A phase transition caught in mid‐course: independent and concomitant analyses of the monoclinic and triclinic structures of ( n Bu 4 N)[Co(orotate) 2 (bipy)]·3H 2 O

The preparation and characterization of the n Bu 4 N + salts of two bis‐orotate(2−) complexes of cobalt, namely bis(tetra‐ n ‐butylammonium) diaquabis(2,4‐dioxo‐1,2,3,4‐tetrahydropyrimidin‐1‐ide‐6‐carboxylato‐κ 2 N 1 , O 6 )cobalt(II) 1.8‐hydrate, (C 16 H 36 N) 2 [Co(C 5 H 2 N 2 O 4 ) 2 (H 2 O) 2 ]·1.8H 2 O, ( 1 ), and tetra‐ n ‐butylammonium (2,2′‐bipyridine‐κ 2 N , N ′)bis(2,4‐dioxo‐1,2,3,4‐tetrahydropyrimidin‐1‐ide‐6‐carboxylato‐κ 2 N 1 , O 6 )cobalt(III) trihydrate, (C 16 H 36 N)[Co(C 5 H 2 N 2 O 4 ) 2 (C 10 H 8 N 2 )]·3H 2 O, ( 2 ), are reported. The Co III complex, ( 2 ), which is monoclinic at room temperature, presents a conservative single‐crystal‐to‐single‐crystal phase transition below 200 K, producing a triclinic twin. The transition, which involves a conformational change in one of the n Bu groups of the cation, is reversible and can be cycled. Both end phases have been characterized structurally and the system was also characterized structurally in a two‐phase intermediate state, using single‐crystal diffraction techniques, with both the monoclinic and triclinic phases present. Thermal analysis allows a rough estimate of the small energy content, viz. 0.25 kJ mol −1 , for both the monoclinic‐to‐triclinic transformation and the reverse transition, in agreement with the nature of the structural changes involving only the n Bu 4 N + cation.