The Stereochemistry of Binuclear Complexes of Chromium(III)

Structure and redox properties of the water-oxidation catalyst [(bpy)2(OH2)RuORu(OH2)(bpy)2]4+

“…The four Ru-N(bpy) distances are within the range 2.029 (5)-2.089 (4) Á and generally are shorter than the values of 2.060 (5)-2.100 (7) Á reported for the analogous nitro dimer [(bpy)2(N02)Ru0Ru(N02)(bpy)2]2+.10 These distances are considerably shorter than the value of 2.104 (4) Á found* 11 *in the hexaammine Ru(III) cation but are comparable to values reported for the [Ru(bpy)2Cl2]+ cation.12 It is interesting to note that because of the electronic asymmetry in the dimer there are essentially three different Ru-N(bpy) distances: (1) the bond trans to coordinated water, Ru-N 1A (2.029 (5) Á), is the shortest of the four Ru-N bonds; (2) the bond trans to the oxo bridge, Ru-N IB' (2.089 (4) Á), is the longest of the four: and (3) the two remaining Ru-N bonds, Ru-N 1 A' (2.059 (4) Á) and Ru-N1B (2.046 (5) Á), are intermediate in length and close in value to the distances 2.054 (2) and 2.056 (2) Á found in the structures of Ru(bpy)2Cl212 and [Ru(bpy)3]2+.13 They are also quite similar The Ru-O distance of 1.869 (1) Á for the oxo bridge is consistent with the values of 1.876 (6) and 1.890 (7) Á observed in the analogous nitro complex and is comparable to Fe-0 distances in a variety of oxo-bridged iron(III) dimers (1.7-1.8 Á)14-20 when allowance is made for the larger covalent radius of Ru(III) (1.30 Á) compared to Fe(III) (1.21 Á).20 The Ru-O distance in the aqua dimer is also comparable to those found in the linear systems ReIV-0-ReIV, RuIV-0-RuIV, and Crln-0-Crm [21][22][23][24] and is much shorter than values observed for Crm-0 and Cun-0 bonds involving hydroxide bridges in systems of the type [LCu(OH)]22+ and [L2Cr(OH)]2 in which there is no multiple bonding.21-29 There is not structural evidence for a direct, through-space metal-metal interaction since the Ru-Ru separation is 3.708 (1) A.…”

A New Study of the Acid Rhodo Complex Salt [(NH3)5CrOHCr(NH3)5]Cl5.H2O Shows That the Crystals are Orthorhombic

“…Attempts to make a description in a superspace group with a commensurate modulation vector of q = c*/2 were unsuccessful. Our next step was to insert the model into space group P41212, suggested by Urushiyama, Nomura & Nakahara (1970), where two half molecules are found per asymmetric unit. The bridging O atoms lie either on a twofold axis perpendicular to the c axis or are disordered.…”

“…The first crystallographic work on the acid rhodo complex was performed by Urushiyama, Nomura & Nakahara (1970), who reported that the crystals belong to the tetragonal space group P4~212 with a= 16.26, c = 14.80 A. This model has two half molecules in the asymmetric unit and two crystallographically different bridging O atoms placed on the twofold rotation axis.…”