Crystal Engineering of a Series of Arylammonium Copper(II

Feb 24, 2010 - Despite the various functionalities on the arylammonium groups, the different interlayer packing interactions, and the differing degree...
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DOI: 10.1021/cg9015349

Crystal Engineering of a Series of Arylammonium Copper(II) Malonates

2010, Vol. 10 1854–1859

Tony D. Keene,*,†,§ Iwan Zimmermann,† Antonia Neels,‡ Olha Sereda,‡ J€ urg Hauser,† † ,† Shi-Xia Liu, and Silvio Decurtins* † Departement f€ ur Chemie und Biochemie, Universit€ at Bern, Freiestrasse 3, CH-3012 Bern, Switzerland, atel, and ‡Centre Suisse d’Electronique et Microtechnique SA, Rue Jacquet-Droz 1, CH-2002 Neuch^ § Switzerland. Current address: School of Chemistry;Building F11, The University of Sydney, NSW 2006, Australia.

Received December 8, 2009; Revised Manuscript Received February 4, 2010

ABSTRACT: We present a series of eight layered copper(II) malonates, each with a {[HA]2[Cu(II)(mal)2(H2O)x]}n A-B-A layer structure, where A is an ammonium cation and B is an anionic copper malonate layer (x=1 or 2; A=benzylamine, 1; S-(R)methylbenzylamine, 2; 4-methylbenzylamine, 3; 4-carboxybenzylamine, 4; 4-trifluoromethylbenzylamine, 5; 4-trifluoromethoxybenzylamine, 6; phenylethylamine, 7; and 4-fluorophenylethylamine, 8). The ammonium cations used are primary amines based around benzylamine and phenylethylamine and include several different functional groups. The different amines give a large array of interlayer interactions, including van der Waals packing, hydrogen bonding, C-H 3 3 3 π, π 3 3 3 π, H 3 3 3 F, and F 3 3 3 F interactions. Despite the various functionalities on the arylammonium groups, the different interlayer packing interactions, and the differing degrees of hydration in the [Cu(II)(mal)2(H2O)x]2- group, the anionic layer structure remains the same, indicating a high stability of this layer and its potential for further engineering of the organic layer components.

Introduction Dicarboxylic acids have attracted much attention in the field of crystal engineering due to their ability to chelate and to bridge metal centers in a reliable manner, such as that seen in oxalate1 and 1,4-benzenedicarboxylate.2 This can lead to the design of materials with specific properties, such as chiral magnetism, or lead to active framework materials. While designing the structure of low-dimensionality materials, thought has to be given to the packing of the desired units in order to achieve a three-dimensional crystal structure that allows a structural investigation to be made. In this investigation, we have used malonate, which is a useful agent in directing structures in combination with copper when compared to oxalate. The additional methylene group between the carboxylates prevents the formation of bis-chelated chains, and the common binary copper malonate compounds are much more soluble than copper oxalate, so enabling other compounds to form before a very stable byproduct drops out. Several literature compounds are based around the [Cu(mal)2(H2O)x]2- unit (Scheme 1), which, like its oxalate counterpart, occurs frequently in the literature and is relatively robust. This unit can form layers when x = 0 where peripheral oxygen atoms on the malonates (as opposed to the four that give the square planar coordination around the copper atoms) bond into the long axis on the copper atom of a neighboring unit to give square3a-e and hexagonal3a layers. When x=1 or 2, the units can build into one-dimensional,3f,g two-dimensional,3e,g,h or three-dimensional3e hydrogen-bonded structures and can also form multidimensional structures with other metal ions.3e Given the robust nature of this unit, we have decided to use it as a supramolecular building block in order to generate *Corresponding authors. Tony Keene: e-mail, [email protected]. au; telephone, þ61-2-9351-7482; fax, þ61-2-9351-3329. Silvio Decurtins: e-mail, [email protected]; telephone, þ41 31 631 42 55; fax,þ41 31 631 39 95. pubs.acs.org/crystal

