DOI: 10.1021/cg900547b
New Copper Coordination Polymers Derived from p- and o-BIMB via Different Reaction Approaches: Toward the Effects of Isomeric Ligands (BIMB=Bis-(imidazol-1-ylmethyl)benzene)
2009, Vol. 9 4533–4537
Mei-Hong Hu,†,‡ Gui-Lan Shen,† Jing-Xiang Zhang,† Ye-Gao Yin,*,† and Dan Li*,† †
Department of Chemistry, Shantou University, Shantou, Guangdong 515063, P. R. China, and Department of Biochemistry, College of Technology, Xiaogan University, Xiaogan, Hubei 432000, P. R. China
‡
Received May 21, 2009; Revised Manuscript Received June 29, 2009
ABSTRACT: To have an insight into the performance of chemically homogeneous but geometrically different isomeric ligands in constructing coordination polymers, two xylene-functionalized N-donors, specifically, p-BIMB and o-BIMB (BIMB = bis-(imidazol-1-ylmethyl)benzene), were treated, in parallel, with CuCN and KI under solvothermal conditions and with CuCl2 and NaN3 in layer diffusion, thereby affording four new coordination polymers with dimensions from 1D to 3D. In particular, the cuprous [Cu2(CN)2(p-BIMB)]n (1) is structured as a 3D framework showing an unprecedented bimodal (8 102)(85.10)2 topology and [Cu2(CN)2(o-BIMB)]n (2) as an undulated sheet based on a (CuCN)n network and the cupric {[Cu(N3)2(p-BIMB)2](H2O)2}n (3) is assembled as a 3D polycatenated framework based on the inclined interpenetrating (4,4) nets and [Cu(N3)2(o-BIMB)2]n (4) as a metal-fused ring catenation. The assemblies of 1-4 are of note for revealing a law that the polymers, comparably derived from two isomeric ligands, are similar in metal coordination but structurally are different. In addition, the responses of 1 and 2 to heat and light reveal that the properties of comparably synthesized compounds are affected by the structural diversity brought by ligand isomerization.
Introduction Coordination polymers (CPs) have attracted considerable attention in modern crystal engineering for their promising applications rooted in the constitutional and constructional particulars.1 With the aim to outline a law for rational design and to further harness the bulk performance of such materials, great efforts have been made in understanding the tectonics of the metal-ligand hybrid architectures.2 However, it is wellknown that the construction of a CP is determined not only by the character of building blocks but also by some nonconstitutional factors, such as solvent,3 temperature,4 and so on; therefore, the approaches to probe the effects of building blocks are usually carried out by keeping nonconstitutional factors invariant. In this way, the effects of different ligands have been investigated5 and so lead to a conclusion that the ligands affect the structures and functionality of CPs by serving as geometrically different modules. Bis(imidazoylmethyl)benzenes (BIMBs) are a set of position-isomers that have been widely used as ligands for the synthesis of CPs. The practice has shown the ability of the members in generating intriguing topologies separately but never systematically.6 With the aim to understand the contrasting roles of the isomeric ligands in building CPs, we chose p- and o-BIMB, as representatives, to react, in parallel, with CuCN þ KI and CuCl2 þ NaN3 in two different ways and finally obtained the CPs, 1-4. Structures of the products are reportable for illustrating a law extendable to the general structural engineering of isomer ligands. In particular, that of the p-BIMB-based 1 presents an unprecedented (8102)(85.10)2 topology for the 1:2 ns3/ns4 connectivity7 and that of 3 shows a polycatenation based on (4,4) nets. Herein, to
embody the effect of the isomer ligands and the novelty of 1 and 3, we report the structures and solid properties of these CPs in comparison. Experimental Section
*To whom correspondence should be addressed. E-mail:
[email protected]. cn (Y.-G.Y.). Tel.: 86-0754-82903699. Fax: 86-0754-82902828;
[email protected]. cn (D.L.).
