The influence of the molecular crystalline arrangement upon the state of a Jahn-Teller-active center has been investigated in crystals of the complex Cu(mtz)(6)(BF4)(2), where mtz = 1-methyltetrazole. Crystal structures at 293, 123, and 93 K were determined by X-ray diffraction for the copper complex and at 293 and 100 K also for the analogous zinc complex, Zn(mtz)(6)(BF4)(2). The respective lattice parameters for the copper complex at 293, 123, and 93 K are as follows : a = 18.137(4), 17.597(4), 17.575(4) Angstrom; b = 10.237(4), 10.131(4), 10.133(4); c = 18.446(5), 18.531(4), 18.535(4) Angstrom; beta = 112.62(2), 113.55(2), 113.61(2)degrees. Those for the zinc complexes at 293 and 100 K, respectively, are as follows : a = 18.153(2), 17.663(2) Angstrom; b = 10.289(1), 10.159(2) Angstrom; c = 18.506(3), 18.578(3) Angstrom; beta = 113.21(1), 114.15(2)degrees. : a = 18.137(4), 17.597(4), 17.575(4) Angstrom; b = 10.237(4), 10.131(4), 10.133(4); c = 18.446(5), 18.531(4), 18.535(4) Angstrom; beta = 112.62(2), 113.55(2), 113.61(2)degrees. Those for the zinc complexes at 293 and 100 K, respectively, are as follows : a = 18.153(2), 17.663(2) Angstrom; b = 10.289(1), 10.159(2) Angstrom; c = 18.506(3), 18.578(3) Angstrom; beta = 113.21(1), 114.15(2)degrees. : a = 18.137(4), 17.597(4), 17.575(4) Angstrom; b = 10.237(4), 10.131(4), 10.133(4); c = 18.446(5), 18.531(4), 18.535(4) Angstrom; beta = 112.62(2), 113.55(2), 113.61(2)degrees. Those for the zinc complexes at 293 and 100 K, respectively, are as follows : a = 18.153(2), 17.663(2) Angstrom; b = 10.289(1), 10.159(2) Angstrom; c = 18.506(3), 18.578(3) Angstrom; beta = 113.21(1), 114.15(2)degrees.