Crystal engineering towards design of macrocyclic coordination compounds: Crystal structure of rubidium tetrachloro- and tetracyanoaurate(III) complexes with 18-crown-6

The new macrocyclic complexes of composition Rb(18-crown-6)AuX4 (X = Cl (1) and CN (2)) have been prepared and characterized by X-ray crystallography (1: monoclinic, space group P2(1)/n, with a = 8.747(1), b = 8.366(1), c = 15.404(1) Angstrom; beta = 104.37(1)degrees V = 1092.0(3) Angstrom(3,), Z = 2; final R1 = 0.025 for 2030 independent reflections used; 2: monoclinic, space group P2(1)/c, with a = 14.765(3), b = 17. 134(3), c = 8.855(2) Angstrom; beta = 90.20(1)degrees, V = 2240.2(8) Angstrom(3), Z = 4; final R1 = 0.080 for 2033 independent reflections used). Both structures consist of Rb(18-crown-6)(+) cations (A) and complex aurate(III) anions AuX4- (B). Complex 1 has a linear polymeric array -A-B-A-B- (Rb-Cl3.604(3), 3.653(3) Angstrom) with the rubidium ions disordered 0.276(2) Angstrom above and below the crown ether plane (Rb-O 2.819(5)-2.884(5) Angstrom, av. 2.846(5) Angstrom). The positioning of the rubidium atom away from the center of the 18-crown-6 is effected by the packing of the Rb(18-crown-6)(+) and AuCl4- moieties, and by the resemblance in the charge and symmetry of the cationic and anionic parts of the structure. Complex 2 has a zig-zag polymeric array -A-B-A-B- (Rb-N 2.92(2), 2.94(1) Angstrom) with orthogonal disposition of Rb(18-crown-6)(+) and Au(CN)(4)(-) planes. The rubidium atom is situated 0.90(2) A above the mean plane of the macrocyclic oxygen atoms (Rb-O 2.93(5)-3.15(4) Angstrom) and adopts a typical "sunrise coordination".