Published on Web 02/24/2010

layered structures where we can control the type and functionality of the counterion and also engineer the method in which the layers formed can stack. We present here the results of this approach, where we have been able to include phenyl-based primary amines with differing functionalities (Scheme 2) into layer structures based on the [Cu(mal)2(H2O)x]2- unit. Experimental Section Experimental Methods. All reagents were purchased from commercial sources and used without further purification. IR measurements were made using a Perkin-Elmer Spectrum One, and peaks are reported as strong (s), medium (m), and weak (w). Elemental analysis was performed on a Carlo Erba Instruments EA 1110 elemental analyzer. Single crystal X-ray diffraction measurements for 1-3 and 5-8 were carried out on a Stoe Mark-II Imaging Plate Diffractometer System equipped with a graphite monochromator. Data collection was at -100 °C using Mo KR radiation (λ=0.71073 A˚). Absorption corrections were made using MULscanABS.4 Compound 4 was measured on a Bruker Smart Apex II area detector diffractometer equipped with a graphite monochromator. Data collection was at -100 °C using Mo KR radiation (λ = 0.71073 A˚). Absorption corrections were made using SADABS.5 Structure solutions were carried out with SHELXS-976 (2 and 6) or SIR927 (1, 3-5, 7-8) and the refinement with SHELXL976 in the WINGX8 environment. Hydrogen atom positions were generated in calculated positions and refined in riding mode on the parent atom using the default parameters in SHELXL-97. All nonhydrogen atoms were refined anisotropically. Crystallographic diagrams were prepared using Diamond 2.1a.9 Crystal structures are also available from the Cambridge Crystallographic Data Centre (CCDC 749502-749510 for 1-9) free of charge at www. ccdc.cam.ac.uk/conts/retrieving.html. General Synthesis of the Compounds. Stoichiometric amounts of the amines (2 mmol) and malonic acid (208 mg, 2 mmol) were dissolved in 10 mL of distilled water, and a solution of CuCl2 3 2H2O (170 mg, 1 mmol) in 5 mL of distilled water was added. The combined solution was stirred and left to evaporate for several days. The resultant crystals were filtered, washed with water and acetone, and left to dry. r 2010 American Chemical Society

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Scheme 1. The [Cu(II)(mal)2(H2O)2]2- Unit

Scheme 2. Ammonium Cations Used in Compounds 1-8 Figure 1. Asymmetric unit and selected symmetry equivalents for 1. Thermal ellipsoids are at the 75% level and nonaqua hydrogen atoms are removed for clarity.

[Benzylammonium]2[copper(II)(malonate)2(H2O)2], 1. Yield: 60%. Expected for C20H28CuN2O10: C, 46.20; H, 5.43; N, 5.39. Found: C, 46.79; H, 5.29; N, 5.42. IR (KBr matrix, cm-1, s = strong, m = medium, w = weak): 3430(s), 3142(m), 3032(m), 3006(m), 2919(m), 2734(w), 2628(w), 2132(w), 1672(s), 1593(s), 1499(m), 1456(m), 1419(s), 1386(m), 1365(m), 1273(w), 1219(w), 1168(w), 1068(w), 958(w), 937(w), 791(w), 741(m), 693(m), 578(w). 470(w). [S-(-)-(r)-Methylbenzylammonium]2[copper(II)(malonate)2(H2O)2], 2. Yield: 40%. Expected for C22H32CuN2O10: C, 48.21; H, 5.88; N, 5.11. Found: C, 48.72; H, 5.93; N, 5.02. IR: 3436(m), 3032(m), 2980(m), 2925(m), 2734(m), 2685(m), 2632(m), 2518(w), 2164(w), 1636(s), 1585(s), 1513(m), 1423(s), 1381(m), 1366(m), 1278(m), 1241(w), 1151(w), 1094(w), 1029(w), 981(w), 958(w), 936(w), 801(w), 765(m), 738(m), 700(m), 540(w), 482(w), 447(w). [4-Methylbenzylammonium]2[copper(II)(malonate)2(H2O)2], 3. Yield: 50%. Expected for C22H32CuN2O10: C, 48.21; H, 5.88; N, 5.11. Found: C, 48.04; H, 5.86; N, 4.97. IR: 3436(s), 3151(m), 3029(m), 2953(m), 2923(m), 2711(w), 2628(w), 2123(w), 1644(s), 1579(s), 1503(m), 1435(s), 1370(m), 1277(w), 1212(w), 1172(w), 1098(w), 982(w), 959(w), 937(w), 907(w), 803(w), 740(m), 548 (m), 465(w). [4-Carboxybenzylammonium]2[copper(II)(malonate)2(H2O)2], 4. Yield: 25%. Expected for C22H28CuN2O14: C, 43.46; H, 4.64; N, 4.61. Found: C, 43.53; H, 4.70; N, 4.57. IR: 3447(s), 2993(s), 2922(s), 2716(m), 2645(m), 2553(m), 2163(w), 1691(s), 1648(s), 1590(s), 1559(s), 1514(m), 1441(s), 1371(s), 1318(m), 1292(s), 1211(w), 1186(m), 1153(w), 1124(w), 1097(w), 1019(w), 984(w), 962(m), 940(m), 911(w), 861(w), 809(w), 777(w), 741(m), 702(w), 620(w), 546(w), 452(w). [4-Trifluoromethylbenzylammonium]2[copper(II)(malonate)2(H2O)2], 5. Yield: 40%. Expected for C22H26CuF6N2O10: C, 40.28; H, 3.99; N, 4.27. Found: C, 40.59; H, 3.95; N, 4.06. IR: 3449(s), 3015(m), 2923(m), 2760(m), 2643(m), 2170(w), 1648(s), 1590(s), l 1435(s), 1369(m), 1328(s), 1280(w), 1171(m), 1127(s), 1102(w), 1068(s), 1021(w), 984(w), 961(w), 937(w), 908(w), 840(w), 812(w), 740(m), 621(m), 589(w), 453(w), 410(w).

