摘要:
Crystal engineering has become an area of great interest in this decade.1So far, however, the rational design and preparation of new materials for specific applications are still at an early evolutionary stage with the current focus mainly on understanding the factors that determine crystal packing. During the last few years, several types of weak interactions, such as versatile hydrogen bonding interactions and electrostatic interactions have been recognized and used in constructing extended networks.2Particularly, the hydrogen bonding interaction has emerged to be a powerful tool for the design of supramolecular systems based on noncovalent synthesis.3,4Although many research groups have focused on the usage of melamine (mel) and its derivatives5to form supramolecular networks by hydrogen bonding to other organic molecules, the concepts have recently been extended into the inorganic domain.6,7Transition metal ions can be incorporated into hydrogen bonding networks by employing bifunctional ligands that contain, in addition to metal binding sites, hydrogen bonding functionalities that are retained on complexation.Tdpd2−(H2tdpd = 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile) has attracted our interest as a potential bifunctional ligand with necessary hydrogen bonding characteristics. We have previously shown that it can construct metal-assembled complexes with triangular and rectangular lattices by coordination bonds.8Tdpd2−is a planar ligand and has both multi metal binding and hydrogen bonding sites. We now present the synthesis and structural study of the two-dimensional compounds [Hmel]2[M(tdpd)2(OH2)2]·2H2O (M = Ni2+(1), Co2+(2)).An aqueous solution (1 ml) of nickel(II) chloride hexahydrate (5 mmol l−1) and H2tdpd (5 mmol l−1) was transferred to a glass tube, then an ethanolic solution of melamine (mel) (5 mmol l−1) poured into the tube without mixing the two solutions. Light green plate crystals (1) began to form in two weeks; yield, 70%.†Elemental analysis data for [Hmel]2[Ni(tdpd)2(OH2)2]·2H2O: calc. for C18H22NiN20O8: C 30.66, H 3.14, N 39.73%; found: C 30.32, H 3.17, N 40.19%; elemental analysis data for [Hmel]2[Co(tdpd)2(OH2)2]·2H2O: calc. for C18H22CoN20O8: C 30.65, H 3.14, N 39.71%; found: C 30.16, H 3.10, N 39.90%.One of these crystals was used for X-ray crystallography. Compound2was synthesized from cobalt(II) acetate tetrahydrate by a procedure similar to that employed for1. Orange plate crystals began to form in two weeks; yield, 60%.†X-ray crystallography reveals that1and2are isostructural to each other (Table 1). The structure of1consists of mononuclear [Ni(tdpd)2(OH2)2]2−dianions, Hmel+cations and uncoordinated water molecules. An ORTEP9drawing of the structure around the nickel ion in1with the atom numbering scheme is shown inFig. 1. The structure of1shows that the desired coordination and aggregation have been achieved with the nickel atom being coordinated to two tdpd2−ligands which are in turn involved in an AAA ≡ DDD (A = hydrogen-bond acceptor, D = hydrogen-bond donor) arrangement with Hmel+cations. The coordination geometry around the nickel ion in the monomer is a distorted octahedron involving the four oxygen atoms of two tdpd2−anions and two water molecules intransposition relative to one another (Ni–O distances: 2.008(1) Å (Ni–O(1) and Ni–O(1’)), 2.046(2) Å (Ni–O(2) and Ni–O(2’)) and 2.110(2) Å (Ni–O(3) and Ni–O(3’))). The triple hydrogen bonding distances between the tdpd2−and Hmel+units are O(1’)···N(9’), 2.762(4) Å; O(2)···N(6’), 2.803(3) Å; N(2)···N(8’), 2.907(3) Å (a,bandc, respectively, inFig. 