [L1][Cd4Cl6(SCN)4]. The residue contend of ca. 7.2% indicates that in the next weight-loss procedure, [L1](SCN)2 fist lost. Then CdCl2 completely evaporates from the intermediate 3CdCl2Cd(SCN)2. The final remaining might be Cd(SCN)2 (Calc.: 8.7%) or CdSCd(SCN)2 (Calc.: 7.7%). As shown in Fig. S2b, 4 can thermal stable to 180 °C. From 180 °C to 350 °C, 4 lost ca. 53% weight, corresponding to the loss of [HL4]2SO4 (Calc.: 53.1%). In the temperature range of 350 °C and 450 °C, a platform is observed, implying that the intermediate [HL4][CdCl3] are stable in this temperature range. Next, [HL4]Cl lost, and the generated CdCl2 thoroughly evaporates. So no residue is found in the TG curve of 4. Fig. S2 plots the experimental and simulated powder XRD patterns of the title compounds. The experimental powder XRD pattern for each compound is in accord with the simulated one

Intensity (a.u.)

430

250

300

350

400

450

500

550

600

650

Wavelength (nm)

(c) Fig. 5. Photoluminescence spectra of 2 (a), 3 (b), and 4 (c).

generated on the basis of structural data, confirming that the assynthesized product is pure phase.

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B. Guo et al. / Polyhedron 127 (2017) 176–185

affects the emission of the molecule; (ii) the frontier orbitals do not contain the orbitals of the substituted X
ion, but the X
ion influences the energy difference of the frontier orbitals. Compared with the emission of the molecule, the emission of 2 shows a larger red shift by 65 nm, the emission of 4 also exhibits a larger red shift by 75 nm, but the emission of 3 hardly change. The emission of the L2 molecule should be attributed to the charge transfer from the p⁄ orbitals of the pyridine rings to the p orbitals of the pyridine rings. Since the emission of 2 is lower in the energy (535 nm), this is not original emission from 2. Its low-energy green-light emission should originate from the trap sites in the crystal [12b]. For 3 and 4, several situations have appeared: (i) 3 and 4 possess the same supramolecular structures; (ii) 3 and 4 exhibits the same emission behaviors; (iii) the emission of L3 is the same as that of 3; (iv) the emission of L4 is obviously different from that of 4. Based on these four situations, we can know that (i) the orbitals of the substituted X
ion are not involved in the frontier orbitals, but it has an effect on the emission of the base molecule; (ii) the effect of the substituted Cl
ion on the emission of L3 is limited, but the role of the substituted Br
ion in L4 is large; (iii) the supramolecular structure of the hybrid affects its emission behavior; (iv) there exist a competition for the emission of 4: the effect of the substituted Br
ion; the effect of the supramolecular structure [23]; (v) the supramolecular structure determines the emission behavior of 4. We believe that the L1 molecule possesses the photoluminescence property [9]. So the reason that 1 dose not emit light should be related to the close packing of the molecules, which leads to the photoluminescence quenching [24]. The decay curve for 2 fit into a double exponential function, and the lifetimes were calculated to be s1 = 1.62 ns and s2 = 4.85 ns, respectively. The luminescence lifetime for 3 was calculated to be s1 = 1.94 ns

3.5. Photoluminescence property The photoluminescence properties of the title compounds in the solid state were investigated. Fig. 5 gives the corresponding photoluminescence spectra. Obviously, 1 does not emit light, while 2–4 all possess the photoluminescence properties. For 2, it exhibits a green-light emission with the maximum at 535 nm, when excited at 465 nm. For 3 and 4, they show the same photoluminescence behaviors upon excitation (428 nm for 3, 430 nm for 4), which is characterized by the similar emission positions (462 nm for 3, 465 nm for 4). In order to investigate the emission intensity, we take the photos for the photoluminescence of 2–4 under the ultraviolet (UV) lamp. As shown in Fig. 6, under the UV lamp, the emission for 2–4 can all be seen, suggesting that the emissions of 2–4 are strong. Under the UV lamp, 2 emits the yellow-green light, while 3 and 4 emit the blue light. These results are in agreement with those from the spectrum analysis. In order to better understand the emission mechanism, the photoluminescence behaviors of the L2, L3, and L4 molecules were also investigated. As shown in Fig. S3, in the emission spectrum of the L2 molecule, just a weak emission peak at 470 nm (kex = 400 nm) is observed. Although 3 and 4 possess the similar the emission properties, the emissions for L3 and L4 display the apparent differences. Upon excitation, the L3 molecule exits the blue light (kex = 380 nm, kem = 460 nm), while the L4 molecule emits the high-energy violet light (kex = 360 nm, kem = 390 nm). Only the 6-position substituent group is different (ACl for L3, ABr for L4), two organic molecules show the distinct emission behaviors. There exist two circumstances: (i) the frontier orbitals (HOMO, the highest occupied molecular orbital; LUMO, the lowest unoccupied molecular orbital) contain the orbitals of the substituted X
ion, so the X
ion directly