[4-Trifluoromethoxybenzylammonium]2[copper(II)(malonate)2(H2O)], 6. Yield: 15%. Expected for C22H24CuF6N2O11: C, 39.44; H, 3.61; N, 4.18. Found: C, 39.84; H, 3.60; N, 4.05. IR: 3401(m), 3134(m), 3019(m), 2993(m), 2924(m), 2729(m), 2650(m), 2177(w), 1631(s), 1593(s), 1561(s), 1515(m), 1423(s), 1370(m), 1259(s), 1231(s), 1162(s), 1022(w), 971(w), 958(w), 896(w), 828(w), 737(m), 602(w), 450(w). [Phenylethylammonium]2[copper(II)(malonate)2(H2O)2], 7. Yield: 65%. Expected for C22H32CuN2O10: C, 48.21; H, 5.89; N, 5.11. Found: C, 48.70; H, 5.84; N, 5.05. IR: 3438(m), 3032(m), 2932(m), 2732(m), 2622(m), 2146(w), 1649(s), 1585(s), 1569(s), 1507(s), 1434(s), 1370(s), 1274(m), 1249(w), 1216(m), 1170(w), 1135(w), 1119(m), 1090(w), 1041(w), 1013(w), 985(w), 958(w), 937(w), 911(w), 859(w), 820(m), 741(m), 700(w), 549(w), 476(w), 446(w), 427(w). [4-Fluorophenylethylammonium]2[copper(II)(malonate)2(H2O)2], 8. Yield: 30%. Expected for C22H30CuF2N2O10: C, 45.24; H, 5.18; N, 4.80. Found: C, 45.53; H, 5.21; N, 4.71. IR: 3437(m), 3028(m), 2924(m), 2852(m), 2778(m), 2668(m), 2158(w), 1638(s), 1587(s), 1497(m), 1465(m), 1435(s), 1369(m), 1277(w), 1171(m), 1031(w), 960(m), 937(w), 909(w), 805(w), 781(w), 737(m), 698(m), 593(w), 450(w).

Results and Discussion Note Regarding Ammonium Group Numbers. Where more than one ammonium group occurs in a structure, the atom numbers are prefixed so that each group has a specific number; for example, a group with N21, C21, C22, etc. is called ring 2 in order to differentiate the groups in the text. Crystal Structures. Compound 1 consists of a copper atom, two malonate anions, two water molecules, and two benzylammonium cations (Figure 1). It crystallizes in the orthorhombic noncentrosymmetric space group P212121. The malonates chelate the copper atom in the dx2-y2 orbital with Cu-O distances in the range of 1.936(1)-1.941(1) A˚, while the water molecules bond to the copper through the dz2 orbital with Cu-O distances of 2.405(1) and 2.691(2) A˚. The water molecules then hydrogen bond to neighboring [Cu(mal)2]2- units to build a two-dimensional hydrogenbonded layer in the ab-plane (Figure 2). The benzylammonium cations hydrogen bond to this layer through the ammonium group with the plane of the benzene ring standing at 55° to that of the ab-plane. This gives an A-B-A layer motif, where A is the ammonium cation and B is the [Cu(II)(mal)2(H2O)2]n2n- layer. The benzylammonium cations form alternating ring 1/ring 2 zigzag rows, running in the b-direction, with the gap between the rows being the a-axis of 8.4584(4) A˚. The gap between these rows allows the benzylammonium cations of the layer above to interdigitate and the layers stack in the c-axis (Figure 3) with an interlayer

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Figure 4. View of the interlayer pairwise π-H packing in 2, looking down the b-axis. Figure 2. View of the hydrogen-bonded [Cu(II)(mal)2(H2O)2]n2nlayer in 1, looking down the c-axis.