1). These complexes, to the best of our knowledge, are the first example of an AAA ≡ DDD system in the self assembled complexes, while theoretical calculations suggested the system AAA ≡ DDD is the most stable relative to ADA ≡ DAD and AAD ≡ DDA systems.6,10One mononuclear complex, two Hmel+cations, and two uncoordinated waters form a building module. In the module, uncoordinated water molecules make two types of hydrogen bonds with ring nitrogen atoms of tdpd2−and amino hydrogen atoms in Hmel+cation (dandeinFig. 1). The triply hydrogen-bonded module, [Hmel]2[Ni(tdpd)2(OH2)2]·2H2O is linked to adjacent modulesviaadditional N(H)···N and N(H)···O hydrogen bonds (f,gandhinFig. 2) to form planar sheets. Adjacent sheets are mutually offset and linkedviaO(H)···N hydrogen bonds between terminal nitrogen atoms of tdpd2−, N(4), and coordinated water oxygen atoms, O(3), which are inserted from above and below into the ‘vacant’ region indicated byAinFig. 2.Crystal data for [Hmel]2[M(tdpd)2(OH2)2]·2H2O (M = Ni2+(1), Co2+(2))PropertiesValuesClickherefor full crystallographic data (CCDC no. 1350/38).μ(CuKα) = 17.05 cm−1(graphite monochromated). An Enraf Nonius CAD-4 diffractometer was used. The structure was solved by direct methods (Rigaku TEXSAN crystallographic software package of Molecular Structure Corporation) and refined with full-matrix least-squares technique (SHELXL-93).11μ(MoKα) = 6.77 cm−1(graphite monochromated). A Mac Science MXC3 diffractometer was used. The structure was solved by direct methods (Rigaku TEXSAN crystallographic software package of Molecular Structure Corporation) and refined with full-matrix least-squares technique (SHELXL-93).Complex12Empirical formulaC18H22NiN20O8C18H22CoN20O8M705.20705.43Crystal system, space groupTriclinic,P&cmb.macr;(no. 2)Triclinic,P&cmb.macr;(no. 2)a/Å9.5650(3)9.517(3)b/Å9.6958(6)9.654(4)c/Å9.9663(3)9.964(1)α/°61.490(4)61.68(2)β/°75.585(3)75.91(2)γ/°62.714(4)63.62(2)V/Å3721.28(7)721.3(4)Z,Dc/g cm−31, 1.6231, 1.624F(000)362.00361.00Rcollected[I > 2σ(I)]31133629T/°C23.023.02&thetas;range/°5.18–148.663–55R, wR20.039, 0.1150.057, 0.142ORTEP drawing of1with labelling scheme and thermal ellipsoids at the 50% probability level for Ni, O, N, and C atoms. Spheres of the hydrogen atoms have been arbitrarily reduced. Hydrogen bonding geometries: N···N/O, H···N/O distances (Å), N/O–H··N/O angles (°):a2.762(4), 1.96, 152;b2.803(3), 1.97, 170;c2.907(3), 2.02, 175;d, 2.919(3), 2.14, 162;e, 2.988(4), 1.93, 158. Click image orhereto access a 3D representation.Part of the hydrogen-bonded planar sheets formed by1showing the intermolecular interactions between adjacent module. Hydrogen bonding geometries: N···N/O, H···N/O distances (Å), N/O–H···N/O angles (°):f3.022(2), 2.13, 171;g3.053(4), 2.38, 132;h3.032(4), 2.18, 161;i2.855(3), 2.18, 147;j2.947(3), 2.16, 176.Arepresents the region where the coordinated water oxygen atom O(3) from adjacent sheets inserts from above and below. Click image orhereto access a 3D representation.We conclude that hydrogen bonding interaction may play an important role in determining the structure of assembled complexes. Complexes [M(tdpd)2(OH2)2]2−with AAA hydrogen bonding recognition sites have been synthesized and shown to form co-crystals with Hmel+cations involved DDD motif. The ligand H2tdpd fulfils its bifunctional role by generating a transition-metal complex as part of a multidimensional co-crystallised network, self-assembled by a combination of coordination and hydrogen bond formation. We are now extending this result by the preparation of the design of supramolecular systems based on noncovalent synthesis through variation of substituted melamine derivatives.
ISSN:1466-8033
DOI:10.1039/b007939l
出版商:RSC
年代:2000
数据来源: RSC