THE COORDINATION OF DIVALENT TRANSITION METAL IONS TO A STERICALLY CONSTRAINED CHELATING PYRAZOLE DERIVATIVE. THE CRYSTAL AND MOLECULAR STRUCTURE OF BIS(AZIDO)(2,5-BIS(3′,5′-DIMETHYLPYRAZOL-1′-YLMETHYL)-2,5-DIAZAHEXANE)NICKEL(II), (NI