Figure 3. View of the interlayer packing in 1, looking down the b-axis.

spacing of half the c-axis (11.024(1) A˚). The benzylammonium cations interact through π-H interactions, so that one proton of each of their methylene groups points to the center of the benzene ring of the group that is interdigitated between it and the next row of cations. These interacting pairs of rows then interact with neighboring rows through π-π interactions. The π-H and π-π interactions occur in the a-axis. Compound 2 has essentially the same basic structure as 1 and consists of a copper atom, two malonate anions, two water molecules, and two S-(-)-R-methylbenzylammonium cations. The copper, water, and malonate components form the same [Cu(II)(mal)2(H2O)2]2- anion, which hydrogen bonds through the water molecules to neighboring units to give the same layer as 1 in the ab-plane. The S-(-)-R-methylbenzylammonium cations then stand above and below the layers to form the same A-B-A motif. In 2, the benzene rings do not stand at the same angle as 1 and lie almost in the ab-plane, thus presenting the benzene rings as the top and bottom surfaces of the A-B-A layer. These layers stack in the c-axis with an interlayer distance corresponding to the c-axis length, 12.631(3) A˚. This stacking is facilitated by π-H interaction between H14c and the ring of the N2 S-(-)R-methylbenzylammonium cation with an average C 3 3 3 H distance of 3.238 A˚ (Figure 4). The orientation of the O2w water molecule is slightly different in that the molecule is canted over to one side so that the Cu1-O2w-H4w angle is 93.2(6)°, somewhat smaller than the normal tetrahedral angle. Despite this, there is a hydrogen bond from H4w that

appears to be quite reasonable and which would otherwise be strained if this water molecule was oriented as expected. (The crystallographic parameters for compounds 1-8 are presented in Table 1, and hydrogen bond distances and angles are presented in Tables 2-9.) Looking at the van der Waals radius of H3w, it would appear there is an interaction occurring between this atom and H28 and H23a which would help to stabilize this orientation. Compound 3 is similar to 1, except one of the two 4-methylbenzylammonium cations is disordered over two sites (rings 1/2). The crystallographically distinct cations are separated into two distinct rows running in the a-axis (i.e., a row of ring 3 and a row of ring 1/2). In these rows, the cations interdigitate so that each alternate ring comes from each of the interfacing layers. Ring 3 forms π-H bonded pairs from H39c with an average H 3 3 3 C distance of 3.093 A˚, and inspection of the van der Waals radii of these rings shows that there is no appreciable interaction between these pairs. In the case of rings 1/2, when pairs of ring 2 occur, they form π-H bonded pairs between H29c and a neighboring ring 2 (average H 3 3 3 C = 3.111 A˚), while pairs of ring 1 interact through π-π interactions. Where a mix of rings 1 and 2 occurs (which given the roughly 2:1 ratio of ring 1:2, should be 4/9ths of the time), we see a similar arrangement to that of a pair of ring 2. The rings in the 1/2 “chain” are closer packed than those in the ring 3 chain. Compound 4 again adopts the same hydrogen-bonded layer structure, with one copper atom, one water molecule, one malonate, and one benzylammonium-4-carboxylic acid cation. The carboxylic acid group remains protonated in the structure and takes part in hydrogen-bonding to another carboxylic acid group in the layer above to form a standard carboxylic acid pair, which determines the crystal packing of the layers (Figure 5). Compound 5 also has an asymmetric unit consisting of only one ammonium cation and half of the complex [Cu(II)(mal)2(H2O)2]2- anion. The trifluoromethylbenzylammonium molecules stand approximately at 45° to the plane of the layer. The layer binding mode this time consists of fluorine-hydrogen interactions. F3 forms an interaction with H17 from the layer above with an H 3 3 3 F distance of 2.524(3) A˚ to form a ribbon running in the b-axis (Figure 6). These ribbons are then further bonded by interactions between fmbnl groups within the same layer from F2 to H12a with H 3 3 3 F=2.675(6) A˚. Compound 6 shows a large amount of disorder about the 4-trifluoromethoxybenzylammonium groups and, more

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Table 1. Crystallographic Parameters for 1-8 compound cation formula crystal system space group a/A˚ b/A˚ c/A˚ R/A˚ β/A˚ γ/A˚ V/A˚3 F/(g cm-3) Z T/K μ/mm-1 reflections collected unique reflections (Rint) reflections F2 > 2σ(F2) data/restraints/ parameters goodness of fit (S) R1/wR2 [F2 > 2σ(F2)] R1/wR2 (all data) Flack parameter

