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Three homoleptic Fe(II) complexes with bidentate thiazole-based ligands exhibit spin-crossover (SCO) at the metal center. Abrupt temperature-driven and light-induced spin transitions are observed due to cooperative interactions between SCO cations. 

Cu( i ) and Au( i ) ions, capped with an N-heterocyclic carbene (NHC), react with (TMS) 3 P 7 (TMS = trimethyl-silyl) to afford an η 4 -coordinated anion [NHC Dipp Cu–P 7 (TMS)] − and a neutral trinuclear complex (NHC Dipp Au) 3 P 7 . Protecting the P 7 cage with the TMS groups is instrumental in controlling the course of these reactions. 

Mononuclear heteroleptic complexes [Fe(tpma)(bimz)](ClO4)2 (1a), [Fe(tpma)(bimz)](BF4)2 (1b), [Fe(bpte)(bimz)](ClO4)2 (2a), and [Fe(bpte)(bimz)](BF4)2 (2b) (tpma = tris(2-pyridylmethyl)amine, bpte = S,S′-bis(2-pyridylmethyl)-1,2-thioethane, bimz = 2,2′-biimidazoline) were prepared by reacting the corresponding Fe(II) salts with stoichiometric amounts of the ligands. All complexes exhibit temperature-induced spin crossover (SCO), but the SCO temperature is substantially lower for complexes 1a and 1b as compared to 2a and 2b, indicating the stronger ligand field afforded by the N2S2-coordinating bpte ligand relative to the N4-coordinating tpma. Our findings suggest that ligands with mixed N/S coordination can be employed to discover new SCO complexes and to tune the transition temperature of known SCO compounds by substituting for purely N-coordinating ligands.