Structural and Magnetic Diversity in Tetraalkylammonium Salts of Anionic M[N(CN)2]3 - (M = Mn and Ni) Three-Dimensional Coordination Polymers

Tetraalkylammonium cations, (NR 4)+ (R = C3H7, C4H9, and C5H11), have been used as templates to form a new family of [M(dca)3]- [M = Mn and Ni; dca = dicyanamide or N(CN)2 -] salts. The tetrapropylammonium (TPrA) salts possess a perovskite-type anion structure. (TPrA)[Mn(dca)3] (1) crystallizes in the tetragonal space group P4̄21 c, with a = 16.2945(8) Å, c = 17.4321(8) Å, and V = 4628.4(6) Å3 at T = 298 K. At room temperature, (TPrA)[Ni(dca)3] (2) crystallizes in the orthorhombic space group Pnna, with a = 17.171(2) Å, b = 22.992(2) Å, c = 22.750(2) Å, and V = 8981(2) Å3, but undergoes a first-order phase transition within the temperature range 150−220 K to the tetragonal space group P4̄21 c, with a = 16.0985(7) Å, c = 17.0287(8) Å, and V = 4413.2(5) Å3 at T = 160 K. At 110 K, 2 returns to the Pnna space group with a = 17.116(2) Å, b = 22.800(3) Å, c = 22.641(3) Å, and V = 8835(3) Å3. The tetrabutylammonium (TBA) salts possess a triple rutile structure. (TBA)[Mn(dca)3] (3) crystallizes in the orthorhombic space group P21212, with a = 16.0107(6) Å, b = 16.0114(6), c = 21.5577(8) Å, and V = 5526.4(5) Å3. (TBA)[Ni(dca)3] (4) also crystallizes in the orthorhombic space group P21212, with a = 15.6842(5) Å, b = 15.6841(6) Å, c = 21.1551(8) Å, and V = 5204.0(5) Å3. The tetrapentylammonium (TPnA) salts crystallize with a LiSbO3 structure type, space group Pnna. Lattice parameters for (TPnA)[Mn(dca)3] (5) are a = 13.2236(6) Å, b = 11.6300(6) Å, c = 20.3176(9) Å, and V = 3124.6(4) Å3, and for (TPnA)[Ni(dca)3] (6), a = 12.9380(4) Å, b = 11.6233(4) Å, c = 19.8038(7) Å, and V = 2978.1(2) Å3. Long-range antiferromagnetic ordering has been observed in the manganese salts below 2.1 K, as indicated by alternating current susceptibility measurements. Magnetic susceptibility data for the nickel salts do not show evidence for long-range magnetic ordering but can be described using an S = 1 zero-field splitting model with the exchange Hamiltonian ℋ = −J∑S i S i +1 + D∑( )2 + gμβ B∑S i , giving |D|/k B values that range between 1.98(1) K and 3.20(2) K.