1

2

3

4

6

7

8

S-mbnl C22H32CuN2O10 monoclinic P21 11.767(3) 8.4377(13) 12.631(3) 90 93.202(19) 90 1252.1(5) 1.454 2 173(2) 0.929 7842

4-mbnl C22H32CuN2O10 triclinic P1 8.4479(7) 11.6750(10) 13.1173(11) 88.503(10) 72.584(9) 88.840(10) 1233.91(18) 1.475 2 173(2) 0.943 9859

cbnl C22H28CuN2O14 monoclinic P21/c 13.8639(6) 8.2453(4) 11.7648(5) 90 102.544(2) 90 1312.76(10) 1.538 2 173(2) 0.906 65362

fmbnl C22H26CuF6N2O10 monoclinic P21/a 11.887(5) 8.328(5) 13.892(5) 90 100.635(5) 90 1351.6(11) 1.612 2 173(2) 0.906 10253

fmobnl C22H24CuF6N2O11 monoclinic P21/n 11.8944(11) 8.3348(6) 27.462(3) 90 92.964(13) 90 2718.9(4) 1.637 4 173(2) 0.905 19027

pea C22H32CuN2O10 monoclinic P21 11.4260(10) 8.3564(5) 12.8680(12) 90 95.210(11) 90 1223.56(17) 1.488 2 173(2) 0.951 7790

fpea C22H30CuF2N2O10 monoclinic P21/c 13.839(3) 8.4833(11) 11.722(2) 90 113.501(15) 90 1262.0(4) 1.537 2 173(2) 0.938 12616

5898 (0.0513) 5653

2877 (0.1326) 1696

4511 (0.0241) 3645

6432 (0.0288) 5517

2636 (0.0339) 2105

5269 (0.1197) 3210

4315 (0.0202) 3894

2385 (0.2059) 1311

5898/6/311

2877/7/150

4511/6/339

6432/3/184

2636/3/193

5269/48/262

4315/7/328

2385/3/178

1.035 0.0275/0.0707

0.861 0.0663/0.1614

1.101 0.0283/0.0746

1.067 0.0285/0.0829

1.014 0.0309/0.0743

1.111 0.1130/0.3001

1.164 0.0274/0.0730

0.801 0.0544/0.1236

0.0289/0.0713 0.010(7)

0.1035/0.1726 0.11(6)

0.0397/0.035 n/a

0.0356/0.0866 n/a

0.0426/0.0778 n/a

0.1590/0.3315 n/a

0.0336/0.0934 0.184(18)

0.0888/0.1316 n/a

Table 2. Hydrogen Bond Distances (A˚) and Angles (deg) for 1a D-H O1w-H1w 3 3 3 O2i O1w-H2w 3 3 3 O4ii O2w-H3w 3 3 3 O6iii O2w-H4w 3 3 3 O8iv N11-H11b 3 3 3 O6v N11-H11c 3 3 3 O2i N21-H21a 3 3 3 O8vi N21-H21b 3 3 3 O4vii N21-H21c 3 3 3 O5viii

5

bnl C20H28CuN2O10 orthorhombic P212121 8.4584(4) 11.7116(5) 22.0485(14) 90 90 90 2184.2(2) 1.581 4 173(2) 1.061 21289

0.880 0.880 0.879 0.881 0.911 0.910 0.910 0.910 0.910

H3 3 3A 1.943 2.038 2.092 1.932 1.938 1.851 1.936 1.880 1.909

D3 3 3A 2.751(2) 2.857(2) 2.913(2) 2.761(2) 2.786(2) 2.755(2) 2.724(2) 2.781(2) 2.806(2)

D-H 3 3 3 A 151.8 154.4 155.2 156.2 154.3 171.7 143.9 170.0 168.2

Table 4. Hydrogen Bond Distances (A˚) and Angles (deg) for 3a D-H O1w-H1w 3 3 3 O8i O1w-H2w 3 3 3 O6ii O2w-H3w 3 3 3 O2iii O2w-H4w 3 3 3 O4iv N11-H11a 3 3 3 O1v N11-H11b 3 3 3 O8ii N11-H11c 3 3 3 O4 N31-H31a 3 3 3 O7iii N31-H31b 3 3 3 O6iv N31-H31c 3 3 3 O2

