Refluxing 1,2-bis(2-cyanoguanidino)ethane (L 1 ) in methanol or ethanol containing copper() sulfate resulted in the formation of [CuL 3m ][MeOSO 3 ] 2 {L 3m = [HN᎐ ᎐ C(OMe)NHC(NH 2 )᎐ ᎐ NCH 2 ] 2 } and [CuL 3e ][EtOSO 3 ] 2 {L 3e = [HN᎐ ᎐ C(OEt)NHC(NH 2 )᎐ ᎐ NCH 2 ] 2 }. Structural analysis of these complexes has revealed hydrogen-bonded supramolecular architectures constructed from [CuL i ] 2ϩ cations with square planar CuN 4 chromophores and [ROSO 3 ] Ϫ anions. The basic supramolecular synthon is a 1-D chain of alternating cations and anions, a motif which is also found with Cl Ϫ and [BF 2 (OMe) 2 ] Ϫ anions. The [ROSO 3 ] Ϫ anion is an ideal fit for the space between two cations; its hydrophobic O-alkyl group is surrounded by the O-alkyl groups of the cations and its hydrophilic SO 3 Ϫ moiety forms N-H ؒ ؒ ؒ O hydrogen bonds with their amino and imino functionalities. In [CuL 3m ][MeOSO 3 ] 2 the chains, which are linear, are hydrogen bonded through a second methyl sulfate anion to give a 2-D sheet motif. The sheets are bound together to form a 3-D framework through very weak Cu ؒ ؒ ؒ O co-ordinative interactions which complete a tetragonally elongated octahedral geometry for the copper() centre. In [CuL 3e ][EtOSO 3 ] 2 the chains, which are sinusoidal, are hydrogen bonded through a second ethyl sulfate anion to give a bilayered arrangement. The bilayers aggregate into a 3-D framework by a combination of hydrogen bonding and weak Cu ؒ ؒ ؒ O co-ordinative interactions which result in a square pyramidal co-ordination geometry for the copper() centre. Despite the fit between [CuL i ] 2ϩ cations and alkyl sulfate anions in the chain, when a mixture of anions (chloride and ethyl sulfate) is present in the crystallisation medium, the preferred chain supramolecular synthon of the product, [CuL 3e ][EtOSO 3 ]Clؒ2H 2 O, is that containing chloride. The ethyl sulfate anions are involved, together with water molecules, in a complex hydrogen-bonding network which connects the chains into 2-D sheets, which are assembled, in turn, into a 3-D network structure by a combination of hydrogen bonding networks and exceedingly weak Cu ؒ ؒ ؒ Cl co-ordinative interactions, which give rise to a square pyramidal copper() co-ordination geometry.

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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.

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