Regulation of Geometry around the Ruthenium Center of Bis(2-pyridinecarboxylato) Complexes by the Nitrosyl Moiety: Syntheses, Structures, and Theoretical Studies

cis-[Ru(NO)Cl(pyca)2] (pyca = 2-pyridinecarboxylato), in which the two pyridyl nitrogen atoms of the two pyca
ligands coordinate at the trans position to each other and the two carboxylic oxygen atoms at the trans position to
the nitrosyl ligand and the chloro ligand, respectively (type I shown as in Chart ), reacted with NaOCH3 to generate
cis-[Ru(NO)(OCH3)(pyca)2] (type I). The geometry of this complex was confirmed to be the same as the starting
complex by X-ray crystallography:  C13.5H13N3O6.5Ru; monoclinic, P21/n; a = 8.120(1), b = 16.650(1), c = 11.510(1) Å; β = 99.07(1)°; V = 1536.7(2) Å3; Z = 4. The cis−trans geometrical change reaction occurred in the
reactions of cis-[Ru(NO)(OCH3)(pyca)2] (type I) in water and alcohol (ROH, R = CH3, C2H5) to form [{trans-Ru(NO)(pyca)2}2(H3O2)]+ (type V) and trans-[Ru(NO)(OR)(pyca)2] (type V). The reactions of the trans-form complexes,
trans-[Ru(NO)(H2O)(pyca)2]+ (type V) and trans-[Ru(NO)(OCH3)(pyca)2] (type V), with Cl- in hydrochloric acid solution
afforded the cis-form complex, cis-[Ru(NO)Cl(pyca)2] (type I). The favorable geometry of [Ru(NO)X(pyca)2]n+ depended
on the nature of the coexisting ligand X. This conclusion was confirmed by theoretical, synthetic, and structural
studies. The mono-pyca-containing nitrosylruthenium complex (C2H5)4N[Ru(NO)Cl3(pyca)] was synthesized by the
reaction of [Ru(NO)Cl5]2- with Hpyca and characterized by X-ray structural analysis:  C14H24N3O3Cl3Ru; triclinic,
P1̄, a = 7.631(1), b = 9.669(1), c = 13.627(1) Å; α = 83.05(2), β = 82.23(1), γ = 81.94(1)°; V = 981.1(1) Å3;
Z = 2. The type II complex of cis-[Ru(NO)Cl(pyca)2] was synthesized by the reaction of [Ru(NO)Cl3(pyca)]- or
[Ru(NO)Cl5]2- with Hpyca and isolated by column chromatography. The structure was determined by X-ray structural
analysis:  C12H8N3O5ClRu; monoclinic, P21/n; a = 10.010(1), b = 13.280(1), c = 11.335(1) Å; β = 113.45(1)°; V
= 1382.4(2) Å3; Z = 4.