0.881 0.877 0.882 0.878 0.911 0.910 0.910 0.910 0.910 0.910

H3 3 3A 1.961 1.923 1.955 1.962 2.098 1.895 1.864 1.957 1.851 1.891

D3 3 3A 2.831(10) 2.771(13) 2.825(9) 2.825(18) 2.865(12) 2.785(3) 2.729(15) 2.793(15) 2.725(13) 2.780(5)

D-H 3 3 3 A 168.9 162.2 168.4 167.3 141.2 165.6 158.0 151.9 160.5 165.0

a Symmetry codes: i: -1/2 þ x, 1/2 - y, 2 - z; ii: 1/2 þ x, 1/2 - y, 2 - z; iii: -1/2 þ x, 11/2 - y, 2 - z; iv: 1/2 þ x, 11/2 - y, 2 - z; v: x, -1 þ y, z; vi: -x, -1/2 þ y, 11/2 - z; vii: 1/2 - x, -y, -1/2 þ z; viii: 1 - x, -1/2 þ y, 11/2 - z.

a Symmetry codes: i: -x, -y, 1 - z; ii: 1 - x, -y, 1 - z; iii: -x, 1 - y, 1 - z; iv: 1 - x, 1 - y, 1 - z; v: 1 þ x, y, z.

Table 3. Hydrogen Bond Distances (A˚) and Angles (deg) for 2a

Table 5. Hydrogen Bond Distances (A˚) and Angles (deg) for 4a

D-H O1w-H1w 3 3 3 O8i O1w-H2w 3 3 3 O6ii O2w-H4w 3 3 3 O2iii N11-H11a 3 3 3 O2iv N11-H11b 3 3 3 O6ii N11-H11c 3 3 3 O3 N21-H21a 3 3 3 O4 N21-H21b 3 3 3 O8v N21-H21c 3 3 3 O5iii

0.873 0.876 0.877 0.909 0.910 0.910 0.911 0.911 0.910

H3 3 3A 1.997 1.919 1.930 1.971 1.927 1.972 1.936 1.835 1.944

D3 3 3A 2.807(16) 2.794(13) 2.748(14) 2.785(11) 2.782(17) 2.843(18) 2.788(17) 2.711(16) 2.838(17)

D-H 3 3 3 A 153.7 177.9 154.6 150.0 155.8 159.7 154.8 160.6 167.1

Symmetry codes: i: -x, 1/2 þ y, 1 - z; ii: -x, -1/2 þ y, 1 - z; iii: 1 - x, - /2 þ y, 1 - z; iv: x, -1 þ y, z; v: 1 - x, 1/2 þ y, 1 - z. a

1

importantly, has a significant change in the copper bis-malonate group in that there is only one water molecule to give a [Cu(II)(mal)2(H2O)]2- unit. Despite the change in the hydration of this unit, the remaining water molecule enables the same layer to form as that for the other compounds. The heavy disorder around the trifluoro groups makes it difficult to describe the interlayer interaction, although it would appear to mainly consist of H 3 3 3 F interactions with no clear π-H interactions visible. Compound 7 crystallizes in the monoclinic noncentrosymmetric space group P21. The asymmetric unit contains one

D-H O1w-H1w 3 3 3 O3i O1w-H2w 3 3 3 O2ii N1-H1a 3 3 3 O2iii N1-H1b 3 3 3 O3iv N1-H1c 3 3 3 O2 O6-H6o 3 3 3 O5v

0.880 0.877 0.910 0.911 0.910 0.840

H3 3 3A 1.930 1.972 1.885 1.901 1.937 1.795

D3 3 3A 2.795(1) 2.802(1) 2.760(1) 2.773(1) 2.740(1) 2.631(2)

D-H 3 3 3 A 167.1 156.9 160.5 159.7 146.1 173.1

a Symmetry codes: i: -x, 1/2 þ y, 1/2 - z; ii: -x, -1/2 þ y, 1/2 - z; iii: x, 1 þ y, z; iv: x, 1/2 - y, 1/2 þ z; v: 1 - x, -y, 2 - z.

Table 6. Hydrogen Bond Distances (A˚) and Angles (deg) for 5a D-H O1w-H1w 3 3 3 O2i O1w-H2w 3 3 3 O4ii N1-H1a 3 3 3 O3 N1-H1b 3 3 3 O2iii N1-H1c 3 3 3 O2i

0.879 0.876 0.911 0.910 0.910

H3 3 3A 1.987 1.972 1.893 1.927 1.924

D3 3 3A 2.821(3) 2.809(2) 2.772(3) 2.744(3) 2.791(3)

D-H 3 3 3 A 157.9 167.4 161.5 148.5 158.4

a Symmetry codes: i: 1/2 þ x, - 1/2 - y, z; ii: 1/2 þ x, 1/2 - y, z; iii: x, 1 þ y, z.

