As you like it: [Ag(η2‐As4)2]+[pftb]− can be used to store yellow arsenic (As4). From it, As4 can be easily released to give concentrated, light‐stable solutions. These As4 solutions, and those of white phosphorus (P4), allowed molecular As4 and P4 to be encapsulated inside giant, spherical aggregates and polymeric matrices, enabling the first determination of their EE (E=P, As) bond lengths by diffraction methods.

Manganocene reacts with LiE(SiMe 3 ) 2 (E = P or As) to give Mn{l-E(SiMe 3 ) 2 }] 2 , where E = P (1) or As (2). The temperature dependence of the magnetic susceptibility in 1 and 2 is due to antiferromagnetic exchange and to spin-crossover (SCO). Compound 2 shows two-step SCO with hysteresis, involving high-spin (S = 5/2) and intermediate-spin S = (3/2) Mn(II).The high-spin/low-spin bistability of spin-crossover (SCO) transition metal complexes is a fascinating property that attracts considerable interest because of its potential applications in molecular switches.1 The largest class of SCO compounds comprises monometallic, octahedral iron(II) complexes with six N-donor ligands, whose bistability involves interconversions of the high-spin (t 2g )4 (e g ) 2 and the low-spin (t 2g ) 6 (e g ) 0 states. 2 SCO has also been observed in five-coordinate iron(II) complexes, 3 a tetrahedral iron(II) complex, 4 and in monometallic complexes of chromium(II), manganese(III) and cobalt(II).5 Polymetallic, exchange-coupled SCO compounds with bridging N-donor ligands are less common, however they are attractive synthetic targets because interactions between SCO centres could lead to significant enhancements in cooperativity and bistability properties.6 Although considerable progress has been made with N-donor ligands, the different electronic properties of ligands based on heavier pnictogens such as phosphorus and arsenic could provide an alternative method of influencing the interplay between magnetic exchange and SCO. Thus, we now report the structures and magnetic properties of the phosphorus-and arsenic-bridged cyclopentadienyl-manganese(II) dimers [CpMn{m-E(SiMe 3 ) 2 }] 2 , with E = P (1) or As (2). In 1 and 2, antiferromagnetic exchange occurs concurrently with thermally induced two-step SCO involving the high-spin S = 5/2 and the rare intermediate-spin S = 3/2 states of manganese(II).Compounds 1 and 2 were synthesized by reacting Cp 2 Mn with LiE(SiMe 3 ) 2 (E = P, As) (Scheme 1). The structures of 1 and 2 were determined by X-ray diffraction,w and are very similar, both consisting of pnictogen-bridged dimers of general formula [(Z 5 -Cp)Mn{m-E(SiMe 3 ) 2 }] 2 . The dimers have approximate molecular D 2h symmetry, and the {CpME 2 } coordination environments have approximate C 2v symmetry. Assuming that an Z 5 -Cp ligand formally occupies three coordination sites, each metal atom in 1 and 2 is five-coordinate.The formally five-coordinate, 15-valence-electron phosphidebridged dimanganese compound [CpMn{m-P(SiMe 3 ) 2 }] 2 (1) crystallizes with two independent molecules in the unit cell, 1a and 1b, which are structurally similar and lie about independent inversion centres ( Fig. 1, S1). In 1a, the two Mn(II) centres are bridged by two m-[(Me 3 Si) 2 P] À ligands. The Mn(1)-P(1) and Mn(1)-P(1A) bond distances in 1a are 2.5075(5) and 2.5123(5) Å and the P-Mn-P and Mn-P-Mn angles are 93.83(2) and 86.17(2)1, respectively. The arsenide-bridged dimanganese compound 2 has only one independent molecule in the unit cell, which li...

