Electronic Supplementary Information for Dalton Transactions This journal is © The Royal Society of Chemistry 2007 1 Pyridazine-bridged copper(I) complexes of bis-bidentate ligands: tetranuclear [2x2] grid versus dinuclear side-by-side architectures as a function of ligand substituents Jason R. Price, a Yanhua Lan a and Sally Brooker* a Comments on crystal structure refinements [Cu I 4 (L p-Me ) 4 ](PF 6 ) 4 .2(CH 3 )CO.2(C 2 H 5 ) 2 O. Two of the four hexafluorophosphate anions are ‘twirl’ disordered with sof of 90:10 for one (F33 - F36 : F37 - F310) and 60:40 for the other one (F43 - F46 : F47 - F410). While the disorder of two acetone molecules of solvation could be readily modelled, the two diethyl ether molecules of solvation were severely disordered and could only be poorly modelled so they were removed using SQUEEZE. 1 SQUEEZE calculated an electron count/cell of 150 which matches well with the expected 2 diethyl ether molecules per asymmetric unit as this would account for 148 electrons/cell. Before SQUEEZE R 1 = 0.0541, afterwards R 1 = 0.0408. [Cu I 4 (L o,p-Me ) 4 ](PF 6 ) 4 . 7 / 2 C 6 H 6 . 1 / 2 H 2 O. Due to this being a weak data set, with a rapid drop off in intensity at moderate to higher angles [R(σ) > 1 at 1.05 - 1.00 Å], SHEL 7.0 1.05 was used to limit the reflections for refinement to 2.92 < θ < 19.78º. Due to severe anisotropy (thin plates), restraints to anisotropic parameters (ISOR, SIMU, DELU) were applied to all atoms in the refinement. There are three full occupancy hexafluorophosphate anions, plus half a hexafluorophosphate anion (P4 F41 F42 F43 F44), which has F43 - P4 - F44 lying along a 2- fold axis, and a half occupancy hexafluorophosphate anion (P5 F51 F52 F53 F54 F55 F56, made SAME as P1 F11 F12 F13 F14 F15 F16), completing the charge balance for the four Cu(I) cations. One of the 2,4-dimethylanilino groups on one of the four independent ligand strands is disordered over two sites (C108 - C115 : C118 - C125) with an occupancy of 65:35, with a partial occupancy water molecule (O170) of solvation associated with the first part (65% occupancy). All of the 2,4-dimethylanilino groups were restrained to be similar by using DFIX with free variables on the similar C-C bond distances. There are three full occupancy and one