[Cu(mal)2(H2O)2]2- unit and two phenylethylammonium cations. The cations interdigitate and are held together

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Table 7. Hydrogen Bond Distances (A˚) and Angles (deg) for 6a D-H O1w-H1w 3 3 3 O2i O1w-H2w 3 3 3 O4ii N11-H11a 3 3 3 O6iii N11-H11b 3 3 3 O4iv N11-H11c 3 3 3 O1 N11-H11c 3 3 3 O7 N21-H21a 3 3 3 O2 N21-H21b 3 3 3 O5ii N21-H21c 3 3 3 O8i

H3 3 3A 1.926 1.970 1.885 1.916 2.124 2.302 1.887 1.831 1.857

0.855 0.860 0.909 0.910 0.908 0.908 0.910 0.910 0.910

D3 3 3A 2.770(4) 2.781(4) 2.793(8) 2.742(8) 2.927(11) 3.039(12) 2.779(5) 2.734(6) 2.737(7)

D-H 3 3 3 A 169.0 156.9 176.2 149.9 144.2 138.0 166.2 171.0 162.3

Symmetry codes: i: /2 - x, /2 þ y, /2 - z; ii: /2 - x, - /2 þ y, /2 - z; iii: 11/2 - x, -1/2 þ y, 1/2 - z; iv: x, -1 þ y, z. 1

a

1

1

1

1

1

Figure 6. View of the H 3 3 3 F packing interaction in the b-axis in 5, viewed just off of the c-axis.

Table 8. Hydrogen Bond Distances (A˚) and Angles (deg) for 7a D-H O1w-H1w 3 3 3 O4i O1w-H2w 3 3 3 O4ii O2w-H3w 3 3 3 O8iii O2w-H4w 3 3 3 O4ii N11-H11a 3 3 3 O8iii N11-H11b 3 3 3 O2iv N11-H11c 3 3 3 O3 N21-H21a 3 3 3 O6v N21-H21b 3 3 3 O7vi N21-H21c 3 3 3 O4vii

0.880 0.881 0.884 0.881 0.890 0.890 0.889 0.890 0.890 0.891

H3 3 3A 1.993 1.946 1.928 1.915 1.903 1.897 1.955 1.827 1.964 1.955

D3 3 3A 2.838(5) 2.777(4) 2.796(4) 2.755(4) 2.763(6) 2.756(6) 2.829(8) 2.677(7) 2.835(8) 2.787(6)

D-H 3 3 3 A 160.6 156.9 166.8 158.7 161.7 161.7 167.0 158.8 165.4 155.0

a Symmetry codes: i: -x, -1/2 þ y, -z; ii: -x, 1/2 þ y, -z; iii: 1 - x, 1/2 þ y, -z; iv: x, 1 þ y, z; v: x, -1 þ y, 1 þ z; vi: x, y, 1 þ z; vii: -x, -1/2 þ y, 1 - z.

Table 9. Hydrogen Bond Distances (A˚) and Angles (deg) for 8a D-H O1w-H1w 3 3 3 O3i O1w-H2w 3 3 3 O1ii N1-H1a 3 3 3 O2iii N1-H1b 3 3 3 O3 N1-H1c 3 3 3 O1i

0.882 0.880 0.890 0.890 0.890

H3 3 3A 1.934 1.994 2.021 1.910 1.907

D3 3 3A 2.783(7) 2.843(4) 2.814(6) 2.728(6) 2.786(5)

Figure 7. View of the two-dimensional π-H packing interaction in 7 (looking down the c-axis).

D-H 3 3 3 A 160.7 161.8 147.7 152.0 168.8

a Symmetry codes: i: x, 1/2 - y, 1/2 þ z; ii: x, -1/2 - y, 1/2 þ z; iii: x, 1 þ y, z.

Figure 8. View of the interlayer π-H chain packing interaction in 8, looking down the c-axis.