2

3

4

Fig. 6. Images below showing photoluminescence behaviors of 2–4 under UV lamp (images above are the samples under sunlight).

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B. Guo et al. / Polyhedron 127 (2017) 176–185

and s2 = 4.25 ns, respectively. The luminescence lifetime for 4 was calculated to be s1 = 1.23 ns and s2 = 2.29 ns, respectively (see Fig. S4). So far, a large number of organically templated halocadmates have been reported, but only the limited examples have the photoluminescence properties [11–18]. They generally emit the high-energy violet or blue light. The emission derives from the charge transfer associated with the organic base molecule. The red- or blue-shift often appears. Although the red shift occurs, the emission is still smaller than 500 nm. 2 really shows a special situation, emitting the low-energy yellow-green light (kem = 535 nm). The close packing of the molecules maybe quenches the emission. Fig. S5 gives the UV–Vis spectra of the title compounds in the solid state for better understanding their photoluminescence properties. Moreover, some viologen-templated halometallates possess the photo(thermo)chromic properties [9], so the thermochromic property of 1 is investigated in the temperature range of 30–100 °C. Unfortunately, 1 does not possess the thermochromic property. 4. Conclusion In summary, we report four new organically templated chlorocadmates(II). In two hybrids, SCN
is introduced, whereas in the other two hybrids, SO2
4 is observed. Based on the structural information and the previous related reports, the role of the introduced
SCN
or SO2
4 group in the hybrid is discussed. For the SCN group, the first role is to serve as the second linker in the inorganic anion. The second role is to act as a cutter, cutting the 2-D CdCl2 into an even smaller oligomer or a mononuclear species. In the hybrid, 2
SO2
4 exists in two ways. For the coordinated SO4 group, it acts 2
as another linker, while for the free SO4 group, it will link the organic base molecule to form a supramolecular aggregation through the hydrogen-bonded interactions, namely a new templating agent. The title three compounds emit light, and their emissions are strong. It is worth stressing that one hybrid emits the low-energy yellow-green light, which is seldom observed in the organically templated chlorocadmates. Acknowledgements This research was supported by the National Natural Science Foundation of China (No. 21271083). Appendix A. Supplementary data CCDC 1442334–1442337 contain the supplementary crystallographic data for compounds 1–4. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10. 1016/j.poly.2017.01.039. References [1] (a) S.P. Zhao, X.M. Ren, Dalton Trans. 40 (2011) 8261–8272; (b) R. Peng, M. Li, D. Li, Coord. Chem. Rev. 254 (2010) 1–18; (c) N. Mercier, N. Louvain, W. Bi, CrystEngComm 11 (2009) 720–734; (d) L.M. Wu, X.T. Wu, L. Chen, Coord. Chem. Rev. 253 (2009) 2787–2804; (e) C.H. Arnby, S. Jagner, I. Dance, CrystEngComm 6 (2004) 257–275; (f) D.B. Mitzi, J. Chem. Soc., Dalton Trans. (2001) 1–12; (g) H. Zhang, X. Wang, K. Zhang, B.K. Teo, Coord. Chem. Rev. 183 (1999) 157– 195; (h) A.B. Corradi, A.M. Ferrari, G.C. Pellacani, Inorg. Chim. Acta 272 (1998) 252– 260; (i) L. Subramanian, R. Hoffmann, Inorg. Chem. 31 (1992) 1021–1029.

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