Structural diversity in the coordination of amidines and guanidines to monovalent metal halides |
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Authors: | Oakley Sarah H Soria Delia B Coles Martyn P Hitchcock Peter B |
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Institution: | Department of Chemistry, School of Life Sciences, University of Sussex, Falmer, Brighton, UK BN1 9QJ. |
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Abstract: | A series of structurally characterised, monovalent metal-halide complexes incorporating neutral amidine and guanidine ligands is reported. N,N'-diphenylbenzamidine reacted with copper(I) chloride to afford the bis-ligand complex CuCl(PhCNPh]NHPh])2]2 (1), that exists as a chlorine bridged dimer in the solid state, with a non-symmetrical distribution of NH...Cl interactions within the 'Cu2Cl2' metallacycle. In contrast, only one equivalent of the guanidine, Me2NCNiPr]NHiPr] (2), is coordinated in the copper(I) iodide complex CuI(Me2NCNiPr]NHiPr])]2 (3), which was also isolated as the dimer with bridging halide atoms. The molecular structure of the bicyclic guanidine, 1,3,4,6,7,8-hexahydro-2H-pyrimido1,2-alpha]pyrimidine (hppH), is reported, revealing a hydrogen bridged dimer with extensive delocalisation throughout the ligand framework. Coordination of hppH to lithium chloride afforded the dimeric bis-ligand complex LiCl(hppH)2]2 (4) in which each hppH molecule interacts with a different chlorine atom of the central 'Li2Cl2' core of the molecule via NH...Cl hydrogen bonding. In contrast the 2:1 ligand to metal complex is formed with silver(I) chloride to afford AgCl(hppH)2 (5), a unique example of a monomeric, three-coordinate silver chloride supported by nitrogen-based ligands. The series of mixed ligand complexes CuX(hppH)(PPh3)]n (6, X = Cl, n= 1; 7, X = Br, n= 2; 8 X = I, n= 2) have also been synthesised and structurally characterised, allowing comparisons of the relative coordinating behaviour of hppH and PPh3 as neutral donors at copper(I) centres to be made. |
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