General Information. The BIMB ligands were prepared according to the literature methods.8 All other chemicals were obtained commercially and used without further treatment. The IR spectra of 1-4 as KBr disks were recorded on a Nicolet Avatar 360 FT-IR spectrometer. The thermal behaviors of 1 and 2 were studied on a Seiko Extar 6000 TG/DTA in N2 atmosphere and their emission spectra were recorded on a Perkin-Elmer LS 55 Luminescence spectrometer at room temperature. Syntheses of [(CuCN)2(p-BIMB)]n (1) and [(CuCN)2(o-BIMB)]n (2). The compounds were prepared in parallel as follows: A CH3CN/H2O (6 mL/6 mL) solution of CuCN (9.000 mg, ∼0.1 mmol), p-BIMB (or o-BIMB) (27.000 mg, ∼0.1 mmol), and KI (16.000 mg, ∼0.1 mmol) was stirred at room temperature for 15 min and then moved to a 25 mL Teflon-lined reactor. The system was sealed and heated to 125 °C and then kept at the temperature for 60 h. After the time period, it was cooled down to room temperature at a rate of -5 °C h-1, and finally gave the yellow crystals of 1 or 2 in a yield of ca. 55% (or 30%). IR data (cm-1) for 1: 3162(w), 2921(m), 2103(s), 1528(m), 1409(m), 694(m), 510(m) and for 2: 3117(m), 2120(s), 2083(s), 1601(m), 1511(s), 1454(w), 1437(w), 1221(s),1106(s), 1078(s), 824(s), 751(s), 722(s). Syntheses of {[Cu(N3)2(p-BIMB)2](H2O)2}n (3) and [Cu(N3)2(o-BIMB)2]n (4). The cupric products were prepared as follows: to the top of an aqueous solution (3 mL) of CuCl2 (0.008 g, 0.05 mmol) and NaN3 (0.013 g, 0.20 mmol) in a test tube (φ = 2 cm) was added carefully a layer of THF as buffer and then a layer of acetonitrilic solution (5 mL) of p-BIMB (or o-BIMB) (27.000 mg, 0.10 mmol). The tube was stopped and allowed to stand at room temperature for several days, and then 3 was harvested as blue crystals in yield of ca. 70% (or 4 of ca. 40%) by filtration. IR data (cm-1) for 3: 3121(m), 2030(s), 1523(m), 1450(w), 1241(m), 1098(m), 751(m), 657(m); and for 4: 3125(w), 3092(m), 2034(s), 1515(m), 1466(m), 1233(m), 1115(m), 1082(m), 1021(w), 735(m), 661(m).
r 2009 American Chemical Society
Published on Web 07/21/2009
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Figure 1. (a) A view of 1 along c, (b) a highlight of its cuprocyanide network (color scheme: Cu red, N blue, and C gray), and (c) its topologic representation (the lines: green CN, yellow p-BIMB, and red Cu2-Cu2). X-ray Crystallography. Data collections were performed at room temperature on a Bruker Smart Apex CCD diffractometer (Mo-KR, λ=0.71073 A˚). Reflection intensities were integrated and a correction on absorptions was made with a SAINT software.9 The structures of 1-4 were solved by direct methods and refined by full-matrix least-squares refinements based on F2. Anisotropic thermal parameters were applied to the nonhydrogen atoms. Hydrogen atoms were generated by geometry (C-H: 0.960 A˚). All the calculations were carried out using SHELXL-97 programs.10 Because of space limitations, the crystallographic data and bond parameters of 1-4 are given in Supporting Information. The CCDC codes of 1-4 are respectively 629745, 629746, 632644, and 632645.
