Barium Thiolates and Selenolates: Syntheses and Structural Principles Karin Ruhlandt-Senge* and Ulrich Englich [a] Dedicated to Professor Ulrich Müller on the occasion of his 60th birthday Abstract: The synthesis and structural characterization of a family of barium thiolates and selenolates is described. The thiolates were synthesized by metal- lation of thiols, the selenolates by re- ductive insertion of the metal into the selenium ± selenium bond of diorgano- diselenides. Both reaction sequences were carried out by using barium metal dissolved in ammonia; this afforded barium thiolates and selenolates in good yield and purity. The structural princi- ples displayed in the target compounds span a wide range of solid-state formu- lations, including monomeric and dimeric species, and separated ion triples, name- ly [Bathf) 4 SMes*) 2 ]1; Mes*  2,4,6- tBu 3 C 6 H 2 ), [Bathf) 4 SeMes*) 2 ]2), [Ba- [18]crown-6)hmpa) 2 ][SeMes*) 2 ]3), the dimeric [{Bapy) 3 thf)SeTrip) 2 } 2 ] 4 ; py  pyridine, Trip  2,4,6-iPr 3 C 6 H 2 ), and [Ba[18]crown-6)SeTrip) 2 ]5). The full range of association modes is com- pleted by [Ba[18]crown-6)hmpa)S- Mes*][SMes*] 6) communicated earlier by this group. In the solid state, this compound displays an intermediate ion coordination mode: one anion is bound to the metal, while the second one is unassociated. Together these com- pounds provide structural information about all three different association modes for alkaline earth metal deriva- tives. This collection of structural data allows important conclusions about the influence of solvation and ligation on structural trends. Keywords: barium ´ chalcogens ´ coordination chemistry ´ structure elucidation ´ synthesis design Introduction Chalcogenolate derivatives of the heavy alkaline earth metal barium have been well established for oxygen-based com- pounds owing to their potential as precursor materials for high temperature superconductors. [1] In contrast, much less attention has been devoted towards the heavier chalcogen congeners, [2] despite their potential in the production of phosphor materials and two-color IR windows. [3] Structurally authenticated examples are limited to the sulfur derivatives [{BaH 2 O) 4 tmtH 2 ) 2 } n ] tmt  2,4,6-trimercaptotriazine, S 3 C 3 - N 3 ), [4] [Ba[18]crown-6)hmpa)SMes*][SMes*]hmpa  hexa- methylphosphoramide; Mes* 2,4,6-tBu 3 C 6 H 2 ), [5] [Bahmpa) 3 - {NaphNNNNCS)} 2 ], [6] [Bahmpa) 3 C S)NOPh) 2 ], [7] and the tellurolate [Bapy) 5 TeSiSiMe 3 ) 3 ) 2 ] py  pyridine). [8] A few more compounds have been reported, including [BaSCMe 3 ) 2 ], [9] [Batmeda) 2 SeSiSiMe 3 ) 3 ) 2 ], [8] and [Ba- thf) 4 TeSiSiMe 3 ) 3 ) 2 ], [8] but structural data are not available. As indicated by this short list of compounds, little is known about barium thiolates and tellurolates, but information is even more scarce for the selenolates; only [Batmeda) 2 - SeSiSiMe 3 ) 3 ) 2 ] is mentioned. [8] As a consequence, few data are available with regard to synthetic strategies or the structure- determining influence of ligation, donation, and solvation. This information is crucial if the compounds are to be used in the production of solid-state materials, since the structural features of a precursor are closely linked to the physical condition necessary for its transformation into the desired solid-state material. This argument is especially significant for alkaline earth metal derivatives, since three different types of ionic association may be observed: contact triples, with two cation ±anion linkages, separated ions, with isolated cations and anions, and an intermediate, with one cation±anion linkage and one unassociated anion Scheme 1). Scheme 1. The three different ion association modes in alkaline earth metal derivatives. Only recently, the first structural characterization of an alkaline earth metal derivative with an intermediate ion association was published by this group, [5] and information on how the structural features of the target compounds may be affected remains scarce. Since the mode of association has a [a] Prof. K. Ruhlandt-Senge, Dr. U. Englich Department of Chemistry, Syracuse University 1-104 Center for Science and Technology Syracuse NY 13244-4100 USA) Fax:  1)315-443-4070 E-mail: kruhland@syr.edu FULL PAPER Chem. Eur. J. 2000, 6, No. 22  WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000 0947-6539/00/0622-4063 $ 17.50+.50/0 4063