Complementarity of halide-mediated hydrogen-bonding and alkyl substitution in the construction of two-dimensional rhombic (4,4) grids using bis(N-alkylamidino-O-alkylurea)copper(ii) halides

Abstract

A series of hydrogen-bonded networks based on bis(N-alkylamidino-O-alkylurea)copper(II) cations, [CuL 2 ] 21 , bridged by either chloride or bromide have been synthesised, of which six have been structurally characterised by single crystal X-ray diffraction methods. The [CuL 2 ] 21 cation acts as a four-connecting centre and forms 2-D rhombic (4,4) grids for the majority of the compounds studied. However, the grids do not adopt a common intermolecular hydrogen-bonding pattern. Three distinct systems can be differentiated: one mediated solely by halide anions, a second mediated by protic solvent molecules as well as halide anions, and a third with no intermolecular interactions. There is evidence for complementarity in (4,4) rhombic grids mediated solely by halide anions, as grid formation only occurs when there is a match between the size of the cavity formed within the grid and the space required by the pendant alkyl groups of the N-alkylamidino-O-alkylurea ligands. Such complementarity occurs for [Cu(L mm ) 2 ]?2Cl (L mm ~N-methylamidino-O-methylurea) and [Cu(L me ) 2 ]?2Br (L me ~N-methylamidino-O-ethylurea). Chloride bridges generate a cavity which can accommodate four juxtaposed methyl groups while bromide bridges generate a cavity large enough to accommodate two methyl and two ethyl groups. Rhombic (4,4) grid formation based on simple halide bridges does not take place for [Cu(L mm ) 2 ]?2Br?2MeOH, [Cu(L ee ) 2 ]?2Cl?H 2 O (L ee ~N-ethylamidino-O-ethylurea), [Cu(L ee ) 2 ]?2Br?MeOH or [Cu(L 2m ) 2 ]?2Cl?2MeOH (L 2m ~N-benzylamidino-O-methylurea). The cavity generated by bromide bridges is too large for the four methyl groups of [Cu(L mm ) 2 ] 21 cations. To overcome this problem and still form a (4,4) grid, the hydrogen-bonding assembly in [Cu(L mm ) 2 ]?2Br?2MeOH incorporates a methanol molecule. The spatial requirements of the four ethyl groups of the [Cu(L ee ) 2 ] 21 cations are greater than can be provided by either of the grids generated by chloride or bromide bridges. Consequently, 1-D chains rather than 2-D rhombic (4,4) grids are formed. The cavity required to accommodate two benzyl groups and two methyl groups of the [Cu(L 2m ) 2 ] 21 cations is far larger than can be provided by chloride bridges. Hence, although the disposition of copper(II) centres in [Cu(L 2m ) 2 ]?2Cl?2MeOH is similar to those in [Cu(L mm ) 2 ]?2Cl and [Cu(L me ) 2 ]?2Br, the molecular units are not linked by hydrogen-bonding interactions. A common feature of the halide bridges is a hydrogen-bonded supramolecular synthon in which the anion acts as acceptor to two pairs of N-H donors thus forming two R 1 2 (6) motifs with a common halide anion.

Deconvolution of supramolecular tectons and analysis of the structural role of the anions for two “wheel-and-axle” silver complexes

“…1), through the hydrogen bonded supramolecular synthon -OH … F-B-F … HO-. 3,15 The two oxygen atoms O1 and O2 are pushed quite close together (3.642(3) A ˚) by the anion, and the alternating molecules A and B are held in a zig-zag orientation with a geometry that anticipates a pro-tetrahedral imprinting in the crystal architecture: the long axes of molecules A and B within a chain form angles of 109.5u (C1(i)-C1-C19-C19(i)). (ii) The most relevant class of contacts shorter than the sum of van der Waals radii regards CH … F interactions formed by all the hydrogen atoms ortho to the pyridinic nitrogen in both complexes (Table 2).…”

The replacement of chlorides by cytosines in copper(II) complexes containing guanidine derivatives

“…In 2003, the copper(II) chloride complex consisting of two L 2 ligands, [Cu(L 2 ) 2 ]Cl 2 , has been structurally studied and reported [22] that the copper(II) center are coordinated by two symmetry-related N,N-bidentate L 2 ligands in a trans configuration to give a square planar geometry. In the present work, compounds 1 and 2 contain only a single molecule of L 1 and L 2 ligands, respectively, which only differ in the N-substitution sidearm groups, NH 2 for 1 and NH 2 CH 2 Ph for 2 (Scheme 1).…”

DNA-interacting and biological properties of copper(ii) complexes from amidino-O-methylurea

“…27 Their binding ability to nucleobases has been previously investigated and found that they are indeed capable of binding to the N3 cytosine by the replacement of the chloride ligands. 28 In addition, the related monomeric copper(II) complexes [Cu(L 1 ) 2 Cl 2 ] and [Cu(L 2 ) 2 Cl 2 ] with a square-planar geometry 29 have also been reported to exhibit potential DNA-interacting properties and antimicrobial activities against Campylobacter. 30 To continue our research, the complexes 1 and 2 have been intensively studied in terms of the DNA interacting and biological properties.…”