Results and Discussion Structural Description. The yellowish single crystals of 1 and 2 for X-ray analyses were isolated from parallel solvothermal reactions of p- and o-BIMB with CuCN in the presence of KI and defined of the CPs, sharing a formula of C16H14N6Cu2 and consisting of Cu(I), CN-, and BIMB ligand in a ratio of 2:2:1. In particular, the p-BIMB-based 1 resulted as a 3D CP, solidifying in a monoclinic P21/n space group and assembling as a robust architecture made of the infinite (CuCN)n motifs and p-BIMB ligands (Figure 1a). In it, the Cu ions are crystallographically categorized into two classes (Supporting Information, Figure S1), of which the Cu1 ion is coordinated by two C atoms of cyanides and a N of p-BIMB, with a deviation from the C2N coordination plane for 0.021 A˚, and the Cu2 is coordinated by two N atoms of cyanides and a N of BIMB with a deviation from the N3 plane for 0.474 A˚. By associating to cyanides, they furnish the sinuated (CuCN)n chains running along the b axis (Figure 1b). Noticeably, the binary motifs give an intermotif dCu2 3 3 3 Cu2 (2.576(2) A˚), drastically shorter than the van der Waals radii sum of two Cu(I) ions (∼2.8 A˚), indicating a profound cuprophilic bonding interaction of contribution to photoemission,12
whose mechanistic details are still unclear.11 By virtue of the cuproophilic force, the 1D (CuCN)n chains are brought into the 2D grid networks extending into the ac plane. Herein, all cyanides take a part of bitopic linker connecting a Cu1 and a Cu2, which agree with the single IR absorption of 1 at 2130 cm-1, but the different Cu1-(CN)-Cu2 separations (4.920, 4.923(5) A˚) advocate an assortment of these anions. Likewise, the p-BIMBs in 1 are also functionally divided into two groups; one acts as the spacers of Cu1s (Cu1 3 3 3 (p-BIMB) 3 3 3 Cu1 =14.38(1) A˚) and one as the spacers of Cu2s (Cu2 3 3 3 (p-BIMB) 3 3 3 Cu2 = 14.86(1) A˚). In a sense, the diverse roles of p-BIMBs implicate a selfaccommodation of the flexible ligands. For the variety of building blocks, the structure of 1 is somewhat complicated. However, in denoting Cu(I) as node and p-BIMB and CN- as linkers, it can be reduced into fiveinterpenetrated 103-utp nets. If the Cu2 3 3 3 Cu2 contacts are further taken into consideration as a linker, the entanglement turns into a (3,4)-connected (8 102)(85.10)2 topologized network (Figure 1c). Although the binodal network defines the connection of nodes, similar to other 1:2 ns3/ns4 nets,7 it is unique in demonstrating a lower diversity of polygons (Figure S2, Supporting Information) most likely due to self-interpenetration. Moreover, we can see that the makeup of 1 is different from the [(CuCN)4(p-BIMB)4], a CP afforded by the hydrothermal reaction of p-BIMB and CuCN with adding HCl, which contains a vase-like (CuCN)n substructure.13 Logically, the structural diversity of two Cu-CN-p-BIMB composites suggests an effect of pH on the construction of CPs. As a contrast of 1, 2 was isolated as a 2D CP solidifying in an orthogonal Pbca space group. Seen in Figure 2a, the o-BIMB-tagged phase is shaped as a three-layer slab sandwiching a (CuCN)n sheet, in which the ligands take a cisconformation and act as bypasses of Cu2(CN)(o-BIMB)
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Figure 2. The structure (a), the paired (CuCN)n helices (b), and the grid (CuCN)n network of 2 (c).
Figure 3. The coordination entities of 3 (left) and 4 (right) with azides omitted for clarity.