Slow diffusion reactions of the pentaphosphaferrocene [Cp*Fe(η(5)-P(5))] (Cp*=η(5)-C(5)Me(5) (1)) with CuX (X=Cl, Br, I) in different stoichiometric ratios and solvent mixtures result in the formation of one- and two-dimensional polymeric compounds 2-6 with molecular formula [{Cu(μ-X)}{Cp*Fe(μ(3),η(5):η(1):η(1)-P(5))}](n) (X=Cl (2a), I (2'c)), [{Cu(μ-I)}{Cp*Fe(μ(3),η(5):η(1):η(1)-P(5))}](n) (3), [{CuX}{Cp*Fe(μ(4),η(5):η(1):η(1):η(1)-P(5))}](n) (X=Cl (4a), Br (4b), I (4c), Br (4'b), I (4'c)), [{Cu(3)(μ-I)(2)(μ(3)-I)}{Cp*Fe(μ(5),η(5):η(1):η(1):η(1):η(1)-P(5))}](n) (5) and [{Cu(4)(μ-X)(4)(CH(3)CN)}{Cp*Fe(μ(7),η(5):η(2):η(1):η(1):η(1):η(1):η(1)-P(5))}](n) (X=Cl (6a), Br (6b)), respectively. The polymeric compounds have been characterised by single-crystal X-ray diffraction analyses and, for selected examples, by magic angle spinning (MAS) NMR spectroscopy. The solid-state structures demonstrate the versatile coordination modes of the cyclo-P(5) ligand of 1, extending from two to five coordinating phosphorus atoms in either σ or σ-and-π fashion. In compounds 2a, 2'c and 3, two phosphorus atoms of 1 coordinate to copper atoms in a 1,2 coordination mode (2a, 2'c) and an unprecedented 1,3 coordination mode (3) to form one-dimensional polymers. Compounds 4a-c, 4'b, 4'c and 5 represent two-dimensional coordination polymers. In compounds 4, three phosphorus atoms coordinate to copper atoms in a 1,2,4 coordination mode, whereas in 5 the cyclo-P(5) ligand binds in an unprecedented 1,2,3,4 coordination mode. The crystal structures of 6a,b display a tilted tube, in which all P atoms of the cyclo-P(5) ligand are coordinated to copper atoms in σ- and π-bonding modes.

The pnictogen-centered nucleophiles LiE(SiMe3)2 (E = N, P, or As) substitute a cyclopentadienide ligand of chromocene (Cp2Cr), with elimination of lithium cyclopentadienide, to give the series of pnictogen-bridged compounds [(μ:η(2):η(5)-Cp)Cr{μ-N(SiMe3)2}2Li] (1) and [(η(5)-Cp)Cr{μ-E(SiMe3)2}]2, with E = P (2) or E = As (3). Whereas 1 is a heterobimetallic coordination polymer, 2 and 3 are homometallic dimers, with the differences being due to a structure-directing influence of the hard or soft character of the bridging group 15 atoms. For compound 1, the experimental magnetic susceptibility data were accurately reproduced by a single-ion model based on high-spin chromium(II) (S = 2), which gave a g-value of 1.93 and an axial zero-field splitting parameter of D = -1.83 cm(-1). Determinations of phosphorus- and arsenic-mediated magnetic exchange coupling constants, J, are rare: in the dimers 2 and 3, variable-temperature magnetic susceptibility measurements identified strong antiferromagnetic exchange between the chromium(II) centers, which was modeled using the spin Hamiltonian H = -2J(S(CrA)·S(CrB)), and produced large coupling constants of J = -166 cm(-1) for 2 and -77.5 cm(-1) for 3.

Lavrentiev prosp. 3, Novosibirsk 630090 (Russland) [**] Diese Arbeit wurde durch die Deutsche Forschungsgemeinschaft (DFG) unterstützt. C.S. dankt dem Fonds der Chemischen Industrie für ein Promotionsstipendium. Hintergrundinformationen zu diesem Beitrag sind im WWW unter http://dx.doi.org/10.1002/ange.201306146 zu finden.