Figure 5. View of the acid-pair hydrogen bonding in 4, which creates the layer packing (looking down the c-axis).

through π-H interactions. Ring 1 acts as a “donor” in two interactions (one with another ring 1, average H 3 3 3 C=3.448 A˚, and one with ring 2, average H 3 3 3 C = 3.326 A˚) and as a receptor for another one from ring 2, average H 3 3 3 C=3.177 A˚, and ring 2 interacts with another ring 2 (average H 3 3 3 C=3.588 A˚). This gives a complex intra- and interlayer interaction system to form the three-dimensional structure (Figure 7). Compound 8 presents the same layer structure although the asymmetric unit contains only one malonate, one water,

and one 4-fluorophenylethylammonium cation. In this compound, the hydrogen bonded layer is in the bc-plane. As with 2, the phenyl rings lie almost flat along the layer surface with the fluorine atom being mostly submerged within the layer, i.e. not appearing on the surface of the A-B-A layer. Again, we see a π-H interaction as the method of layer stacking, between H17b and a neighboring 4-fluorophenylethylammonium cation with an average C 3 3 3 H distance of 3.227 A˚. This interaction runs as a chain in the b-axis with the molecule acting as a donor and acceptor in this interaction (Figure 8). Discussion. Each of the compounds, apart from compound 6, takes essentially similar structures in that a hydrogen-bonded [Cu(mal)2(H2O)2]n2n- layer has ammonium cations hydrogen bonded above and below to form an A-B-A layer structure. While similar malonate materials do exist in the literature,3a-e they often form a slightly

Article

different layer structure due to the orientation of the coordinated water molecules affecting the hydrogen bonding with the layer. By changing the functional groups on the amine molecules, we can alter the interactions between the layers. In the case of 1, we see interdigitation of the ammonium cations, while, in 2 and 8, we see that the layer surfaces present the benzene rings which take part in π-H bonding. In 3 and 7, both interdigitation and π-H bonding occur. In the case of 4, we see hydrogen bonding as the layer-stacking interaction, through the formation of hydrogen-bonded carboxylic acid pairs. Compounds 5 and 6 show H 3 3 3 F interactions, and 5 also has π-H interactions. The interlayer interactions also have differing dimensionalities-compounds 3, 4, and 6 have pairwise interactions between the cations, 1, 2, and 8 have one-dimensional interactions, and 5 and 7 have two-dimensional interactions. Despite the five different interlayer bonding interactions and the differing dimensionalities of these interactions, we retain the basic layer each time. The fact that this layer remains constant, while the layer stacking type changes, suggests that this layer motif is very stable. In each case for 1-8, we see cell constants in the layer in the range of 8.2453-8.4833 A˚ for the shorter side of the layer and 11.4260-11.8944 A˚ for the longer side, indicating that the layer has some degree of flexibility in its hydrogen bonding, which helps to maintain the layer motif while absorbing changes in the ligand and interlayer interactions. Compared to the other literature examples of [Cu(mal)2(H2O)2]n2n- layers,3a-e we have a subtly different layer motif, and this appears to link to the use of bulky primary ammonium salts. The other layer types occur when secondary or small primary ammonium salts are used. Thus, by using bulky primary ammonium cations, we can reliably induce the layer type we report here. Other systems exist where primary amines can induce a given layer type with a fair degree of reliability, of which the single-10 and double-layer11 perovskites are a good example. These can also contain functional molecules which impart useful properties, such as photoactivity,12 conductivity,11,12 and use as a polymerization scaffold.13 The perovskite layers share some similarities with the malonate layers in that there are a variety of layer-stacking interactions possible that are modified by the ammonium cation used in the structure. We experimented with the use of double amines, and in the one case where suitable crystals were forthcoming, we found that a different layer type forms around a [Cu(II)(mal)2(H2O)]n2n- layer (see the Supporting Information for compound 9). The low yield reported in several of the compounds is due to the crystallization of ammonium malonate salts at concentrations only slightly higher than that at which the desired copper-containing product crystallizes. In each of those cases, we made the decision to isolate the product before the crystallization of byproduct occurred, thus avoiding issues of contamination.

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An attractive feature of this series of compounds is that we can retain the basic layer while adding different functionality to the amine molecules. While the amines used in this investigation have little useful functionality, the reproducibility of the basic structure makes this series a useful tool for the incorporation of other amine cations where the functionality can be used. Conclusions We have engineered a series of Cu(II) malonates which retain their basic layer structures while allowing substantial modification of both the functionality of the ammonium cations and the interactions between them in determining the interlayer packing. Using the synthetic principles from this class of compounds, it should be possible to tailor specific layer compounds with desirable functional group properties. Acknowledgment. This work was supported by the Swiss National Science Foundation (Grant No. 200020-116003). Supporting Information Available: Asymmetric unit diagrams of 2-8, full description and characterization of 9, and CIF files for 1-9. This material is available free of charge via the Internet at http://pubs.acs.org.

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