loops. The role of o-BIMB stops the extension of 2 to c and makes 2 1D lower than 1. In addition, for the presence of demanding cis o-BIMB, the cuprocyanide chains of 2 are constructed as the paired M and P helices (Figure 2b), propagating along b, with a pitch of 14.55(1) A˚, and give a Cu1 3 3 3 Cu1 distance only for 2.511 A˚, even shorter than the Cu2 3 3 3 Cu2 of 1. Furthermore, the o-isomer causes a tension in the chains, reflected by the IR bands of cyanides at 2120 and 2083 cm-1. Now that the isolations of 1 and 2 are different only in ligands, the structural divergence can be rationally ascribed to the influence of isomeric ligands. Even so, the products are actually architectural isomers, sharing a formula C16H14N6Cu2 (Figure 2a). More than that, the Cu(I)’s in 2, like those in 1, are divided into two groups, both featured with the coordination by two CNs and a BIMB, and the Cu-involving bonds (Cu-N 2.041(2), 2.058(2) A˚; Cu-X 1.864(2)-2.017(2) A˚ (X = C or N of CN)) of 2 are comparable with those of 1. Besides, 2 involves also a grid cuprocyanide net (Figure 2c), formed from (CuCN)n chains via cuprophilicity, as building block. The observations on the structures of 1 and 2 seem to show that alteration of isomeric ligands does not bring on a significant difference in the coordination of CPs owing to the homogeneity of isomeric ligands in reactivity but a drastic change in structures for the geometric diversity of ligands. The suggestion is validated by the structures of 3 and 4, two CPs obtained from parallel reactions of p- and o-BIMB with CuCl2 þ NaN3 in layer-diffusion. Illustratively, the ligand-discriminated compounds show a similar surrounding of Cu(II) ions by four imidazoles (Figure 3) and two azides in an octahedral geometry. For the chemical homogeneity of isomeric ligands, the Cu-Nim bonds of two compounds are nearly identical (1.987-2.027 A˚ 3; 1.9862.029 A˚ 4) and the Cu-Naz bonds (3 2.624(1), 4 2.788(1) A˚)
Figure 4. (a) The interpenetration of (4,4) networks and (b) the relations of waters (yellow) to azides (blue) in 3.
Figure 5. Solid room temperature photoluminescence spectra of 1 (λex=280 nm) and 2 (λex=300 nm).
are comparable, falling in the normal bonding range.14 On the other hand, as a consequence of the geometric diversity of ligands, the p-BIMB-based 3 is 1D higher than the o-BIMBbased 4. Seen in Figure 3, this is apparently a result of the different functionalization of p-BIMB, as a linear connector allowing catenation of 3, and o-BIMB, as an angular linker, prohibiting extension of 4 to the a direction. As auxiliary proof of the suggestion, the reactions of p- and o-BIMB with CuSCNþNaSCN gave two CPs with similar metal coordination, but different dimensions (Figure S2, Supporting Information). Up to now, it is rational to conclude that the parallel reactions of isomeric ligands usually generate the CPs with analogous metal coordination but diverse structures. The awareness is significant to crystal
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Figure 6. Thermogravimetric (TG) and differential thermal (DT) plots of 1 (a) and 2 (b).
engineering suggesting a way to modify the coordinationbased properties of CPs with altering the isomeric ligands. The structure of 3 is reminiscent of the [Mn(N3)(p-BIMB)2]n:15 a CP different from 3 in metal ions and free hydration. In contrast to the cited being a single (4,4) network and showing a layered stacking in solid, 3 exhibits an inclined interpenetration of (4,4) networks (Figure 4a) and constructs as a 3D polycatenated framework. More interestingly, the interpenetrated networks of 3 are not the same; those, locating in (0,1,1) plane, consist of Cu1 ions and the p-BIMBs, spacing two Cu1 ions for 14.000(9) A˚ or 14.693(9) A˚, and those, locating in (1,1,1), consist of Cu2 and the p-BIMB spacing Cu2s for 14.107(8) or for 13.678(8) A˚. Conceptually, the assembly of p-BIMB-Cu entities preferred is a polycatenation but not a heteronet interpenetration because the nets involved are made of the same components.16 Heteronet interpenetrations, such as 1D þ 3D,17 2Dþ2D,18 and 1D þ 2D,6a,19 of p-BIMB-derived CPs have been well illustrated, but, to our knowledge, a polycatenated framework on the basis of (4,4) nets is still new. The architectural uniqueness of 3 may relate to the presence of lattice waters because the hydrated thiocyanide extra also shows such an assembly (Figure S3, Supporting Information). Moreover, the nonframe species, by uneven interaction to azides, affect the assembly of Cu-p-BIMB networks. Seen in Figure 4b, the azide N12N13N14, near Cu1, gives a N12-O1W distance of 2.824 A˚ and shows a disorder about (1,1,0), while the N9N10N11, near Cu2, gives a N11-O1W distance (3.020 A˚) longer and shows a disorder about (0,1,1). Photoluminescence of 1 and 2. The photoresponses of 1 and 2 to light revealed an effect of structural diversity brought by isomeric ligands on the bulk property of CPs. Seen in Figure 5, the solids, when excited by 280 nm, gave the band packages including several high-energy (HE) prewaves and a broad low-energy (LE) peak within 350-450 nm (Figure 5). In light of the assignation to [(CuCN)4(p-BIMB)],13 the bands are tentatively ascribed to the metal-ligand charge transfer (MLCT) and the metal-centered (MC) transitions. However, it is noticeable that the bands of 2, relative to those of 1, have bathochromic shifts, suggesting a discrepancy of 2 from 1 in the intramolecular interactions. For the mechanistic complexity, it is difficult to explicate all the shifts; nevertheless, the red shift of LE can be proposed of a result of the shorter dCuCu of 2 (2.511 A˚) than that of 1 (2.576 A˚) since the bonding interaction is responsible for the lowlaying emission.10 The hypothesis is agreed by the fact that the spectrum of [(CuCN)4(p-BIMB)]13 is more comparable
to that of o-BIMB-based 2, but not 1, because the reference has a dCuCu of 2.4904 A˚, close to that of 2. From a crystal engineer’s view, the observation provides a chance to tune the bulk properties of CPs with using isomeric ligands. Thermal Behavior of 1 and 2. Relatively, the effect of structure diversity of 1 and 2 on the response to heat is not so apparent as to light. Upon heating, the solids gave thermogravimetric (TG) plots similarly exhibiting two major slopes in the range of 250-600 °C (Figure 6). By the weight losses measured (1 60.7% and 2 61.2%), the processes can be assigned to the departure of BIMB and CN ligands (59.5%) and further by the exothermal peaks on differential thermal (DT) plots; the second slope on each TG plot can be attributed to the oxidative desertion of cyanides. Even so, it is noticeable that the enthalpy change of 2 (ΔH = -7.22 kJ/g), relating to the loss of cyanides, is much larger than that of 1 (ΔH = -5.94 kJ/g), logically meaning a lower stability of the cyanides in 2. This may be due to the cis o-BIMB-caused stress in 2, reflected by the longer Cu-XCN (1.876-2.328(1) A˚) than those of 1 (1.874-2.017(2) A˚). More than that, it is found also that the p-BIMB ligands in 1, unlike the o-BIMBs in 2, are liberated in steps. Varied-temperature powder X-ray diffraction (XRD) spectra of 1 (Figure S4, Supporting Information) designate the steps to the transition of a series of crystalline states in varied ligand contents. Conclusion In conclusion, the attempt to show the effect of o- and p-BIMB on the assembly of coordination polymers led to the isolation of the copper coordination polymers 1-4. Construction of the products and two additional samples reveals that the parallel reactions of two isomeric ligands give products with similar coordination modes but different structures; in all cases, the dimension of p-BIMB-derived is 1D higher than the comparably o-BIMB-derived. In addition, the diverse thermoand photobehavior of 1 and 2 indicate that the bulk properties of the CPs, comparably synthesized from two isomers, are different and so suggest a way to tune the coordination-based properties of CPs using isomeric ligands. Acknowledgment. We are grateful to the Natural Science Foundation of Guangdong Province of China (04010987) and the Research Foundation of the Education Department of Guangdong Province (Z03034) for financial support on this work. Supporting Information Available: Crystallographic information files (CIF) and some supplementary drawings beneficial for discussion;
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the powder XRD spectra of 1 at 255 and 410 °C. This information is available free of charge via the Internet at http://pubs.acs.org.
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